Session ZP08: Poster Session: Postdeadline Posters (9:30am - 12:30pm)

Spectral sensitivity to perturbative modes in cylindrical implosion simulations

Laser-driven implosion of cylindrical targets are being used to understand inertial confinement fusion (ICF). Convergent Rayleigh-Taylor instability (RTI) growth seeded by perturbations in the targets have been captured by high-fidelity experiments and 2D Eulerian simulations. In this work, we consider sensitivities of RTI growth and implosion dynamics to geometric uncertainties, such as manufacturing tolerances. We characterize the frequency-domain uncertainty in the modal decomposition and the measurable accuracy of a sensitivity analysis using spectral analysis of perturbative modes, driven by M periodically-seeded perturbations in the plane perpendicular to the axis. The minimum detectable and maximum allowable input parameter variations are considered at progressive stages of the simulation. This study helps establish the level of robustness and simulation fidelity in laser-driven experiments, as well as forecasts future computational scaling and requirements.   

Modeling of Chemotaxis in Porous Media.

Peritrichous bacterial motility is characterized by a sequence of run and tumble events. In the presence of chemical gradients, tumble frequency gets reduced, and the bacteria population experiences a drift towards higher concentration of chemoattractants (favourable chemicals). The understanding of the movement of bacteria in porous media like agar gel is important to develop a point of care devices. Here, how the microbe's motility gets affected due to collision with solid walls is not clearly understood. How the microbe's motility gets altered due to pore size distribution is unknown. In this work, we model the movement of bacteria in a porous medium based on the continuous-time random walk (CTRW) approach. This result in the system being described by a fractional differential equation. Here we present a mathematical model that incorporates changes of bacterial motility as exhibiting anomalous diffusive behaviour in porous media. We use a finite difference numerical method for solving the governing fractional differential equations. These model equations are relevant in the context of biological systems with crowding. We also design a diffusion-based microfluidic device for generating a steady and stable concentration gradient for studying chemotaxis in agar gel, which contains a fluid-filled porous medium. Results obtained from numerical simulation are compared with experimental data. \textbf{Keywords:} Chemotaxis, Fractional calculus, Anomalous diffusion, Random walk. \textbf{\textit{References}} \begin{enumerate} \item Bhattacharjee, T. {\&} Datta, S. S. Bacterial hopping and trapping in porous media. \textit{Nat. Commun.} \textbf{10}, 2075 (2019). \end{enumerate}   

Spectral sensitivity to perturbative modes in cylindrical implosion simulations

Laser-driven implosion of cylindrical targets are being used to understand inertial confinement fusion (ICF). Convergent Rayleigh-Taylor instability (RTI) growth seeded by perturbations in the targets have been captured by high-fidelity experiments and 2D Eulerian simulations. In this work, we consider sensitivities of RTI growth and implosion dynamics to geometric uncertainties, such as manufacturing tolerances. We characterize the frequency-domain uncertainty in the modal decomposition and the measurable accuracy of a sensitivity analysis using spectral analysis of perturbative modes, driven by M periodically-seeded perturbations in the plane perpendicular to the axis. The minimum detectable and maximum allowable input parameter variations are considered at progressive stages of the simulation. This study helps establish the level of robustness and simulation fidelity in laser-driven experiments, as well as forecasts future computational scaling and requirements.   

Design of a high energy density experiment for measuring the suppression of the Rayleigh-Taylor instability in an applied magnetic field

We simulate the suppression of the 2D Rayleigh Taylor Instability (RTI) in an external magnetic field at high energy density conditions in order to design a target package for a Discovery Science experiment at the National Ignition Facility investigating this effect. Our simulations indicate magnetic tension is the key suppression mechanism, resistive MHD effects are important and point to target designs involving low-density materials. Simulations show that at NIF-scale, resistive MHD allows the magnetic field to diffuse ahead of the shock front and RTI growth if the plasma conductivity is insufficient. Low density allows for faster hydrodynamics and higher conductivity mitigating the issue of the magnetic field diffusing away. With the low-density target, we observe noticeable RTI suppression in a 30 T By-field compared to a 0 T field.   

