Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Plasma Physics
Volume 67, Number 15
Monday–Friday, October 17–21, 2022; Spokane, Washington
Session GP11: Poster Session III: In-Person, Hall A (9:30-11:00am) and Virtual Poster Presentations (11:15am-12:30pm)
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Room: Exhibit Hall A and Online |
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GP11.00001: MFE: DIII-D Session Chairs: |
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GP11.00002: DIII-D: Closing the Gaps to Future Fusion Reactors Richard J Buttery The DIII-D program is pursuing an ambitious plan to close critical design gaps to a Fusion Pilot Plant (FPP), including integrating performance and exhaust solutions, addressing plasma interacting material and technology issues, and resolving a high fusion gain path to ITER and a pulsed FPP. Increasing the ECH power will furnish low-torque electron heating and profile control, while new reactor-relevant solutions for efficient off-axis current drive will be pioneered byhigh-field-side LHCD, helicon waves and top launch ECCD to enable FPP steady-state scenarios. A series of closed, modular divertors will allow the exploration of innovative plasma solutions for combined core and plasma exhaust in high opacity/low collisionality regimes made possible by stronger shaping to maximize the pedestal pressure and density along with a BT rise to 2.5T and 20 gyrotrons to access reactor physics regimes. A dedicated material interaction test stationwill help close gaps in compatible fusion materials. The control and mitigation of plasma transients will be addressed through a passive runaway electron dissipation coil and installing novel techniques for disruption mitigation (EM launch, hyper-velocity tungsten pellets). An exciting option for a negative triangularity path is being assessed. |
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GP11.00003: Highlights of Recent DIII-D Experimental Results* Max E Fenstermacher Recent DIII-D experiments contributed to the ITER physics basis and to physics understanding for a Fusion Pilot Plant (FPP). Changes in the 3D structure of the divertor target heat and particle fluxes were explained by the multimodal plasma response to applied 3D RMP fields. Also a robust RMP regime with increased particle confinement was observed. H-mode edge ionization source and plasma profiles data show quantitative evidence of a 2 m/s inward particle pinch and 0.2 m2/s diffusion during density pedestal rebuild after ELMs. Micro-tearing modes (MTMs) can dominate electron heat transport in ELMy H-mode pedestals. Levels of edge ExB shear determine regulation of the pedestal to standard vs wide pedestal QH-mode. ITG dominates core heat and particle transport inside r = 0.45 (diffusion~1/Z), and grad-n TEM dominates at larger radii (diffusion~Z). Simultaneous control of n=1 and 2 RWMs was demonstrated in high-β, high-qmin plasmas. Deep learning was applied to tangential imaging of divertor CIII emission to develop real-time capable models for estimating the level of detachment. Tungsten migration data were used to validate impurity sourcing and transport in simulations of the V-shaped SAS divertor. P_L-H is also lower in the SAS than in an open divertor. |
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GP11.00004: DIII-D research towards long-pulse high-performance tokamak operation Andrea M. Garofalo, Siye Ding The ultimate potential of a tokamak, embodied in the ARIES-AT fusion power plant design [1], calls for plasmas that are quite unlike most regimes in current tokamaks. The high bP regime is the most similar to ARIES-AT, in terms of the key features of high bootstrap current fraction and Shafranov shift stabilization of turbulence. ARIES-AT employed L-mode edge profiles to address power and particle exhaust issues. DIII-D shows that the high bP regime approaches this solution from the H-mode side, leveraging a synergy between the large-radius internal transport barrier (ITB) strength, and the edge pedestal weakness: pedestal degradation caused by detached divertor operation leads to stronger ITB, maintaining or even increasing the global energy confinement quality. Furthermore, a degraded pedestal (low pressure, high density) moves into a small/no ELM operating space [2]. The values of bN (>3.5) and q95 (<7) achieved on DIII-D yield fully noninductive operation in ITER or a reactor. |
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GP11.00005: Predictive modeling of high $\beta$ DIII-D plasmas Brian Victor, Christopher T Holcomb, Nikolas C Logan, Siye Ding, Andrea M Garofalo Predictive modeling tools are used to test the effects of various actuators and plasma parameters in order to optimize the development and sustainment of high $\beta_N$ discharges on DIII-D. Two discharges are used as starting points for this modeling: 1. A high q$_{min}$ shot with $\beta_N \sim 3.5$, q$_{min} > 2$, and q$_{95} \sim 6.1$; 2. A hybrid shot with $\beta_N \sim 3.7$, q$_{min} \sim 1$, and q$_{95} \sim 5.6$. For the high q$_{min}$ discharge, the goal is to understand how to best utilize additional heating and current drive actuators, such as electron cyclotron heating (ECH), to increase beta and improve stability. Predictive modeling is performed using TGLF in TRANSP over several seconds of shot time. The density and temperature profiles are fixed in the pedestal region and TGLF models the evolution of T$_e$, T$_i$, and ne based on the plasma and current drive actuators. Results of these simulations show that additional ECH power broadens the current density profile and increases the ideal-wall stability limits. For the hybrid discharge, a single time slice during the high confinement portion of the shot (H$_{98y2} \sim 2$) is analyzed in detail using TGYRO. The rotation profile is scaled to separate the effects of rotation and pedestal height on confinement. These rotation scans will then be performed experimentally in the future by varying the ratio of co- and counter-Ip neutral beam current drive. |
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GP11.00006: Global confinement behavior with small shape changes in DIII-D negative triangularity discharges Max Austin, Alessandro Marinoni, Kathreen E Thome DIII-D negative triangularity plasmas have exhibited H-mode confinement with an ELM-free boundary and a tolerance for high normalized beta operation (N ~3). In an experiment on DIII-D with a lower-single-null negative triangularity shape, the upper triangularity was altered shot-to-shot with the same heating trajectory. As the upper triangularity was relaxed from upper = -0.40 to -0.20, the edge pedestal pressure increased by ~70% from 0.9 kPa to 1.6 kPa as the plasma transitioned from an L-mode to an ELM'ing H-mode-like edge. The stored energy and confinement, and hence the H-factor remained nearly the same with H98Y2 ~ 1. This constancy of global confinement with varying pedestal height is counter to typical H-mode behavior. A study of kinetic profiles shows the lower stored energy of the pedestal is compensated with increased stored energy in the core as the triangularity becomes more negative. There is a small contribution due to increased plasma volume. The fast ion energy content remains constant at about 25%. The ability to vary the edge pedestal and confinement mode with a small change in shape yet retain good energy confinement would be an attractive feature in a reactor. |
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GP11.00007: H-mode Access and Limit Cycle Oscillations in DIII-D Negative Triangularity Plasmas Lothar Schmitz, K. J Callahan, L. Zeng, T. L Rhodes, M E Austin, Z. Yan, G. R McKee, K. E Thome, A. O Nelson, C. Paz-Soldan, A. Marinoni Negative triangularity L-mode plasmas in DIII-D exhibit H-mode-like thermal confinement and normalized pressure beta_n [1]. Their increased scrape-off layer width potentially opens a path for mitigating divertor power loading in future burning plasmas. Calculations show a reduced ballooning mode threshold prevents access to high pedestal pressure [2]. At moderate negative upper triangularity dU ~-0.2, ELMing H-mode is still sustained in DIII-D, with a moderately increased power threshold PLH ~3.5 MW compared to positive dU plasmas with similar NBI torque. However, plasmas with high negative upper triangularity (dU= -0.325) access ELMing H-mode only transiently, followed by extended limit cycle oscillations (LCO [3]), The edge electric field and normalized edge pressure gradient periodically increase but remain well below H-mode values up to the highest coupled power (~11 MW). Detailed gyrofluid stability analysis of the outer core plasma is presented. |
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GP11.00008: Impact of Faraday-effect-constrained equilibrium reconstruction on predicting instability onset in DIII-D Thomas E Benedett, Jie Chen, David L Brower, Mihir D Pandya, Brett E Chapman Understanding the behavior of equilibrium and fluctuating magnetic fields inside fusion plasmas is critical to maintaining control and stability and thus to enabling net fusion power generation. The radial Faraday-effect polarimeter on the DIII-D tokamak measures line-integrated internal magnetic fields at Z=0 and +/-13.5 cm with high temporal resolution up to the megahertz range for the full duration of plasma shots, making it useful for equilibrium reconstruction, especially when Motional Stark Effect measurements are not available, and for fluctuation evaluations. By using Faraday-effect-constrained Grad-Shafranov equilibrium reconstruction, a preliminary exploration of its impact is presented. The present status of the Faraday-effect constraint on EFIT is discussed, including its verification and sensitivity tests. The constraint is applied to questions concerning tokamak core physics: correlations between internal magnetic field and sawtooth crashes are investigated; current profile evolution during runaway electron plateaus are sought and characterized; correlation between current profile and tearing mode evolution is also investigated, particularly between current profile peaking and n=1 mode onset. |
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GP11.00009: Validation of nonlinear gyrokinetic modeling of isotope-dependent impurity transport in the DIII-D tokamak Tomas Odstrcil, Kathreen E Thome, Colin Chrystal, George R McKee, Tom Osborne, Theresa M Wilks, Eric M Hollmann Experimental investigation of impurity transport with laser blow-off in DIII-D revealed a difference in calcium transport between deuterium (D) and dimensionally similar hydrogen (H) plasma. Impurity confinement time in D is up to 3x longer and with a stronger dependence on ECH power than in H. Only a weak isotope dependence of mid-radius impurity diffusion was observed in ECH heated plasmas. In contrast, the diffusion is an order of magnitude lower in D than in H in the NBI-only heated case. The ratio between mid-radius impurity convection and diffusion remained unchanged between the isotopes. The experimental observations are compared with local non-linear gyrokinetic modeling using the CGYRO code. The heat flux matched CGYRO simulations reproduce the observed increase of impurity diffusion and pinch with additional ECH power for both isotopes. However, the magnitude of diffusion in NBI heated H plasma is underestimated by a factor of four. Parameters sensitivity scan performed by CGYRO indicates that the variation in transport coefficients is a consequence of indirect changes between H and D plasma, such as in the profiles gradients, Te/Ti ratio, and beta stabilization, rather than a direct influence of the isotope mass. |
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GP11.00010: Database generation for validation of TGLF and retraining of neural network accelerated TGLF-NN Tom F Neiser, Orso Meneghini, Sterling P Smith, Joseph T McClenaghan, David Orozco, Joseph B Hall, Gary M Staebler, Emily A Belli, Jeff Candy The trapped gyro-Landau fluid (TGLF) code is a quasi-linear model of gyrokinetic turbulence that relies on so-called saturation rules SAT0, SAT1, and SAT2 to capture the nonlinear physics necessary to compute particle, heat and momentum transport in fusion plasmas. Any free parameters in these saturation rules are calibrated against high-fidelity simulations with the CGYRO code. A large database of five million TGLF simulations has been generated with experimental parameters from 2500 DIII-D discharges in order to increase the accuracy of TGLF-NN, which is a neural network accelerated representation of TGLF. This database includes perturbations in four plasma parameters, namely the electron and ion temperature gradients, the density gradient and the E×B shearing rate. The response of TGLF fluxes to these perturbations also serves as a sensitivity study to aid validation of TGLF against this experimental database. For example, the TGLF heat flux is found to be predominantly driven by ion temperature gradient modes, trapped electron modes and kinetic ballooning modes, which is verified by linear CGYRO simulations on selected cases. Lastly, the sensitivity study allows estimation of critical gradients for turbulence onset and heat flux stiffness as a function of saturation rule to complement ongoing validation and model development efforts. |
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GP11.00011: Analysis of Dependence of Transport Coefficients on Safety Factor Profile in DIII-D Jarred Loughran, Saskia Mordijck, Ryan A Chaban, Shaun R Haskey, Jerry W Hughes, Florian M. Laggner, Tom Osborne, Aaron M Rosenthal, Theresa M Wilks We have expanded previous work [Mordijck NF 2020] on the dependence of plasma transport coefficients on collisionality to analyze dependence on safety factor profile, q, by examining shots over a range of q95. Future fusion devices will have edge pedestals that will ionize neutrals outside of the separatrix [Romanelli NF 2015], meaning these pedestals will be dominated by charged particle and heat transport. Gas puff modulation is a common method to extract perturbed transport coefficients. Curvature pinch transport is linked to the gradient of q(r), motivating our investigation. This technique is well established for the core but allowing the source term of the particle balance equation to vary and optimizing our fitted transport profile with the source included extends our analysis to the edge. Future work could also include Lyman-alpha diagnostics for absolute edge source measurements. Currently, we are developing a self-consistent set of tools to extract transport coefficients from a wider range of data to advance understanding of transport dependence on various parameters. Future work can apply these tools to develop predictive transport modelling, and extend to comparison of models with non-modulated shots. |
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GP11.00012: Turbulence wavenumber spectra and comparisons to theory using an optimized Doppler backscattering system in DIII-D* Julius Damba, Quinn Pratt, Rongjie Hong, Valerian H Hall-Chen, Terry L Rhodes Measurement of turbulent wavenumber spectra provides a tool to both characterize the plasma turbulence as well as test simulations and theory. The recently validated UCLA Doppler backscattering (DBS) system enables previously inaccessible measurements (for DBS on DIII-D) of higher wavenumber density fluctuations associated with turbulent transport. DBS as a plasma diagnostic measures wavenumber-resolved density turbulence fluctuation levels, ñ, localized E×B velocity, radial electric field, and plasma flows. The new DBS system has demonstrated measurements of kñ up to 20 cm-1 or kñρs ≤ 10. This wavenumber range is relevant to a broad range of instabilities of interest including KBM, ITG, MTM, TEM, and ETG. The measurement locations are in the radial range ρ = 0.5–1.0. These measurements produce spectral shapes (power vs fluctuation frequency) that, when obtained as a function of the wavenumber, allow us to characterize the potential turbulence instability modes. These experimental measurements can be further investigated and compared with the theoretical predictions from linear and/or non-linear simulation codes. |
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GP11.00013: Quasi-stationary ELM-free H-modes with 3rd harmonic ECH in the DIII-D Tokamak Quinn Pratt, Terry L Rhodes, Troy Carter Analysis of DIII-D ECH H-mode discharges possessing long, ELM-free periods is presented. Purely electron-heated H-mode plasmas with natural density control and without ELMs are of particular interest for fusion energy. The discharges have plasma current, Ip = 700 kA, toroidal field B = -1.3 T and edge safety factor, q95 = 5.5. Auxiliary heating is performed with 2 MW of 3rd harmonic (X3) ECH and no NBI. The plasma density and temperature profiles exhibit the typical H-mode edge transport barrier. The normalized energy confinement is H98y2 = 0.9 and the plasma beta is βn = 1.2. In one case, the ELM-free period exists for > 2 seconds (much longer than the energy confinement time, τE ∽ 80 ms). Core MHD with periodicity m/n = 3/2 exists throughout the ELM-free phase and is believed to be responsible for density control in the absence of ELMs. These DIII-D discharges share some key aspects (X3 ECH, core MHD) with the Quasi-Stationary ELM free H-mode (QSEFHM) observed on TCV1. Analysis of transport, fluctuations, and MHD/ELM stability will be presented. |
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GP11.00014: Investigating the generation of intrinsic rotation via turbulence-driven Reynolds Stress Xijie Qin, George McKee, Benedikt Geiger, Dinh D Truong, Zheng Yan Understanding the generation of intrinsic rotation in fusion plasmas is essential to ensure stable operation and good confinement. The mechanism of intrinsic rotation generation via turbulence-driven Reynolds Stress is investigated at DIII-D using 2D BES and UF-CHERS fluctuation measurements. Beam Emission Spectroscopy (BES) measures long wavelength (k⊥ρs<1) density fluctuations, which can be used to calculate turbulence characteristics and a 2D velocity field (ṽr, ṽΘ). Ultra-Fast Charge Exchange Recombination Spectroscopy (UF-CHERS) measures ion temperature and toroidal velocity fluctuations (ṽΦ). Multi-field correlation analysis shows that density and toroidal velocity exhibit correlated broadband fluctuations in the local turbulence. Poloidal〈ṽrṽΘ〉and toroidal〈ṽrṽΦ〉Reynolds Stress are calculated with the measured velocity fluctuations. An additional experiment will be conducted at DIII-D to perform a scan of with ECRH and vary via plasma current, which enables studies of their effects on the dominant instabilities, turbulence characteristics, turbulent momentum transport, Reynolds Stress, and generation of intrinsic rotation. |
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GP11.00015: Electron temperature and density turbulence behavior during sawtooth oscillations in DIII-D Guiding Wang, Terry L Rhodes, William A Peebles, Neal A Crocker, Rongjie Hong, Quinn Pratt, Max Austin, Michael Van Zeeland, Sterling P Smith The sawtooth instabilities in tokamaks are periodic magnetic reconnection events, where the plasma pressure profiles inside a certain plasma minor radius (the inversion radius) drop abruptly. This work reports on recent observations of the electron temperature (Te) and density (Ne) turbulence behavior during sawtooth oscillations in a DIII-D hydrogen L-mode plasma with an inner wall limited configuration, measured by the correlation electron-cyclotron-emission (CECE) radiometer and Doppler backscattering (DBS) systems. It is observed that both Te and Ne turbulence amplitudes vary with time during sawtooth cycles. Before each sawtooth crash, the Te and Ne turbulence amplitudes reach a maximum level, then they show clear decrease immediately after sawtooth crash well inside the inversion radius, while no obvious change occurs near and outside the inversion radius. A critical Te gradient behavior is found inside the inversion radius but not near or outside the inversion radius. Evidence of radial propagation of Te turbulence is observed at the sawtooth crash. These observations combined with data from magnetic probes and linear stability turbulence simulations will be presented. |
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GP11.00016: Investigation of Core Transport Barriers in DIII-D discharges with off-axis Te Profile peaks Ruifeng Xie, Max Austin, Kenneth W Gentle Hollow electron temperature (Te) profiles of sustained duration have been observed in DIII-D H-mode discharges driven solely by off-axis electron cyclotron heating (ECH). These off-axis Te peaks appear just inside the ECH deposition location after the L-H transition and grow to be approximately 30% higher than Te(0). Electron heat transport properties near these off-axis temperature peaks have been studied using modulated ECH to infer electron diffusive and convective transport coefficients. Modeling with a transport analysis code GEvol, which solves the electron thermal diffusion equation, finds that the hollow experimental profile can be reproduced with a local electron diffusivity, χe being an order of magnitude lower than the average value across the plasma, suggesting the presence of an electron internal transport barrier (ITB) inside the ECH heating location. Using equilibrium reconstructions created with the EFIT code using kinetic pressure and current constraints from TRANSP modeling, the formation of these ITBs appears to be correlated with off-axis values of the safety factor q being near 1. |
