Bulletin of the American Physical Society
56th Annual Meeting of the APS Division of Plasma Physics
Volume 59, Number 15
Monday–Friday, October 27–31, 2014; New Orleans, Louisiana
Session UP8: Poster Session VIII: FRC, Spheromaks, Stellarators and Other Magnetic Confinement Systems; HEDP & ICF: Hydro, Simulations and Diagnostics |
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Room: Preservation Hall |
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UP8.00001: FRC, SPHEROMAKS, STELLARATORS AND OTHER MAGNETIC CONFINEMENT SYSTEMS |
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UP8.00002: Overview of the C-2 Field-Reversed Configuration Experimental Program and Future Plan on C-2 Upgrade Xiaokang Yang, Hiroshi Gota, Michl Binderbauer, Michel Tuszewski, Houyang Guo, Eusebio Garate, Dan Barnes, Sergei Putvinski, Toshiki Tajima, Leigh Sevier C-2 is the world's largest compact-toroid (CT) device at Tri Alpha Energy that produces field-reversed configuration (FRC) plasmas by colliding/merging oppositely-directed CTs and seeks to study the evolution, heating and sustainment effects of neutral-beam (NB) injection into FRCs [1, 2]. Recently, significant progress has been made in C-2 on both technology and physics fronts, achieving $\sim$ 5 ms stable plasmas with a dramatic improvement in confinement. FRCs are stabilized with an edge biasing using end-on plasma-guns and/or electrodes, and are partially sustained with NB injection (20 keV Hydrogen, $\sim$ 4 MW). Recent work to reduce scrape-off layer and radiative losses has succeeded in reducing the average power balance deficit to $\sim$ 1.5 MW. Increasing plasma pressure and electron temperature are now observed during brief periods of the discharge, which indicate a sign of NB injection effect such as accumulating fast-ions as well as heating core/edge plasmas. Highlights of these advances, broader C-2 experimental program, and future plan on upgrading the C-2 device with new NBs (15 keV, up to 10 MW injection power, selectable beam injection angle) will be presented. \\[4pt] [1] M.W. Binderbauer \textit{et al.}, Phys. Rev. Lett. \textbf{105}, 045003 (2010).\\[0pt] [2] M. Tuszewski \textit{et al.}, Phys. Rev. Lett. \textbf{108}, 255008 (2012). [Preview Abstract] |
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UP8.00003: Three-Dimensional Hybrid Simulations of Field-Reversed Theta-Pinch Discharges Yuri Omelchenko, Homa Karimabadi The field-reversed theta-pinch discharge is a well-known method for creating the field-reversed configuration (FRC) considered to be one of the most promising candidates for an economical fusion reactor. Using an asynchronous parallel hybrid code, HYPERS, we have conducted first-ever 3D simulations of such discharges under realistic physical conditions that include applied magnetic flux coils, ion-ion collisions and the Chodura resistivity. Unlike all other existing hybrid codes, HYPERS does not step spatially distributed variables synchronously in time but instead performs numerical time integration by executing asynchronous discrete events: updates of particles and fields carried out as frequently as dictated by local physical time scales. As a result, not only HYPERS produces robust and accurate results with speedups of several orders of magnitude compared to traditional simulations but for the first time this code made it possible to study end-to-end kinetic dynamics of 3D laboratory plasma systems under experimental plasma conditions that make application of other codes very difficult if not altogether impossible. We discuss physical properties of FRCs obtained in simulations and mechanisms responsible for their spontaneous toroidal spin-up. [Preview Abstract] |
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UP8.00004: A Field-Reversed Configuration Plasma Translated into a Neutral Gas Atmosphere Jun'ichi Sekiguchi, Tomohiko Asai, Tsutomu Takahashi, Hirotoshi Ando, Mamiko Arai, Seri Katayama, Toshiki Takahashi A field-reversed configuration (FRC) is a compact toroid dominantly with poloidal magnetic field. Because of its simply-connected configuration, an FRC can be translated axially along a gradient of guide magnetic field, and trapped in a confinement region with quasi-static external magnetic field. FRC translation experiments have been performed several facilities. Translation speed of those translated FRCs is comparable with super-Alfvenic speed of approximately 200km/s. In this experiments, FRC translation has been performed on the FAT (FRC Amplification via Translation) facility. Achieved translation speed in the case of translation into a confinement chamber maintained as the vacuum state is in the range from 130 to 210 km/s. On the other hand, FRC translation into a statically filled deuterium gas atmosphere has also been performed. In the case of translation into filled neutral gas, FRC translation speed is approximately 80km/s and the separatrix volume has extremely expanded compared with the case of a vacuum state. The phenomenon suggests the presence of regeneration process of translation kinetic energy back into the internal plasma energy during the translation process. [Preview Abstract] |
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UP8.00005: Numerical study of rotational instabilities and beam ion effects in FRC using the HYM code Elena Belova, D. Barnes, S. Dettrick, A. Necas Numerical study of FRC spin-up and the effects of end-biasing on FRC stability has been performed using a 3D nonlinear hybrid version of the HYM code for TAE FRC experimental parameters. The n$=$1 tilt mode is found to be weakly unstable in S*$=$9 FRC, and it saturates nonlinearly at small amplitude. Simulations including the particle loss and periodic BCs show all low-n modes stable for large resistivity. End-shorting results in faster spin-up and instability of n$=$1 tilt and subsequent growth of the n$=$2 rotational mode. Depending on value of applied end-biasing electric field, the n$=$1 wobble or n$=$2 rotational mode becomes unstable. Hybrid simulations with non-symmetric BCs with/without end-shorting show strongly unstable n$=$1 radial shift (wobble) mode. The effects of energetic beam ions on FRC stability properties have been also investigated numerically using a hybrid version of the HYM code. Stability properties of co-interchange (kink) modes with different toroidal mode numbers n$=$1-4 and the beam driven instabilities have been studied for realistic TAE equilibrium and slowing down distribution for the beam ions. [Preview Abstract] |
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UP8.00006: Kinetic particle simulation of turbulence in an FRC geometry Daniel Fulton, Calvin Lau, Ihor Holod, Zhihong Lin, Sean Dettrick, Michl Binderbauer, Toshiki Tajima Core turbulence in a Field Reversed Configuration (FRC) is studied using the Gyrokinetic Toroidal Code with modified equilibrium geometry. The code solves the gyrokinetic equation for ions and the drift kinetic equation for electrons. The simulation region is an annulus which excludes plasma near the O-point to avoid breakdown of the gyrokinetic dynamics of ions. The C-2 FRC equilibrium is introduced to study similar conditions as found in the C-2 experiments, where the core is found to be relatively quiescent. In simulation, we find the C-2 plasma is stable to ion temperature gradient instabilities using realistic experimental parameters, consistent with experimental results obtained in C-2. When temperature and density gradients are enhanced beyond typical C-2 parameters, we observe a class of instabilities that appear as flute-like drift modes. These results shed light on a possible reason why transport temperature scaling in the C-2 core is radically different from that of typical turbulent transport scaling such as the Bohm-like regime. Progress is also reported on simulations of scrape off layer turbulence and electron driven turbulence. [Preview Abstract] |
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UP8.00007: Latest Electron Temperature and Density Measurement in C-2 High Performance Regimes Kan Zhai, John Kinley, Helen Zhang, Benoit LeBlanc A new high performance regime of C-2 FRC Plasma was found and experimentally investigated during our latest campaigns. With the recently added capability of measuring electron density profiles with the Thomson scattering system, the electron temperature and density profiles and their temporal evolution are investigated for this new operational regime and are compared with the cases of our previously obtained high performance regime. It is found that for the new regime the electron temperature is higher, both in the FRC core and edge regions. In the period from 0.5ms to 1ms, both the core and the edge electron temperature increase. Analogously the excluded magnetic flux radius increases during this period as well, which suggests possible electron heating as well as the potential toward sustainment of the C-2 FRC plasma. The electron density measurement shows flat and hollow radial profiles and the core/edge density stays flat in time. Detailed experimental setup and results will be presented in the meeting. [Preview Abstract] |
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UP8.00008: Development of Compact Toroid Injector for C-2 FRCs Tadafumi Matsumoto, Junichi Sekiguchi, Tomohiko Asai, Hiroshi Gota, Eusebio Garate, Ian Allfrey, Travis Valentine, Brett Smith, Mark Morehouse Collaborative research project with Tri Alpha Energy has been started and we have developed a new compact toroid (CT) injector for the C-2 device [1], mainly for fueling field-reversed configurations (FRCs). The CT is formed by a magnetized coaxial plasma-gun (MCPG), which consists of coaxial cylinder electrodes; a spheromak-like plasma is generated by discharge and pushed out from the gun by Lorentz force. The inner diameter of outer electrode is 83.1 mm and the outer diameter of inner electrode is 54.0 mm. The surface of the inner electrode is coated with tungsten in order to reduce impurities coming out from the electrode. The bias coil is mounted inside of the inner electrode. We have recently conducted test experiments and achieved a supersonic CT translation speed of up to $\sim$ 100 km/s. Other typical plasma parameters are as follows: electron density $\sim$ 5x10$^{21}$ m$^{-3}$, electron temperature $\sim$ 40 eV, and the number of particles $\sim$ 0.5--1.0x10$^{19}$. The CT injector is now planned to be installed on C-2 and the first CT injection experiment will be conducted in the near future. The detailed MCPG design as well as the test experimental results will be presented. \\[4pt] [1] M.W. Binderbauer \textit{et al.}, Phys. Rev. Lett. \textbf{105}, 045003 (2010). [Preview Abstract] |
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UP8.00009: Z-effective from Bremsstrahlung Emission in the C-2$^{\ast \, }$FRC Eusebio Garate, Nathan Bolte, Deepak Gupta, Hiroshi Gota, Ian Allfrey, John Kinley, Kurt Knapp An absolutely-calibrated 12-chord Bremsstrahlung array has been implemented on C-2 and is being used to infer Z-effective profiles and line-averaged values. Electron-ion Bremsstrahlung light at a given wavelength is a function of electron temperature, electron density, and the average ionic charge, Z-effective. Electron density is measured with interferometry and electron temperature is measured directly with Thompson scattering or is inferred by pressure balance. Custom band-pass filters at 523.4 nm were chosen to avoid line-radiation. Z-effective radial profiles show a peak near the separatrix and line-averaged values show an increase in time. For shots where density and temperature profiles were available, Z-effective inside the separatrix was found to be 1.28 for the first ms. These data suggest that C-2 FRC's do not suffer from high levels of edge-light contamination, which allows Z-effective monitoring with a single chord. * M. W. Binderbauer, High Performance Field Reversed Configurations (APS DPP 2014 Invited Talk) [Preview Abstract] |
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UP8.00010: Beam-instabilities and their impact on anomalous neutron reactivity Ales Necas, Scott Nicks, Toshiki Tajima, Richard Magee Field Reversed Configuration (FRC) toroidal current is sustained with the neutral beam injection (NBI). ~ ~Thermal plasma is deuterium and beams are hydrogen. ~If there exists some beam driven modes that can make clumpy distribution in its phase space of the beam-plasma system, the plasma bulk portion of the clumpiness can contribute to enhance the fusion reactivity (Anomalous increase of neutrons originating from thermonuclear D$+$D reaction is observed signaling rise of thermal ions temperature. It is useful to~study a beam heating of the thermal ions via a beam-driven instability). ~Thus it is of crucial interest if and what kind of beam-driven instabilities are available for the C-2 experimental conditions under which this anomalous neutron yield is observed (see accompanying abstract). ~As a starter, the hot plasma electrostatic dispersion relation with the ion beam is~investigated as to determine possible growth rate and heating associated with the beam.~ [Preview Abstract] |
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UP8.00011: Advanced Biasing Experiments on the C-2 Field-Reversed Configuration Device Matthew Thompson, Sergey Korepanov, Eusebio Garate, Xiaokang Yang, Hiroshi Gota, Jon Douglass, Ian Allfrey, Travis Valentine, Nolan Uchizono The C-2 experiment seeks to study the evolution, heating and sustainment effects of neutral beam injection on field-reversed configuration (FRC) plasmas. Recently, substantial improvements in plasma performance were achieved through the application of edge biasing with coaxial plasma guns located in the divertors [1]. Edge biasing provides rotation control that reduces instabilities and E x B shear that improves confinement. Typically, the plasma gun arcs are run at $\sim$ 10 MW for the entire shot duration ($\sim$ 5 ms), which will become unsustainable as the plasma duration increases. We have conducted several advanced biasing experiments with reduced-average-power plasma gun operating modes and alternative biasing cathodes in an effort to develop an effective biasing scenario applicable to steady state FRC plasmas. Early results show that several techniques can potentially provide effective, long-duration edge biasing. \\[4pt] [1] M. Tuszewski et al., Phys. Rev. Lett. 108, 255008 (2012) [Preview Abstract] |
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UP8.00012: Fast Global Imaging of the C-2 Field-Reversed Configuration and Divertor Plasmas Erik Granstedt, A.L. Roquemore, A. Longman, R. Hayashi, E. Yankoski Two high-speed, filtered cameras have been used to view the dynamics of the C-2.\footnote{M. Tuszewski, \emph{et al} Physical Review Letters {\bf 108}, 255008 (2012)} Field-Reversed Configuration (FRC) and divertor plasmas. The first used a re-entrant viewport to achieve a global, quasi-axial view of the FRC plasma in order to examine macroscopic plasma evolution, rotation, and non-axisymmetric perturbations. This instrument consisted of a Phantom v7.3 camera coupled to imaging optics via a 15-ft, 1000$\times$800 pixel coherent fiber bundle. A filter wheel was set between shots to view edge-dominated emission from neutral D, C III, or Li I--II, or core-dominated emission from O III--V. Perturbations rotating in the ion diamagnetic direction were observed both during the FRC and after the transition to an open field-line plasma. The divertor instrument consisted of a Phantom v5.2 camera with D$_\alpha$ filter and was used to examine divertor neutral density under various gas puffing, magnetic field, and electrode biasing configurations. Both instruments were photometrically calibrated to measure absolute emissivity in order to obtain estimates of neutral and impurity density. [Preview Abstract] |