Evaluation selectivity of cold atmospheric plasma and chemotherapy drug on cancer and normal cells.

Here, we investigated the efficacy of CAP individually and co-treatment with paclitaxel on ovarian cancer. to this end, for the first time, A2780 CP cancer cells and GCS normal cells were subjected to CAP treatment for the duration of 0 to 240 sec. To comparison of selectivity of CAP with conventional treatments, normal and cancer ovarian cells were treated at different dosages of Paclitaxel. The MTT assay was performed to evaluate cell survival, and One-way ANOVA and two-way ANOVA were used to assess the significance level of quantitative data. Real-time PCR was used for the analysis of apoptosis-related genes. Our results demonstrated that plasma with strong selectivity targets cisplatin-resistant cancer cells while it does not cause damage to healthy cells. We found increasing Fetal bovine serum improved selectivity performance of plasma. Besides, our result revealed that Paclitaxel with targeting normal cells reduced the viability of them more than the cancer cells, therefore it has negative selectivity on ovarian cancer. Collectively, our result revealed that CAP is a potential and promising treatment for chemotherapy-resistant ovarian cancer.   

Photon Radiation-Pressure (R-P) in Laser Light Reflectivity off Liquid-Metals (L-M) through Solid Metals Melting-Points and Liquid Metals Vaporization Points PhotoAcoustics (P-A) of Burst-Acoustic Emission (BAE) : Laser-Light Vaporization of Liquid-Metals

Plasma-production in laser melting/welding/cutting of metals/alloys via photon radiation-pressure in laser-light Drude-theory reflectivity off liquid-metals/alloys through solid/metals/alloys melting point and liquid metals/alloys vaporization-points with photo acoustics of Siegel BAE[“BAE Measurement of Creep-Plasticity”, Phys.Stat.Sol. (72)”-2 papers;”BAE Bauschinger-Effect Plasticity Hysteresis”:IEEE Ultrasonics Symp., Monterrey (73);Acta Metalurgica (77)]BAE laser-light photo vaporization to plasma-state of liquid-metals/alloys into metal/alloy plasmas production computation via Siegel[J.Non-Xline Solids 40,453 (80)] (G…P) ontology explicitly for optical-phonons/polaritons embodying Noether’s-theorem (N-T) ontology within Siegel[Symp. on Fractals, MRS Fall Mtg., Boston (89)-6 papers] agree with experimental plasma-production during laser-melting/welding/cutting of metals/alloys via very first Siegel/Gregson/G.M.-Valcartier (70-73) CO2-TEA laser. Siegel-Percus-Yevick (SPY)[Phys./Chem. Liquids (75);ibid. (76) theory agrees with experiments in laser metal/alloy melting/welding/cutting as implemented in G.M. manufacturing-practices at several G.M. divisions!: “Et Lux Perpetua Luceat Eis”!   

Symmetric Ideal Magnetofluidostatic Equilibira with Non-Vanishing Pressure Gradients in Asymmetric Confinement Vessels

We study the possibility of constructing steady magnetic fields satisfying the force balance equation of ideal magnetohydrodynamics with tangential boundary conditions in asymmetric confinement vessels, i.e. bounded regions that are not invariant under continuous Euclidean isometries (translations, rotations, or their combination). This problem is often encountered in the design of next-generation fusion reactors. We show that such configurations are possible if one relaxes the standard assumption that the vessel boundary corresponds to a pressure isosurface. We exhibit a smooth solution that possesses an Euclidean symmetry and yet solves the boundary value problem in an asymmetric ellipsoidal domain while sustaining a non-vanishing pressure gradient. This result provides a definitive answer to the problem of existence of regular ideal magnetofluidostatic equilibria in asymmetric bounded domains. The question remains open whether regular asymmetric solutions of the boundary value problem exist.   