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GP11.00017: Interpretation of Te Response to Neutral Beam Injection on DIII-D Bingzhe Zhao, Max Austin Electron cyclotron emission (ECE) measurements closely trace electron temperature responses to neutral beam injection (NBI) and thus provide a direct experimental indicator of beam deposition, which is normally only available through Monte Carlo (MC) methods. The power is deposited into the electron population through fast ion collisions with thermal electrons, which has an interaction time scale of 10-100 ms. Meanwhile due to the short thermalization time (~0.1 ms) and low temperature (~10 eV) of the beam electron source, the NBI pulses display a prompt Te cooling effect through dilution. These two opposing effects are separable with ECE data due to difference in effective time scales, and in general the cooling effects dominate at higher Te (Te>2keV). The beam deposition calculated from the Te response is compared with calculations from MC beam code NUBEAM. Both power and source deposition profiles for electrons were overall in reasonable agreement. However, the electron source deposition profile from measurements is more core-biased than the MC calculation: up to 2 times higher on-axis but drops off about twice as fast. This core discrepancy is likely related to beam halo and thermal neutral transport. |
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GP11.00018: Core and edge turbulence measurements in wide pedestal quiescent H-mode plasmas without power degradation of energy confinement Saeid Houshmandyar, Keith H Burrell, Michael R Halfmoon, Rongjie Hong, Zheng Yan, George R McKee, Michael Van Zeeland, David R Hatch, Max Austin Wide pedestal quiescent H-mode plasmas at the DIII-D tokamak have shown insensitivity of the energy confinement time to the heating power (PNBI). In an earlier work, we have shown that the lack of power degradation of confinement in these plasmas is due to the formation of ion internal transport barriers (ITB) and thus, to the increased stored energy as PNBI increased. Flux-matched TGLF analysis via TGYRO predicts that the ITB is stabilized by E×B shear, Ti/Te ratio and at the high PNBI, by the Shafranov shift. Here, we document the core and edge fluctuation measurements for these plasmas measured by the turbulence diagnostics. Density fluctuations measured by the multichannel CO2 interferometer show a decrease inside ITB. Within the pedestal, low-k turbulence measured by beam emission spectroscopy (BES) shows reduction in density fluctuations as PNBI increased, while the BES measurements in the pedestal-top show an opposite trend. Additionally, intermediate-k turbulence measured by the Doppler backscattering diagnostic shows reduction in density fluctuations. However, magnetic fluctuations increase in amplitude. Preliminary gyrokinetic simulations and comparison to transport fingerprints suggests electrostatic transport. Details of the measurements and their comparisons with simulations will be presented. |
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GP11.00019: Energetic Particle-Induced Geodesic Acoustic Modes on DIII-D Daniel J Lin, William W Heidbrink, Neal A Crocker, Xiaodi Du, Raffi M Nazikian, Michael Van Zeeland, Kshitish Kumar Barada Various properties of the energetic particle-induced geodesic acoustic mode (EGAM) are explored in this large database analysis of DIII-D experimental data. EGAMs are n=0 modes with m=0 electrostatic potential fluctuations (where n/m = toroidal/poloidal mode number), m=1 density fluctuations and m=2 magnetic fluctuations. The fundamental frequency (∼20-40 kHz) of the mode is typically observed to be around half of the traditional geodesic acoustic mode (GAM) frequency. They are most easily destabilized by beams in the counter plasma current (counter-Ip) direction as compared to co-Ip and off-axis beams. During counter beam injection, the mode frequency is found to have the strongest linear correlation with the safety factor (q) with a value of r=−0.712. The stability of the mode in the space of q and poloidal beta (βp) shows a clear boundary for the mode stability. The stability of the mode is found to be largely determined by the damping rate rather than the drive. |
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GP11.00020: A research program to measure spin polarized fusion reactions in DIII-D William W Heidbrink, Andrew M J Sandorfi, Alvin V Garcia, Larry R BAYLOR, Gary L Jackson, G. W Miller, David C Pace, Sterling P Smith, Sina Tafti, Xiangdong Wei, Xiaochao Zheng The use of spin polarized fuel could increase fusion reactivity by a factor of 1.5 and, owing to alpha heating, increase fusion Q in ITER even more. The use of polarized D and 3He in a DIII-D experiment avoids the complexities of handling tritium, while encompassing the same nuclear reaction spin-physics. Polarized fuels can be prepared by permeating optically-pumped 3He into an ICF shell pellet, and by either dynamically polarizing 7Li-D or generating pellets of frozen-spin H-D. The polarization lifetimes in cooled fuel capsules are long (days -to- months for D, days for 3He). Such cryogenically-frozen pellets can be injected vertically by special injectors that minimize depolarizing field gradients. Modeling shows that a readily producible plasma with Ti > 10 keV generates 14.7 MeV proton and 3.6 MeV alpha signals that are sensitive to spin-induced changes in differential cross sections with high accuracy. Additionally, all major reactor-relevant depolarization mechanisms are accessible for study in DIII-D, making it an attractive facility to assess this high impact reactor fueling technique experimentally. |
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GP11.00021: Conceptual design of DIII-D experiments to diagnose the lifetime of spin polarized fuel Alvin V Garcia, William W Heidbrink, Andrew M J Sandorfi The D-T and D-3He fusion cross sections are increased by 50% if the fuel remains spin polarized parallel to the magnetic field, offering significant increase in fusion energy Q. The goal here is to assess the feasibility of spin polarization lifetime measurements on the DIII-D tokamak using relative changes in detected charged fusion product pitch, poloidal and energy distributions that depend upon the differential fusion cross section. Two realistic TRANSP calculated plasma scenarios are prepared: 1) Thermonuclear—utilizes polarized 3He and D pellet injection into a hot plasma, 2) Beam-plasma—uses polarized D pellets and unpolarized 3He neutral beams into an L-mode plasma. In both scenarios, there is pitch sensitivity for 15-MeV proton detection at a poloidal angle of -56o, and sensitivity for 3.6-MeV alpha flux detection by an array of poloidal detectors. Energy-resolved measurements of protons in the beam-plasma scenario also show sensitivity at -56o. A realistic assessment in the thermonuclear case show count rates ~104 and 105 cps for pitch-resolved proton and alpha flux measurements, respectively. Reduced chi-squared calculations show polarization lifetime measurements are feasible for proton or alpha detection. |
Author not Attending |
GP11.00022: Intermittent Fluctuations of Fast Ions Across Phase Space on DIII-D Kenneth R Gage, Xiaodi Du, Javier Gonzalez-Martin, William W Heidbrink, Deyong Liu Fluctuation measurements of both Fast Ion Loss Detectors (FILDs) and an Imaging Neutral Particle Analyser (INPA) show intermittent transport of fast ions during Alfvén Eigenmode (AE) induced critical gradient behavior. Previous work on the current ramp phase of L-mode, inner-wall-limited plasmas have shown bursts of losses in FILD data, increasing in frequency with total injected beam power [1]. Here, we expand on these findings with the use of an upgrade to the fast ion fluctuation diagnostics on DIII-D – the most important of which is the installation of a fluctuation measurement on the INPA to see the effect of the critical gradient on confined particles. Along with an increased number of FILD fluctuation measurements and a new optical setup for measuring fluctuations in Fast Ion Dα (FIDA), these new measurements form a more complete picture of energetic particle transport across phase space. Beam Emission Spectroscopy (BES) data is also used to compare against recent theory suggesting that microturbulence affects the intermittent behavior of fast ions [2]. |
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GP11.00023: Commissioning and Characterizing Top Launch ECCD Systems on the DIII-D Tokamak Xi Chen, Craig C Petty, Jared P Squire, Mirela Cengher, Yuri A Gorelov, Michael P Ross, Perry Nesbet, Ian Holmes, Rigo Brambila, William Grosnickle, Antonio C Torrezan, Max Austin Following the successful demonstration of doubling off-axis ECCD efficiency via top launch ECCD compared to low field side (LFS) launch on DIII-D in 2019 using a top launcher (TL) installed at toroidal 300 deg, a second TL system is installed at toroidal 90 deg. Commissioning and characterizing the new top launch system and the re-installed improved 300 deg top launch system has been carried out. Both systems are equipped with a waveguide switch enabling flexible switching between TL and LFS launch, so dedicated gyrotrons are not needed. The aiming of both TLs is fixed at the same design value which is predicted to be optimal for off-axis ECCD in a typical DIII-D AT plasma in reversed BT at 1.65 T. Injection at full power of the connected gyrotron with modulated or constant waveform for >4 second has been demonstrated for both TL systems. Experiments were performed to comprehensively characterize the polarization and aiming of the two TLs. The toroidal magnetic field and the inclination and ellipticity of the injected EC waves were systematically scanned in ohmic and H-mode plasmas. Comparisons were made between: (1) X-mode and O-mode launch, (2) TL and LFS launch, and (3) slow and fast modulation. |
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GP11.00024: Upgrades and New Features to the ECH System on DIII-D Perry Nesbet, Yuri A Gorelov, Mirela Cengher, John Lohr, Antonio C Torrezan, William Grosnickle, Rigo Brambila, Clayton Gray, Michael P Ross, Esteban Bagdy, Jared Squire, George Sips The Electron Cyclotron Heating system on DIII-D currently consists of four 110 GHz gyrotrons which combine to inject a total of 2.5 MW into the plasma. Over this past year, the ECH system has experienced several key upgrades. First, a building expansion for the ECH gyrotron vault is nearing completion, and this will provide a total of 3 additional gyrotron sockets. Another recent upgrade was the installation and commissioning of one new top launcher system and one upgraded top launcher mirror assembly for increased current drive capabilities. New instrumentation and controls were installed to support the two top launchers as well as refurbishing and upgrading the existing ECH launchers instrumentation. Some of the new instrumentation features for the top launchers include temperature sensors and arc detection. We have also completed the conditioning process for our newest gyrotron, Yoda, and it was accepted into operations earlier this year with a generated power of 780 kW and a pulse length of 5 s. Lastly, we are expecting to receive 2 repaired gyrotrons and 1 new gyrotron by the end of 2022. This will bring the total number of gyrotrons on DIII-D up to 7, and this is expected to increase the total ECH power to over 4 MW. |
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GP11.00025: RF Systems Development on DIII-D Mirela Cengher, James Anderson, kyle Thackston, Bart v Compernolle, Stephen J Wukitch, Yijun Lin, Ivan Garcia, Mohamed Mohamed, Samuel Pierson, J. Ridzon, Evan Leppink, Grant Rutherford, Andrew Seltzman, Shawn Tang, Charles P Moeller, Robert I Pinsker, A. Nagy, Bruce Lombardo, Jared P Squire, Daniel Kellman, Craig C Petty, Xi Chen, Joseph Tooker, Adrianus C Sips The DIII-D RF Systems include an Electron Cyclotron Heating and Current Drive system (ECH/ECCD) System, a Helicon System, and a high field side Lower Hybrid Current Drive (LHCD) system. The ECH system is expected to add three more 110 GHz gyrotrons in 2022, and a 3rd top launcher is funded. The ECH waveguide upgrade to larger size for enhanced transmission in the ECH lines is studied. |
Author not Attending |
GP11.00026: Interpretation of Doppler Shifted Dα Spectroscopy on the DIII-D Neutral Beam System Brendan J Crowley, Yannick L De Jong, Shaun R Haskey, J T Scoville Neutral Beam Injection (NBI) is used for non-inductive heating, current drive, fueling and diagnostics in most major magnetic confinement fusion devices. The DIII-D device comprises eight NBI ion sources based on the US Common Long Pulse Source (CLPS), with a total output power of up to 20 MW. |
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GP11.00027: Progress of DIII-D High Field Side Lower Hybrid Current Drive Experiment Stephen J Wukitch, Evan Leppink, Yijun Lin, Grant Rutherford, Andrew Seltzman, Christopher T Holcomb, Robert I Pinsker A high field side lower hybrid current drive (HFS LHCD) system is scheduled for operation in FY23. HFS LHCD is designed to drive off-axis current at r/a~0.6-0.8 with peak current density up to 0.4 MA/m$^2$ and 0.4 MA/MW coupled with n||~2.7 at 4.6 GHz. Due to improved wave accessibility and penetration from HFS, very high single pass absorption is expected. A novel, compact launcher distributes power poloidally utilizing a traveling wave, 4-way splitter and toroidally with a multi-junction that also determines the launched wave spectrum. The splitter utilizes imbedded RF elements to ensure proper power splitting and minimize reflection. The imbedded RF elements were enabled by additive manufacturing and the expected disruption loads and 400C bake compelled the use of a high strength copper alloy. The klystron system has been installed in the Lower Hybrid Vault and the control system has been integrated with the DIII-D plasma control. A HVPS has been relocated to DIII-D and tested. The waveguide runs between the klystrons and circulators have been installed allowing klystron testing into dummy load to verify operation. The latest simulations, design and system status will be presented. |
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GP11.00028: Predicted Performance of a Tangential Viewing Hard X-Ray Camera for the DIII-D High Field Side Lower Hybrid Current Drive Experiment Grant Rutherford, Andrew Seltzman, Stephen J Wukitch High field side (HFS) launch of lower hybrid current drive (LHCD) has improved accessibility and penetration over low field side launch on DIII-D. Simulations predict single pass absorption under a wide range of plasma conditions. Hard x-ray (HXR) measurement of LHCD generated fast electron bremsstrahlung (50-250 keV) will validate wave propagation and absorption. Emissivity profiles are recovered from 1D inversion of HXR brightness to determine LH damping location and fast electron energy and slowing down time. The camera will be implemented by populating 32 tangential sightlines of the existing Gamma Ray Imager with Kromek SPEAR™ CZT detectors sensitive to 30-250 keV photons. 10 keV energy and <0.5 ms time resolution are expected. Pulses are processed using 250 ns shaping time Cremat CR-200 gaussian shaping modules and digitized by 25 MHz D-TACQ ACQ216 digitizers. Performance of the HXR camera is evaluated by comparing predicted fast electron density profiles and inverted synthetic brightnesses obtained from GENRAY/CQL3D. Inversions closely matched predicted fast electron profiles for a range of experimental parameters. The latest simulations, designs, and results will be presented. |
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GP11.00029: First Results from the High-Field Side Scrape-Off Layer Reflectometer on DIII-D Evan Leppink, Cornwall H Lau, Yijun Lin, Stephen J Wukitch A high-field-side (HFS) scrape-off layer (SOL) reflectometer has recently been designed and installed on the DIII-D tokamak. The reflectometer will provide the HFS SOL density profile with high spatial and temporal resolution, operating in the 6-27 GHz range in O-mode polarization, corresponding to a density range of approximately $4 \times 10^{17}$ - $9 \times 10^{18} m^{-3}$. To fit within the extremely limited space of the HFS, the reflectometer utilizes novel compact double ridged rectangular horn antennas designed specifically for the reflectometer measurement, which were 3D printed from a high temperature copper alloy, GrCop-84. The diagnostic is obtaining data on DIII-D with installation and calibration completed in early 2022. The primary mission of this diagnostic is the characterization of the HFS SOL for lower hybrid current drive (LHCD) coupling studies as the SOL conditions play a critical role in LHCD performance. Additionally, the reflectometer is capable of other SOL studies, such as anisotropy between the low-field and high-field sides. The design of the reflectometer as well as the first experimental results will be presented. |
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GP11.00030: Development of a High Frequency Heterodyne Phase Contrast Imaging System to Detect Helicon Waves on DIII-D Alessandro Marinoni, Charles P Moeller, Jon C Rost, Miklos Porkolab, Robert I Pinsker The Phase Contrast Imaging (PCI) diagnostic on the DIII-D tokamak is being upgraded with a novel optical heterodyne scheme to measure the density perturbation induced by the recently commissioned helicon antenna [1]. The PCI, being an absolutely calibrated interferometer that images in real space line-integrated electron density fluctuations, is uniquely able to measure both the internal structure and the absolute amplitude of such a wave, thereby extending the purely temporal measurements that are otherwise typically available. In order for the imaging method to be applicable to the helicon wave at 476 MHz, the intensity of the PCI laser beam must be modulated in such a way that the low-frequency sideband falls within the PCI 2 MHz detector bandwidth. A transverse Pockels cell made of a water cooled CdTe birefringent crystal is driven by a cascade of two RF amplifiers and a tuned cavity providing 2 kV pk-pk voltage at 475 MHz. Calibration data on the spectral purity of the sinusoidal modulation as well as on its depth will be presented. |
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GP11.00031: Excitation of parametric instabilities during helicon wave injection into DIII-D* Miklos Porkolab, Seung G Baek, Bart Van Compernolle, Severin Denk, Robert I Pinsker, Shaun X Tang High power helicon (whistler) waves at 0.476 GHz have been launched on DIII-D with the goal of demonstrating efficient off-axis current generation. We have shown in past work [1,2] that under typical experimental conditions strong parametric decay instability (PDI) is expected in the pedestal region that may scatter the incident helicon wave and compromise the expected current drive efficiency. The dominant driver of the PDI is the ExB and/or polarization drift velocity which can drive ion cyclotron quasi-modes and lower hybrid (or high k ion-plasma or ion-Bernstein) sideband waves unstable. Using magnetic pickup loops, initial experimental results indicated evidence of PDI corresponding to the cyclotron frequency and its harmonics at the outboard edge of the plasma. Here we present numerical calculations of growth rates and frequencies and thereby estimate convective thresholds and PDI saturation levels and compare them with experimental observations [1,3]. |
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GP11.00032: Magnetic fluctuation measurements from first high-power helicon experiments on DIII-D Shawn Tang, Genevieve H DeGrandchamp, Robert I Pinsker, Bart G Van Compernolle, Miklos Porkolab, Kathreen E Thome Parametric Decay Instabilities (PDI) have been observed in experiments with slow and fast wave coupling in the lower hybrid range and were predicted to occur in helicon current drive experiments at 476 MHz in DIII-D [1]. Initial experiments with a helicon system at DIII-D have been conducted with a 30-module comb-line traveling wave antenna to couple up to 0.3 MW of RF power at 476 MHz with n|| = 3 to L- and H-mode plasmas with toroidal fields BT(0)= 1.85—2.0 T. The Ion Cyclotron Emission (ICE) diagnostic was used to obtain magnetic fluctuation spectral measurements from 1 to 100 MHz. ICE was expanded to acquire high-frequency (‘HICE’) signals up to 500 MHz with pickup loops near the midplane on both the high- and low-field sides, enabling the observation of PDI in helicon experiments. Measurements showed the ‘pump’ peak at 476 MHz as well as sidebands up to -10 dB of the pump amplitude separated by where is the ion cyclotron frequency near the outboard plasma edge. Corresponding ion cyclotron harmonic quasi-modes were also observed at the low frequency end of the spectrum. |