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UP8.00013: Gyro-Scale Turbulence in the C-2 Field Reversed Configuration L. Schmitz, B. Deng, H. Gota, T. Tajima, D. Gupta, J. Douglass, M. Binderbauer, E. Ruskov Short-scale electron-mode turbulence (0.5$\le k_{\theta }\rho _{\mathrm{s}}\le $40; where $k_{\theta }$ is the toroidal wavenumber and $\rho_{\mathrm{s}}$ is the ion sound gyroradius) has been observed in the C-2 FRC via multi-channel Doppler Backscattering. Density fluctuation levels \textit{\~{n}/n }are substantial near the separatrix and in the scrape-off layer (SOL) plasma, and very low in the FRC core. Turbulent structures are observed to propagate radially outwards from the separatrix into the SOL. SOL fluctuation levels are reduced by a large factor ($\le $10) at high mirror plug ratio ($R_{\mathrm{p}}=$20), with concomitant improvements in FRC particle and energy confinement. Reduced radial correlation lengths ($\lambda_{\mathrm{c}}$\textless $\rho_{\mathrm{s}})$ and turbulence decorrelation rates are measured near the separatrix. A non-monotonic toroidal wavenumber spectrum is observed in the FRC core (\textit{\~{n}/n} \textit{increases} with toroidal wavenumber for $k_{\theta }\rho_{\mathrm{s}}\le $10 and \textit{decreases} exponentially for high $k_{\theta }\rho_{\mathrm{s}})$. These observations are qualitatively consistent with quenching of long wavelength ion modes via \textbf{\textit{E}}x\textbf{\textit{B}} velocity shear or Finite Larmor radius effects, and dominant residual electron-mode core plasma turbulence. [Preview Abstract] |
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UP8.00014: Time-evolution of ion-temperature radial profiles for high performance FRC (HPF) plasma in C-2 Deepak Gupta, E. Granstedt, S. Gupta, R. Magee, D. Osin, M. Tuszewski Measurements of ion temperature profile and its time evolution is important for the understanding of FRC confinement and transport properties. Recently, in C-2 plasma device, FRCs with significantly improved confinement and transport properties are observed (HPF14) using higher formation DC field and Lithium wall conditioning. Time evolutions of ion-temperature profiles in these FRCs are measured using upgraded impurity ions passive Doppler spectroscopy system. Measured line integration profiles are inverted to get the local ion-temperature profiles, by taking in to consideration the local emissivity and directed ion-velocity. These profiles are measured under different C-2 operation conditions; for example, Neutral Beam power, plasma gun and magnetic field configurations. Radial profiles of ion temperature and its time evolution will be presented. Comparison of ion-temperature time-evolution with neutron measurements, deuterium-ion temperature measurements, and 1-d transport modeling will also be presented. [Preview Abstract] |
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UP8.00015: Measurement of density fluctuations and particle transport in C-2 Bihe Deng, Scott Aefsky, John Kinley In the C-2 field reversed configuration experiment [1], long wavelength density fluctuations are measured for the first time by a newly developed far infrared (FIR) laser far forward scattering diagnostics. The dynamics of the frequency spectrum, spatial distribution, scaling with density gradient and other plasma equilibrium parameters are characterized. On the other hand, density profile evolution and particle transport are measured by the multi-chord two-color CO2/HeNe interferometer. The correlation between measured density fluctuations and particle transport will be examined. \\[4pt] [1] M. W. Binderbauer \textit{et al.}, Phys.Rev.Lett. \textbf{105,} 045003 (2010). [Preview Abstract] |
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UP8.00016: VUV Spectra observed in C-2 FRC plasma Dmitry Osin, Jon Douglass, Michel Tuszewski A grazing incidence flat-field spectrometer was installed for observation of vuv-spectra in C-2 FRC experiment. Wavelength calibration was done by observing spectra of six different gases produced by a hollow-cathode discharge lamp . In addition, in-situ calibration and alignment were performed utilizing neutral-beam heated gases. Wavelength regions between 16 nm and 170 nm was investigated with accuracy of about 0.02 nm. VUV-spectral lines of the most abundant impurity ions were identified both for Plasma Gun and C-2 plasmas. In addition to D spectrum, strong lines of O III-VI, N IV-V, C II-III, and Fe II ions were observed during the plasma lifetime. VUV radiative power losses within energy range from 7.3 eV to 81 eV were estimated based on the calculated FRC dimensions. [Preview Abstract] |
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UP8.00017: Transport study of the C-2 FRC plasma Marco Onofri, Sean Dettrick, Daniel Barnes, Toshiki Tajima, Sangeeta Gupta, Erik Trask, Lothar Schmitz The 2D transport code Q2D is used to study transport in the C-2 Field Reversed Configuration with neutral beam injection. The code solves the MHD equations including source terms due to neutral beams, which are calculated by a Monte Carlo technique. We compare numerical simulations with experimental results obtained in C-2, where 6 neutral beams are injected into the plasma with energy of 20 keV and total power of 4.2 MW. Q2D simulations of C-2 start from an initial equilibrium and different values of the transport coefficients are used to study their effect on the evolution of the FRC. We investigate different transport coefficients, including those based on the TAE transport scaling. For the recent HPF14 confinement regime in C-2 we study the coupling between the scrape-off layer (SOL) and the FRC core by changing the mirror-plug constriction. We also observe that the number of fast ions is affected by the density of neutrals, which cause charge exchange, and by beam shinethrough, which also depends on SOL transport. These results are also compared with the 1D version of our transport code Q1D. [Preview Abstract] |
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UP8.00018: C2 Lithium Campaign Power Balance Erik Trask, Bihe Deng, Jon Douglass, Eusebio Garate, Deepak Gupta, Sangeeta Gupta, Michel Tuszewski Several key changes have lead to record performance of the Tri Alpha Energy's (TAE) C2 Field Reversed Configuration (FRC) device. Wall conditioning changes from titanium to lithium have decreased radiative losses, while changes in the magnetic field of the SOL and jet have substantially increased energy confinement times. An overview of 0D power flows and timescales will be presented demonstrating that ions behave classically, that anomalous electron losses have been substantially reduced, and that plasma sustainment will require modest increases in heating power. These observations will be quantitatively analyzed as well as compared with both theoretical modeling of the TAE transport and numerical simulations (Q2D). [Preview Abstract] |
(Author Not Attending)
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UP8.00019: Plasma flow and electron losses in the expander divertor of FRC P. Yushmanov, D. Barnes, S. Dettrick, S. Gupta, D. Ryutov, S. Krasheninnikov, A. Necas, S. Putvinski Expander divertor is planned to be used in the design of next generation FRC device. The main goal of magnetic field expansion is to decrease heat load on the target plates and slow down heat losses through electron channel. A comprehensive study of expander divertor physics is initiated in Tri Alpha. It started with revision of pre-sheath electrostatic potential formation in the expander using both analytic and numerical means. An adaptation of 3D code KSOL has been developed to analyze electron physics and electrostatic potential formation. Initial results are presented. The key issue of the study is the analysis of the interaction of plasma with neutrals. Presence of neutrals affects expander physics in several ways. First of all, charge exchange and ionization modify pattern of ion flow in the expander magnetic field. That changes plasma density profile and affects formation of pre-sheath electrostatic potential. Second, ionization (as well as secondary electron emission) creates population of cold electrons in the expander which flow into confinement vessel and enhance out-flux of hot electrons. Distribution of neutrals is calculated in realistic geometry of expander divertor and effect on electron losses is evaluated. [Preview Abstract] |
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UP8.00020: Propagation and dynamics of microwaves in the ECRH frequency range for the FRC Francesco Ceccherini, Laura Galeotti, Marco Brambilla, Daniel C. Barnes, Xiaokang Yang A previously developed FLR code for ICRH studies has been recently upgraded to include the frequency range of interest for ECRH applications. This full wave code is able to use very fine meshes (grid spacing down to $10^{-3}$ cm on a single cpu) so that even wavelengths very short with respect to the wall radius can be resolved well. The first wave propagation scheme we have addressed - and in part used for benchmark purposes also - is given by a source placed at a few cm from the first wall with a current oscillating in the longitudinal direction and an ordinary wave propagating in the radial direction. Such a wave propagates through the plasma until the required conditions for O-X-B mode conversion are encountered. The mode-converted electrostatic wave generated at the upper hybrid frequency behaves according to the expected dispersion relation and it is studied in terms of the launched frequency. Initial results indicate that in an elongated FRC configuration under study, the possibility to satisfy all conditions required to have electron absorption in the region beyond the SOL through the O-X-B conversion process strongly depends on the plasma radial profile. Details on this scheme and different examples will be presented. [Preview Abstract] |
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UP8.00021: Measurements of classical fast ion confinement with fusion product diagnostics Richard Magee, Ryan Clary, Sergey Korepanov, Artem Smirnov, Eusebio Garate, Ian Allfrey, Travis Valentine Neutral beam injected fast ions play a critical role in the C-2 field reversed configuration plasma,\footnote{M. Tuszewski et al., Phys. Rev. Lett. \textbf{108}, 255008 (2012).} helping to sustain magnetic flux against resistive decay and heating the plasma via Coulomb collisions. The fast ions are well confined; due to the relatively low magnetic field strength the fast ions have large, machine-size orbits that permit them to average over otherwise deleterious fluctuations. These same orbits however, have large radial excursions that result in greater interaction of fast ions with edge neutrals and a greater potential for charge exchange losses. In this presentation, the fast ion slowing down time is determined from the decay in neutron flux following beam termination. It is found that the slowing down scaling is close to classical (i.e., $\tau \sim T_e^{3/2} / n_e$) and that charge exchange losses are only significant for ions with 1.5x the nominal injection energy. We will also present initial data from a newly installed proton detector, which complements the temporal resolution of the neutron detector with spatial resolution. The detector will be used to diagnose the axial profile of confined fast ions. [Preview Abstract] |
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UP8.00022: Improved Magnetic Reconnection Experiment at FRC Device Ming Xu, Ruijie Zhou, Daniel Vasquez, Tian-Sen Huang With experimental facility's improvement, magnetic reconnection has been further studied at Prairie View rotamak device. By adding one toroidal current in the central part of the rotamak device, the cutting of one magnetic field reverse configuration (FRC) as two FRCs in the experiment process becomes more obvious. Differing from the magnetic reconnection experiments conducted at other labs, where magnetic reconnection is formed with two ware-coiled currents buried in a chamber with large scale magnetic field, in our magnetic reconnection experiment the main source of the magnetic field is plasma current. Thus, the magnetic reconnection experiments conducted at rotamak device are closer to the one occurring in the space and on the sun. At the present stage, our experiments focus on the study of the change in electron temperature during the magnetic reconnection process. Furthermore, the ion temperature and plasma flow can be easily achieved from fast ion Doppler spectroscopy (IDS) diagnostic system [1], which makes the magnetic reconnection process more clearly. \\[4pt] [1] Petrov, Y., X. Yang, et al., Physics of Plasmas, 15(7): 072509-072508 (2008)\\[0pt] [2] Houshmandyar, S., X. Yang, et al., Review of Scientific Instruments 83(10): 10D506 (2012) [Preview Abstract] |
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UP8.00023: Microwave Heating Experimental at Prairie View Rotamak Ruijie Zhou, Ming Xu, Daniel Vasquez, Tian-Sen Huang A 6kW 2.45GHz microwave generator has been added, and a study of microwave heating experiment is performed at Prairie View Rotamak. This is the first time to apply microwave heating to a rotating magnetic field drive field reversed configuration. Rotamak is a compact torus that the toroidal plasma current is driven by means of an externally applied rotating magnetic field (RMF) with a large plasma current being generated to reverse the external equilibrium magnetic field on the symmetry axis, so a field-reversed configuration (FRC) is formed. The plasma current is produced by external rotating magnetic field, the plasma equilibrium shape is controlled by the magnetic shaping coils. The added microwave with power adjustable is injected from the top of the plasma chamber. In the experiment: f$_{\mathrm{pe}}\approx $10$^{4}$ GHz and f$_{\mathrm{ce}}\approx $30MHz (f$_{\mathrm{ce}}$\textless \textless f\textless \textless f$_{\mathrm{pe}}$, where f$_{\mathrm{pe}}$, f$_{\mathrm{ce}}$ are respectively electron plasma and cyclotron frequencies and f is the frequency of microwave). Consequently, the interaction between microwave and plasma is more complicated, and a series of experiments are performed at Prairie View Rotamak and some results are achieved for the following experiment. At first, a comparison experiment is performed for FRC and ST cases, and the coupling effect between high frequency microwave and plasma is being studied. Secondly, the microwave can offer a new method to affect some of MHD instabilities (such as tilt mode). n$=$1 tilt instability has been suppressed by magnetic shaping coils previously. [Preview Abstract] |
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UP8.00024: Results on a 15-Joule theta-pinch FRC-physics test cell for space propulsion research Carrie Hill, Nolan Uchizono, Michael Holmes The U.S. Air Force Research Laboratory-Edwards has developed a new experimental test cell to study the physics of Field-Reversed-Configuration (FRC) formation, equilibrium, and acceleration at low-energy for space propulsion. The test-cell is compatible with a variety of plasma sources, including theta-pinch and rotating magnetic field sources. The first plasma source installed in the test-cell was a low-energy (15 J/pulse) theta-pinch source. This source has been tested at full energy with a xenon propellant and argon propellant at a range of fill densities (1-50 mTorr) and bias fields up to 1 kG. The test-cell was equipped with a suite of diagnostics to monitor plasmoid formation, include voltage and current transducers, an excluded flux array, internal magnetic field probes, emission spectroscopy, and Langmuir probes. Several pre-ionization schemes were tested with the source as well to investigate their effectiveness on plasmoid formation. Results on the theta-pinch plasma studies are presented here. [Preview Abstract] |