Magnetohydrodynamic Helicity Generator

I outline a new device configuration having spatially periodic magnetic cusps and currents to drive a stable Taylor-Couette magnetohydrodynamic singular structure flow relevant to fusion and the production of kinematic laminar plasma dynamos.   

Tearing modes of the type of toroidal Alfv\'en eigenmodes

The coupling of micro-tearing modes and Alfv\'en modes is investigated. It is found that the electron inertia and finite resistivity may lead to the excitation of tearing modes of the type of toroidal Alfv\'en eigenmodes even in the Alfv\'en continuum. Or in other words, a new branch of toroidal Alfv\'en eigenmodes can possibly appear when the electron inertia and finite resistivity are taken into account. The modes result from the coupling of two counter-propagating waves of TAE type and, nevertheless, the perturbed radial magnetic field is excited at the rational surfaces. This leads the reconnections to occur at the rational surfaces. This may offer an alternative explanation for the experimental observations of enhanced radial transport when the TAE type of modes prevails.   

Farley-Buneman instabilities in the Auroral region: Continuous hybrid simulations

The magnetosphere couples with the high-latitude ionosphere through the Earth’s magnetic field lines. This coupling occurs mainly through energetic particle precipitations and electromagnetic fields. In the auroral E region, these processes cause Hall currents that drive Farley-Buneman instabilities, generating a spectrum of field-aligned plasma density irregularities. Although fully kinetic particle-in-cell simulations of Farley-Buneman instabilities offer the most complete description of the underlying physics, its computational cost for studying non-local phenomena is tremendous. To capture non-local physics, new methods based on hybrid and continuous approaches have to be explored. In this work, we present a new continuous hybrid simulation of Farley-Buneman waves, where electrons and ions are modeled using a fluid and kinetic formalism, respectively. We investigate phase speed saturation and examine whether the phase speeds scale with the background electric field in the way observed by radars. We also try to quantify wave turning effects, examine whether wave heating is commensurate with incoherent scatter radar observations, and determine the dominant wavelength of the waves.   

An Empirical Neural Network Transport Model Fit to a Large DIII-D Database

An experimentally trained saturation rule for the quasilinear TGLF turbulent transport model has been obtained. The wavenumber (k) spectrum of the rule is prescribed as a $+$ b log (k) / k$^{\mathrm{c}}$, and the coefficients a,b,c are the output of a neural network trained to produce fluxes similar to experimentally inferred fluxes for the nominal parameters of a database of DIII-D discharges. Different neural network architectures and hyperparameters were tested, including reducing the coefficients produced by the model from 6 (having a separate saturation rule per unstable mode) to 3 (one rule for all modes). Using symbolic regression through genetic algorithms, analytic expressions were obtained to map the relationships between a,b,c and input parameters. The correlations of a with collisionality and c with electron temperature gradient scale length are particularly strong. Other forms of the saturation rule wavenumber spectrum prescription are explored.   

Confirmation of helicon mode at IShTAR plasma source

IShTAR (Ion Sheath Test ARrangement) is a dedicated test facility to investigate the interaction of ICRF wave and plasma at the Max-Planck Institute for Plasma Physics in Garching, Germany. Plasma is provided by a plasma source (length$=$ 0.1m, diameter $=$ 0.4m) equipped with a helical type antenna. This source is designed to achieve helicon mode of discharge and can only work with its full capacity if the source reaches helicon mode. However, previously there was no confirmation that this plasma source can attain helicon mode and the main objective of this work was to achieve the helicon mode of discharge for this source. Plasma characteristics (electron density, electron temperature, plasma potential) at different operating conditions (gas pressure, power) were measured with an RF compensated single Langmuir probe. To understand the plasma behaviour and to validate the experimental results a global model of particle and power balance was implemented. Experimental electron density and electron temperature are in good agreement with the model results while plasma potential shows discrepancy at higher gas pressure. From power balance, it was found that absorption of power is high at lower magnetic fields (\textless 35mT) than higher magnetic fields (\textgreater 35mT). The density plot as a function of power also shows helicon type transition at lower magnetic fields (\textless 35mT). This indicates the presence of helicon mode of discharge at IShTAR plasma source when it is operational at low magnetic fields. To get the highest density of plasma, the optimization of the plasma source is presented to reach helicon mode at the highest available magnetic field.   