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GP11.00033: Tearing Modes in DIII-D IBS Discharges, CTMs or NTMs? James D Callen, Robert J La Haye, Edward J Strait This poster explores whether classical tearing modes (CTMs) or neoclassical tearing modes (NTMs) are dominant in DIII-D ITER Baseline Scenario (IBS) discharges. Growing tearing modes are problematic in IBS discharges because they can lead to plasma disruptions. Tearing mode evolution is governed by the modified Rutherford equation (MRE). CTMs are driven by Δ' ∼ d j∥ / dr; NTMs are driven by dNTM ∼ 3 jboot / j‖ ∼ dP / dr. When 2/1 tearing modes are growing robustly in DIII-D IBS discharges, the MRE predicts CTMs should grow as t 2 and NTMs should grow as t. As an example, in DIII-D IBS discharge 174446, assuming a reasonable positive r0'Δ=1 for CTMs, the Mirnov magnetic signal δB should grow by about 1 Gauss (G) in 160 ms. In contrast NTMs with dNTM = 0.5 should increase δB by about 1 G in 9 ms. The 174446 data for δB > 5G exhibits linear growth in t and δB increases by 1 G in 8.5 ms, at a rate of 120 G/s. NTM predictions agree with this experimental data. In contrast, the MRE-predicted CTM t 2 scaling disagrees with it and its growth time is too long. Other DIII-D IBS data provide similar results. Thus, the experimental data strongly indicate NTMs are the dominant tearing modes in DIII-D IBS discharges. |
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GP11.00034: Early internal detection of tearing modes in high-qmin DIII-D plasmas and correlation with ideal and resistive stability calculations Mihir D Pandya, Brett E Chapman, Karsten J McCollam, John S Sarff, Brian S Victor, Dylan P Brennan, Jie Chen, David L Brower, Weixing Ding, Christopher T Holcomb, Nikolas C Logan, Edward J Strait, Rachel A Myers Faraday-effect polarimetry via the Radial Interferometer Polarimeter (RIP) detects internal magnetic fluctuations in high-qmin DIII-D plasmas up to 300 ms before the edge magnetic sensing coils. In these qmin > 1.4 plasmas, the goal of achieving g high ??N is often limited by the emergence of tearing modes (TM). RIP measures the line integral of magnetic fluctuations across the plasma center, enabling detection of n > 1, core-resonant modes whose narrow eigenfunctions render them challenging to detect at the edge. The DCON ideal stability code was used to calculate ideal-wall kink-mode ??N limits for different n as a proxy for linear TM stability. For these plasmas, the ??N limit for the n = 3 mode is generally the lowest, and is detected on RIP before the n = 2 or 1 modes. In one example, a 6/3 mode (resonant at the q = 2 surface) occurs initially without 4/2 or 2/1 modes. This might be consistent with the lower ??N limit for the n = 3 kink mode. However, resistive DCON shows that Delta' for the 6/3 TM is initially near zero and only increases later, after the equilibrium becomes ideally unstable, indicating that at initial detection, the mode may not be a classical TM. |
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GP11.00035: Empirical boundary detection of tearing mode onset at DIII-D Jinxiang Zhu, Cristina Rea, Robert S Granetz, Earl S Marmar, Ryan M Sweeney, Francesca Turco, Keith Erickson, Jayson L Barr, Roy A Tinguely An empirical boundary for the n=1 tearing mode (TM) is developed via data-driven method and verified on thousands of DIII-D shots. The locked n=1 TM is a key precursor leading to disruptions and its predictive ability is strongly desirable for ITER and SPARC. The fitted boundary is a linear function of equilibrium parameters like collisionality, poloidal beta and the MHD risk factor (a combination of the normalized electron temperature profile width, q95 and elongation). The boundary indicates with a value related to the probability of having the TM onset within 200 ms and it achieves ~85% of shot-by-shot accuracy in offline analysis of DIII-D data. Preliminary cross-machine analysis of TM onset prediction shows potential applicability of the empirical boundary to C-Mod and EAST data as well, but the relative importance of the individual parameters is different for different devices. This suggests the existence of different trigger mechanisms for the TMs, implying that the boundary could be generalized using data from various tokamaks representing different trigger mechanisms to improve its extrapolability. Finally, this new proximity metric to the n=1 TM onset has been incorporated into the real-time in DIII-D plasma control system and results from experiments will be discussed. |
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GP11.00036: Low-n MHD mode in Interchange Mode Regime with Negative Triangularity Configuration Michio Okabayashi, Qiming Hu, Takemura Yuki, Max Austin, Nikolas C Logan, Ted Strait, Linda E Sugiyama A low-n MHD mode with broad radial structure has been found in negative triangularity (NT) configurations in the DIII-D tokamak. Traditional positive triangularity (PT) configurations, stabilized with a combination of magnetic shear and a magnetic well, suppress the growth of low-n plasma pressure non-uniformity, which has been considered a key to the successful achievement of high-beta toroidal fusion reactors. Recent exploration of DIII-D NT configurations that are geometrically favorable for plasma exhaust optimization has formed high beta plasmas comparable to the PT configurations. A betan of ~3 has been achieved with q(0)~1 and q95~5. In contrast to typical PT configurations, low-n MHD activities are often excited. An example is a continuous low-n mode with broad radial width in the core. ECE perturbative mapping shows the complexity of the mode structure at the rational surfaces at 3/2 and 2/1. This mode appears to provide a process to dissipate unstable energy sources, similar to the sawtooth process in the PT configuration. The achievability of even higher betan in NT is thus likely to depend on the successful control of this n=1 mode’s radial structure. |
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GP11.00037: Variable-spectrum mode control of high poloidal beta discharges Jeremy M Hanson, Mitchell D Clement, Andrea M Garofalo, Edward J Strait DIII-D experiments show that the changing structure of the least-stable plasma kink mode with q95 can be tracked using a specially designed control strategy. In the new setup, DIII-D’s two rows of internal coils are configured as separate feedback loops with dedicated sensors that minimize the local n=1 perturbed magnetic field. The loops independently adjust amplitudes and toroidal phases of their control fields, bringing about changes in the poloidal spectrum of the total applied field. In the experiments, q95 was varied between 11 and 6 while the pressure exceeded the ideal MHD no-wall stability limit by 40%. The relative phase-shift of the coil rows changed by approximately 50 degrees over this q95 range, and approached the value typically used in traditional hard-wired coil setups at q95=6. The dependence of the coil phase-difference on q95 is qualitatively compatible with VALEN simulations of the coil couplings to the least-stable plasma mode. This new strategy provides a spectral optimization for kink mode control that works over large variations in plasma q. |
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GP11.00038: Utilizing two identical shattered pellet injections for thermal mitigation on DIII-D Jeffrey L Herfindal, Daisuke Shiraki, Larry R BAYLOR, Eric M Hollmann, Zana Popovic, Claudio Marini, Nicholas Eidietis, Andrey Lvovskiy Experiments on DIII-D used two SPIs with pellets of equal composition (~200 torr-L of pure Ne each) simultaneously or with a slight time delay between injections. Simultaneous injection exhibits a reduction in the pre-thermal quench time (time from when SPI fragments reach the plasma edge until the start of the thermal quench), relative to similar single SPI mitigated shutdowns. Radial electron density measurements increase in a similar fashion while a vertical array shows a much faster electron density increase in the plasma core for simultaneous SPIs. Total radiated energy during the thermal quench, determined through summing radiated energy at three toroidal locations, and the current quench (CQ) duration are approximately the same for single or simultaneous injection. Additionally, fast visible camera images and analysis of impurity radiation from fast bolometer fan arrays show the injected impurities spread primarily in the parallel direction, away from the injection location in two distinct regions, corresponding to each of the SPIs. This separation of radiative zones suggests a lower radiation peaking factor, which is a promising result towards the success of the massively parallel ITER SPI system. |
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GP11.00039: LOW TEMPERATURE PLASMA Session Chairs: |
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GP11.00040: Overview of the initial diagnostic suite planned for MPEX Theodore M Biewer, Ted Boyd, T Bjorholm, Drew B Elliott, Keisuke Fujii, Travis Gray, Nischal Kafle, William Sides The Material Plasma Exposure eXperiment (MPEX) is a planned steady-state device at ORNL that will be used to study plasma-material interactions to advance the progress of engineered materials for the plasma facing components of fusion reactors. The final design review of MPEX has concluded, including the diagnostic suite of instrumentation. Similar to other fusion-relevant devices, MPEX diagnostics will serve a variety of roles: machine protection, basic operation, advanced plasma control, and scientific utilization. The initial (Phase I) diagnostic suite is planned to include: Thomson scattering, optical emission spectroscopy, interferometers, visible and infra-red camera imaging, pyrometers, microwave diodes, residual gas analysis, and in vacuo surface analysis techniques. MPEX diagnostics will be implemented in a staged approach; Phase I diagnostics are those necessary to meet key performance parameters, while Phase II diagnostics are those necessary for the initial scientific utilization of MPEX. It is envisioned that Phase II diagnostics could be implemented in collaboration with institutions outside of ORNL. This presentation will give an overview of the planned diagnostic layout for MPEX. |
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GP11.00041: Validation and testing of high heat flux in-vessel components of the Material Plasma Exposure eXperiment (MPEX) Travis Gray, Aftab Hussain, Adam Aaron, William McGinnis, Vimal ramanuj, Vivek Rao, Douglas E Wolfe, Dennis Youchison The Material Plasma Exposure eXperiment (MPEX) is a new linear plasma facility under construction at Oak Ridge National Laboratory to study reactor relevant plasma material interactions, novel plasma facing materials and neutron-irradiated samples under steady-state conditions. MPEX will be capable of operating steady-state (~ 2 weeks) with ~1 MW input power, thus in-vessel components require active cooling and monitoring. These in-vessel components include the microwave absorbers (MWA) used to absorber stray microwaves; tungsten limiters to form the outer boundary of the plasma column; an upstream dump (UD) that intercepts helicon plasma; and the target assembly located downstream from the helicon and RF heating regions of MPEX where plasma-material interaction (PMI) science will be performed with multiple plasma diagnostics such as spectroscopy and Thomson Scattering. Test articles of each of these in-vessel components have been designed and fabricated to closely match the MPEX design. The test articles are subject to MPEX relevant heat fluxes using an electron-beam to provide high heat fluxes (HHF) to the test article to validate the performance of thermal interfaces in each component. In the case of brazed thermal interfaces, ultrasonic testing (UT) has been used pre and post HHF testing to quantify the quality of the interface. HHF testing of the test articles is underway and results will be presented. |
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GP11.00042: Supercontinuum diagnostic for detecting solvated electrons produced by atmospheric pressure plasma Adam D Light Contamination of groundwater by poly-fluoroalkyl substances (PFAS) is increasingly recognized as a major environmental issue. These compounds bioaccumulate, can cause adverse health outcomes, and are difficult to break down. Low temperature plasma (LTP) offers promising avenues to remediation, especially via the production of free electrons dissolved in water (“solvated electrons”). We present the design of recently-funded experiments focused on understanding this process. We plan to measure the time-dependent concentration of solvated electrons produced by atmospheric pressure plasma at the water’s surface using a pulsed supercontinuum light source. Supercontinuum transient absorption spectroscopy is a well-established method for studying time-resolved chemical and physical processes, but it has not yet been applied to LTP or to the plasma/water interface. By coupling supercontinuum transient absorption spectroscopy with the total internal reflection geometry of Rumbach, et. al (2015), we hope to obtain surface-sensitive measurements with nanosecond time resolution over a wide absorption band. We will describe the current diagnostic design and discuss the expected challenges, workarounds, and enhancement techniques that may be necessary to improve the signal to noise ratio. |
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GP11.00043: Magnetic Measurements of Arc Instabilities in Segmented Arc Heater Column Magnus A Haw, Sebastian V Colom The Aerodynamic Heating Facility (AHF) at NASA Ames Research Center (ARC) generates high enthalpy, supersonic flow environments for ground testing of NASA heat shield materials. This arc jet heater operates by passing a DC arc (<3200A, <2500V) through a gas column (~10cm diameter, 2m length) and ejecting the heated gas through a supersonic nozzle into a test chamber. The arc plasma is a partially ionized air mixture at low temperature (< 2 eV) but needs to be stable for long test times (up to 30 min) at high power (< 20 MW). Currently, the operational envelope of the facility is limited by arc instabilities including the kink instability. Consequently, it is of interest to characterize these instabilities to better understand facility limits and inform methods to extend stable operational ranges. Due to the high enthalpy and long timescales (i.e., minutes) diagnostics must be non-invasive. This work will cover the development of two sets of magnetic sensors: differential B-dot sensors and tri-axial magnetic hall sensors and will describe initial measurements of arc motion using these sensors. |
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GP11.00044: Near and on-substrate plasma characterization in pulsed laser deposition processes. Diego A Oportus, Hugo M Ruiz, Luis Sebastian Caballero Bendixsen, Felipe Veloso, Mario Favre Although pulsed laser deposition (PLD) of thin films is a mature technique, the actual plasma processes and plasma properties close to the substrate have not been characterized in detail. We present a spectroscopic characterization of the near and on-substrate plasma using a Nd:YAG laser, 340 mJ, 3.5 ns, at 1.06 mm, focused on a rotating calcium doped graphite target, at ~2×109 W/cm2, in Argon background. Plasma temperature is inferred from Boltzmann plots of ArII lines and spectra fitting of C2 swan bands emission. CII and CaII Stark broadening of emission lines is used to infer the plasma electron density. A comparison is made between a free streaming and on substrate plasma. Characteristic temperatures of the free streaming plasma are in the range ~2.5±0.3 eV at early times, ~100 ns after laser plasma formation, which decreases to ~1.2±0.2 eV, at later times, ~560 ns, with electron density ~1016 cm-3. Characteristic plasma parameters for the on-substrate plasma are found to be ~0.8 eV and ~1018 cm-3, being the higher electron density attributed to on-substrate plasma stagnation. These observations contribute to a better understanding of the plasma processes in PLD. |
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GP11.00045: Measurements of argon metastable species in an electron beam generated plasma V S Santosh K K Kondeti, Shurik Yatom, Nirbhav S Chopra, Yevgeny Raitses Electron beam (e-beam) generated plasmas show promise for their use in the processing of materials by enabling control over the electron energy while maintaining a low electron temperature [1]. In this work, we used laser induced fluorescence (LIF) to measure the argon metastable Ar (1s5) density in a partially magnetized ExB argon plasma produced by a keV-range e-beam in the pressure range of 25-90 mtorr. Langmuir probe measurements were made to obtain the electron temperature and density. The Ar (1s5) metastable density increased with pressure and was in the range of (3-8) x 1016 m-3 in the core of the discharge. We will discuss this effect of the argon pressure and physical mechanisms governing the measured spatial distribution of the argon metastable. |
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GP11.00046: Princeton Collaborative Low Temperature Plasma Research Facility (PCRF): status update and new solicitation of user proposals Yevgeny Raitses, Igor D Kaganovich, Mikhail N Shneider, Sophia Gershman, Shurik Yatom, Arthur Dogariu, V S Santosh K K Kondeti, Ivan Romadanov, Nirbhav S Chopra, Alexander V Khrabrov, Willca Villafana, Anatoly Morozov The Princeton Collaborative Low Temperature Plasma Research Facility (PCRF) [1] is a collaborative research facility providing expertise and instrumentation for comprehensive characterization of low temperature plasmas (LTPs) with the goal of advancing methods of predictive control of LTP. PCRF collaborative users have access to the state-of-the-art research capabilities, including advanced plasma diagnostics (e.g. Laser-Induced Fluorescence (LIF), Two-Photon Absorption LIF, Thomson scattering, Electric Field-Induced Second Harmonic Generation, Hybrid Coherent Anti-Stokes Raman Scattering), a variety of plasma sources, computational codes (e.g. 2-D and 3-D Particle-in-Cell codes and fluid codes), and theory support. Since its launch in 2019, about 70 users from the plasma and a broader scientific community have been awarded runtime at the PCRF. The projects cover: i) plasma-liquid and plasma-solid interactions, ii) plasma transport, iii) collective phenomena in LTP, iv) use of LTP in modern applications, including plasma processing and synthesis of materials, plasma medicine, plasma-assisted catalysis, sustainability, and aerospace. In this presentation, we will discuss PCRF research capabilities, recent user projects and opportunities for collaboration. |
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GP11.00047: Measurements of ion velocity distribution function using a confocal laser induced fluorescence with annular laser beam Ivan Romadanov, Yevgeny Raitses Laser Induced Fluorescence (LIF) is a widely used diagnostic, which allows for measurements of velocity distribution functions and temperature of ion or neutral species in plasma. Conventional LIF diagnostic requires access to plasma from two sides: for the laser beam injection and in perpendicular direction for the fluorescence emission collection [1]. It is not always possible to have such access to the plasma volume. Alignment of two optical branches is more complicated for the conventional LIF as well. Confocal configuration of laser induced diagnostics is widely used in biology and medicine and there are several works discussing its application for plasma diagnostic [2-4]. Its main advantage is that laser beam injection and fluorescence collection branches coincide. Axicon lenses were used to create an annular laser beam, which is focused into the argon plasma. In this work we present the results of initial measurements of argon ion velocity distribution function with the axicon based confocal LIF system. |
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GP11.00048: Bdot probe and Rogowski coil cross calibration and sensor fusion in pulsed direct current capacitor discharges Mark B. Moffett, David L Chesny, Kaleb W Hatfield, Jake M Cole, Razvan Rusovici Bdot probes and Rogowski coils are used in the measurement of transient magnetic fields and currents, respectively. They both share the mechanism of creating an induced electromotive force response via Faraday's law, which scales linearly with the pulsed magnetic field. High power capacitor direct current (DC) discharge systems release a single pulse of current that is both very high (kA) and very fast (< 1ms). To capture this transient data and characterize these systems, high current tolerant and fast response time sensors are required. Using robust analytical calculations, finite element analyses, and empirical methods, we have developed a sensor fusion protocol for current and magnetic field probes (relative errors of ±13% and ±15%, respectively) for use in any geometry of high speed pulsed DC current calibrated capacitor discharge systems. This work comprehensively outlines the design and sensor fusion methodologies that allow for the deployment of in-house built Bdot probes and Rogowski coils to a wide range of pulsed DC systems and demonstrates their use in a characteristic plasma environment. |