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UP8.00025: Gasification and Ionization of Chemically Complex Liquids for FRC Injection Michael Holmes, Carrie Hill Ion thrusters provide reliable and efficient spacecraft propulsion but are limited to noble gas propellants to limit chemical attack of components. However, thrusters based on Field Reversed Configuration (FRC) plasmas are becoming a reality. High beta compact-toroids are generated within an FRC thruster and then expelled to provide thrust. The closed field lines restrict the plasma from attacking thruster components. More convenient propellants such as water are therefore possible. The FRC thruster would generate a series of compact-toroids (plasmoids) to develop continuous spacecraft thrust. Each plasmoid ejection would empty the discharge region. The feed system would then refill the discharge region with partially ionized gas for the next discharge. The ionization part of this feed system is the subject of this paper. The question is how to produce a uniform, chemically complex, ionized gas within the discharge region that optimizes compact-toroid formation? We will be measuring chemical state, ionization state, and uniformity as the propellant enters the discharge region. [Preview Abstract] |
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UP8.00026: Effects of electrode coating on the CTIX injector performance during high-Z CT formation and acceleration D. Buchenauer, R.D. Horton, R. Evans, R. Klauser, B.E. Mills, D.Q. Hwang One application of high velocity compact toroids (CTs) is the ability to deliver ions of various species to the magnetic axis of tokamak plasmas. The fast formation and acceleration of the CTs can react to rapidly changing events in a tokamak operation such as disruptions. As proposed in theoretical models, high-Z ions delivered to the magnetic axis of a reactor-grade tokamak have the benefit of cooling runaway electrons by the bremsstrahlung process and limiting the runaway electrons final energy and the potential damage to tokamak components. The Compact Toroid Injection Experiment (CTIX) is currently being used to demonstrate efficient production of high-Z CT plasmas using accretion of noble gases (He, Ne, Ar) puffed in the acceleration region. From previous observations of electrode damage due to repetitive operation of the CTIX injector with hydrogen CT's, it was decided to coat the inner electrode surfaces with vacuum-sprayed tungsten. The CT characteristics are measured using optical techniques, interferometry, and internal magnetic field probes. A detailed comparison of the CT behavior and parameters using the different electrodes, stainless steel and tungsten-coated Inconel, will be reported. In addition, analysis of the measured damage to the electrode surface will guide future improvements to the injector design that will yield the best high-Z CTs for the mitigation of runaway electrons. [Preview Abstract] |
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UP8.00027: High-beta spherical tokamak startup in TS-4 merging experiment by use of toroidal field ramp-up Yasuhiro Kaminou, Toru Ii, Joji Kato, Michiaki Inomoto, Yasushi Ono We demonstrated the formation method of an ultrahigh-beta spherical tokamak by use of a field-reversed configuration and a spheromak in TS-4 device (R $\sim$ 0.5m, A $\sim$ 1.5, Ip $\sim$ 30-100kA, B $\sim$ 100mT). This method is composed of the following steps: 1. Two spheromaks are merged together and a high-beta spheromak or FRC is formed by reconnection heating. 2. External toroidal magnetic field is added (current rising time $\sim$ 50$\mu$s), and spherical tokamak-like configuration is formed. In this way, the ultrahigh-beta ST is formed. The ultrahigh-beta ST formed by FRC has a diamagnetic toroidal field, and it presumed to be in a second-stable state for ballooning stability, and the one formed by spheromak has a weak paramagnetic toroidal magnetic field, while a spheormak has a strong paramagnetic toroidal magnetic field. This diamagnetic current derives from inductive electric field by ramping up the external toroidal magnetic field, and the diamagnetic current sustains high thermal pressure of the ultrahigh-beta spherical tokamak. And the beta of the ultrahigh-beta ST formed by FRC reaches about 50{\%}. To sustain the high-beta state, 0.6MW neutral beam injection and center solenoid coils are installed to the TS-4 device. In the poster, we report the experimental results of ultrahigh-beta spherical tokamak startup and sustainment by NBI and CS current driving experiment. [Preview Abstract] |
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UP8.00028: Prospects for US Stellarator Research Jeffrey Harris Stellarators ensure plasma confinement using flux surfaces generated by external coils. The confinement properties of a stellarator are entirely determined by its complex 3D magnetic configuration. A suitably designed stellarator reactor thus offers the prospect of steady-state, ignited, disruption-free operation with minimal active control. The challenge for stellarator research is to develop techniques that allow optimization and confident extrapolation of configuration designs to reactor-scale devices. US researchers have made significant contributions to stellarator analysis and optimization which are in use around the world, but the US domestic stellarator program is small, and operates only two university-scale stellarator facilities: HSX (University of Wisconsin) and CTH (Auburn University). To increase its role in stellarator development in the next ten years, the US stellarator community is leveraging its expertise in national collaborative efforts on the large, superconducting stellarator devices W7-X (Germany) and LHD (Japan), with a particular focus on 3D divertor physics. Progress on these large experiments will set the stage for a new US stellarator experiment to explore the physics of quasi-symmetric stellarator confinement. [Preview Abstract] |
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UP8.00029: The Physics Program for the QUASAR facility D.A. Gates, S.A. Lazerson, G.H. Neilson, M. Zarnstorff, O. Schmitz, H. Frerichs The QUASi-Axisymmetric Research (QUASAR) stellarator is a new facility which can solve two critical problems for fusion, disruptions and steady-state, and which provides new insights into the role of symmetry in plasma confinement. The principle of quasi-axisymmetry will be used in QUASAR to study how tokamak-like systems can be made disruption-free and steady-state with low recirculating power, while also improving upon features of tokamaks, such as; stable at high pressure with high confinement, and scalable to a compact reactor. The two large stellarator experiments - LHD and W7-X - are pioneering facilities capable of developing 3D physics understanding at large scale and for very long pulses. The QUASAR design is unique in being QA and optimized for confinement, stability, and moderate aspect ratio (4.5). Important elements of the physics program for QUASAR are: establishing the physics basis of the design by demonstrating stable operation at high-$\beta $ simultaneous with good neoclassical confinement, understanding the concomitant turbulent transport, and understanding the dependence of the underlying transport on magnetic geometry. An additional important element of the program will be understanding the physics characteristics of a QA stellarator with an high flux expansion ergodic edge. [Preview Abstract] |
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UP8.00030: Plans for first plasma operation on Wendelstein 7-X Thomas Sunn Pedersen Wendelstein 7-X construction is nearing completion and the commissioning phase has started, in preparation for first plasma. The first plasma operation phase (OP1.1) will be performed entirely without a divertor. Instead, five symmetrically placed inboard graphite limiter stripes will intersect and absorb the convective plasma heat loads. These un-cooled limiter stripes will limit the injected heating energy per pulse to about 2 MJ, for example, 0.5 second pulse length with 4 MW of ECRH heating. These plasmas will serve to commission the main physics tools for the machine, in particular the vacuum system,the diagnostics and the ECRH heating system. OP1.1 will last about 3 months and will, despite the relatively short pulse lengths, provide the opportunity to study a number of interesting phenomena, including limiter scrape-off layer physics, heat pulse propagation, energy, particle, and impurity confinement in the electron root, and measurements and, if necessary, correction of resonant field errors. A progress report on commissioning will be given, and elements of the physics program planned for OP1.1 will be explained, together with a status report on the installation and commissioning of key diagnostics. [Preview Abstract] |
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UP8.00031: The impact of profile variability on bootstrap current and ballooning stability in W7-X A.S. Ware, S.P. Hirshman The impact of a range of density, electron temperature, and ion temperature profiles on self-consistent bootstrap current, ballooning stability and the magnetic structure of equilibria in computational studies of the W7-X stellarator is examined. Previous work has shown that even a small bootstrap current can change the rotational transform profile and thus, change the magnetic configuration, especially in the edge region. In this work, free-boundary equilibria for the W7-X coil configuration have been obtained over a range of pressure, density and temperature profiles, including equilibria with self-consistent bootstrap current (i.e., where the plasma current is solely from the bootstrap current). The impact of these profiles on bootstrap current, magnetic structure in the edge, and ballooning stability is examined. The formation of islands in the edge regions and correlation with ballooning stability is discussed. Methods of ameliorating the impact of bootstrap current will be discussed. [Preview Abstract] |
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UP8.00032: A Specialized IR Endoscope for High Resolution Views in the W7-X Stellarator Glen Wurden, Marcin Jakubowski, Juergen Baldzuhn As part of the US/German collaboration on W7-X, we report on the design and preparation of a relay lens-based endoscope for infrared observations of the W7-X limiter and divertor components, during early operation. We plan a 100 degree field of view which can be steered with a stainless turning mirror, directed towards either a graphite limiter in OP1.1, or a test divertor unit with scraper element in OP1.2. Optical access is obtained using a water-cooled, shutter-protected, reentrant viewing tube, which can be mounted in several possible diagnostic ports. It will contain 2.2 meter long borescope optics working at f/4 in the 3-5 micron wavelength band. Software for real-time acquisition and analysis written in Matlab with multi-core GPU image processing will also be discussed. [Preview Abstract] |
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UP8.00033: Initial characterization of electron cyclotron heated plasmas in the Columbia Non-Neutral Torus Kenneth Hammond, Francesco Volpe, Samuel Lazerson The Columbia Non-Neutral Torus (CNT) is a stellarator at Columbia University recently modified for the study of quasi-neutral plasmas heated by 2.45 GHz electron cyclotron waves. Using a simple configuration of four circular planar coils, it generates magnetic surfaces with the lowest aspect ratios (1.9-2.7) ever attained by a stellarator. The low magnetic field (0.09 T), combined with the possibility of electron Bernstein wave heating above the cutoff density, could make CNT suitable for research of magnetohydrodynamic equilibrium and stability at high beta. Additional plans for future work include novel microwave and magnetic diagnostics, heating with electron cyclotron and helicon waves, and error field studies. Here we present an experimental characterization of the parameters of CNT's first microwave-heated plasmas. We present Langmuir probe measurements of temperature and density profiles, fast camera images, and equilibrium reconstructions computed by the VMEC code. [Preview Abstract] |
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UP8.00034: Constructing a Small Modular Stellarator in Latin America Ivan Vargas, Jaime Mora, Carlos Otarola, Jose Asenjo, Esteban Zamora, Jeferson Gonzalez, Carlos Piedra The small modular stellerator SCR-1 (Stellerator of Costa Rica 1) is a 2-field period device with a circular cross-section vessel under construction in Costa Rica (R$_{o}=$0.238 m, \textless a\textgreater $=$0.059 m, R$_{o}$/a \textgreater\ 4.0, expected plasma volume $\approx $ 0.016 m$^{3}$, 10 mm thickness 6061-T6 aluminum vacuum vessel). The magnetic field strength at the centre is around 44 mT which will be produced by 12 copper modular coils with 4.35 kA-turn each. This field is EC resonant at R$_{o}$ with 2.45 GHz as 2$^{nd}$ harmonic, from 2/3 kW magnetrons. SCR-1 was redesigned from stellerator UST\textunderscore 1. As a first step, the objectives focus on training human resources and identifying problems related to the design and construction of small modular stellarators. We present the engineering problems encountered and the proposed solutions related to: thickness, material and construction method for the vacuum vessel, layout and design of ports, method of construction for coils, coils fixing, welding procedure, microwave input, control and data acquisition systems, design and test of diagnostics. Temperature, resistance, voltage and power calculations as a function of time were performed for the electrical circuit under different wire configurations per modular coil to select the power supply taking into account the available budget. [Preview Abstract] |
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UP8.00035: Two-dimensional impurity transport study in stochastic magnetic field layer at low- and high-density discharges of LHD Shigeru Morita, Tetsutarou Oishi, Hongming Zhang, Masahiro Kobayashi, Motoshi Goto, Gakushi Kawamura, Xianli Huang Edge stochastic magnetic field layer of Large Helical Device (LHD) consists of short and long open magnetic fields ranging in 10$\le $L$_{c}\le $2000m. When the edge density increases, the friction force along magnetic field is entirely dominant in outer region of the stochastic magnetic layer which leads to the impurity screening. In order to study the parallel impurity transport two-dimensional impurity emissions from several impurity spices have been measured in EUV wavelength range (10-500{\AA}) and a clear impurity footprint along poloidal X-point trajectory is observed. The poloidal impurity footprint, e.g. CIV, is separated into double trajectories at high-density discharges (n$_{e}\ge $5x10$^{13}$cm$^{-3})$, whereas it shows single trajectory at low-density discharges (n$_{e}\le $2x10$^{13}$cm$^{-3})$. The result clearly indicates the presence of the friction force. The 2-D distribution analyzed by 3-D edge transport code, EMC3-EIRENE is discussed on the friction force and temperature gradient force along magnetic fields. [Preview Abstract] |
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UP8.00036: Chaotic coordinates for the Large Helical Device Stuart Hudson, Yasuhiro Suzuki The study of dynamical systems is facilitated by a coordinate framework with coordinate surfaces that coincide with invariant structures of the dynamical flow. For axisymmetric systems, a continuous family of invariant surfaces is guaranteed and straight-fieldline coordinates may be constructed. For non-integrable systems, e.g. stellarators, perturbed tokamaks, this continuous family is broken. Nevertheless, coordinates can still be constructed that simplify the description of the dynamics. The Poincare-Birkhoff theorem, the Aubry-Mather theorem, and the KAM theorem show that there are important structures that are invariant under the perturbed dynamics; namely the periodic orbits, the cantori, and the irrational flux surfaces. Coordinates adapted to these invariant sets, which we call chaotic coordinates, provide substantial advantages. The regular motion becomes straight, and the irregular motion is bounded by, and dissected by, coordinate surfaces that coincide with surfaces of locally-minimal magnetic-fieldline flux. The chaotic edge of the magnetic field, as calculated by HINT2 code, in the Large Helical Device (LHD) is examined, and a coordinate system is constructed so that the flux surfaces are ``straight'' and the islands become ``square.'' [Preview Abstract] |