IPPEX Virtual Tokamak -- 0D Simulation Game

The IPPEX Virtual Tokamak is a 0D simulation game and educational resource available to the public at ippex.pppl.gov. The Virtual Tokamak gives players an intuitive idea of the functioning of a fusion reactor, from the basic tokamak operation, to the generation of electricity. The user can change parameters of the tokamak like Density, Auxiliary Power, and Magnetic Field and see how their changes affect the electrical power output of the reactor. Recent additions include a new section of the game which allows the user to also change the major radius, minor radius, elongation, and triangularity of the reactor and see the plasma cross section. Other updates include the option to choose the type of superconductor technology (Low Temperature Superconductor or High Temperature Superconductor) being used for the magnetic field coils. This is used to calculate the maximum axis magnetic field strength which becomes the maximum of the magnetic field slider in the game which makes the game more realistic. The option to add or remove the blanket and shield from the reactor has also been included. Finally, there is now another view to the game which gives more information about the power balance and other important fusion aspects to the user.   

On Demand

The helically symmetric experiment (HSX) is an optimized stellarator using quasi-helical symmetry (QHS) of the magnetic fields to confine its plasmas. It has been in operation since 2001 and has successfully demonstrated minimized neoclassical transport and relevant turbulence physics. HSX performance is limited by the frequency of its electron cyclotron heating (ECH) source, which does not allow plasma densities higher than 1x10$^{\mathrm{19}}$ m$^{\mathrm{-3}}$. In order to triple this limit, HSX is upgrading its facilities to operate with a gyrotron recently acquired from the Max Planck Institute for Plasma Physics in Germany. The new 70GHz, 500kW ECH system will use the X2 mode at 1.25 Tesla, requiring a 25{\%} higher magnetic field. With higher temperatures in a denser plasma, neutral densities will be reduced, which will reduce the neutral damping of flow in the symmetry direction. 1D modelling results of the expected performance predict increased coupling between electrons and ions and reduced charge-exchange losses. Along with new wall conditioning techniques and strike line protection, this might provide ion temperatures as high as 300eV such that low collisionality ion confinement can be studied for the first time in a quasi-symmetric stellarator.   

Effect of metastable excited species in non-equilibrium gas-discharge plasma of UV excimer lasers and excilamps.

Extreme UV plasma sources including UV excimer lasers and excilamps are of great interest for modern science and technology, for instance, in nanolithography [1,2]. But despite the advances in excimer plasma physics, non-equilibrium kinetics of excimer plasma is still not entirely clear, in particular, regarding metastable excited species (MES). We tried to study this issue more detail. Experiments were carried out in various rare gas mixtures in different gas-discharge conditions using electrical and optical diagnostics. Measurements showed that excimer plasma processes are accompanied by the formation of long-lived MES. Computational simulation with 0D-kinetic and 1D-fluid models, considering excitation, ionization, dissociation-recombination, relaxation, collisional quenching, and UV radiation, revealed the most probable mechanisms of reactions in excimer plasma. The effects of metastables involving electronically excited molecules and atoms were examined. The study confirmed the role of MES in excimer plasma kinetics and indicated the way to more efficient UV plasma processing. [1] D. Basting, G. Marowsky , Excimer Laser Technology, Springer, 2005. [2] E. Sosnin, V. Tarasenko, M. Lomaev, \textit{UV and VUV excilamps}, Lambert Academic Publishing, 2012.   