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GP11.00049: Electron density characterisation using plasma loaded microwave cavity resonators Luc S Houriez, Jesse A Rodriguez, Mark A Cappelli Gas discharge tubes present a convenient and cost-effective way to produce plasmas for studying electromagnetically active systems. Their electron density can be tuned over a given range by varying the discharge voltage. Furthermore, the plasma column can be magnetised to exhibit gyrotropic properties. These characteristics have led to the increasing use of gas discharge tubes in the fields of photonics and topological materials. Although sometimes estimated through analytical investigation and simulations, the plasma proprieties of these gas tubes often remain imprecisely determined. We present a scalable, reproducible and economic method to determine plasma frequency and electron density tuning range in non-magnetised and magnetised gas discharge tubes. Experiments and simulations are carried out for 0-50mT magnetic fields and 2-18 GHz microwave frequencies for multiple gas discharge tubes with plasma frequencies in the 3-10GHz range. |
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GP11.00050: Time-Resolved Radial Velocity Profile Measurements on a Coaxial Plasma Accelerator Aduragbemi A Jibodu, Jesse A Rodriguez, Arnaud M Ballande, Mark A Cappelli We report on measurements of the radial profile of the axial velocity component of a gas-fed shear-flow stabilized coaxial Z-pinch plasma accelerator operating in a deflagration mode. Doppler-shifted axially-directed spectral line emission of hydrogen and impurities are recorded from the plasma jet generated by the Stanford Coaxial High ENerGy (CHENG) device using a Raman monochromator paired with a high frame rate (10 MHz) intensified camera allowing for resolutions of up to 100 ns. This configuration affords single-shot video of 1D-1V dynamics (time-dependence) of the Stark-broadened/Doppler shifted spectral lines to determine axial velocity, temperature, and electron number density as a function of radial position. Derived velocities are compared to time-of-flight velocity measurements taken on the same device for the same conditions. |
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GP11.00051: Effect of pressure on the fundamental parameters' spatio-temporal evolution in a µs pulsed-power glow discharge in low vacuum as studied via laser scattering techniques Gerardo Gamez, Steven J Ray, Kevin Finch Laser scattering (LS) plasma-diagnostic techniques (Thomson, Raman, and Rayleigh) have inherent spatio-temporal resolution, minimal-to-no plasma perturbation, and do not require local thermodynamic equilibrium assumptions. While LS instrumentation can be complex for low-density plasmas, e.g. low vacuum glow discharge (GD), they are the method of choice when available, given all their advantages. |
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GP11.00052: Characterization of a Small-Scale Helicon Based Plasma Ion Source Foisal Bin Touhid Siddiki, Marcel D Granetzny, Michael Zepp, Oliver Schmitz, Thilo M Hauser, Eric Alderson, Levon McQuown Ion beams are widely used in semiconducting industries, in applications based on accelerators as well as in space propulsion. At UW-Madison, we are developing a small-scale high-density helicon plasma source as an ion source. Helicon sources are known for their high degree of ionization and a small-scale source can provide a high current ion beam in the range of 0.1-10 mA [1]. The source (R = 17 mm, L = 178 mm) is equipped with a helicon antenna that delivers power at 16.2 MHz with RF power up to 850 W. The source is surrounded by two magnetic coils and can provide up to 700 G of axial magnetic field at 5.5 A. With this setup, a stable helicon plasma, as detected by the typical blue Ar-II core was produced. To verify the helicon dispersion behavior, a neural network based on line-ratio spectroscopy is being developed to measure the plasma parameters (ne ,Te). The results from the neural network will be validated with the measurement from the laser-induced fluorescence (LIF) diagnostic. The ion beam current will be measured with a Faraday cup. Here, measured plasma parameters and ion beam current will be presented at different operating parameters. |
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GP11.00053: Measuring azimuthal magnetic field magnitudes in a plasma gun generated single flux rope with laser induced fluorescence Tyler J Gilbert, Peiyun Shi, Katey Stevenson, Earl Scime It has been shown that laser induced fluorescence measurements of Zeeman split spectra offer a method to non-perturbatively measure magnetic fields in laboratory plasmas.1,2 Laser induced fluorescence is a non-perturbative laser spectroscopic technique that uses the Doppler motion of a species and a narrow linewidth laser to measure the velocity distribution function of the particles. Prior measurements demonstrated a magnetic field resolution of 10 G is achievable with CW laser in a steady-state plasma.2 For the results presented here, a Quantel pulsed dye laser is free-space injected parallel to the background guiding magnetic field into the PHAse Space MApping experiment (PHASMA), which is a helicon plasma source equipped with two plasma guns capable of generating 10 ms long flux ropes. Zeeman split Ar I σ-peaks are measured in a pulsed, single flux rope plasma. Here we present measurements of the azimuthal magnetic field created from a single flux rope. These initial measurements show the viability of using this technique for future magnetic imaging of laboratory magnetic reconnection events arising from the merger of two flux ropes. |
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GP11.00054: Multi-Dimensional Electron Velocity Distribution Functions Measured Via Incoherent Thomson Scattering System in PHASMA Peiyun Shi, Earl Scime For weakly collisional, magnetized plasmas, particle temperatures perpendicular and parallel to background magnetic field can be different. Such temperature anisotropy occurs in the expanding solar wind, during magnetic reconnection in the magnetosphere, and in laboratory plasmas. Electron temperature anisotropies are also believed to play an important role in laboratory magnetic mirror and terrella experiments. However, direct measurement of electron temperature anisotropies is quite challenging. Having demonstrated 1D electron velocity distribution functions (EVDFs) measurement via incoherent Thomson scattering system in the PHAse Space MApping (PHASMA) device [Shi et al., Rev. Sci. Instrum. 92, 033102 (2021)], we have now enhanced the Thomson scattering system in PHASMA to provide 3D EVDF measurements for the first time in a laboratory plasma. Our approach is to add one more injection path along the axial direction and one more collection path in the perpendicular plane. Four Thomson scattering spectra are measured along four different directions, defining an over-determined set of measurements of 3D . Preliminary 3D EVDF measurements for the pulsed gun plasmas and static helicon plasmas will be presented. |
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GP11.00055: Spatiotemporal Characterization of an Electrothermal Arc Plasma Beam Darren J Craig, Theodore M Biewer, Drew B Elliott, Keisuke Fujii, Trey E Gebhart, Lauren Nuckols The Electrothermal Arc (ET-Arc) plasma source can provide transiently-relevant particle and heat fluxes (~ 1 GW/m2) to simulate the extreme conditions that occur, for example, during edge localized modes (ELMs) in tokamak divertors. We extend previous studies of a source developed at Oak Ridge National Lab (ORNL) to better characterize the temporal and spatial dependence of the plasma beam parameters using optical emission spectroscopy (OES) and Thomson Scattering (TS). The OES system provides time-resolved measurements of line brightness (for line-ratio measurement of plasma density and electron temperature), line broadening (for plasma density and ion temperature), and line shift (for ion velocity). Emission from hydrogen, helium (the working gas), and boron is analyzed and compared. Simultaneous collection of emission from up to 22 different lines of sight provides information about how the beam parameters vary along the beam trajectory. Shot-to-shot adjustment of the data collection time provides information about the time dependence of the emission (and derived plasma parameters) throughout the 1 ms long plasma discharge. The different atomic species and measurement techniques provide the opportunity to measure some of the same plasma parameters (e.g. plasma density and electron temperature) with two or more independent techniques, allowing underlying assumptions to be evaluated. |
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GP11.00056: Studying Time-Dependent Filamentation in Magnetized Low Temperature Plasma with MDPX Elon Price Studying complex or "dusty" plasmas will provide valuable insight, from diagnostics to first principles, into interdisciplinary areas of research including astrophysics, energy applications, agriculture, and medicine. Based upon the charge-to-mass ratio of the dust component, a magnetic field of B ⩾ 1 T is required in order to observe effects due to magnetic forces. However, with fields higher than 1.5 T, an instability occurs in the radio-frequency (RF) generated background plasma called filamentation. With the use of optical diagnostics via 3D Particle Image Velocimetry (PIV), the spatial morphology of these filaments has been observed and categorized into three different types or filamentary modes. In addition, the filaments have appeared to transform modes over time. This poster aims to explore the time-dependence of the spatial modes through image analysis, looking at properties such as discreteness of type and filamentation formation. Understanding both the spatial and temporal characteristics will support a first principles theoretical framework for this instability. |
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GP11.00057: Study of magnetically controlled plasma for efficient laser-plasma-induced EUV generation Joohwan Kim, Mathieu Bailly-Grandvaux, Farhat N Beg Efficient generation of 13.5 nm light, increased conversion efficiency and output power, are extremely important for the application of extreme ultraviolet (EUV) lithography. However, little work has been done on magnetically control of plasmas in the generation of EUV sources. In this work, we computationally studied the effect of magnetic field on laser-plasma interaction, plasma dynamics, and radiation with different laser wavelengths, 1-10µm. We benchmarked existing experimental data using two-stage simulations: radiation hydrodynamics code FLASH with a tabulated equation of state and an atomic code SPECT3D. After benchmarking the code, we studied the impact of magnetic field, up to 10s of Tesla on laser driven Sn plasma. Simulations show that plasma dynamics in time are restricted depending on B-field direction, resulting in target heating to higher temperature compared to laser driven plasma without B-field as it shows isotropic expansion. Additionally, these different plasma dynamics affect EUV generation, total flux, and in-band emission in 2% bandwidth around 13.5 nm. Detailed methods and results of systematic simulations will be presented. |
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GP11.00058: A General Analytic Electron-Impact Ionization Electron Energy Sharing Model for Monte Carlo Plasma Modeling Ryan M Park, Brett Scheiner, James Colgan, Christopher J Fontes, William Kupets, Eddy M Timmermans, Xianzhu Tang, Nathan Garland Modeling non-equilibrium plasmas with Monte Carlo collision codes or Boltzmann equation solver codes requires input of collision cross sections and or scattering models. Recently we have developed a general analytic scattering model for calculating the electron-impact ionization electron energy sharing distribution function, which can be readily implemented in Monte Carlo simulation codes. Here we present our approach and show the utility and accuracy of the model for a wide range of impact energies, species, ions, and species excited states. We compare this approach to scattering models generally utilized by Boltzmann equation solver and collisional Monte Carlo codes, e.g. the commonly used model of C. B. Opal et al. J. Chem. Phys. 55, 4100 (1971), the equal-energy sharing approximation, and approximating the primary electron to take all of the excess energy. We note that unlike the commonly used approach of Opal, the present analytic model is applicable to all species, requires minimal input data from the user, and does not rely on experimentally determined parameters. |
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GP11.00059: An Open Source, Three-Dimensional Kinetic Code for Modelling Low-Temperature Plasmas on Modern Supercomputing Architectures Andrew T Powis, Johan A Carlsson, Stephane A Ethier, Alexander Khaneles, Grant Johnson, Maxwell Rosen, Igor D Kaganovich Over the past four years the Princeton Plasma Physics Laboratory has been developing a new kinetic particle-in-cell code designed for use by the low-temperature plasma community. The code, LTP-PIC models complex geometry on a uniform Cartesian mesh in two and three dimensions, incorporating a geometric multigrid linear algebra solver for the Poisson equation. LTP-PIC can handle an arbitrary number of charged species, which can interact with a uniform neutral background via elastic and inelastic collisional processes, including ionization and charge exchange. Surface interactions including secondary electron emission and charge accumulation on dielectric surfaces can also be modelled. |
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GP11.00060: Quantifying the relaxation rate of the electron-energy distribution function to determine the fidelity of tabulated rates for fluid plasma models A. Stephen Richardson, Tzvetelina B Petrova, Stephen B Swanekamp Rate coefficients for fluid models of low-temperature plasmas (LTP) are often calculated with an equilibrium Boltzmann solver, and then tabulated as a function of the reduced electric field (E/N, where E is the electric field and N is the density of the neutral background gas). This approach produces excellent results for LTP simulations, as long as the equilibration time is short compared to the intrinsic time scales in the problem (the adiabatic approximation). In some cases, the problem time scale is shorter than the time it takes for the electron energy distribution function (EEDF) to reach equilibrium, and in this case the adiabatic approximation is not valid. In this work we attempt to quantify the EEDF relaxation time by using a time-dependent Boltzmann solver to measure how long it takes for the EEDF to respond to a change in the applied electric field. We illustrate our method by applying it to a toy model of molecular nitrogen chemistry, which includes elastic scattering and three representative inelastic processes. In this case we find relaxation times can reach 100's of nanoseconds, which is much longer than the time scale of some pulsed electron-beam driven problems of interest. This indicates that using equilibrium rates may not be appropriate for modeling these fast pulsed problems. |
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GP11.00061: Identifying Complex Plasma Crystals using Digital Image Analysis Mason S Sake, Uwe Konopka Complex (dusty) plasmas are the mixture of electrons, ions, and neutral atoms with the addition of charged macroscopic dust particles of nanometer to micrometer size. These systems exhibit gaseous, fluidic, and crystal-like phases depending on the electrostatic and kinetic energies of the system. Previously, these systems have been characterized using spatial correlation functions, particle dynamics, and calculation of the rotational invariance maps through using particle tracking velocimetry (PTV). This article aims to expand on that work to further identify specific crystal structures such as face centered cubic (fcc) by calculating the rotational invariance maps directly from digital images, sidestepping the need for PTV data. This technique has potential advantages for real time analysis and experimental control. We present a Python library package workflow for identifying the different phases; as well, we show preliminary results of the temporal evolution of crystal formation in a dusty plasma cross section. |
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GP11.00062: Nanosecond pulsed discharge regime transitions in response to dynamic combustion environments Colin A Pavan, Santosh Shanbhogue, Drew Weibel, Felipe G del Campo, Ahmed F Ghoniem, Carmen Guerra-Garcia Nanosecond pulsed discharges are a promising technology to improve the static and dynamic stability of flames. Whereas most works have centered on the impact of the plasma on the flame, fewer studies have focused on the implications of having a strongly inhomogeneous and unsteady environment on the discharge characteristics. In this contribution we present experimental efforts to quantify the response of the discharge mode and energy deposition to dynamic combustion environments. The first experimental setup considers a premixed methane/air mesoscale combustor, that allows for 1D laminar flame propagation and provides a simple-to-characterize gaseous background, coupled to nanosecond repetitively pulsed discharges in a dielectric barrier discharge configuration. The study reveals the strong coupling of the discharge mode and energy deposition with the relative positioning of the flame. The second experiment considers a burner of more practical interest: a swirl-stabilized combustor of 14kW power under lean conditions and experiencing a 120Hz acoustic instability. The discharge is now generated in a pin-to-ring configuration with the objective of suppressing this instability. In a similar way to the 1D laminar experiment, the discharge evolves over the oscillation cycle of the flame. The results from this work have implications when designing plasma-assisted actuation strategies. |
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GP11.00063: Anomalous electron decay in nanosecond repetitively pulsed discharges Alexey Shashurin, Xingxing Wang, Adam R Patel Nanosecond pulsed discharges (ns-discharges) have recently been proven valuable over a wide range of applications in the fields of combustion, aerodynamics, medicine, and many others. A comprehensive study of the properties of ns-discharges including dynamics of plasma generation and subsequent decay is critical for tailoring the plasma to a particular application. |
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GP11.00064: Towards once-through plasma removal of PFAS in ground water John E Foster, Joseph R Groele, Roxanne Z-P Walker Per- and polyfluoroalkyl substances (PFAS) are long lived, recalcitrant compounds found in drinking water sources. Removal of these carcinogentic compounds to regulatory limits is costly involving typically a sorptive stage followed by high temperature incineration. Plasma methods offer a nonthermal destructive approach that has shown great efficacy at PFAS removal. Here we present results from the treatment of PFAS contaminated ground water using a pulsed plasma reactor with liquid dielectric barriers. The reactor demonstrated the capacity to reduce the contaminant levels below regulatory action levels. Here we present on plasma discharge performance as well as discuss an approach that enables once through treatment at large flows in contrast to batch mode processing. |
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GP11.00065: Correlation of Plasma Properties with Gas Phase Products in Nonthermal Plasma-Assisted Pyrolysis/Hydrogenolysis of Polymers Roxanne Z-P Walker, Sophia Gershman, Henry Fetsch, John E Foster Plastic disposal is of global concern, and upcycling plastics via pyrolysis is limited by high bulk temperature requirements and low product selectivity. The use of nonthermal plasma can mitigate these problems. This work provides an exploratory study of plasma properties and correlated gas phase products in a nanosecond pulsed nonthermal plasma spark discharge over a bed of common polymer powders, in argon, hydrogen (to promote hydrogenolysis), and nitrogen gas mixtures. Optical emission spectroscopy is used to determine plasma density, electron, and gas temperatures and Fourier Transform infrared absorption is used to determine the concentrations of gas phase products. The work provides insight into the design of plasma reactors for depolymerization and highlights the importance of hydrogen gas and heat addition in the reaction chemistry. |