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UP8.00037: Electromagnetic gyrokinetic simulation of turbulent transport in high ion temperature discharge of Large Helical Device Akihiro Ishizawa, Tomo-Hiko Watanabe, Hideo Sugama, Shinya Maeyama, Masanori Nunami, Noriyoshi Nakajima Turbulent transport in a high ion temperature discharge of Large Helical Device (LHD) is investigated by means of electromagnetic gyrokinetic simulations including kinetic electrons. A new electromagnetic gyrokinetic simulation code GKV+ enables us to examine electron heat and particle fluxes as well as ion heat flux in finite beta heliotron/stellarator plasmas [1]. This problem has not been previously explored because of numerical difficulties associated with complex three-dimensional magnetic structures as well as multiple spatio-temporal scales related to electromagnetic ion and electron dynamics. The turbulent fluxes, which are evaluated through a nonlinear simulation carried out in the K-super computer system, will be reported.\\[4pt] [1] A. Ishizawa, et.al., Nuclear Fusion 53, 053007 (2013). [Preview Abstract] |
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UP8.00038: Effect of neoclassical poloidal viscosity and resonant magnetic perturbation on the response of the m/n=1/1 magnetic island in LHD Huang Botsz, Shinsuke Satake, Ryutaro Kanno, Yoshiro Narushima, Satoru Sakakibara, Satoshi Ohdachi In the LHD experiments in which m/n=1/1 resonant magnetic perturbation (RMP) amplitude is ramped up, it is observed that the perturbed field is initially shielded, and when the amplitude exceeds a threshold value, the field penetrates into the plasma and m/n/=1/1 magnetic island appears. It is also found that the threshold amplitude depends on the magnetic field configuration of LHD, that is, on the magnetic axis position. It is expected that the poloidal force balance between the electromagnetic force and the drug force from poloidal rotation determines the threshold of island formation. Since neoclassical poloidal viscosity (NPV) in LHD strongly depends on the magnetic axis position, we investigate the relationship between NPV and the threshold amplitude of m/n=1/1 RMP to penetrate by using drift-kinetic simulation code FORTEC-3D. ExB poloidal rotation determined from the ambipolar radial flux condition is taken into account in the evaluation of NPV. We mainly focus on the situation that the external magnetic perturbation is compensated by the plasma response and therefore the effect of RMP on the total NPV is shielded. However, by using a simple model to express the penetrated magnetic perturbation, we will also study the dependence of NPV on the RMP amplitude. [Preview Abstract] |
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UP8.00039: MHD instabilities limiting beta value in LHD and the interaction with error field Satoru Sakakibara, Yuki Takemura, Kiyomasa Watanabe, Satoshi Ohdachi, Yoshiro Narushima, Katsuji Ichiguchi, Katsumi Ida, Kenji Tanaka, Tokihiko Tokuzawa, Ichihiro Yamada, Hiroshi Yamada, Yasuhiko Takeiri Characteristics of MHD instabilities limiting beta value have been investigated in unstable regime of ideal interchange mode in LHD to optimize magnetic configuration of heliotron-type fusion reactor. We accessed ideal-unstable regimes by enhancing magnetic hill and reducing magnetic shear. The magnetic hill was enhanced by shifting magnetic axis position, Rax, to the inward, whereas the magnetic shear was reduced by increasing plasma current and plasma aspect ratio. In the enhanced magnetic hill configuration, m/n $=$ 2/1 mode with a finite frequency appeared when Rax \textless 3.55 m, and strong growth of the mode was observed after stop of the mode rotation. Then central beta value was dropped by 30{\%}. In the reduced magnetic shear configuration, m/n $=$ 1/1 mode was destabilized when the plasma current exceeded a threshold, the mode significantly grew after the stop of the rotation as well as the case of m/n $=$ 2/1 mode, which degraded the central beta by about 60{\%}. The onset of the mode was qualitatively consistent with ideal stability boundary, the occurrence of the collapse was independent of an existence of an error field (EF). In the configuration with the error field, the spatial structure of the mode after the stop of the rotation was almost the same as that of the EF, while it changed at random in the reduced EF case. [Preview Abstract] |
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UP8.00040: Modeling propagating heat pulses in the Large Helical Device Hao Zhu, Richard Dendy, Sandra Chapman, Shigeru Inagaki Rapid edge cooling induced by pellet injection in Large Helical Device plasmas generates inward propagating pulses with either large positive or negative deviations of the electron temperature at the core [Inagaki et al, Plasma Phys. Control. Fusion 52 (2010) 075002]. By applying a traveling wave transformation, we extend a recent model [Dendy et al, Plasma Phys. Control. Fusion 55 (2013) 115009] for local temporal evolution, to include also spatial dependence. The extended model comprises two coupled nonlinear first order differential equations for the (x,t) evolution of the deviation from steady state of two variables, the temperature gradient and heat flux. It also defines the pulse velocity in terms of plasma quantities. This enables us to model spatiotemporal pulse evolution, from first principles, in terms of the electron temperature. We have tested the model against LHD datasets using appropriate initial and boundary conditions. We find that this model can match experimental data for pulse peaks, shapes and propagation velocities within a broad radial range from plasma edge to core. [Preview Abstract] |
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UP8.00041: Overview of CTH research M.C. ArchMiller, M.R. Cianciosa, D.A. Ennis, M.M. Goforth, J.D. Hanson, G.J. Hartwell, J.D. Hebert, J.L. Herfindal, S.F. Knowlton, X. Ma, D.A. Maurer, M.D. Pandya, N.A. Roberds, P.J. Traverso Goals of the Compact Toroidal Hybrid (CTH) experiment are to: (1) investigate the dependence of plasma disruptive behavior on the level of applied 3D magnetic shaping; (2) test and advance the V3FIT reconstruction code; and (3) study the implementation of an island divertor. Progress towards these goals and other developments are summarized. The disruptive density limit exceeds the Greenwald limit as the vacuum transform is increased, but a threshold for avoidance is not observed. Low-$q$ disruptions, with 1.1 \textless $q(a)$ \textless 2.0, cease to occur if the vacuum transform is raised above $\sim $ 0.07. Application of vacuum transform can reduce and eliminate the vertical drift of elongated discharges that would otherwise be vertically unstable. While reconstructions using external magnetics give accurate estimates of the enclosed toroidal flux and quantities near the plasma boundary, internal diagnostics (such as Thomson scattering and 2D two-color SXR cameras) are being developed to extend the range of accuracy into the plasma core. NIMROD is used to model the current ramp phase and predicts the formation of symmetry-breaking magnetic islands. An island divertor design has begun with connection length studies to model energy deposition on divertor plates located in an edge 1/3 island. [Preview Abstract] |
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UP8.00042: Characteristics of Low-q(a) Disruptions in the Compact Toroidal Hybrid M.D. Pandya, M.C. ArchMiller, D.A. Ennis, G.J. Hartwell, D.A. Maurer \newcommand{\g}{\raisebox{-3pt}{$\mathchar'26\mkern-14mu$} $\iota$} Tokamak disruptions are dramatic events that lead to a sudden loss of plasma confinement. Disruptions that occur at low edge safety-factor, $q(a)$, limit the operation of tokamaks to $q(a)\ge2$. The Compact Toroidal Hybrid (CTH) is a torsatron-tokamak hybrid with a helical field coil and vertical field coils to establish a stellartor equilibrium, while an ohmic coil induces plasma current. A feature of the CTH device is the ability to adjust the vacuum rotational transform, \g$_{vac}$ (\g$=\frac{1}{q}$), by varying the ratio of current in the helical and toroidal field coils. The value of edge \g$_{vac}$ can be varied from about 0.02 to 0.3 ($q_{vac}(a)\ \sim$ 50 to 3.3). Plasma discharges in CTH are routinely observed to operate with $q(a)<2$, and in some cases as low as $q(a)\sim 1.1$. In CTH, low-q(a) disruptions are observed with a dominant m/n=3/2 precursor. The disruptivity of plasma discharges is over 80\% when \g$_{vac}(a)<0.04$ ($q_{vac}(a)< 25$) and as \g$_{vac}(a)$ is increased further, the disruptivity of the plasma discharges decreases. The disruptions are completely suppressed for \g$_{vac}(a)>0.07$ ($q_{vac}(a) \sim$14). [Preview Abstract] |
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UP8.00043: 3D Equilibrium Reconstruction with Improved Magnetic Diagnostics on the Compact Toroidal Hybrid X. Ma, M. Cianciosa, J.D. Hanson, G.J. Hartwell, S.F. Knowlton, D.A. Maurer We present non-axisymmetric equilibrium reconstruction of stellarator plasmas whose magnetic configuration is strongly modified by ohmically driven plasma current. These experiments were performed on the Compact Toroidal Hybrid device using the V3FIT reconstruction code [1] and a set of 50 magnetic diagnostics external to the plasma edge. The reconstructed equilibria gives accurate estimates of the toroidal flux within the last closed flux surface and information near the plasma boundary region including the edge safety factor, plasma shape, and current density of these highly non-axisymmetric plasmas. While the polodial cross-section of these discharges becomes more circular with the addition of driven plasma current, toroidally the underlying $n=5$ stellarator periodicity is enhanced. Eddy current effects are small for the eddy current model considered in the presence of plasma current.The remaining systematic error is associated with a vertical shift of the plasma breaking stellarator symmetry along with the use of only external magnetic diagnostics.\\[4pt] [1] J. D. Hanson et al., Nucl. Fusion \textbf{49}, 075031 (2009) [Preview Abstract] |
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UP8.00044: Design and implementation of a Thomson scattering diagnostic for the Compact Toroidal Hybrid Experiment P.J. Traverso, D.A. Maurer, D.A. Ennis, G.J. Hartwell, M.M. Goforth, S.D. Loch, A.J. Pearce, M.R. Cianciosa A Thomson scattering system using standard commercially available components has been designed for the non-axisymmetric plasmas of the Compact Toroidal Hybrid (CTH). The initial system takes a single point measurement and will be used to assess options for an upgrade to a multi-point system providing electron temperature and density profiles. This single point measurement will reduce the uncertainty in the reconstructed peak pressure by an order of magnitude for both ohmically driven, current-carrying plasmas and future gyrotron-heated stellarator plasmas. A principle design goal is to minimize stray laser light, geometrically on the machine side and spectrally on the collection side, to allow measurements of both full and half Thomson scattered spectral profiles. The beam, generated by a frequency doubled Continuum 2 J Nd:YaG laser, is passed vertically through an entrance Brewster window and an aperturing baffle system to minimize stray light. Light collection, spectral processing, and signal detection are accomplished with an $ f/{\#} \sim$ 1 aspheric lens, a Holospec f/1.8 spectrometer, and an Andor iStar DH740-18U-C3 image intensified camera. The estimated number of scattered photons per channel will be of the order of $5\times10^{3}$ with a signal to noise ratio of $S/N=19$ [Preview Abstract] |
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UP8.00045: Development of a Coherence Imaging Diagnostic for the Compact Toroidal Hybrid D.A. Ennis, M.C. ArchMiller, M.R. Cianciosa, J.D. Hanson, G.J. Hartwell, D.A. Maurer A new optical coherence imaging diagnostic is planned for time-resolved measurements of ion emissivity, velocity, and temperature in the Compact Toroidal Hybrid (CTH). The coherence imaging technique\footnote{J. Howard \textit{et al}., Plasma Phys. Control. Fusion, \textbf{45}, 1143 (2003).} measures the spectral coherence of a visible emission line with an imaging interferometer of fixed delay. Coherence imaging has a number of potential advantages when compared to dispersive Doppler spectroscopy, including higher throughput and the capacity to provide 2D spectral images, making it advantageous for investigating the non-axisymmetric geometry of CTH plasmas. The coherence imaging technique can also be extended to yield the orientation and magnitude of the magnetic field by measuring the polarized spectral components due to Zeeman splitting. A spectral survey of the visible emission for a range of CTH discharges is being conducted to identify possible spectral lines that will motivate forward modeling of the plasma emissivity using the V3FIT equilibrium reconstruction code. Initial results from this diagnostic will aid in characterizing the equilibrium ion parameters in both the edge and the core of CTH plasmas for planned island divertor and MHD mode-locking experiments. [Preview Abstract] |
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UP8.00046: Observations of the Sawtooth Instability in the Compact Toroidal Hybrid J.L. Herfindal, D.A. Maurer, G.J. Hartwell, D.A. Ennis, S.F. Knowlton, M.C. ArchMiller Sawtooth instabilities have been observed in the Compact Toroidal Hybrid (CTH), a current-carrying stellarator/tokamak hybrid device. The sawtooth instability is driven by ohmic heating of the core plasma until the safety factor drops below unity resulting in the growth of an $m=1$ kink-tearing mode. Experiments varying the vacuum rotational transform are being conducted to study sawtooth property dependance on vacuum flux surface structure. CTH has an extensive collection of internal diagnostics capable of detecting the signatures of sawtooth instabilities: three two-color SXR cameras, a bolometer, and a three-channel 1 mm interferometer. The conditions for the onset of sawteeth, size of the inversion radius, and characteristics such as the rise and crash timescales are investigated as functions of the vacuum rotational transform, electron density and temperature. [Preview Abstract] |
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UP8.00047: Enhancements, Parallelization and Future Directions of the V3FIT 3-D Equilibrium Reconstruction Code M.R. Cianciosa, J.D. Hanson, D.A. Maurer, G.J. Hartwell, M.C. ArchMiller, X. Ma, J. Herfindal Three-dimensional equilibrium reconstruction is spreading beyond its original application to stellarators. Three-dimensional effects in nominally axisymmetric systems, including quasi-helical states in reversed field pinches and error fields in tokamaks, are becoming increasingly important. V3FIT is a fully three dimensional equilibrium reconstruction code in widespread use throughout the fusion community. The code has recently undergone extensive revision to prepare for the next generation of equilibrium reconstruction problems. The most notable changes are the abstraction of the equilibrium model, the propagation of experimental errors to the reconstructed results, support for multicolor soft x-ray emissivity cameras, and recent efforts to add parallelization for efficient computation on multi-processor system. Work presented will contain discussions on these new capabilities. We will compare probability distributions of reconstructed parameters with results from whole shot reconstructions. We will show benchmarking and profiling results of initial performance improvements through the addition of OpenMP and MPI support. We will discuss future directions of the V3FIT code including steps taken for support of the W-7X stellarator. [Preview Abstract] |