Study of the Void-Induced Plasma Emission in Capacitively-coupled RF Complex Plasmas

Complex or dusty plasma is a medium containing ionized gas and micron-sized solid particles. A Void --- a microparticle-free area --- can disturb the microparticle suspension homogeneity. The void also determines the nanoparticle generation cycle in plasma reactors. Although the void formation has been studied for decades, understanding of its behaviour is still incomplete. We experimentally demonstrate that the void in the RF discharge complex plasma can exist in two qualitative different regimes. The ``bright'' void is characterized by bright plasma emission associated with the void, whereas the ``dim'' void possesses no emission feature. The transition from the dim to the bright regime occurs with the increase of the discharge power and has a threshold character. The threshold is manifested by a kink in the void size power dependencies. We reproduce the bright void by a simplified time-averaged 1D fluid model. To reproduce the dim void, we artificially include the radial ion diffusion into the continuity equation for ions, which allows to mechanically stabilize the void boundary due to very week electrostatic forces. The electric field at the void boundary occurs to be so small that it, in accord with the experimental observation, causes no void-related emission feature.   

Plasma dynamics and quasi equilibrium in simply toroidal plasma in open field line configuration

In simply magnetized toroidal (SMT) device plasma is confined purely by toroidal field having close field line configuration. The crossfield transport arising from the E x B drift severely affects the plasma confinement and causes the entire plasma to be lost to the outer wall and prevents the plasma to be in MHD equilibrium. In this study a finite vertical field of 0.3 mT is superimposed to the toroidal field of 0.04 T, resulting in opening of the field lines characterized by a pitch ratio of r$_{\mathrm{B}}=$B$_{\mathrm{Z}}$/B\textasciitilde 7.5 x 10$^{\mathrm{-3}}$ and L$_{\mathrm{C}}=$2a(B$_{\mathrm{T}}$/B$_{\mathrm{Z}})$\textasciitilde 2333 cm in filamentary hydrogen plasma. This short circuiting the current and limiting the electric field buildup and hence brings system to a quasi-stationary equilibrium. The time averaged profiles were analyzed and spatiotemporal evolution of structures has been studied by conditional sampling techniques and other statistical tools. Typical plasma parameters are n$_{\mathrm{e}}$\textasciitilde 10$^{\mathrm{16\thinspace }}$m$^{\mathrm{-3}}$, T$_{\mathrm{e}}=$1-10 eV, T$_{\mathrm{i}}=$1 eV, $\nu =_{\mathrm{ExB}}=$3 x 10$^{\mathrm{3}}$ m/s and $\Gamma _{\mathrm{ExB}}=$10$^{\mathrm{19}}$m$^{\mathrm{-2}}$s$^{\mathrm{-1}}$.   

Reduced predictive models for Micro-tearing modes in the pedestal

The experimental discovery that magnetic fluctuations observed in the tokamak pedestal seem to show a remarkable sensitivity to the toroidal mode numbers $n$ poses a very interesting and challenging problem. The theoretical challenge becomes even more acute when gyrokinetic simulations of the microtearing modes (MTM) seem to reproduce exactly the same effect. We have developed a pedestal specific model that shows that the $n$ sensitivity is likely to be a consequence of a deeper interaction between magnetic shear (that determines the mode rational surface) and the sharply varying profile of $\omega_{*e}$; it is this combination that determines the conditions for the existence and stability of the MTM. It is found that the MTMs tend to localize at the peak in the $\omega_{*e}$ profile, and are unstable only when a given rational surface aligns with this peak. This idea will be explored and tested using data from DIII-D as well as other experiments. Investigations based on this idea have provided insight into the magnetic spectrograms across several machines for several discharges and; in particular, we were able to, effectively, predict the gaps between frequency bands and toroidal mode numbers.   

3-D electron temperature and x-ray emission tomography of the ICF hotspot at the National Ignition Facility

A 3-D reconstruction of x-ray emission distribution of the inertial confinement fusion (ICF) hotspot can help to characterize and compare the thermophysical states of stagnated fusion plasmas. We apply and test the iterative algorithm, Algebraic Reconstruction Technique (ART), to reconstruct the 3-D x-ray distribution of the ICF hotspot from very limited number of two-dimensional x-ray projection images. Furthermore, we infer the 3-D hotspot electron temperature distribution by using the x-ray reconstructions from different x-ray energy channels ranging from 20 to 30 keV, where the ablator becomes optically thin. We will present our x-ray brightness and electron temperature reconstructions and compare results using two versus three lines-of-sight with synthetic and experimental data. Release Number LLNL-ABS-815375   