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GP11.00066: Plasma processing for color center qubit optimization - simulations and experiments Kaushalya Jhuria, Arun Persaud, Wei Liu, Qing Ji, Alexander V Khrabrov, Igor D Kaganovich, Thomas Schenkel Color centers in semiconductors are promising qubits for applications in quantum sensing and quantum communication. Color centers often form when dopants are introduced into the host crystal matrix combined with energetic radiation and thermal annealing. QIS applications benefit from color centers that can be formed reliably of high quality and this poses new challenges and opportunities for materials processing including with ion beams and plasmas. We utilize EDIPIC-2D, a simulation code that is parallelized, to estimate the energy and particle distribution for a variety of hydrogen plasma conditions. We report on plasma simulations that inform experiments on plasma doping and color center formation and on experimental results from color center characterization in silicon and diamond. |
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GP11.00067: A Comparative Study Enhancing Seed Germination and Plant Growth Using Plasma in Vacuum and Plasma at Atmospheric Pressure Marycarmen Morales Two devices were used to treat watermelon and melon seeds with plasma. The first device was a Dielectric Barrier Discharge (DBD) Structure to generate non-thermal atmospheric plasma. A voltage source of 20 kV and 20kHz was applied to a structure made of stainless steel rods. The seeds to be treated were placed under the structure and were treated with plasma for an optimal of 3 minutes as previously determined. The second device used was the Plasmionique PBII300 using nitrogen gas at pressure of about 1.1E-1 Torr to create plasma. Seeds in the vacuum were treated for 3 minutes. Along with seeds that were not treated by either method all seeds were planted and their germination process was monitored. Only 80% of the seeds planted that were non-treated sprouted while those treated by plasma in vacuum had a 100% success and those treated with plasma at atmospheric pressure had a success rate of 90%. A further study testing various times for using the plasma in vacuum method showed that the optimal time for the seed treatment is 60 second. Further work comparing the treatment of seeds for 3 minutes at atmospheric pressure and 60 seconds using plasma in vacuum is being done. |
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GP11.00068: Growth and analysis of carbonaceous and metallic microparticles using capacitively coupled rf plasmas Bhavesh Ramkorun, Saikat C Thakur, Swapneal Jain, Ryan Comes, Edward Thomas, Jr. This presentation reports on the formation of carbonaceous nanometer to micrometer sized particle formed in a capacitively coupled rf plasma using a mixture of argon and acetylene and/or metal-organic gaseous precursors. Experiments are performed using a 13.56 MHz rf source that delivers up to 10 W of input power to various gas mixture. Particles spontaneously grow in this plasma and form a dust cloud which levitates in between the electrodes. Particle growth is cyclic as particles grow large enough to no longer remain suspended in the plasma; leading to a subsequent growth process. Particle that fall out of the plasma are captured on a glass slide at the bottom of the experiment. Ex-situ analysis is performed on the particles to determine their size distribution and chemical composition. For the carbonaceous particles, optical microscopy images reveal that their average diameter increases from ~0.5 to ~0.9 μm with increasing acetylene flow rate. Upcoming experiments will examine the properties of the metallic particles. The long term goal of these studies is to fully characterize particle growth of a variety of particle types ahead of future experiments to study particle growth in strongly magnetized plasmas. |
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GP11.00069: Numerical simulation of plasma sheaths inside the Hollow cathode discharge using the 2D-2V continuum-kinetic method Moises A Angulo Enriquez, Michael D Campanell
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GP11.00070: Spectral characterization of LaB6 Hollow Cathode operation on Kr gas Oleg Batishchev, Frederick Sheehan Krypton gas is a viable alternative to Xenon propellant [1] for Electric Propulsion. Hall Effect Thrusters are being used commercially with Kr due to its significantly lower cost, but such operation was not studied as intensively as for Xe. We have previously reported initial results for Busek’s BHT-200 200W thruster running on Kr propellant [2]. In the present work we are investigating the Kr operation of the corresponding hollow cathode using a LaB6 emitter. Broad EUV-VIS spectra of the hollow cathode are presented first by looking straight into the cathode orifice with vacuum spectrometer. Next, detailed NIR-VIS spectra are discussed. Particular attention is given to LaB6 erosion product emission lines and their dependance on propellant flow rate and discharge current. The high-resolution spectroscopic system [3] is used to decipher discharge composition with sub-pm resolution inside the cathode and in the emitted plasma plume. |
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GP11.00071: Expanded Semi-Empirical Model of RF-driven Nitrogen Gas Discharge Alexander Hyde, Oleg Batishchev Nitrogen is the most abundant atmospheric gas with the strongest covalent bond. N2 gas discharges are widely used in industry and scientific research. We report on the continued development of a power-mass balance model for an axisymmetric RF discharge [1-3] in nitrogen that includes the dominant physical processes such as axial and radial transport, molecular dissociation, ionization, excitation, wall loses, etc. The molecular gas brings additional complexity to the numerical model, which was originally developed for argon [4]. The model considers several molecular and atomic metastable levels. It also includes emission from the strongest systems that have been detected in experiment: 1st and 2nd positive, 1st negative and Lyman–Birge–Hopfield. Spectral data from vacuum EUV spectrometer and high-resolution NUV-NIR spectroscopic system [5] are presented and compared to the simulated data. Hysteresis of the light-to-plasma sources transition is predicted numerically and discussed. |
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GP11.00072: Plasma Parameter Scaling at High Powers for a Magnetically Shielded Hall Thruster Operating on Krypton Leanne Su, Thomas Marks, Benjamin A Jorns Hall thrusters are a mature electric propulsion technology with the potential to scale to the 100-kW range, which may enable crewed deep space travel. Magnetic shielding, a magnetic field topology that reduces thruster erosion, has extended the lifetimes of these devices, but the internal plasma properties of the thrusters differ from the traditional "unshielded" configuration. Additionally, while the traditional propellant of choice is xenon for its high mass and low ionization energy, the price of xenon has increased rapidly in recent years. Krypton is one possible alternate propellant, but its performance--particularly on shielded thrusters--is poor compared to xenon. There is therefore an apparent need to understand the performance of magnetically shielded Hall thrusters operating on krypton and how they scale to higher powers. This poster will present results from a multifluid simulation of a Hall thruster that have been calibrated with performance metrics such as thrust, discharge current, and ion velocity profiles. These simulations are then used to determine how various internal plasma parameters scale with both increasing current and voltage. The results are discussed in context of how they may impact thruster efficiencies at various operating conditions. |
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GP11.00073: Cross field transport in low energy beam produced plasma Elijah J Wilson, John E Foster Currently, plasma diffusion across magnetic field lines in low temperature plasma devices is not well understood. In this work we study the collection of plasma at a large electrode oriented orthogonal to an applied magnetic field along which a low energy electron beam is injected. Here the electron beam is used with background argon gas to generate the plasma. The cross-field diffusion of cold plasma electrons to the biased orthogonally oriented electrode is studied as a function of field strength and gas pressure. The local electron energy distribution function is characterized as well as the sheath thickness. Behavior in the transverse diffusion coefficient is inferred and compared with that which one would expect for classical diffusion. |
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GP11.00074: Electron cyclotron drift instability in PIC and Vlasov simulations Arash Tavassoli, Mina Papahn Zadeh, Andrei Smolyakov, Magdi M Shoucri, Raymond Spiteri The linear and nonlinear characteristics of the electron cyclotron drift instability (ECDI) have been studied through the particle--in--cell (PIC) and continuum Vlasov simulation methods. In the nonlinear regime, more intense ECDI fluctuations were observed in the PIC simulations than the Vlasov simulations, leading to an intensified heating and slightly larger anomalous current. We show that, because the intensity of the fluctuations decreases with increasing the number of macroparticles per cell, this effect is likely a result of the noise in the PIC simulations. In addition, the effect of the azimuthal length (in the E×B direction) is investigated. It is shown that using a larger length, in the PIC and Vlasov simulations, leads to a more accurate linear spectrum which can lead to significant impacts on the nonlinear regime. |
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GP11.00075: Non-Perturbative Characterization of Electron Drift in a Hollow Cathode Discharge Parker J Roberts, Benjamin A Jorns Hollow cathodes thermionically emit electrons in order to sustain and neutralize a variety of plasma propulsion devices, including gridded ion thrusters and Hall thrusters. A key efficiency loss in these types of devices is the voltage drop required for the cathode plume to couple electrically to the main ion beam which produces thrust. Historically, this cathode coupling voltage has exceeded theoretical calculations, termed "anomalous" resistivity. These non-classical forces are typically attributed to plasma wave behavior, in particular ion acoustic turbulence which propagates axially in the cathode plume. Particle-in-cell simulations and and nonlinear wave theory suggest that the initial electron Mach number has a strong impact on the growth and saturation properties of these waves. Therefore, in order to better understand the first-principles mechanisms which may enable predictive and self-consistent modeling of hollow cathode behavior, it is necessary to non-perturbatively measure the electron distribution function in this device. We implement an incoherent Thomson scattering diagnostic to obtain the spectrum of scattered laser light from electrons in the plasma, which can be related to the distribution of electron velocities and characterize transport. |
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GP11.00076: Dual-View Imaging of Laser-Induced Plasma Expansion at Varying Pressures Ian Wagner, Gabe Xu Using a prism-based dual-view setup, we observed laser-induced plasma expansion at varying pressures and energies. In this experiment, a pulsed Nd:YAG laser at 532 nm was focused through a plano-convex lens and fired at a carbon target of carbon within a vacuum chamber. This plasma was then imaged at different pressures and laser energies to observe plasma expansion using a combined high-speed camera and light intensifier setup. Pressures ranged from 100 millitorr to 760 torr and laser energies of 100-400 mJ. A mirror and prism setup was used to capture the side and front views of the plasma emissions at the same time in a split-screen. This was done using a set of five mirrors and a right-angle prism mirror to capture both split-screen views into one image. Split-screen images at various pressures and laser fluences were compared with each other to evaluate differences in plasma expansion. It was found that the plasma expansion was wider and more dispersed at lower pressures compared to higher pressures. |
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GP11.00077: Cold atmospheric plasma for neural regeneration Gal Haspel, Maria Belen Harreguy, Sophia Gershman In small amounts, reactive oxygen species that are otherwise deleterious to tissue can promote growth, regeneration, and longevity. This phenomenon could be harnessed to improve the outcome of traumatic brain or spinal cord injury. Our goal is to identify plasma bioactive properties and dose that promotes neuronal regeneration. We use precise Yb-doped fiber laser microsurgery to cut a single axon without collateral damage, in an otherwise intact animal and test for neuronal regeneration and for recovery of locomotion behavior with and without plasma treatment with different plasma exposure duration and composition. |
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GP11.00078: A Study of Glow Discharge in a Strong Transverse Magnetic Field Harrison Adler, Oleg Batishchev Glow discharges in axial magnetic field have been studied intensively since the 1930s [1-2]. The radial field case has been studied as well [3], but solely for coaxial electrodes placed in a weaker field. In this work, we investigate the gas discharge from cold cathode Geissler tubes in a transverse B-field of about 2T. Though the initial goal was detection and analysis of the Zeeman effect as reported here in a different section [4], we have discovered the formation of a dense plasma layer under specific physical conditions. Interestingly, this layer forms in Ar, but not in other tested noble gases, i.e., Ne, Kr and Xe. At the same time, a weak HeII ion line was detected in a He tube. As the gas becomes ionized, plasma begins to etch the wall material, in this case, AR glass with known chemical composition. The erosion products' emission lines are identified using high-res spectroscopy. Measured broad NUV-NIR spectra are presented as well for different gases and conditions. |
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GP11.00079: Comparison of argon and helium atmospheric pressure plasma jets Evan Aguirre, Surabhi Jaiswal, Thijs van der Gaag Presented here is work on atmospheric pressure plasma jets in helium and argon. The argon plasma jet produces the metastable oxygen states O(1S) and O(1D) with emission of the “auroral” green line while the helium plasma jet does not. The electron probability distribution function is investigated with a method based on machine learning using the continuum spectra for both plasma jets. We used schlieren imaging to study plume dynamics and gas shielding effects. The surrounding gas or ambient atmosphere has a profound effect on the argon excimer emission and plasma jet behavior. Plasma parameters were determined from Lissajous plot techniques and BOLSIG+. A detailed comparison of these plasma jets will be presented which offer insight for a variety of technological applications of plasma. |
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GP11.00080: Low pressure nitrogen and air ExB plasmas generated by non-thermal electron sources Nirbhav S Chopra, Yevgeny Raitses Electron beam generated plasmas are promising for applications requiring efficient generation of ions and radicals in low pressure environments [1,2]. In this work, we discuss measurements of plasma properties and production of radical species by an electron beam generated plasma in low pressure (0.1-10 mTorr) air and nitrogen. We investigate low temperature plasmas in an applied magnetic field with magnetized electrons and unmagnetized ions. These plasmas are generated by two different sources: i) a high energy electron beam in the keV range produced by an ion-induced secondary electron emitting cathode [2] and ii) a lower energy non thermal electron source (< 100 eV) produced by a hot-filament thermionic cathode. We compare electron kinetic properties and chemical composition of the plasmas created by these two sources. In addition, we analyze plasma instabilities in both plasma systems and compare them with relevant theoretical predictions [3,4]. |
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GP11.00081: On the self-pulsating behavior of dc-driven streamer coronas Lee R Strobel, Benjamin C Martell, Anatoly Morozov, Arthur Dogariu, Carmen Guerra-Garcia Impulsive coronas, driven by dc voltage, can be traced back to the classical works of Loeb and his school. Despite the dc voltage, the discharge is a superposition of a localized glow corona, characterized by electrical and visual stability, and impulsive discharges of a few hundred ns-duration that develop at high repetition rates (1-10 kHz in the positive polarity for point-to-plate geometry, cm-gaps, in atmospheric pressure air). The self-pulsating behavior has been generally attributed to space charge shielding by the ion cloud generated by a streamer burst and gradual field recovery driven by the ion drift motion. However, up until recently, direct confirmation of this effect was not feasible. In this contribution, we report on direct measurements of the electric field at several locations within the discharge, using the Electric Field-Induced Second Harmonic (E-FISH) technique, to quantitatively explore this phenomenon. Unexpectedly, the measurements do not show a monotonically increasing field during the inter-pulse period, but rather hint a propagating wave-like feature from the plate-cathode to the tip-anode. Future work will explore these observations from a theoretical perspective. |
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GP11.00082: Atmospheric pressure plasma jet producing the auroral transition O(1S) to O(1D) Surabhi Jaiswal, Evan Aguirre, Thijs van der Gaag An atmospheric pressure plasma jet that produces the metastable oxygen states O(1S) and O(1D) with emission of the “auroral” green line has been studied. This phenomenon is caused by the 99.999% pure argon as a working gas for the plasma generation. Optical emission spectroscopy was used to infer the mechanism of O(1S) creation and destruction. The continuum spectrum was used in conjunction with a method based on machine learning for determining the arbitrary electron probability distribution function. Discharge and plasma properties were derived from Lissajous plots and calculations with the BOLSIG+ software. Fast images of the plasma jet was used to characterize the plasma flow. The metastable oxygen forms for all operating parameters of the plasma jet system in a linear electrode configuration. The plasma jet behavior changed considerably when the powered and grounded electrodes are switched but the metastable oxygen was always present. Small admixtures of oxygen and nitrogen were introduced in the plasma jet to understand the kinetic processes of metastable oxygen destruction and the 557.7 nm auroral line. This behavior has implications for plasma reactive chemistry in fundamental areas such as auroral physics as well as technological applications of plasmas. |
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GP11.00083: Numerical Modeling of Liquid Metal Free Surface Response to Large Current Pulses William Brown, Stefano Brizzolara, Daniel P Weber, Colin S Adams, Bhuvana Srinivasan Liquid metal walls may offer a unique solution to challenges with large heat flux mitigation and tritium production in several fusion concepts that are presently being explored. One such fusion concept that may make use of liquid walls is a Z-pinch, where the current path can travel from the plasma through the liquid electrode rather than a solid conductor. In this work, we perform numerical simulations on liquid metal free surface responses to large current and magnetic field pulses as could be encountered in Z-pinches. The Liquid Metal eXperimental (LEX) from Virginia Tech is used to validate a fluid model that is solved using a general purpose finite volume, implicit, unsteady Reynolds-averaged Navier-Stokes Equations (RANSE) solver with realizable k-$\omega$ shear stress transport (SST) turbulence. The simulation domain is comprised of a two-fluid mixture with a high resolution sharp interface capturing (HRIC) algorithm, which combined with the previously mentioned solver, achieves second order accuracy in space and first order accuracy in time. The simulation makes use of both a hydrodynamic model (where the electromagnetic forces have been approximated) and an electrodynamic model making use of magnetohydrodynamics to study the reaction of the liquid metal to the Lorentz force. A parametric study is also conducted to further explore the free surface response of the liquid metal in regimes that are challenging for the experiment to access. |