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UP8.00048: VMEC Initialized NIMROD Simulations of CTH N.A. Roberds, J.D. Hanson, M. Cianciosa, J. Hebert, S.E. Kruger, J.R. King Using an experimentally reconstructed equilibrium for initial conditions, a whole device fluid simulation can be used to gain insight into the dynamics of an experimental shot. A module has been developed to initialize the extended MHD code NIMROD [1] using the output from VMEC [2]. VMEC is a 3D inverse equilibrium code used in reconstructions of Compact Toroidal Hybrid (CTH) discharges. While this module is essential for simulations of CTH based on reconstructions, it could also be useful for simulating tokamaks and other devices where 3D shaping of the equilibrium fields is important. Results are presented for free boundary simulations of CTH in support of efforts to investigate disruptions. Additionally, a NIMROD simulation of the Biro-Wu MHD shocktube benchmark case is presented. \\[4pt] [1] C.R. Sovinec et al, J. Comput. Phys. 195, 355 (2004).\\[0pt] [2] S. P. Hirshman and J. C. Whitson, Phys. Fluids 26 3553 (1983). [Preview Abstract] |
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UP8.00049: Island Formation in the Current Rise Phase of CTH Discharges J.D. Hebert, J.D. Hanson \newcommand{\g}{\raisebox{-3pt}{$\mathchar'26\mkern-14mu$} $\iota$} The 3D extended MHD code NIMROD [1] has been modified to model the Compact Toroidal Hybrid (CTH), a five-field period torsatron/tokamak hybrid device located at Auburn University. In many shots with inductively driven current in CTH, hesitations in the current rise portion of the discharge are observed. V3FIT reconstructions of the current rise demonstrate that the edge rotational transform (\g$_{edge}$) is near a low order rational suggesting that island formation at or near the edge may be responsible for the current hesitations. The initial stages of the current drive were self-consistently modeled using NIMROD and experimentally relevant vacuum fields, loop voltages, initial temperatures and initial densities. Results show the formation of field-period-symmetry-preserving islands near the plasma edge as well as the coalescence of these islands into larger, symmetry-breaking island chains which modify the distribution of the current in the plasma, phenomenologically similar to what is expected during a current hesitation in the experiment. \\[4pt] [1] C.R. Sovinec et al Journal of Computational Physics, 195, 355 (2004). [Preview Abstract] |
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UP8.00050: Modeling of Divertor Plates in the Compact Toroidal Hybrid G.J. Hartwell, C.M. Small, D.A. Ennis, J.D. Hanson, S.F. Knowlton, D.A. Maurer \newcommand{\g}{\raisebox{-3pt}{$\mathchar'26\mkern-14mu$} $\iota$} In long pulse length stellarator experiments, edge island divertors can be used as a method of plasma particle and heat exhaust. Knowledge of the detailed power loading on these structures and its relationship to the long connection length scrape off layer physics is a new Compact Toroidal Hybrid research thrust. We report the results of connection length studies for divertor plates to be installed in the Compact Toroidal Hybrid (CTH), a five field period torsatron with $R_0=0.75$\,m, $a_p\sim 0.2$\,m, and B~$\leq 0.7\,$T. For these studies, CTH will be operated as a pure stellarator with no ohmically generated plasma current. The CTH edge rotational transform can be varied from \g$_{vac}$(a)=0.02--0.35 by adjusting the ratio of currents in the helical and toroidal field coils. A poloidal field coil is used to adjust the shear of the rotational transform profile, and hence the size of edge islands, while the phase of the island is rotated with a set of five error coils producing an n=1 perturbation. For the studies conducted, a magnetic configuration with a large n=1, m=3 magnetic island at the edge is generated. Results from multiple possible divertor plate locations relative to the island structure will be presented. [Preview Abstract] |
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UP8.00051: Overview of the Present HSX Program and Plans for HSX/U David Anderson Heat pulse propagation experiments yield electron thermal diffusivities comparable to those obtained from power balance, showing that HSX electron transport is not stiff. Nonlinear gyrokinetic calculations using GENE are used to calculate the saturated heat flux under experimental conditions. A new 80-coil internal magnetic diagnostic array is used for equilibrium reconstruction using the V3FIT code including the effect of eddy currents as modeled with the SPARK code. CXRS measurements of Pfirsh-Schl\"{u}ter ion flows give inferred radial electric fields larger than previous estimates, but still smaller than neoclassically predicted values. New MSE systems to directly measure and model the radial electric field are under implementation. Measurements of the edge properties and structure in HSX are compared to models from EMC3-EIRENE. A proposed major upgrade is under consideration for HSX to modify the vacuum vessel and to use neutral beam injection to increase the ion temperature. This would allow access to low ion collisionality and ion-root discharges. Higher density operation provides for increased divertor parameters, impurity transport studies, and operational flexibility. A particular emphasis of the upgrade would allow for flexible divertor configurations as part of an expanded domestic initiative to improve the stellarator concept for extrapolation to a reactor. [Preview Abstract] |
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UP8.00052: Targeted Physics Optimization in the HSX Stellarator Joseph Talmadge, Benjamin Faber To plan out future experiments in HSX, we have developed a code to vary the currents in the auxiliary coils and optimize for specific target physics functions. One such function is related to the bounce-averaged grad-B drift velocity of trapped particles such as alphas in a fusion reactor. In an HSX reactor, the alpha particle confinement is degraded because of the modular coil ripple. Increasing the number of coils improves the alpha confinement, but also leads to an increase in the effective ripple. Thus, minimizing effective ripple by itself is not a sufficient figure of merit for energetic particle confinement. Of particular interest for optimization is the exploration of configurations in HSX which can lower turbulent transport. Optimizing for ITG turbulence in HSX configuration can be achieved so that the calculated saturated turbulent heat flux is reduced by a factor of 2 from the standard QHS configuration. However, experimental data showed that the confinement was degraded in the new configuration; gyrokinetic calculations confirm that TEM and ETG are the dominant microinstabilities in HSX, not ITG. Present optimization studies are focused on plasma flows and TEM stabilization. [Preview Abstract] |
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UP8.00053: 3-D Plasma Equilibrium Reconstruction at the HSX Stellarator - Impact of Eddy Currents and Magnetic Islands E. Chlechowitz, A.W. Brooks, A. Zolfaghari, D.T. Anderson Rapid equilibrium reconstruction is critical for understanding the operation and control of fusion devices. A new array of 80 internal magnetic coils was installed at HSX and optimized to reconstruct, using the V3FIT code [1], specific parameters describing the plasma pressure and plasma current profile. The impact of eddy currents inside the vacuum vessel is shown to be responsible for a change in the obtained profiles when the equilibrium reconstruction is performed using a set of 96 external magnetic coils. The SPARK code [2] is used to calculate the eddy currents caused by changes in the plasma current and the main magnetic field. The magnetic field topology of HSX may be varied using auxiliary field coils, and magnetic islands have been generated within the LCFS to test the accuracy of ideal MHD equilibrium reconstructions. Additionally, a moveable limiter can be used to alter the currents inside the plasma edge and in the islands. \\[4pt] [1] J.D. Hanson et al, Nucl. Fusion 49 075031 (2009) \newline [2] D. W. Weissenburger, PPPL-2494 (1988) [Preview Abstract] |
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UP8.00054: Measurements of Edge Plasma Properties in the HSX Stellarator with Comparison to EMC3-EIRENE A.R. Akerson, A. Bader, O. Schmitz, F.S.B. Anderson, C.C. Hegna, D.T. Anderson 2D profiles of plasma edge temperature, density and flow have been obtained in the edge of the Helical Symmetric Experiment (HSX) using a multi-pin Langmuir probe. Comparison of these profiles with a 3D edge fluid and kinetic neutral transport model (EMC3-EIRENE) show significant deviations. In particular, measurements show peaked density profiles within the edge magnetic island and sonic flows near the island X-point. The origin of these discrepancies is under investigation and may be related to prominent potential structures observed within the island. These observations are important because the presence of potential structures and corresponding ExB flows are not included in the EMC3-EIRENE modeling, necessitating further investigation to understand the origin and impact that these structures have on edge plasma properties. [Preview Abstract] |
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UP8.00055: The design of a MSE polarimetry diagnostic for the measurement of radial electric fields on the HSX stellarator T. Dobbins, S.T.A. Kumar, D.T. Anderson, F.S.B. Anderson HSX is a quasi-symmetric stellarator that is designed to reduce neoclassical transport. Neoclassical codes estimate a large positive radial electric field (40-50 kV/m) near the core of the HSX plasma. Impurity ion flow measurements could not resolve this large electric field. A single channel, dual PEM (Photo Elastic Modulators) MSE polarimetry diagnostic has therefore been designed for the HSX stellarator to directly measure the radial electric field near the core of the plasma. The design has been optimized to get a maximum change in polarization angle from a radial electric field with a good spatial resolution. A change in radial electric field as small as 1.5 kV/m can be detected with a careful selection of the sightline. The diagnostic design and initial characterization are presented. [Preview Abstract] |
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UP8.00056: Spectral MSE study on HSX and Non-Statistical Beam Level Populations C. Ruiz, S.T.A. Kumar, O. Marchuck, F.S.B. Anderson, D.T. Anderson A spectral MSE diagnostic is investigated for measuring Er and B field in the plasma. This method relies on the spectral fitting of the Stark multiplet components and knowledge of the excited beam level populations. In some cases a statistical approach to the populations has been shown to deviate from experimental results. Here, we present a method for measuring Er and the B field components using two simultaneous views of the plasma without the knowledge of the beam level populations if the line emission from the Stark multiplet components is resolvable. However, this is not the case with a 30 keV diagnostic neutral beam and a 1 T magnetic field and knowledge of the beam level populations is required. In our experiment with line average densities ranging from [2-5] x 10$^{18}$ m$^3$ the atomic levels are expected to be non-statistically populated. A systematic study is then performed and data is compared to collisional-radiative models which calculate the level populations for a specific set of experimental parameters of density and magnetic field. Spectra from H-alpha and H-beta line emissions are simultaneously measured and their ratio is taken and compared to the statistical and non-statistical case. [Preview Abstract] |
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UP8.00057: Core Density Turbulence in the HSX Stellarator C.B. Deng, D.L. Brower, D.T. Anderson, F.S.B. Anderson, B. Faber, S.T.A. Kumar, K.M. Likin, J.N. Talmadge Density fluctuations are measured in the core of the HSX stellarator using a non-perturbing, multi-channel, interferometer system. Measurements show that broadband density turbulences with $k_{\perp} < 2$ cm$^{-1}$, f$=$ (20-200) kHz correlates with density gradient and plasma flow. The density fluctuation level is observed to decrease with increasing ECRH power as both the electron temperature, and its gradient, along with plasma flow increase. Electron temperature gradient is eliminated as drive for the observed turbulence. GENE simulations show that the density-gradient-driven TEM may be responsible for the observed density fluctuations. Low-frequency coherent modes are also observed in different magnetic configurations, mirror and QHS. The identifications of these coherent modes will be explored. [Preview Abstract] |
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UP8.00058: Neoclassical calculations of radial electric field and plasma flow in HSX beyond the monoenergetic assumption J. Smoniewski, J.N. Talmadge, S.T.A. Kumar, S. Satake, M. Landreman The radial electric field in the plasma core has been measured to be in the range of 2-5 kV/m during ECRH. The measured value is in good agreement with the ion root electric field calculated using the neoclassical code PENTA. However, PENTA also calculates that there should be a large electron root very close to the axis on the order of 30-50 kV/m. To date, no evidence of this electric field has been found. The PENTA code is a momentum conserving extension of the DKES code. The underlying DKES code makes a monoenergetic approximation which is known to break down when the electric field is near resonant values. We present electric field and plasma flow results from the SFINCS and FORTEC-3D codes, neither of which make the monoenergetic assumption, to benchmark the PENTA calculations. SFINCS is a drift-kinetic continuum code, and FORTEC-3D is a Monte Carlo code that also retains radial coupling. Initial results appear to show little difference between the three codes for HSX relevant parameters. In addition, we present recent results from bias probe experiments. [Preview Abstract] |
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UP8.00059: Measurement of Pfirsch-Schluter flows and radial electric field in the HSX Stellarator S.T.A. Kumar, F.S.B. Anderson, D.T. Anderson, J.N. Talmadge Inboard-outboard asymmetry in the toroidal C$+$6 ion flow has been measured using the Charge Exchange Recombination Spectroscopy in the HSX stellarator. Measurements indicate the presence of counter-streaming Pfirsch-Schluter (PS) ion flows. Experiments are done in 100 kW ECRH heated methane plasmas of line averaged density $\sim$ 4e18/m3 and central electron temperature $\sim$ 2 keV. Measurements are made for both the quasi-helically symmetric configuration and for the configuration where the symmetry is deliberately broken using auxiliary coils. It has been observed that the flows, both mean and the PS flows, are larger for the broken symmetry configuration compared to the helically symmetric configuration. The radial electric field, which is proportional to the magnitude of the PS flow, is larger than the previous measurements but still significantly less than the neoclassically calculated value. [Preview Abstract] |