Computational investigation of impulse-fluence scaling in x-ray illuminated materials on the National Ignition Facility

A number of systems in high-energy-density physics involve conversion of x-rays into material impulse through absorption processes. In such systems, x-rays of a given energy are deposited within the material up to a depth dictated by the material's opacity. This energy deposition causes an increase in pressure, driving the heated surface layer to blow off and sending a compressive wave into the bulk of the material. The material impulse generated by x-ray energy deposition scales with the overall fluence of the incident x-rays. This scaling is sensitive to the x-ray source spectra and opacity. Modeling the relationship between impulse and x-ray source is challenging; analytical models tend to be overly simplistic, entirely ignoring the sensitivity of this relationship to spectral detail. For a high-fidelity treatment of this problem requires numerical simulation, we utilize the codes Mercury and Ares to simulate x-ray deposition and the resulting impulse generation, respectively. We validate our numerical method and the constitutive models used therein with data obtained from experiments on the National Ignition Facility. We employ this method to quantify the sensitivity of impulse to the source spectrum and the dependence of impulse-fluence scaling on this sensitivity.   

Initial results from MAST Upgrade

The MAST Upgrade spherical tokamak has unique capabilities to address some of the key issues facing the development of fusion energy. Its main objectives are: 1) development of novel exhaust concepts, 2) contribution to the knowledge base for ITER and 3) to explore potential routes to smaller/cheaper fusion reactors. To fulfil these aims, it is equipped with 19 new poloidal field coils and closed divertors with Super-X capability. The maximum BT has been increased by 50{\%} and the pulse length and Ip have increased to 5s and 2MA respectively. Auxiliary heating is provided by on and off axis NBI. The divertors are diagnosed with probes, bolometers, Thomson scattering, IR, visible imaging and spectroscopy. Fast ion physics studies are enhanced with a new fast ion loss detector. Currently, integrated commissioning is nearing completion; the poloidal field coils in the main chamber are fully operational and the solenoid and toroidal field are close to ready for the experimental campaign. Results from initial plasma operations will be presented and plans for the experimental campaign.   

Confinement time of ion kinetic energy in a controlled nuclear fusion system

The single most important scientific question in fusion research is confinement in a fusion plasma. A theoretical model is presented for the confinement time of ion kinetic energy in a material where fusion reactions occur. After a review of ion stopping in neutral materials, a formula is derived for the confinement (or decaying) time of ion kinetic energy in neutral materials. Under the assumption that ion stopping cross section in a neutral material is comparable that in a plasma, an estimate is obtained for the confinement time of ion kinetic energy in a D-T plasma, which is orders of magnitude lower than what is required in the Lawson criterion. The estimate is compared with indirect indications from experiments at TFTR and Wendelstein 7-X. An experiment program is proposed for studying and improving the confinement time of ion kinetic energy in plasmas.   

Emissive cathode operation in a large magnetized plasma and its role in a basic heat transport experiment

A model is derived to describe the effects produced by thermionic electron injection into a magnetized plasma column in which the separation between cathode and anode is much larger than the mean free-path of the electrons. Analytic expressions are found for the spatial pattern of the global current system, the partition of potential across the plasma sheath, and the effective plasma resistance. The associated radial electric field produces global sheared ExB flows while particle injection and Ohmic heating lead to rearrangements in density and temperature. The linear stability of the radial gradients in the self-consistent profiles to drift-Alfv\'{e}n fluctuations is assessed and the nonlinear evolution of the fluctuating profiles is simulated numerically. Predictions of the model are found to be in excellent quantitative agreement with measurements performed in the Large Plasma Device (LAPD) at the University of California, Los Angeles (UCLA). It is demonstrated experimentally by selective biasing of the cathode structure that flow-shear generated by thermionic emission, under externally controlled conditions, can suppress the growth of drift-Alfv\'{e}n instabilities.