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GP11.00084: Femtosecond TALIF allows imaging atomic oxygen from interfacial plasmas in gas and liquid Arthur Dogariu, Brayden Myers, Katharina Stapelmann Measuring the density of reactive species using direct fluorescent emission in interfacial plasmas is challenging due to the fast quenching of the excited atomic species at and below the gas-liquid interface. Exciting atomic species in a liquid using femtosecond pulses allows for fluorescent emission on time scales comparable or smaller than those allowed by the fast collision rates in a liquid. Using femtosecond two-photon absorption laser induced fluorescence (fs-TALIF) we have succeeded in demonstrating direct imaging of atomic oxygen created by an atmospheric plasma jet impinging upon water, both above and below the gas/liquid interface. We used the fs-TALIF technique for mapping the O-density in the jet above the interface with high spatial resolution. The same resonant UV two-photon excitation of O atoms followed by fluorescent emission in the liquid allowed us to determine that atomic oxygen persists for tens of microseconds in water, penetrating hundreds of micrometers into the liquid. The high spatial and temporal resolution of fs-TALIF imaging in liquids opens the door for studying reaction rates of reactive species in interfacial plasmas. |
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GP11.00085: Imaging of a nanosecond pulse discharge in a quasi stationary bubble on time scales from nanoseconds to microseconds Sophia Gershman, Nicholas L Sponsel, Maria J Herrera Quesda, Jacob T Mast, Katharina Stapelmann Fast imaging and precise timing allows us to investigate the initiation and development of a nanosecond pulse discharge in deionized water with a quasi stationary gas bubble between two submerged electrodes. The applied voltage pulse is an unmatched 20 kV with a 7 ns rise time and ~30 ns duration of the first pulse followed by decaying oscillations lasting approximately 500 ns. When observed on a time scale of hundreds of nanoseconds or longer, the discharge appears to bridge the gap between the electrodes, while imaging on a nanosecond and ten nanosecond scale presents a different picture. Discharge initiates at the sharp positive electrode and then appears in the bubble on the positive side. The timing of the appearance of the discharge in the bubble depends on the distance between the bubble apex and the electrode tip. Imaging with delay times of 10 - 100 ns extending to the subsequent repeated voltage pulses captures repeated partial discharges in the same quasi stationary bubble. Extending the imaging to microseconds and longer reveals the formation of bubbles in the electrode region as well as the breakup of the original bubble. |
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GP11.00086: Correlations of Plasma Properties and Dielectric Surface Charge in a DC Discharge Brian Jensen, Yevgeny Raitses Charging of dielectric surfaces by a plasma occurs naturally in a host of systems ranging from laboratory plasma experiments [1], dusty plasmas [2], and electronic processing devices [3] to plasma thrusters [4] and space satellites [5]. Here, we describe measurements of bulk plasma parameters and their correspondence to surface charge. We explore a range of plasma pressures (~10mTorr – atmospheric), compositions, and substrates to determine plasma properties and their correlations with measurements of surface charge. Plasma properties are determined from measurements of the electron energy distribution function using an electrostatic Langmuir probe while surface charge is obtained with a non-contacting Kelvin probe. Our analysis addresses the effects of material properties (e.g. secondary electron emission) and structures (e.g. surface roughness) on these correlations. |
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GP11.00087: Molecular dynamics simulations of boronized graphite surfaces under bombardment by deuterium Sierra E Jubin, Aaditya Rau, Joseph R Vella, Stephane A Ethier, Igor D Kaganovich The addition of boron to graphite plasma facing components in fusion devices has been shown reduce the sputtering of wall material and increase deuterium retention. This has the effect of preventing cooling of the plasma by sputtered material, improving the performance of these fusion devices. Using the molecular dynamics code LAMMPS, we investigate the boronization of graphite surfaces, describing the formation of an amorphous boron/carbon layer. We explore the effect of boron bombardment energy on the nature of this amorphous layer, and further study the sputtering products and evolution of the boronized graphite surfaces under bombardment by deuterium. |
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GP11.00088: Electron and Ion Induced Electron Emission from Volumetrically Complex Materials for Plasma Facing Surfaces angelica ottaviano, Richard E Wirz Materials with architectured surfaces have been shown to reduce electron and ion-induced electron emission yield (SEE and IIEE respectively) because their micro-cavities can trap emitted electrons. These materials are useful for various plasma applications including electric propulsion devices, propulsion testing facilities, and confining surfaces for nuclear fusion. Electron emission can contribute to the degradation of plasma facing surfaces due to an excess of outgoing negative flux which may reduce the sheath and cause rapid wearing of the walls. In addition, electron emission can contribute to increased instabilities, anomalous cross-field currents, and cooling of bulk plasmas. In fusion energy devices, secondary electrons quickly cool down the bulk plasma, reducing the fusion reaction capability of the device. In both of these applications, understanding the nature of SEE from textured surfaces can lead to designing materials with well-characterized electron emission properties. In this work, the SEE yield of carbon foams with a fixed ligament to pore diameter ratio (aspect ratio, ??R = 0.2) is evaluated experimentally as a function of foam pore and ligament geometries using scanning electron microscopy. An analytical view factor-based model is also developed (Analytical Model for Particle Sputtering and Electron emission, AMPS-E) to validate electron emission yield trends from foams for both SEE and IIEE. Foam transparency to primary particles to a flat backplate is established and derived as a metric for incorporating foam geometric dimensions and thickness into one parameter. It is found that increased transparency increases the electron emission yield by up to 7%. Foam parameters for electron emission yield reduction of up to 38% are reported compared to flat surfaces for SEE and IIEE yield. |
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GP11.00089: Sputtering Reduction Optimization via Volumetrically Complex Materials Graeme T Sabiston, Richard E Wirz Volumetrically complex materials (VCMs) have been experimentally proven to be up to ten times more robust in harsh plasma environments, with the implied potential to significantly increase the lifetime of confining surfaces for nuclear fusion, plasma electrodes, and space propulsion components. The objective of this effort is to use advanced ion-solid interaction simulation codes and fast gradient-based optimization algorithms to investigate optimal strategies to using volumetrically complex materials for plasma-facing environments. |
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GP11.00090: Interpretation of scanning reference electrode measurements for characterization of plasma-liquid systems Elijah J Thimsen, Trey Oldham Plasma-liquid systems have been used over the past several years for the purpose of promoting chemical transformations in the liquid phase, but methods of characterizing the reaction environment in the solvent are still in nascent development. We have been using a technique that involves measuring the electrostatic potential difference between two nominally identical Ag/AgCl reference electrodes, wherein one electrode is placed near the plasma-liquid interface (PLI), and another is placed far away in the bulk solution.1-3 The electrode at the PLI can be scanned to reveal the spatial distribution of the reaction environment, and we have identified distinct zones that promote reduction and oxidation half-reactions.2 The scanning reference electrode technique has been useful to reveal the qualitative electrochemical structure of the PLI, but quantitative interpretation in plasma-liquid systems has not yet been elucidated. In this presentation, I will elucidate the fundamental meaning of the measurement by derivation from the local electrochemical equilibrium expressions and clarify the criteria that must be met for the measurement to reveal the spatial distribution of reduction potential at the PLI. Examples from well-defined electrochemical experiments involving dissimilar metals, in electrical contact though an external circuit, and ionic contact through an electrolyte, will be used to illustrate the argument. |
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GP11.00091: FUND: DUSTY PLASMAS Session Chairs: |
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GP11.00092: Mechanism for the efficient homogeneous nucleation of ice in a weakly-ionized, ultra-cold plasma Paul M Bellan It is proposed that the rapid observed homogeneous nucleation of ice dust in a cold, weakly-ionized plasma [1,2] depends on the formation of negative hydroxyl ions [called hydroxide or (OH-)] by fast electrons impacting water molecules. These OH- ions attract neutral water molecules because of the high dipole moment of the water molecules and so hydrates of the form OH-(H2O)n are formed. The hydrates continuously grow in the cold environment to become macroscopic ice grains. These ice grains are negatively charged as a result of electron impact and so continue to attract water molecules. Because hydroxide is a negative ion, unlike positive ions it does not suffer recombination loss from collision with plasma electrons. Recombination with positive ions is minimal because positive ions are few in number (weak ionization) and slow-moving as result of being in thermal equilibrium with the cold background gas. |
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GP11.00093: Current research activities in the Magnetized Plasma Research Laboratory (MPRL) at Auburn University Saikat Chakraborty Thakur, Uwe Konopka, Edward Thomas The Magnetized Plasma Research Laboratory (MPRL) at Auburn University explores a wide range of fundamental plasma and complex/dusty plasma phenomena covering the unique parameter regime of high magnetic fields (B < 4 T), at relatively low electron (Te ~ 5 eV) and ion temperature (Ti < 0.1 eV). The centerpiece of the laboratory is the Magnetized Dusty Plasma Experiment (MDPX), a highly flexible, high magnetic field plasma device with a mission to serve as an open access, multi-user collaborative research facility for the dusty plasma, basic plasma, and fusion plasma communities. Other instruments include ALEXIS, an RF driven magnetized linear plasma device for simulating space plasma and basic plasma experiments, and a wide variety of “tabletop” scale unmagnetized low temperature plasma devices. Here, we will summarize results from recent studies at MPRL, including nanoparticle growth in plasmas, pattern formation at high magnetic fields, controlling dust charging and dust dynamics by externally applied UV light, dust acoustic waves at high magnetic field, dust thermodynamics under microgravity conditions, using the dust as a diagnostic, development of new plasma diagnostics etc. |
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GP11.00094: Impedance Probe Measurements in Dusty Plasmas Brandon D Doyle, Uwe Konopka Impedance probes measure frequency-dependent transmission or reflection (S21 or S11) of low-power RF signals (10-5 W), and the resulting spectra are interpreted to measure ne and Te. Impedance probes are a promising diagnostic tool for dusty plasmas because they are less perturbing to plasma and dust than traditional Langmuir probes. One potential use of impedance probes in dusty plasmas is to combine their measurements of ne with an ion density measurement to measure the electric charge absorbed by a cloud of dust particles. |
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GP11.00095: New Dust Charge Measurement Techniques for Dusty Plasmas in a Magnetic Field Dylan Funk, Uwe Konopka, Edward Thomas Dusty plasmas consist of components typically found in a plasma (electrons, ions and neutral particles) as well as micrometer sized dust particles. The structural and dynamic properties of a dusty plasma system are governed by the dust particle charging state. As such the knowledge of the exact charging state of the individual dust particles is very important. Theories such as OML and ABR theories as well as modified versions of these have been used to determine dust charge value. Some recent experiments to determine particle charge indicate differences from theoretical models in the presence of a magnetic field. A molecular dynamic simulation has been created to study particle dynamics in the presence of a magnetic field. In a flowing system, a dust particle density gradient can build up due to the Lorentz force (similarly to the classical Hall effect) and this gradient can be used to determine the particle charge in multiple coupling regimes. This is a new method for determining dust charge value which will be useful in many future experiments. |
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GP11.00096: Nonlinear dynamics in dusty plasmas subjected to photo-discharging Michael McKinlay, Edward Thomas, Saikat Chakraborty Thakur Experiments on the DPX apparatus at Auburn University, indicate that LaB6 microparticles suspended in a low-temperature argon plasma can be photoelectrically discharged by a high-intensity UV source. Different particles in the experiment exhibited more periodic or chaotic responses to the discharge. In order to better understand the hypothesized role that particle shape may play in determining this behavior, a campaign of simulated discharges of ellipsoidal dust particles was generated. These simulations indicate that when the discharge is presumed to be proportional to the area which the particle projects along the axis illuminated by the discharging UV source, then more spherical particles trend towards periodic behavior, while more elongated or flattened particles trend towards chaotic behavior. Examples of simulated behavior in real and phase space are presented and an analysis of the relationship between particle symmetry and the dynamics resulting from photo-discharge are discussed. |
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GP11.00097: Anomalous plasma diffusion and modified dust transport at high magnetic fields in the Magnetized Dusty Plasma Experiment (MDPX) Edward Thomas, Stephen Williams, Jared C Powell, Saikat Chakraborty Thakur, Uwe Konopka Operating a steady state, low temperature at high magnetic field (B > 1 T) represents a relatively unexplored regime of laboratory plasma science. Previous experiments using the MDPX device have focused on the pattern formation (filamentation), plasma and dusty plasma waves, and particle growth in a rf generated, capacitively coupled plasma (CCP) configuration. This presentation will report on recent experimental and computational studies of transport processes in strongly magnetized plasmas. In the first study, the transport of dust particles between filamentary structures in the plasma is used to diagnose the potential structure of these self-organized plasma phenomena. Experimental observations will be compared with preliminary numerical modeling. The second study reports on experimental observations of anomalously slow diffusive processes in experiments with B > 1 T where the motion of a probe can leave a visible imprint on the plasma for several seconds after removal from the plasma volume. This presentation will report on how this phenomenon scales with neutral gas pressure and magnetic field strength. |
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GP11.00098: Impact of ion wakes on two-dimensional dust structure stability Rahul Banka, Katrina Vermillion, Jorge A Martinez Ortiz, Bryant Wyatt, Lorin S Matthews, Truell W Hyde, Lenaic Couedel Two-dimensional dust crystals can be formed in the sheath of a gas discharge plasma. Ions from the bulk plasma are accelerated in the sheath electric field, flowing past the grains to create a positive ion wake downstream from the grains. Interaction between the ion wake and neighboring grains creates additional coupling between oscillation modes and can trigger mode-coupling instability (MCI). Recent experiments show that for a given microparticle monolayer at a fixed discharge power there exist two threshold pressures above and below which the monolayer always crystallizes or melts due to the MCI, respectively. Between these pressures, the microparticle monolayer can be either in a fluid or crystalline phase. In this work, a molecular dynamics simulation of the ions and dust charging is used to self-consistently determine the dust charge and ion wake characteristics for different experimental conditions. An iterative approach is used to determine plasma parameters which optimizes a balance between the electric and gravitational field forces on the dust grain and the ion flow speed. This data is then utilized in an N-body model of dust dynamics using a dynamic point charge model to study the role of ion wakes in triggering the mode coupling instability. |
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GP11.00099: Using 2d dust structures ot probe plasma conditions Alexandria Mendoza, Katrina Vermillion, Khandaker Sharmin S Ashrafi, Lorin S Matthews, Truell W Hyde Complex plasmas are of interest as they allow the self-assembly of micron sized dust particles to form both stable and unstable structures. The dust particle interaction with ions flowing towards a negatively charge surface creates an ion wake field, affecting both the charge on the dust grains as well as the electrostatic interaction between the grains. This interaction is partially responsible for the stability of a dust structure. The dust structures can be manipulated by changing the confinement forces of the system, an example of which is placing a glass box on the lower electrode of a modified Gaseous Electronics Conference (GEC) cell. The box allows formation of vertical dust chains. Changing the power of the system can transform a 1D chain to two chains side-by-side, making a 2D zig-zag structure. |
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GP11.00100: Effect of Hot Electrons on the Behavior of Dust Grains in a Complex Plasma André Nicolov, Paul M Bellan In a dusty plasma, dust grains acquire charge through collisions with ambient ions and electrons. As electrons dominate this process, their energy distribution has a significant effect on charging, which in turn affects dynamics and formation processes. A method is devised for calculating the effects of varying electron distributions on dust charging and morphology, and this is applied to a range of plasma parameters with atmospheric and astrophysical relevance. It is found that the hottest electrons dominate the equilibrium charge, such that small fractions of high-energy electrons cause significant changes to equilibrium dust charge. The electron distributions of various space plasma environments are estimated, and the deviations in dust charging from a simple Maxwellian case are explored. |
Author not Attending |
GP11.00101: Dust flow dynamics around a dust void in a strongly coupled dusty plasma medium Yoshiko Bailung, Joyanti Chutia, Heremba Bailung Dusty plasma, also known as complex plasma, comprises electrons, ions, and neutral background with additional micron or nano-sized charged components in it. The micron particles (dust) are large enough to be visualized individually using laser light scattering and hence their motion can be tracked easily by optical instruments. Depending on the Coulomb coupling strength of the dust grains, a dusty plasma can exist in gaseous, liquid as well as in crystalline phases [1-2]. Particle Image Velocimetry (PIV) analysis in dusty plasma, holds the scope to study dust particle dynamics and its associated pattern formations at the particle most level. In this work, we present a detailed analysis of dust particle behavior around a dust void for two cases. Firstly, we consider the case of dusty plasma flow around a stationary dust void and secondly we study the behavior of a moving dust void in a stationary dusty plasma layer. The experiments are performed with gold-coated silica dust particles levitated in an RF discharge (~13.56 MHz and 5W power) plasma environment. The PIV analysis is performed using a MATLAB-based open-access PIV code on experimental data recorded both at 30 frames per second and100 frames per second [3]. The analysis results portraying the detailed particle behavior will be discussed. |