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UP8.00060: Exploration of improved neutral fueling and exhaust by a pumped limiter at the edge magnetic island chain of the HSX Stellarator L. Stephey, A. Bader, S. Kumar, O. Schmitz, D.T. Anderson, J.N. Talmadge, F.S.B. Anderson, C. Hegna A carbon limiter was introduced into the natural 8/7 magnetic island flux tube in the edge of HSX. Global H-alpha measurements suggest that this limiter can concentrate the neutral recycling. This limiter setup is similar to the local island divertor at LHD and is an important step on the way to equipping HSX with a localized neutral particle exhaust capability. The aim is to reduce the currently dominant fueling from wall recycling. Molecular dissociation and charge exchange contribute to a high neutral density in the core of HSX. With the recycling source concentrated at the limiter and the exhaust directly removed, fueling from designated gas sources will be significantly enhanced over the contribution from wall recycling. A sophisticated setup of suited spectroscopic diagnostics will be implemented to study the neutral fueling processes and how they are impacted by the limiter. Results from these exploratory steps from the initial observations with a test limiter will be presented. The initial results will also be compared to EMC3-EIRENE modeling. *Supported by DOE grant DE-FG02-93ER54222 [Preview Abstract] |
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UP8.00061: Simulated Stellarator Edge Behavior with Modified HSX Coils A. Bader, L.A. Stephey, D.T. Anderson, Y. Feng, C.C. Hegna, O. Schmitz, J.N. Talmadge Predicting the edge behavior of a 3D device is a difficult but necessary requirement in the design of new fusion devices. In this poster we focus on prototypical stellarators generated through modifications to the HSX coils. We employ both helical coils to change the island size without altering the rotational transform, and divertor dipole coils to alter the internal structure of the islands. To determine the edge behavior of the designs we use simple metrics obtained through vacuum field-line following along with advanced simulation capabilities from the coupled codes EMC3-EIRENE. We show that strike point locations and concentrations can be altered with substantial changes to edge island sizes. Changes to the internal structure of the islands, producing alterations to flow structures and plasma density, but do not have a significant impact on strike point calculations or predicted heat flux. Results have implications on the role of islands in edges of stellarators and other 3D devices. [Preview Abstract] |
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UP8.00062: Overview of the HIT-SI3 experiment D.A. Sutherland, T.R. Jarboe, B.A. Nelson, B.S. Victor, A.C. Hossack, K.D. Morgan, G.J. Marklin, C.H. Hansen, T.K. Fryett Operations have begun on the upgraded steady-inductive helicity injected torus experiment (HIT-SI3) at the University of Washington. This experiment uses three coplanar inductive helicity injectors to form and sustain a spheromak equilibrium. Toroidal currents of 40 kA have been obtained in helium plasmas with 6 MW of injector power. We seek to further the understanding and development of imposed-dynamo current drive (IDCD) and demonstrate current profile control and externally driven plasma rotation on HIT-SI3. Validated and verified MHD codes (NIMROD and PSI-TET) are being developed using HIT-SI3 as a validation platform. Dynamic neutrals are being added to PSI-TET in an effort to encapsulate their likely important role in HIT-SI3 that is not captured by either code presently. A two-photon absorption laser induced fluorescence (TALIF) system is being implemented to provide spatial neutral profile information that will be compared with PSI-TET. The digital-feedback control system for HIT-SI3 has been upgraded to three integrated Blackfin micro-controller boards per injector. Two boards drive the flux and voltage tank circuits, presently in a pre-programmed manner. The third board monitors the injector current and informs the voltage and flux boards of the presence of plasma, allowing a change in pulse-width duty cycle for the plasma load. [Preview Abstract] |
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UP8.00063: Ion Dynamics in HIT-SI and HIT-SI3 with Comparisons to NIMROD and PSI-TET Simulations A.C. Hossack, R.N. Chandra, K.D. Morgan, C.J. Hansen, T.R. Jarboe, B.A. Nelson, C. Akcay, B.S. Victor, T. Hanao, M. Nagata The helicity injected torus with steady inductive current drive (HIT-SI) is a spheromak with 55 cm major radius and bow-tie cross section. Two inductive helicity injectors, on opposite sides of the confinement volume, form and sustain the spheromak plasma. A one meter focal length, ion Doppler spectrometer with a high speed video camera is used to simultaneously image light from chords across toroidal and poloidal sections of HIT-SI. C III emission data were collected at 145 kHz, ten times the helicity injector frequency, to resolve the dynamics of the injectors. Plasma motion and flows are shown to be predominately driven by the oscillating helicity injectors. Measurements are compared to synthetic diagnostics and velocity fields from 3D, extended-MHD NIMROD and PSI-TET simulations. Both codes evolve the Hall-MHD equations with dynamic pressure. Biorthogonal decomposition of measured and synthetic spectroscopy data is presented as a noise filtering and analysis technique. Additionally, initial results from HIT-SI3 are presented. Work supported by USDoE and ARRA. [Preview Abstract] |
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UP8.00064: Advances in NIMROD Modeling of the HIT-SI Experiment Kyle Morgan, T.R. Jarboe, C. Akcay Previous two-fluid simulations of the HIT-SI experiment using the NIMROD code at low injector frequencies have served as a launching point for modeling of both pressure effects related to Steady Inductive Helicity Injection (SIHI) and the new HIT-SI3 injector configuration. Results from the end of HIT-SI operation have encouraged the inclusion of pressure effects in NIMROD modeling. Previous calculations using NIMROD assumed uniform temperature and density profiles, producing good agreement with low injector frequency operations ($f_{inj}<\frac{v_{th}}{a}$) but poor agreement at high injector frequencies ($f_{inj}>\frac{v_{th}}{a}$). Experimental observations at these higher frequencies give evidence of pressure driven activity, as well as a higher volume averaged $\beta$. The full anisotropic Braginskii thermal conduction model has been applied in NIMROD calculations of HIT-SI and shows improvement in qualitative agreement at high injector frequencies, while maintaining results at low frequencies. In addition, modeling of the new 3-injector configuration of HIT-SI3 will serve as a source of validation of the model. [Preview Abstract] |
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UP8.00065: Sustained spheromaks with ideal n $=$ 1 kink stability and pressure confinement B.S. Victor, C. Akcay, C.J. Hansen, A.C. Hossack, T.R. Jarboe, K.D. Morgan, B.A. Nelson, D.A. Sutherland Increasing the injector frequency up to 68.5 kHz on the HIT-SI experiment produced, for the first time, sustained spheromaks with pressure confinement and current gains of nearly 4. During sustainment only imposed n $=$ 1 activity is observed indicating n~$=$~1 kink stability at injector frequencies of 14.5, 36.8, 53.5 and 68.5 kHz. The injectors drive the edge of the plasma to a high $\lambda $~($=$~$\mu_{o}$j/B) with a low $\lambda $ region forming in the center. Imposed fluctuations cause the current penetration that maintains the kink-stable profile. A Shafranov shift is consistently seen at frequencies of 53.5 and 68.5 kHz, which is above the estimated sound transit frequency, v$_{i}$/a, of HIT-SI. The PSI-TRI equilibrium solver is used to estimate the plasma pressure. In addition the magnetic profiles have improved toroidal symmetry at higher injector frequencies. Initial analysis of the density evolution and the internal magnetic fields of HIT-SI3 will also be presented. [Preview Abstract] |
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UP8.00066: An Imposed Dynamo Current Drive Experiment: Demonstration of Confinement Thomas Jarboe, Chris Hansen, Aaron Hossack, George Marklin, Kyle Morgan, Brian Nelson, Derek Sutherland, Brian Victor An experiment for studying and developing the efficient sustainment of a spheromak with sufficient confinement (current-drive power heats the plasma to its stability $\beta $-limit) and in the keV temperature range is discussed. A high-$\beta $ spheromak sustained by imposed dynamo current drive (IDCD) is justified because: previous transient experiments showed sufficient confinement in the keV range with no external toroidal field coil; recent results on HIT-SI show sustainment with sufficient confinement at low temperature; the potential of IDCD of solving other fusion issues; a very attractive reactor concept; and the general need for efficient current drive in magnetic fusion. The design of a 0.55 m minor radius machine with the required density control, wall loading, and neutral shielding for a 2 s pulse is presented. Peak temperatures of 1 keV and toroidal currents of 1.35~MA and 16{\%} wall-normalized plasma beta are envisioned. The experiment is large enough to address the key issues yet small enough for rapid modification and for extended MHD modeling of startup and code validation. [Preview Abstract] |
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UP8.00067: Plasma Control in Symmetric Mirror Machines W. Horton, W.L. Rowan, Igor Alvarado, X.R. Fu, A.D. Beklemishev Plasma confinement\footnote{Vortex Confinement, A.D. Beklemishev, et al. 2010.} in the symmetric rotating mirror plasma at the Budker Institute shows enhanced confinement with high electron temperatures with end plates biasing. Improved confinement is achieved by biasing end plate cells in the expansion tanks so as to achieve an inward pointing radial electric field. The negative potential well produces vortex plasma rotation similar to that in the negative potential well of Ohmic heated tokamaks. This plasma state has similarity with the lower turbulence level regimes documented in the Helimak\footnote{Helimak, Perez et al. PoP 2006.} where negative biasing of the end plates produces an inward radial electric field. To understand this vortex confinement we carry out 3D simulations with nonlinear partial differential equations for the electric potential and density in plasmas with an axially localized region of unfavorable and favorable magnetic curvature. The simulations show that the plasma density rapidly adjusts to be higher in the region of favorable curvature regions and remains relatively well confined while rapidly rotating. The results support the concept of using plasma-biasing electrodes in large expander tanks to achieve enhanced mirror plasma confinement. [Preview Abstract] |
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UP8.00068: Proto-CIRCUS tilted-coil tokamak-torsatron hybrid: design and construction M. Doumet, B.Y. Israeli, K.C. Hammond, R.M. Sweeney, F.A. Volpe, D.A. Spong, A.W. Clark, Y. Kornbluth An innovative magnetic confinement concept is based on a toroidal configuration in which the toroidal field coils are tilted and interlinked with each other. Field line tracing and equilibrium calculations suggest that this configuration can generate rotational transform with lower plasma current and exhibit less effective magnetic ripple than tokamaks of comparable size. These properties may have interesting implications for disruptions and steady-state operation. Proto-CIRCUS is a tabletop device recently constructed at Columbia University to test this concept. It features six interlocked coils with independently adjustable radial positions and tilt angles. Plasmas will have major and minor radii of approximately 16 cm and 5 cm, respectively. Start-up, heating and current drive will initially rely on 2.45 GHz electron cyclotron waves. Here we describe the design and construction of the device and present the results of numerical optimizations aimed at minimizing the required plasma current. Flux surface measurements will confirm whether this relatively simple concept can generate the expected rotational transform. [Preview Abstract] |
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UP8.00069: ABSTRACT WITHDRAWN |
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UP8.00070: Simulation of Neutral Beam current drive in C2 FRC Plasmas Sangeeta Gupta, Sean Dettrick, Dan Barnes, Toshiki Tajima, Erik Trask Recently, improved high confinement regime is observed in C2 FRC plasma due to better wall conditions and higher formation magnetic field. In this regime, measured excluded flux increases in time and then decreases as the neutral beam coupling with FRC decreases. These plasmas were simulated using Quasi-1D (Q1D) plasma transport code using reduced parallel and perpendicular transport coefficients. In the simulations a reduced poloidal flux decay rate is observed in the presence of neutral beams. Numerical results showing comparison with experimentally observed excluded flux radius, line integrated electron density, electron and ion temperature will be presented. [Preview Abstract] |
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UP8.00071: HEDP \& ICF: HYDRO, SIMULATIONS \& DIAGNOSTICS |
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UP8.00072: The corrugation instability of a piston-driven shock wave Jason Bates We investigate the dynamics of a shock wave that is driven into an inviscid fluid by the steady motion of a two-dimensional planar piston with small corrugations on its surface. This problem was first considered by Freeman [Proc. Royal Soc. A.~{\bf 228}, 341 (1955)], who showed that piston-driven shocks are unconditionally stable when the medium through which they propagate is an ideal gas. Here, we generalize his work to account for a fluid with an arbitrary equation of state. We find that shocks are stable when $-1 < h < h_c$ , where $h$ is the D'yakov parameter and $h_c$ is a critical value less than unity. For values of $h$ within this range, linear perturbations imparted to the front at time $t = 0$ attenuate asymptotically as $t^{-3/2}$ or $t^{-1/2}$. Outside of this range, they grow --- at first quadratically and later linearly --- with time. Such instabilities are associated with non-equilibrium fluid states and imply a non-unique solution to the hydrodynamic equations. These results may have important implications for driven shocks in laser-fusion and astrophysical environments. As a benchmark of this analysis, we compare our solution with one derived independently by Zaidel' [J.~Appl.~Math.~Mech.~{\bf 24}, 316 (1960)] for stable $h$-values and find excellent agreement. [Preview Abstract] |
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UP8.00073: Radiative shock experiments on LIL and Gekko Michel Koenig, Roman Yurchak, Claire Michaut, Patrice Barroso, Emeric Falize, Alexis Casner, Stephane Laffite, Serge Bouquet, Youichi Sakawa, Taichi Morita, Paul Drake, Alexander Pelka, S\'ebastien Lepape For more than a decade, we have currently performed laboratory experiments in connection with astrophysical phenomena in order to improve our understanding in the field of radiation hydrodynamics so to validate numerical schemes and assumptions in simulations. Here, recent experimental results on highly radiative shocks generated by high-power lasers such as Gekko (Japan) and LIL (laser integration line) are presented. Many visible diagnostics were implemented (interferometry, self-optical pyrometry, 2D snapshot imagers) providing measurements of the shock and precursor velocities, temperature, electronic density and 2D shock front shape. Results will be compared with 2D radiation hydrodynamic simulations [Preview Abstract] |