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GP11.00102: Studying nonlinear waves in Dusty Plasma Medium William Joysey, Surabhi Jaiswal, Evan Aguirre In this work we studied the phenomena associated to the interaction of nonlinear plasma waves with charged bodies. Nonlinear waves and structures generated by plasma flows are far from being understood in simulations and experimental matters. These phenomena resemble the structure formation in astrophysical scenarios therefore their fundamental properties must be firmly understood using laboratory settings [1]. We have studied nonlinear structure using a dusty plasma medium at Eastern Michigan University plasma lab. A dusty plasma medium provides easy access to study linear and nonlinear waves due to its diagnostic convenience over electron-ion plasma [2]. We complemented our experiments with theoretical calculation/simulation where we solved a set of fluid equations to extract the properties of nonlinear plasma waves and their interaction with stationary charged bodies. A detailed comparison of the experiment and simulation results will be presented at the conference. |
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GP11.00103: Experimental investigation of flow induced vortices in a dusty plasma Krishan Kumar, Pintu Bandyopadhyay, Swarnima Singh, Abhijit Sen We report experimental observations of the formation of dust vortices in a flowing dusty plasma. The experiments are performed in an inverted Pi-shaped dusty plasma experimental (DPEx) device, and the dusty plasma is created in a DC glow discharge Argon plasma using micron-sized Kaolin dust particles. A pulsed gas valve with 0.5 mm orifice is installed axially in the device to initiate a directional motion of the dust particles in a particular dust layer. The average velocity of the dust particles is tuned by altering the difference of the background plasma pressure and the inlet pressure of the pulsed valve. It is found that the velocity of the dust layer increases with an increase in the inlet gas pressure for a given background |
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GP11.00104: Structural phase transition in a monodisperse 2D complex plasma Swarnima Singh, Krishan Kumar, Pintu Bandyopadhyay, Abhijit Sen We present experimental observations of a structural phase transition in a monodisperse complex plasma wherein a 2-Dimensional plasma crystal with inherent hexagonal configuration transitions to a bilayer square configuration. The experiments were carried out in the Dusty Plasma Experimental (DPEx-II) device in DC glow discharge Argon plasma environment. We have found that mitigating particle wake interactions in the dust system is a crucial prerequisite for the attainment of transition. The unique electrode configuration of our device and the specific discharge conditions are helpful in providing such a mitigation. When the vertical confinement of the dust particles is decreased, subsequent to suppressing the particle-wake interaction, the 2D dust system buckles and triggers a transverse instability in the system which results in the structural phase transition. Local bond order and structure static factor are used to distinguish different structural phases of the system. The formation of a square lattice is accompanied by the bifurcation of the monolayer to a bilayer system where the interlayer distance increases with decrease of confinement strength. Our results also demonstrate a clear hysteresis in the system. Molecular dynamics (MD) simulation is also performed by incorporating the various forces which are dominant in our experimental conditions. The MD results reproduce the main features of our experimental observations. |
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GP11.00105: Ring structural transions in strongly coupled dusty plasmas Vikram S Dharodi, Evdokiya Kostadinova In dusty plasmas, a structural transition may occur due to a variation of the coupling strength between dust particles and/or due to an external applied field. Here, we examine how a strongly coupled dusty plasma can be transformed from a circular monolayer structure (a collection of rings with different diameters nested within the same plane) to a cylindrical surface structure (a collection rings with same diameters aligned in parallel planes) and vice-versa. This transformation has been observed numerically under the varying strength of an external applied circular potential with a central barrier, i.e., a "Mexican hat" potential. The transition of the trapped dust particles from a monolayer to a cylindrical surface is found proportional to the strength of the applied potential. For a fixed number of particles, we have also observed smaller number of rings in the cylindrical structure than the monolayer. To observe this structural transition molecular dynamics simulations have been performed where dust particles interact through Yukawa potential. |
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GP11.00106: Resonant instabilities mediated by drag and electrostatic interactions in laboratory and astrophysical dusty plasmas Ben Y Israeli, Amitava Bhattacharjee In this work, we present analysis of a number of resonance-induced instabilities relevant to dusty plasmas in both laboratory and astrophysical environments. We show that the perturbative approach introduced by Hopkins and Squire to describe the linear growth of resonant drag instabilities (RDIs) is generally applicable to a range of instabilities in dusty plasmas due to the large separation of species mass and density in these systems. We focus on the acoustic RDI, dust-ion-acoustic streaming instability, and filamentary ionization instability. Calculating their growth rates under varied conditions, we find that these modes should appear in strongly overlapping regimes, suggesting the relevance of experimental studies to astrophysical environments such as active galactic nucleus outflows, planetary nebula winds, and shocked interstellar medium. We then consider the nonlinear evolution, interaction, and eventual saturation of these modes, and the resulting impact on the evolution of astrophysical dusty plasmas. |
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GP11.00107: Analyzing phase separation processes in binary dusty plasmas using a polarization-sensitive camera Andre Melzer, Daniel Maier, Stefan Schütt Under the weightlessness conditions of parabolic flights, phase separation processes in a binary mixture of dust particles in a dusty plasma have been experimentally studied using a polarization-sensitive camera. The camera allows a pixel-wise derivation of the polarization state of the light scattered by the dust. With this, the light scattered from individual particles in a dust cloud consisting of dust particles with two different sizes has been analyzed. By comparison with analytical calculations of the scattered light polarizations, a technique has been developed to discriminate between the two different species, even for small size disparities. With that, the dynamics of the phase separation process of the two species is followed over the entire parabola and it is found that the larger particles preferably assemble on the outer parts of the dust cloud whereas the smaller particles accumulate on the inner parts. |
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GP11.00108: Temporally resolved size measurement of MF-particles in an rf-discharge Dietmar Block, Soeren Wohlfahrt The particle size is an essential quantity in a dusty plasma. Any force acting on a particle scales at least linear with the particle size. Thus, confinement and especially binary mixtures critically depend on a precise knowledge of the particle size. However, the particle size is not a fixed quantity. Due to plasma surface interaction the particle size is typically a function of time. The widely used MF-particles are known to shink due to plasma interaction. This poster presentation will introduce our latest developments to make high precision and temporally resolved measurements of particle size in-situ. Using Mie-theory, the particle size can be tracked with nanometer precision, the refractive index of the particles can be measured and first insight into plasma surface processes can be obtained. Special attention is paid on how to minimize ambiguities comparing experimental data and theory by means of an improved experimental setup. |
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GP11.00109: Construction of an electron beam source for dust plasma studies Jeremiah D Williams The kinetic effects on the dust particles in a plasma crystal locally irradiated by a narrow, pulsed electron beam (EB) with energies from 10 – 15 keV have recently been presented. [C.M. Ticoş, et. al., Phys. Plasmas, Phys. Plasmas 26, 043702 (2019)., C.M. Ticoş, et. al., Plasma Phys. Control. Fusion 62, 025003 (2020)] These preliminary studies have revealed that the EB pushes the dust particles in the irradiation zone, leading to both laminar and turbulent flow. To extend these preliminary studies, we have begun constructing an electron beam source that is capable of operating over a wider parameter space. In this poster, we present work in the construction of this improved electron source, simulations of the electron beam-dust interaction and planned experiments. |
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GP11.00110: Magnetized sheath dynamics in the presence of secondary electron emission Kolter Bradshaw, Bhuvana Srinivasan
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GP11.00111: Particle-in-cell simulation of electron and ion dynamics in low pressure capacitively coupled plasma discharges operated by pulsed radio-frequency (RF) Sarveshwar Sharma, Soham Banerjee, Peng Tian, Jason Kenney, Shahid Rauf, Dmytro Sydorenko, Alexander V Khrabrov, Igor D Kaganovich In last few decades, Capacitively Coupled Plasma (CCP) discharges have been widely used in semiconductor industry for etching processes. Among the numerous innovative techniques applied in CCP discharges to get high quality uniform etching, pulsed radio-frequency (RF) CCP discharges is one of the renowned method which provide better control over ion fluxes and ion energies. It is also seen that by varying the properties of the driven pulsed power provides extra control over the electron energy distribution function (EEDF) and, subsequently, gives us the ability to tune the ion flux. We have used a 1D/2D Electrostatic Direct Implicit Particle-In-Cell (EDIPIC) code to investigate the electron and ion dynamics of low pressure (of the order of mTorr) argon CCP discharges driven by a high-frequency RF (MHz) power source with a low frequency tailored voltage waveform (kHz). We have observed that by varying input parameters, such as the amplitude of voltage, frequency, duty cycle, and ramp results in non-linear plasma dynamics which significantly changes the plasma properties. We track and present the observed trends in electron and ion distribution functions, power absorptions, electron densities in different energy ranges etc. |
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GP11.00112: Vlasov-Poisson studies of sheaths in the presence of biased potential walls Chirag R Skolar, Kolter Bradshaw, Bhuvana Srinivasan The shear flow stabilized Z-pinch is being studied for its potential as a thermonuclear fusion reactor. The pinch current is generated via two electrodes with a potential bias. The sheath formation between the plasma and the electrode walls is studied to understand its effects on the upstream current as well as the fluxes to the electrode walls. Simulations are performed using the 1X-1V Vlasov-Poisson system for a proton-electron plasma in the code Gkeyll in regimes of relevance to pulsed-power fusion concepts including FuZE (Fusion Z-pinch Experiment). The electrodes are modeled as perfectly absorbing walls. The impact of bias potential on sheath formation is investigated by a parametric scan ranging from 0 to 10 kV. The results indicate that the current density in the domain is spatially constant with the ions dominating at the lower potential wall and the electrons dominating at the higher potential wall. Furthermore, the current density reaches an asymptotic limit with increasing bias potential. The particle and heat fluxes at the electrode walls are also presented. The results generally follow theoretical trends with differences attributed to kinetic effects. Initial work on more realistic boundary conditions that include secondary electron emissions is also presented. |
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GP11.00113: FUND: PLASMA SOURCES Session Chairs: |
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GP11.00114: Overview of the Basic Plasma Science Facility Troy Carter, Walter N Gekelman, Patrick Pribyl, George J Morales, Christoph Niemann, Shreekrishna Tripathi, Stephen T Vincena The Basic Plasma Science Facility (BaPSF) at UCLA is a collaborative |
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GP11.00115: Gas puffing for creation of high density, quiescent and uniform plasmas in the Large Plasma Device at UCLA Walter N Gekelman, Shreekrishna Tripathi, Patrick Pribyl, Stephen T Vincena, Zalton Lucky, Shawn W. Tang, Yuchen Qian, Troy Carter, Christoph Niemann, Thomas Look A large (38.5 cm diameter) Lanthanum Hexaboride source has replaced a Barium Oxide cathode in the LAPD device at UCLA. Traditional gas feed using mass flow controllers produced plasmas that had radial and axial density temperature variations. The gas feed was replaced with two piezoelectric valves creating gas puffs (H, He, Ar..) at the radial edge of the cathode and located 10 cm from the moly anode. Gas puffing has produced plasmas with flat density profiles and little axial density variation over the 19 m long plasma column. Densities as high as 2X1013 cm-3 have been achieved. Electron density was measured with Langmuir probes, spectroscopically using ratios of neutral line emission , a 100 GHz microwave interferometer and Thomson scattering. The electron temperature ( .5 < Te < 12 eV) was measured using probes, Thomson scattering and line ratios. The ion temperature ( .5 < Ti < 9 eV) in helium was obtained spectroscopically using the 640.56 nm ion line with a 1.3 m monochromator, with a 2400 l/mm grating and thermoelectrically cooled phototube. The higher densities were confirmed from the dispersion of shear Alfvén waves launched with a RMF antenna and received by a pair of B-dot probes. Measurements of these quantities as a function of space and time and input discharge power will be presented. |
Author not Attending |
GP11.00116: Neutral Gas Behavior During Gas Puffing in the Large Plasma Device Shruti Iyer, Thomas Look, Jessica Gonzalez, Shreekrishna Tripathi, Patrick Pribyl, Troy Carter, Walter N Gekelman The Large Plasma Device at UCLA has been upgraded with a new large-area Lanthanum Hexaboride plasma source. To optimize performance of this source, a new gas puff system has been installed and utilized to generate quiescent, uniform, high density plasmas. In this work, we document the dynamics of neutrals in the LAPD during gas puffing experiments. We use nude Bayard-Alpert Ion Gauges placed inside the vacuum chamber at three axial locations to measure the time-dependent behavior of neutral gas pressure during puff-fueled shots under varying machine parameters. These gauges are shielded from plasma discharge light in order to prevent photocurrent pollution of the collector signal. The gauges and puff valves will be calibrated in a specialized chamber to obtain neutral particles per puff. Gauge signals are a complex combination of neutral flow caused by pressure gradients, charge exchange, recombination, and other loss mechanisms. Enhanced axial transport of neutrals is observed during plasma discharge. Neutral dynamics are key to understanding the final plasma states that are observed. |
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GP11.00117: Design of the Lanthanum Hexaboride (LaB6) based plasma source for the Large Plasma Device at UCLA. Walter N Gekelman, Yuchen Qian, Patrick Pribyl, Tom Sketchley, Shreekrishna Tripathi, Zalton Lucky, Marvin Drandell, Stephen T Vincena, Troy Carter The original LAPD cathode was BaO based. A uniform layer of a cathode mixture was sprayed on a Ni sheet and heated in vacuum to produce the coating. BaO is very sensitive of contamination if the machine is opened the cathode must be cleaned and recoated. LaB6 , on the other hand has a much higher electron emissivity ( > 10 A/cm2 ) and is capable of producing dense (n > 1013 cm3) plasmas. It is not very sensitive to contamination and may be reused after machine opening. The challenge that comes with this material is that it must be heated to 1800o C. The cathode temperature must be highly uniform across its surface to produce a uniform plasma. As the LAPD runs 24/7 the cathode ( 38.5 cm dia) and heater design must be robust and withstand cracking and other failure modes under continuous heater power ( 77 kW) and JXB forces ( 12 kA operation at several kG). The heater is made from six parallel elements. The predicted temperature and deformation of the heater, cathode, reflectors and encasing oven was simulated using COMSOL for various designs. The LaB6 was cut into 4 tiles in a tongue and groove configuration and held in place with specially designed carbon springs. The simulations results, machine drawings and photographs of the cathode at emission along with temperature measurements with a 2 color pyrometer will be presented. The emission as a function of heater power and parameters of the resulting plasma will be shown. |
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GP11.00118: Profile reconstruction in the Large Plasma Device using a generative ML model Phil Travis, Steve Vincena, Troy Carter Plasma processes in LAPD are typically studied by gathering high-spatial-resolution data using probes, combining measurements over many discharges at a 1 Hz shot rate. ML can instead be used to infer behavior over larger spatial regions from a few localized probe measurements and global or spatially-averaged diagnostics. An auxiliary system was appended to the current labview data acquisition routines to record LAPD MSI and auxiliary diagnostics including interferometers, visible light diodes, a diamagnetic loop, and a fast framing camera. An implicitly-generative, neural network-based energy based model (EBM) constructed in pytorch was trained on these auxiliary diagnostics, MSI, and probe measurements. Artificial discharges are sampled from the learned model via Langevin dynamics to predict time evolution of ion saturation current profiles. The EBM is able to reproduce trends in profile evolution for a variety of machine configurations. In addition, the EBM can be conditionally sampled to find the machine state required for a desired profile or to reconstruct missing diagnostics. Results from this model will be presented and the scientific prospects of EBMs will be discussed. |
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GP11.00119: Investigating Hydrogen Plasma Dynamics Via Two-Color Optical Diagnostics Joshua Q Morgan, Paul M Bellan The Caltech MHD Plasma Jet Experiment exhibits a kink-driven Rayleigh-Taylor instability (RTI) that generates localized bursts of EUV and X-Ray radiation. One possible source of these radiation bursts is the formation of a double-layer at the RTI location. Using a specially constructed two color image-splitter, the RTI in a hydrogen plasma jet will be investigated to measure spatial and temporal temperature profiles. The diagnostic tool is designed to create two separate monochromatic images at Hα and Hβ wavelengths captured side by side on a single frame taken by an Imacon 200 high speed camera. The operating principle of the diagnostic tool will be discussed and a description of the post-processing will be given. Movies of plasma temperature will be generated from the ratio of the intensity of the Hα and Hβ images. These movies are expected to reveal new dynamics associated with the RTI. The correlation between local temperature change and observed dimming will also be examined. These measurements should provide insight into mechanisms by which the plasma locally changes from cold and collisional to hot and collisionless. |
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GP11.00120: Absolute Temperature and Emissivity Determination of Flame-Heated Materials Using Multispectral IR-Imaging and 2-Band Ratio Pyrometry Benjamin Saute, Tanja Pelzmann, Jean-Philippe Gagnon, Fabien Dupont Monitoring temperature of critical components in the extreme environments found within experimental fusion reactors presents a unique challenge. Typical contact-based temperature measurement devices such as a thermocouple require the placement of components on the surface to be measured, requiring exposure to the extreme conditions within the plasma vessel as well as potentially disturbing production and maintenance of the plasma itself. Non-contact temperature determination techniques such as two-color pyrometry avoid these issues but are limited to point measurements. Telops is developing a 2-band ratio-pyrometry algorithm that extends point-based two-color pyrometry principles to calculate the absolute temperature and emissivity of a multispectral thermal infrared image on a per-pixel basis. |
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GP11.00121: Chirped Pulse Line Velocimetry: a new diagnostic tool for dynamic compression experiments Sophie E Parsons, Christian M Childs, Paulius Grivickas, Jason G Mance, Brandon M La Lone, Michael R Armstrong, Kyle Sullivan Currently, PDV is one of the most common velocimetry technique used in dynamic compression experiments. However, it is limited by design to a single point measurement and therefore requires multiple probes and scope channels to obtain spatially resolved information, both of which can be costly. Line VISAR is another diagnostic that has been used in velocimetry measurements. It is able to detect profiles along a continuous line on a surface, but due to its complexity and sensitivity, it is usually paired only with large laser facilities. Here we present Chirped Pulse Line Velocimetry (CPLV). CPLV stems from ultrafast laser applications and it's development takes advantage of the recent advances in fiber optics used by the telecom industry. A prototype system is currently developed with chirped pulses extending up to 100 ns. This opens new diagnostic possibilities in laser compression experiments. We further discuss key factors of the system architecture and present a few implementation examples. |
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GP11.00122: Plasma Impedance Tomography for Imaging Plasma Dynamics Erik M Tejero, Ami M DuBois, George Gatling, Carl L Enloe, David D Blackwell, Bill Amatucci Plasma impedance probes measuring the self-impedance of the antenna-plasma system have been shown to provide accurate measurements of electron plasma density for space and laboratory plasmas. Plasma impedance probes measuring the mutual impedance between two antennas and a plasma dielectric have been successfully flown on sounding rockets and satellites. At the US Naval Research Laboratory, we have recently developed a noninvasive method for generating real-time images of plasma density and magnetic field. The method consists of measurements of the complex mutual impedance between elements of an antenna array and an image reconstruction algorithm. The impedance spectra are collected after a short pulse has been applied to each element in sequence. These spectra provide path-independent information about the plasma dielectric that are used to reconstruct images of plasma density and magnetic field. The goal is to develop a system capable of providing tomographic reconstructions at a rate of a 1% of the peak plasma frequency of the system. Recent numerical and experimental results will be presented. |
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GP11.00123: Modelling nonequilibrium Thomson scattering from above-threshold ionized plasma Audrey Farrell, Chaojie Zhang, Zan Nie, Noa Nambu, Yipeng Wu, Kenneth A Marsh, Chandrashekhar Joshi Optical Thomson scattering is now a mature diagnostic tool for precisely measuring local plasma density and temperature. These measurements typically take advantage of a simplified analytical model of the scattered spectrum, which is built upon the assumption that each plasma species is in equilibrium and Maxwellian. However, this assumption fails for plasmas produced using high field ionization of atoms via ultrashort laser pulses. For example, in the above-threshold ionization (ATI) process, electrons are produced with several narrow and equally spaced peaks in energy corresponding to the number of photons absorbed above the ionization threshold. These electrons are born with momentum along the polarization of the laser, and are essentially cold in the two transverse directions. In other words, the plasma is not only nonthermal but also grossly anisotropic. This ATI plasma is unstable to several kinetic instabilities that are not taken into account in the conventional Thomson scattering model. We present a new method for extracting the Thomson scattered spectrum from any plasma (equilibrium or nonequilibrium) directly from fully kinetic particle-in-cell simulations, without simulating the probe laser itself. With this method we can predict the spectrum measured from an ATI plasma, revealing new features in the collective Thomson spectrum that cannot be predicted by Maxwellian Thomson theory. |
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GP11.00124: Preliminary Results from a Three Photon Laser Induced Fluorescence Diagnostic in a Cold Krypton Gas Thomas E Steinberger, Jacob McLaughlin, Ripudaman S Nirwan, Earl Scime
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GP11.00125: Resistive MHD Modeling of a Coaxial Plasma Gun With a Gas Puff Inlet Kaleb Hatfield, David L Chesny, Mark B. Moffett A coaxial plasma gun (CPG) is a cylindrically symmetric, pulsed power device that forms an axially propagating plasma sheath. They are often used in applications where plasma formation and/or acceleration are required, such as in material processing, space propulsion, and nuclear fusion reactors. A custom CPG was constructed for the purpose of investigating resistive torsional fan magnetic reconnection. For this investigation, it is a design requirement to reliably produce a plasma sheath from a snowplow. Through gas puff operation in a low pressure environment (0.7 Torr), a transition of the plasma from a deflagration mode into a snowplow mode was observed using high-speed camera imaging and Rogowski coil diagnostics. This observation is further supported by numerically solving the resistive MHD equations using laboratory conditions during the CPG operation. The results of these simulations are qualitatively compared to the high-speed camera images obtained and used to bolster the argument that a transition of the plasma from gas puff initiated plasma deflagration into a snowplow plasma sheath formation is occurring as observed. Additionally, the simulation helps constrain the experimental timing of introducing an external magnetic field to interact with the snowplow mode. |
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GP11.00126: An experimental study of ferrite-core driven inductively-coupled low-pressure plasmas Ryan Przybocki, Hossein Mehrpour Bernety, Selin Ertan, Mark A Cappelli We report on the properties of a ferrite-core driven radio-frequency inductively-coupled plasma. The ferrite core enhances field density for enhanced plasma coupling and improved plasma confinement and focusing. Ferromagnetic-enhanced plasma applicators have been used previously in applications ranging from fusion devices to lighting. Our interests are in furthering this construction to drive continuous and quasi-continuous inductive plasma thrusters for space propulsion applications. Here, we present initial observations of the plasma structure and compare this to simplified models and simulations. We use high frequency 10 MHz videography using an intensified high-speed camera to capture spatial-temporal global plasma behavior, and optical emission spectroscopy to estimate plasma properties while varying gas pressure, composition, and input power. |
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GP11.00127: Particle-in-cell simulations of radio frequency discharge scenarios for initiation of multipole plasma trap experiments Nathaniel K Hicks, Ludomil Wojtkowski, Autumn Fox, Osias Salem, Mya Schroder The multipole plasma trap (MPT) [1] is a three-dimensional confinement volume bounded by an envelope of radio-frequency (RF) electrodes. In this work, scenarios for initiating a plasma discharge within the MPT are investigated via particle-in-cell (PIC) simulations using the VSim 11 software package [2], to accomplish in situ generation of trapped particles. Spherical and cylindrical electrode geometries are considered, and neutral gas may be puffed into the trapping volume to commence the RF discharge. The discharge may also be aided by directing an electron beam from an external source into the MPT volume. The evolution of the discharge over many RF periods is studied, with particular attention to diffusion of the trapped plasma across the confinement boundary. The progression of the discharge is optimized in simulation in order to inform and streamline the experimental approach to a similar MPT configuration. The inclusion of a variable multicusp magnetic field (via electromagnetic coils co-located with the RF electrodes) is explored as a means of modifying the electron loss rate, and neutral gas pressures consistent with negative ion production in an electronegative discharge are considered as well. |
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GP11.00128: Characterization of a Neutral Calcium Plasma Source Jacob McLaughlin, Fred N Skiff Neutral calcium plasma is particularly interesting for studies of ion wave dynamics. Apart from the Barium Q-machine, single-photon laser induced fluorescence (LIF) measurements in most contexts rely on excitation from metastable states. However, under many circumstances involving inhomogeneous plasma or large perturbations, the metastable distribution function may be very different from the total ion distribution and may even be closer to the neutral atom velocity distribution. Achieving ground-state LIF in most plasmas (e.g. He, Ar) requires pump laser frequencies on the order of petahertz, which is currently unfeasible. In calcium, this can be achieved with a tunable diode laser operating at several hundred terahertz by pumping the 3p64s 2S1/2 to 3p64p 2P01/2 transition (397nm) and observing emission as the ion deexcites to the 3p63d 2D3/2 state (854 nm). Presented is a novel plasma source designed for producing ionized calcium. Neutral gas (Ar, Xe, Ca, etc.) is passed through a cylindrical cavity where the TE111 mode is excited. Ionization efficiency is increased by external permanent magnets tuned for electron cyclotron resonance (ECR) at the cavity mode frequency. Ionization has been sustained in argon and xenon with as little as 100mW rf power at the antenna. The permanent magnetic field profile has been adjusted to allow extraction of the plasma from the source, which will be characterized with a Langmuir probe, microwave interferometry, and various LIF diagnostic techniques. |
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GP11.00129: Minimum Density Requirements for Critical Ionization Velocity in a Rapidly Rotating Plasma Jenny R Smith, Remington Reid Rapidly rotating plasmas show promise in applications such as fusion energy and large-scale x-ray generation because of their potential to confine plasma in a magnetic mirror configuration and the tendency of the shear velocity to mitigate instabilities from forming [1]. The Maryland Centrifugal Experiment (MCX) was a magnetized rapidly rotating plasma experiment that was able to reach the critical ionization velocity (CIV) at the midplane of the experiment's geometry [2]. CIV is the velocity, in this case the rotational velocity of the plasma, that when exceeded, a neutral traveling through a magnetized plasma will rapidly ionize [3]. A second generation of MCX is being built at the Air Force Research Laboratories (AFRL) to explore CIV phenomena further. One primary objective of this experiment is to pinpoint the neutral density needed for CIV to occur. There is no minimum density of neutral seed gas listed in the literature and this would be useful knowledge in the field of rapidly rotating plasmas. Preliminary results will be presented. |
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GP11.00130: History of generating and controlling a radially inhomogeneous ExB velocity profile from a radially localized radial electric field in a solenoidally magnetized plasma column Serdar A Bilgili, Mark E Koepke Ion-cyclotron range of frequencies (ICRF) heating is highly effective in heating lab plasmas to high temperatures in toroidal devices. High-latitude ionospheric observations of thermal ion outflows (mainly O+) can be explained as resulting from ICRF-resonant heating, thus contributing to atmospheric loss from the planet. Our objective is to advance the understanding of EM waves driven by a combination of B-field-aligned current (FAC) and ExB-drift inhomogeneity (shear) that are destabilized in the ICRF. We contrast various configurations utilized in previous experiments for generating either FAC or radially inhomogeneous perpendicular-velocity shear in a magnetized plasma column, specifically, Segmented-Electrode + Single-Source (SESS), Single-Mask + Single-Source (SMSS), Single-Mask + Double-Source (SMDS), and Double-Mask + Double-Source (DMDS), and explain the cause and effect of many design features. We document the performance of these designs in terms of the radial profiles for floating potential, plasma potential, and Er x B drift, as well as the inhomogeneity length scale, LE, and its ratio with the ion gyroradius, ρi /LE. Past experiments operated at ?? < 1e-6, whereas LAPD experiments now can operate at higher plasma beta (?? ~ 0.1) that is needed to explore EM signatures of ICRF waves. |
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GP11.00131: Field Direction Dependent Particle Heating in a Helicon Source Katey Stevenson, Earl Scime, Timothy N Good, Mitchell C Paul, Tyler J Gilbert, Prabhakar Srivastava, Thomas E Steinberger, Peiyun Shi Experiments have demonstrated that ion phenomena, such as the lower hybrid resonance, play an important role in helicon source operation. Damping of the slow branch of the bounded whistler wave at the edge of a helicon source (i.e., the Trivelpiece-Gould mode) has been correlated with the creation of energetic electrons, heating of ions at the plasma edge, and anisotropic ion heating. Here we present ion velocity distribution function measurements, and electron density and temperature measurements, on both sides of a m = ± 1 helical antenna in a helicon source as a function of the antenna frequency and magnetic field strength. These measurements were obtained for two different ambient magnetic field directions. For both field directions, significant perpendicular ion heating at frequencies near the lower hybrid resonance was observed. Three crucial differences in the two background field directions were found. (1) Hotter ions were observed for one of the field directions, (2) edge heating of the ions was observed for only one of the field directions, and (3) dramatic differences in the downstream electron density were found. The preferred direction for optimal coupling of RF energy into the particles is when the magnetic field is such that the helical antenna couples to a m = +1 wave that is launched into the region of interest (upstream or downstream of the antenna). The resonant behavior at the lower hybrid frequency suggests that the enhanced energy coupling occurs specifically for m = +1 Trivelpiece-Gould waves. At low plasma densities (as in the edge of a helicon source), the lower-hybrid resonance is dominated by ion motion and therefore ion energization is expected. At higher plasma densities, it is coupling to the electrons that dominates and right-hand polarization (m = +1) is optimal for coupling to the electrons. We include measurements of the wave polarization at the plasma edge for both magnetic field directions. |
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GP11.00132: The absorption profile analysis of electron cyclotron waves by three dimensional ray tracing simulation under the overdense state in the magnetospheric plasma device RT-1 Takahiro Mori, Masaki Nishiura, Naoki Kenmochi, Ryoma Yanai, Kenji UEDA In the magnetospheric plasma device RT-1, in which a superconducting ring magnet is levitated in the vacuum to produce a dipole magnetic field, the plasmas are produced by electron cyclotron heating (ECH) using 2.45 GHz. In this condition, inward diffusion causes a peaked density profile beyond the cutoff density, even though the electron density is higher than the O-mode cutoff density of 2.45 GHz EM wave. We found that the density limit appears beyond the cutoff density. Therefore, we clarify the mechanism in terms of wave physics in plasmas. |
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GP11.00133: Metriplectic foundations of gyrokinetic Vlasov-Maxwell-Landau theory Alain J Brizard, Eero Hirvijoki, Joshua W Burby The metriplectic formulation of a collisional, nonlinear full-f electromagnetic gyrokinetic theory is presented, with explicit energy conservation properties and monotonic entropy production. In an axisymmetric backgroind magnetic field, the toroidal canonical angular momentum is also conserved. A new collisional current, which appears in the gyrokinetic Maxwell-Ampere equation and the gyrokinetic charge conservation law, is discussed. |
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GP11.00134: Optimizing the Tradeoff Between Trotter Error and Gate Error in Three- and Four-Wave Plasma Problems Amy F Brown, Yuan Shi, Vinay Tripathi, Bram Evert, Yujin Cho, Max D Porter, Xian Wu, Vasily I Geyko, Alexander D Hill, Christina Young, Eyob A Sete, Ilon Joseph, Jonathan L DuBois, Matthew J Reagor, Daniel A Lidar Simulations on near-term quantum hardware are limited by hardware error, from gate infidelity and decoherence, and by algorithmic error introduced by approximations, such as the Trotter-Suzuki expansion. Using compilation techniques and an optimal Trotter step size, the algorithmic error incurred by the Trotter-Suzuki expansion, referred to as the "Trotter error," can be mitigated, and the simulation depth can be improved. In this paper, we explore the tradeoff between Trotter error and gate error in pursuit of the optimal Trotter step size. In particular, we simulate the three-wave and four-wave interaction Hamiltonian, describing a nonlinear optical process, on quantum hardware using a single compiled gate, which we repeatedly apply in a series of Trotterized steps to reach a desired simulation period. We evaluate expectation values of occupation numbers to assess the quality of simulations and use these results to evaluate an optimal Trotter step size. These results serve to facilitate the plasma community's interest and investment in quantum simulations by demonstrating successful simulation of nonlinear dynamics using product formulas and Trotter expansions to simulate the three-wave and four-wave unitary of interest. |
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GP11.00135: Physical Regimes of Electrostatic Wave-Wave nonlinear interactions generated by an Electron Beam Propagation in Background Plasma Haomin Sun, Jian Chen, Igor D Kaganovich, Alexander Khrabrov, Dmytro Sydorenko We study the collective processes for an electron beam propagating through a background plasma using simulations and analytical theory. A new regime where the instability of a Langmuir wave packet can grow locally much faster than ion frequency is clearly identified. The key feature of this new regime is an Electron Modulational Instability that rapidly creates a local Langmuir wave packet, which in its turn produces local charge separation and strong ion density perturbations because of the action of the ponderomotive force, such that the beam-plasma wave interaction stops being resonant. Three evolution stages of the process and observed periodic burst features are discussed. Different physical regimes in the plasma and beam parameter space are demonstrated for the first time. |
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GP11.00136: Antibiotic and anticancer drug degradation in artificial wastewater using non-thermal pencil plasma jet Vikas Rathore, Akanksha Pandey, Shruti Patel, Jignasa Savjani, Shital Butani, Hemen Dave, Sudhir Nema The present work showed ampicillin and cloxacillin (antibiotics), and methotrexate (anticancer) drugs degradation using a non-thermal pencil plasma jet (NT-PPJ) in artificial wastewater. The presence of antibiotics and anticancer drugs is observed in wastewater due to dumping of these drugs by pharmaceutical industries, hospitals, and veterinary waste, etc. in river or backyard. Hence, these drugs creates environmental toxicity toward aquatic plants and animals, etc. The plasma-water interaction results in generation of various reactive species in water and changes the physicochemical properties of water that result in degradation of antibiotic and anticancer drugs present in water. A 9 minutes plasma treatment with drug-water solution showed 76.1%, 100%, and 100% degradation of ampicillin, cloxacillin, and methotrexate. Moreover, the observed mineralization of these drugs is given as 88.8%, 78.6%, and 84.5%, respectively. The analysis showed significantly reduction in toxicity of plasma-treated drug solutions compared to virgin drug solutions. The study reveals that the NT-PPJ treatment of artificial wastewater provides substantially higher drug degradation with low plasma treatment time compared to convention and other drug degradation techniques. |
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