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UP8.00074: Science on NIF Eagle Nebula Jave Kane, David Martinez, Marc Pound, Robert Heeter, Alexis Casner, Bruno Villette, Roberto Mancini For over fifteen years astronomers at the University of Maryland and scientists at LLNL have investigated the origin and dynamics of the famous Pillars of the Eagle Nebula and similar parsec-scale structures at the boundaries of HII regions in molecular hydrogen clouds. Eagle Nebula is one of the National Ignition Facility (NIF) Science programs, and has been awarded two days of NIF shots to study the cometary model of pillar formation. The NIF shots will feature a new long-duration x-ray source prototyped at the Omega EP laser, in which multiple hohlraums mimicking a cluster of stars are driven with UV light in series for 10 ns each to create a 30 ns output x-ray pulse. The drive generates deeply nonlinear hydrodynamics in the Eagle science package, which consists of a dense layered plastic and foam core embedded in lower-density background foam. The scaled Omega EP shots validated the multi-hohlraum concept, showing that earlier time hohlraums do not degrade later time hohlraums by preheat or by ejecting ablated plumes that deflect the later beams. The Omega EP shots illuminated three 2.8 mm long by 1.4 mm diameter Cu hohlraums with 4.3 kJ per hohlraum. At NIF each hohlraum will be 4 mm long by 3 mm in diameter and will be driven with 80--100 kJ. [Preview Abstract] |
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UP8.00075: Additions and Improvements to the FLASH Code for Simulating High Energy Density Physics Experiments Donald Lamb, Christopher Daley, Anshu Dubey, Milad Fatenejad, Norbert Flocke, Carlo Graziani, Dongwook Lee, Petros Tzeferacos, Klaus Weide FLASH is an open source, finite-volume Eulerian, spatially adaptive, radiation hydrodynamics and magnetohydrodynamics code that incorporates capabilities for a broad range of physical processes, performs well on a wide range of computer architectures, and has a broad user base. Extensive capabilities have been added to FLASH to make it an open toolset for the academic high energy density physics community. We summarize these capabilities, with particular emphasis on recent additions and improvements, and present the results of several verification tests. We also describe several collaborations with the National Laboratories and the academic community in which FLASH has been used to simulate high energy density physics experiments. [Preview Abstract] |
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UP8.00076: New Features of Radiation-Hydrodynamics Code HELIOS Igor Golovkin, Joseph MacFarlane, Viktoriya Golovkina, Subodh Kulkarni HELIOS is a 1-D magneto-radiation-hydrodynamics code designed to study the hydrodynamic evolution of plasmas in planar, cylindrical, or spherical geometries. Applied energy sources include laser or particle beams, external radiation sources, or electrical currents (in cylindrical geometry). HELIOS-CR is an enhanced version of HELIOS which includes the option to simulate the dynamics of non-LTE plasmas using an inline collisional-radiative (C-R) model. Radiation transport models include flux-limited diffusion and multi-angle short characteristics method. We will discuss major features of HELIOS as well as recently developed angle-dependent radiation boundary conditions. Time-, angle-, and photon-energy-dependent radiation drive for this model can be computed with 3-D view factor code VISRAD. [Preview Abstract] |
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UP8.00077: VISRAD, 3-D Target Design and Radiation Simulation Code Viktoriya Golovkina, Joseph MacFarlane, Igor Golovkin, Subodh Kulkarni The 3-D view factor code VISRAD is widely used in designing HEDP experiments at major laser and pulsed-power facilities, including NIF, OMEGA, OMEGA-EP, ORION, LMJ, Z, and PLX. It simulates target designs by generating a 3-D grid of surface elements, utilizing a variety of 3-D primitives and surface removal algorithms, and can be used to compute the radiation flux throughout the surface element grid by computing element-to-element view factors and solving power balance equations. Target set-up and beam pointing are facilitated by allowing users to specify positions and angular orientations using a variety of coordinates systems (e.g., that of any laser beam, target component, or diagnostic port). Analytic modeling for laser beam spatial profiles for OMEGA DPPs and NIF CPPs is used to compute laser intensity profiles throughout the grid of surface elements. We will discuss recent improvements to the software package and plans for future developments. [Preview Abstract] |
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UP8.00078: Integrating 3D Printing into Target Fabrication at the University of Michigan Sallee Klein, Robb Gillespie, Michael Deininger, Carlos Di Stefano, Mario Manuel, Wesley Wan, Carolyn Kuranz, Paul Keiter, R. Paul Drake The integration of 3D printing into target fabrication in the past several years has been a challenge. As target designs for high-energy-density experiments have become more complex, utilizing 3D printing is the natural progression, opening up the possibilities of very sophisticated, repeatable, yet inexpensive targets that require far less lead time than traditional means. At the University of Michigan we utilize the technique of machined acrylic bodies and mating components, to minimize target-to-target variability and assemble more reproducible targets. By combining 3D printing with traditional machining, we are able to take advantage of the very best part of both aspects of manufacturing. We present several recent campaigns to showcase and introduce our techniques and our integration of 3D printing, which has maintained our success of complex target designs with simple and inexpensive construction. [Preview Abstract] |
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UP8.00079: A Non-Born-Oppenheimer Molecular Dynamics Method for Dense Plasmas David Michta, Liam Stanton, Mike Surh, Frank Graziani, Michael Murillo Warm Dense Matter, characterized by partially degenerate and moderately coupled electrons, is a regime realized in laser experiments, planetary interiors, and early stages of inertial confinement fusion. ``Ab initio'' molecular dynamics is an extremely accurate method built upon a Born-Oppenheimer (BO), plane-wave, pseudopotential electronic structure calculation. However, these assumptions are not appropriate for several important problems in dense plasmas. We desire an electron treatment that is both dynamical and quantum mechanical. Our approach combines ion MD with an electron fluid model based on orbital-free density functional theory (OF-DFT), which ensures high-quality equation of state. We discuss theoretical predictions of collective modes (electron plasma waves, ion-acoustic waves, etc.) and density fluctuations (dynamic structure factor, etc.). We have implemented fast, conservative numerical methods based on implicit time stepping and finite volume. We apply this to charged particle stopping, providing a stringent test of non-BO dynamics. We end with an outlook toward developments in numerical methods, improved OF-DFT models, and various applications. [Preview Abstract] |
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UP8.00080: Exploring the limits of the ``SNB'' multi-group diffusion nonlocal model Jonathan Brodrick, Christopher Ridgers, Robert Kingham A correct treatment of nonlocal transport in the presence of steep temperature gradients found in laser and inertial fusion plasmas has long been highly desirable over the use of an ad-hoc flux limiter. Therefore, an implementation of the ``SNB'' nonlocal model (G P Schurtz, P D Nicola\"i \& M Busquet Phys. Plas. 7 4238 (2000)) has been benchmarked against a fully-implicit kinetic code: IMPACT. A variety of scenarios, including relaxation of temperature sinusoids and Gaussians in addition to continuous laser heating have been investigated. Results highlight the effect of neglecting electron inertia $\left(\frac{\partial \mathbf{f_1}}{\partial t}\right)$ as well as question the feasibility of a nonlocal model that does not continuously track the evolution of the distribution function. Deviations from the Spitzer electric fields used in the model across steep gradients are also investigated. Regimes of validity for such a model are identified and discussed, and possible improvements to the model are suggested. [Preview Abstract] |
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UP8.00081: Discrete Diffusion Monte Carlo for Electron Thermal Transport Jeffrey Chenhall, Duc Cao, Ryan Wollaeger, Gregory Moses The iSNB (implicit Schurtz Nicolai Busquet\footnote{Schurtz et. al. Phys. Plasmas \textbf{7}, 4238 (2000)} electron thermal transport method of Cao et. al.\footnote{Cao et. al. J. Comput. Phys$.$ (Submitted 2014)} is adapted to a Discrete Diffusion Monte Carlo (DDMC) solution method for eventual inclusion in a hybrid IMC-DDMC (Implicit Monte Carlo) method. The hybrid method will combine the efficiency of a diffusion method in short mean free path regions with the accuracy of a transport method in long mean free path regions. The Monte Carlo nature of the approach allows the algorithm to be massively parallelized. Work to date on the iSNB-DDMC method will be presented. This work was supported by Sandia National Laboratory - Albuquerque. [Preview Abstract] |
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UP8.00082: iFP: an optimal, fully conservative, fully implicit, 1D-2V Vlasov-Fokker-Planck solver for ICF capsule simulation L. Chacon, W. Taitano, A.N. Simakov, D.A. Knoll ICF plasmas can become weakly collisional during the implosion process, with collisional mean-free-paths comparable to the system size. In this regime, kinetic phenomena become important, and a fully kinetic treatment is needed to assess their impact on compression and yield in ICF capsules. In this study, we present the first (to our knowledge) fully conservative (mass, momentum, and energy), fully nonlinearly implicit Vlasov-Rosenbluth-Fokker-Planck solver in 1D-2V. The approach achieves exact numerical conservation by nonlinearly enforcing the collision operator symmetries, and by enslaving numerical truncation errors.\footnote{W. Taitano et al, {\em J. Comput. Phys.}, submitted (2014)} The approach features an adaptive scheme in velocity space that optimally resolves the distribution function locally, thus substantially decreasing the velocity space resolution requirements regardless of temperature disparity and variations. Solver-wise, the code relies on demonstrated Jacobian-free Newton-Krylov strategies.\footnote{L. Chac\'on et al, {\em J. Comput. Phys.}, {\bf 157}, 654-682 (2000)} We will demonstrate the efficiency and accuracy properties of the scheme with several challenging 0D-2V and 1D-2V numerical examples. [Preview Abstract] |
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UP8.00083: Improved inline model for nonlocal electron transport in HYDRA M.M. Marinak, G.D. Kerbel, M.V. Patel, H. Robey, C.P. Ridgers, R.J. Kingham The nonlocal electron transport model in HYDRA has been improved in several respects. The original multigroup model has been extended to include the cascade in energy as particles slow down, yielding a more accurate range. The model was also extended to account for contributions to the energy loss rate due to bound electrons. These are among the important modifications that have enabled the package to simulate classes of suprathermal electrons. We show recent calculations using the model that suggest superthermal electrons could be having a significant effect on performance of cryogenic capsule implosions on the National Ignition Facility. We evaluate the nonlocal transport model's accuracy by comparison with an electron VFP code. Comparisons assess the accuracy of the calculated thermal transport for plasmas relevant to NIF experiments. [Preview Abstract] |
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UP8.00084: Design process for applying the nonlocal thermal transport iSNB model to a Polar-Drive ICF simulation Duc Cao, Gregory Moses, Jacques Delettrez, Timothy Collins A design process is presented for the nonlocal thermal transport iSNB (implicit Schurtz, Nicolai, and Busquet\footnote{Schurtz, Nicolai, and Busquet. Phys. Plasmas \textbf{7}, 4238 (2000)}) model to provide reliable nonlocal thermal transport in polar-drive ICF simulations. Results from the iSNB model are known to be sensitive to changes in the SNB ``mean free path'' formula, and the latter's original form required modification to obtain realistic preheat levels.\footnote{Cao, Moses, and Delettrez. al \textbf{J}. Comput. Phys. (Submitted 2014)} In the presented design process, SNB mean free paths are first modified until the model can match temperatures from Goncharov's thermal transport model in 1D temperature relaxation simulations. Afterwards the same mean free paths are tested in a 1D polar-drive surrogate simulation to match adiabats from Goncharov's model. After passing the two previous steps, the model can then be run in a full 2D polar-drive simulation. This research is supported by the University of Rochester Laboratory for Laser Energetics. [Preview Abstract] |
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UP8.00085: Towards a Full Braginskii Formulation in HYDRA Joseph Koning The magnetic field package in the ICF radiation transport simulation code HYDRA currently contains a resistive MHD solver and includes the dielectric pressure source term, anisotropic electron thermal conduction and magnetic field effects on alpha charged particle transport. This package has been improved with the addition of Nernst and Hall terms implemented using a discrete differential forms method. The Nernst magnetic term includes a limiting method for any large thermal or magnetic gradients. The Nernst thermal term results in a non-symmetric matrix solved using GMRES. The Hall term is discretized using methods based on constrained transport magnetic advection. All of the terms utilize discrete differential forms methods to maintain zero magnetic divergence exactly while properly treating the appropriate continuity of all vector field terms. [Preview Abstract] |
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UP8.00086: Radiation Hydrodynamic Parameter Study of Inertial Fusion Energy Reactor Chambers Ryan Sacks, Gregory Moses Inertial fusion energy reactors present great promise for the future as they are capable of providing baseline power with no carbon footprint.\footnote{J.F. LATKOWSKI \textit{et al., Fusion Sci. Tech.} \textbf{60}, 54 (2011)} Simulation work regarding the chamber response and first wall insult is performed with the 1-D radiation hydrodynamics code BUCKY.\footnote{R.R. PETERSON \textit{et al.,} \textit{Phys. Of Plasmas} \textbf{9}, 2287 (2002)} Simulation with differing chamber parameters are implemented to study the effect of gas fill, gas mixtures and chamber radii. Xenon and argon gases are of particular interest as shielding for the first wall due to their high opacity values and ready availability. Mixing of the two gases is an attempt to engineer a gas cocktail to provide the maximum amount of shielding with the least amount of cost. A parameter study of different chamber radii shows a consistent relationship with that of first wall temperature ($\sim$ 1/r$^{2}$) and overpressure ($\sim$ 1/r$^{3}$).\footnote{R. SACKS \textit{et al.}, \textit{Fusion Sci. Tech., publication pending}.} This work is performed under collaboration with Lawrence Livermore National Laboratory. [Preview Abstract] |
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UP8.00087: A Two-Dimensional Hydrocode to Study the Deceleration Phase and Hot-Spot Formation in Inertial Confinement Fusion Implosions K.M. Woo, A. Bose, R. Betti, J.A. Delettrez, K.S. Anderson, R. Epstein A hydrocode\footnote{K. Anderson, R. Betti, and T. A. Gardiner, Bull. Am. Phys. Soc. \textbf{46}, 280 (2001).} was developed to study the final stage of an implosion starting from the coasting phase, including hot-spot formation and thermonuclear burn. Recently, a flux-limited multigroup diffusion approximation model has been added to study the transport of radiation energy in the deceleration phase of a spherical inertial confinement fusion target. Numerical results from the multigroup model indicate a good agreement with \textit{LILAC} 1-D simulations. The code is used to study effects of radiation on the hotspot formation and distortion. Results from 2-D runs are presented and the effect of radiation transport on the deceleration-phase Rayleigh--Taylor instability is discussed. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944 and the Office of Fusion Energy Sciences Number DE-FG02-04ER54786. [Preview Abstract] |
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UP8.00088: Simulations of Xenon Activation in Indirect Drive Exploding Pushers on NIF Scott M. Sepke, Laura Berzak Hopkins, Charles Cerjan, Marty Marinak The indirect drive exploding pusher (IDEP) has proven to be a robust and well understood platform for experiments at the National Ignition Facility. We investigate the effect of adding xenon dopant in different concentrations to the DT gaseous fuel in IDEP capsules at various fill densities of experimental relevance --- 1.5--3 mg/cc --- through integrated capsule-hohlraum simulations using HYDRA. The primary metrics used to evaluate the performance are changes in neutron shock flash time and bang time, neutron yield, and the neutron time of flight temperature. In addition, the new post-processing code KUDU is used to explore the nuclear activation of the xenon dopant for natural xenon as well as pure Xe-124 and Xe-134 using the new post-processing code KUDU: a multiprocess (MPI), multithreaded (POSIX threads), and accelerator capable (CUDA and \mbox{OpenACC}) rate equation solver developed at Lawrence Livermore National Laboratory for radiochemistry modeling. [Preview Abstract] |
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UP8.00089: Multispecies plasma transport issues in ICF Erik Vold, Kim Molvig, Archis Joglekar, Mario Ortega In recent years there has been a renewed interest in plasma transport, both at the kinetic level and in multi-species fluid approximations, to better understand observed degradation in ICF performance. Analysis and numerical computations of multispecies fluid approximations examine the roles of plasma viscosity and species mass flux driven by gradients in composition, ion and electron pressure (barodiffusion) and temperature (Soret effect). The mix layer between plasma species and the pressure and temperature gradient coefficients are sensitive to the choice of composition as a molar or mass fraction, and implications are examined. A central focus here is to compare the coefficients of the gradient force terms determined from a rigorous kinetic derivation (Molvig, et.al., 2014) to other forms derived for the transport coefficients. The particle velocity dependence of the Coulomb collisions determines species friction drag and thus limits the species drift flux, leading to a dependence of the diffusion coefficient on the averaged particle mass through the mix layer profile, unlike that in molecular diffusion. This factor combined with the barodiffusion and kinetic coefficients determines a highly asymmetric mix layer profile shape between~low z and high z plasma components near total pressure and temperature equilibrium. The temperature gradient can act to inhibit or increase the species mass flux and examples relevant to ICF are given. Plasma viscosity in the momentum equation is shown to significantly modify a 1D ICF convergence trajectory and reduces maximum temperature, while accounting for viscous dissipation of the energy. [Preview Abstract] |
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UP8.00090: Kinetic Effects at Material Interfaces in ICF Implosions S.C. Wilks, W. Cabot, H. Whitley, J. Greenough, B.I. Cohen, J. Belof, G. Zimmerman, P.A. Amendt, S. LePape, L. Divol, A. Dimits, F. Graziani, K. Molvig, E. Dodd, C.K. Li, R. Petrasso, S. Laffite, O. Larroche, M. Casanova, L. Masse The mixing of materials at an interface during an ICF implosion, for example the DT- Carbon interface in an ICF capsule, is a complex process. In general, rad-hydro codes do an excellent job of modeling the important processes during an ICF implosion. However, there are certain times during the implosion when kinetic effects of the ions may play a role in how two materials mix across the interface between them, even in the absence of shocks moving through them. The Knudsen layer effect is one such example. We will describe results of multi-ion species hybrid LSP simulations where the ions are treated kinetically and the electrons are treated as a fluid. We observe that the DT and carbon ions diffuse across the interface in a self-similar manner, at a rate proportional to the square root of time, in agreement with diffusion theory. The resulting ion distributions for each species (on both sides of the interface) will be presented, and the result of this mixing on the yield will be discussed for ICF capsules. Preliminary results of a related mixing that occurs at the gas-hohlraum wall interface will also be presented. \\[4pt] [1] K. Molvig, et al., PRL, \textbf{109}, 095001 (2012)\\[0pt] [2] D. R. Welch, et al, Nucl. Instrum. Methods Phys. Res. A \textbf{464} 134-139 (2001). LLNL-ABS-653679 [Preview Abstract] |
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UP8.00091: Validation of a Laser-Ray Package in an Eulerian Code Paul Bradley, Mike Hall, Patrick McKenty, Tim Collins, David Keller A laser-ray absorption package was recently installed in the RAGE code by the Laboratory for Laser Energetics (LLE). In this presentation, we describe our use of this package to implode Omega 60 beam symmetric direct drive capsules. The capsules have outer diameters of about 860 microns, CH plastic shell thicknesses between 8 and 32 microns, DD or DT gas fills between 5 and 20 atmospheres, and a 1 ns square pulse of 23 to 27 kJ. These capsule implosions were previously modeled with a calibrated energy source in the outer layer of the capsule, where we matched bang time and burn ion temperature well, but the simulated yields were two to three times higher than the data. We will run simulations with laser ray energy deposition to the experiments and the results to the yield and spectroscopic data. Work performed by Los Alamos National Laboratory under contract DE-AC52-06NA25396 for the National Nuclear Security Administration of the U.S. Department of Energy.. [Preview Abstract] |
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UP8.00092: Computational Simulations of Radiation Driven Low -- Convergence NIF Capsules Robert Peterson, Richard Olson, John Kline, Stephan Maclaren, Jay Salmonson Experiments are planned on the NIF laser at Lawrence Livermore National Laboratory, in which capsules with thick CH ablators will be imploded with x-rays produced in vacuum or near vacuum hohlraums. These capsules are expected to implode to convergence ratios of 13 to 37 and will serve as a test of the ability of simulation codes to agree with experimental measurements in the regime. The convergence ratio will be adjustable by modifying the DT gas density. The CH ablators are going to be thick enough that we believe that the predominant instabilities on the ablator/gas surface will be Richtmyer-Meshkov. The Rayleigh-Taylor instabilities generated on the surface of the ablator should not penetrate the ablator. This presentation will show 2-D computer code simulations of these experiments and will show how the neutron yield varies with the asymmetry of the radiation drive. The drive symmetry in the experiments will be controlled by the laser. The experimental neutron yields will be compared with the 2-D simulation values, once the experiments take place. [Preview Abstract] |
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UP8.00093: Analysis of results from high-foot NIF ignition capsules T.R. Dittrich, J.D. Salmonson, P.A. Amendt, L.F. Berzak Hopkins, D.A. Callahan, D.E. Hinkel, O.A. Hurricane, T. Ma, A.E. Pak, H.-S. Park, G.B. Zimmerman, G.A. Kyrala, M.J. Rosenberg, H.G. Rinderknecht Encouraging results have been obtained using a strong first shock during the implosion of carbon-based ablator ignition capsules. These ``high-foot'' implosion results show that capsule performance deviates from 1D expectations as laser power and energy are increased. Possible causes of this deviation include disruption of the hot spot by jets originating in the capsule fill tube and kinetic effects in the fuel. Results of simulations investigating these effects will be presented. [Preview Abstract] |
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UP8.00094: Investigation of Inter-Ion Species Diffusion in Inertial Confinement Fusion Implosions Hans W. Herrmann, Yongho Kim, Nelson M. Hoffman, Mark J. Schmitt, Grigory Kagan, Steven H. Batha, Warren J. Garbett, Colin J. Horsfield, Michael S. Rubery, Steven Gales Anomalous fusion yield degradation has been observed for gas fill mixtures in inertial confinement fusion (ICF) implosions. These mixtures have included D/3He [Rygg, et al., Phys Plasmas, \textbf{13}, 052702 (2006)], D/T/3He [Herrmann, et al., Phys Plasmas, \textbf{16}, 056312 (2009)], D/Ar [Lindl, et al., Phys Plasmas, \textbf{11}, 339-491 (2004)] and even D/T [Casey, et al., PRL \textbf{108}, 075005 (2012)]. Fuel ion segregation has been suggested as a possible cause [Amendt, et al., PRL \textbf{18}, 056308 (2011); Kagan, et al., Phys Ltr A 10.1016 (2014)]. Segregation may be caused by inter-ion species diffusion driven by gradients in plasma pressure, temperature and electric field, either across a relatively narrow shock boundary or across the entire interior of the compressed capsule. It is expected that lower Z {\&}/or A ions will diffuse outward while higher Z {\&}/or A diffuse inward. In the case of D/T/3He, the 3He diffuses inward to the hotter core, reducing the DT reactivity. A D/T/H mixture should result in H diffusing outward, leaving the hotter core D {\&} T rich and hence enhance reactivity over the simulated expectation. Past results will be reviewed and plans for a hydro-equivalent comparison D/T/$^{\mathrm{3}}$He and D/T/H will be presented. [Preview Abstract] |
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UP8.00095: Calculations for Indirectly Driven Be capsule Implosion Experiments at Omega George Kyrala, John Kline, Elizabeth Merritt Beryllium (Be) ablators offer an attractive path to ignition on the National Ignition Facility (NIF). They offer better ablation rate, higher efficiency, and higher ablation velocity than the currently used CH or Diamond capsules. We have designed a capsule of Be for implosions at Omega to test our understanding of Be implosions in the foot of the anticipated NIF pulse, $\sim$ 100-110 eV for a period of 1 -2 ns drive. We calculated the emission profile, diameter, and implosion time. We will present a comparison to the completed experiments using either Be or CH ablator. We also will provide calculations of the effect of adding different amounts of an Argon dopant on the expected x-ray yield and emission shapes. [Preview Abstract] |
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UP8.00096: Transport implications of hydrodynamic mix on hot-spot performance in inertial confinement fusion Bhuvana Srinivasan, Xianzhu Tang In an inertial confinement fusion target, energy loss due to thermal conduction from the hot-spot will inevitably ablate fuel ice into the hot-spot, resulting in a more massive but cooler hot-spot, which negatively impacts fusion yield. Hydrodynamic mix due to the Rayleigh-Taylor instability at the gas-ice interface can aggravate the problem via an increased gas-ice interfacial area across which energy transfer from the hot-spot and ice can be enhanced. We quantify this mix-enhanced transport effect on hot-spot fusion-performance degradation using contrasting 1-D and 2-D hydrodynamic simulations, and identify its dependence on effective acceleration, Atwood number, and ablation speed. In the presence of magnetic fields, the thermal conduction is reduced which reduces the effect of ablative stabilization on mix mitigation while also reducing the amount of cold fuel being ablated into the hot-spot. A characterization of the transport enhanced mix characteristics with and without magnetic fields is performed to identify a regime where fusion-performance degradation is reduced by mix mitigation, through which the amount of cold fuel being ablated into the hot-spot is minimized. [Preview Abstract] |
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UP8.00097: Perturbation theory and numerical modelling of weakly and moderately nonlinear incompressible Richtmyer-Meshkov instability M. Herrmann, A.L. Velikovich, S.I. Abarzhi A study of incompressible two-dimensional Richtmyer--Meshkov instability by means of high-order Eulerian perturbation theory and numerical simulations is reported. Nonlinear corrections to Richtmyer's impulsive formula for the bubble and spike growth rates have been calculated analytically for arbitrary Atwood number and an explicit formula has been obtained for it in the Boussinesq limit. Conditions for early-time acceleration and deceleration of the bubble and the spike have been derived. In our simulations we have solved 2D unsteady Navier--Stokes equations for immiscible incompressible fluids using the finite volume fractional step flow solver NGA developed by Desjardins et al., J. Comput. Phys. \textbf{227}, 7125 (2008), coupled to the level set based interface solver LIT, Herrmann, J. Comput. Phys. \textbf{227}, 2674 (2008). The impact of small amounts of viscosity and surface tension on the RMI flow dynamics is studied numerically. Simulation results are compared to the theory to demonstrate successful code verification and highlight the influence of the theory's ideal inviscid flow assumption. Theoretical time histories of the interface curvature at the bubble and spike tip and the profiles of vertical and horizontal velocities have been favorably compared to simulation results, which converge to the theoretical predictions as the Reynolds and Weber numbers are increased. [Preview Abstract] |
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UP8.00098: Mitigation of initial imprinting with diamond ablator Hiroki Kato, Keisuke Shigemori, Youichirou Hironaka, Hidenori Terasaki, Tatsuhiro Sakaiya, Ryouta Hosogi, Mitsuo Nakai, Hiroshi Azechi In direct drive inertial confinement fusion, where laser light directly irradiates the target, surface perturbations on the target are seeded by initial imprint due to laser irradiation nonuniformity. It is the initial imprint that become the seed of the hydrodynamic instability, and decisive solutions for the mitigation of initial imprinting is required. We focused on material stiffness of ablator as an idea that was effective for mitigation of imprinting and adopted the diamond with low compressibility as an ablator material. In the imprint experiments, the diamond foils were irradiated with a foot pulse at an intensity of $\sim$ 4.0 $\times$ 10$^{12}$W/cm$^{2}$ with 1.3 ns width, on which a stationary spatial nonuniformity with sinusoidal shape of 100$\mu$m wavelength was imposed by implementing a grid mask. The foils were subsequently accelerated by a uniform main laser pulse of $\sim$ 1.0 $\times$ 10$^{14}$ W/cm$^{2}$ and imprinted perturbation were observed to be amplified by Rayleigh-Taylor instability through face-on x-ray backlight measurements. We deduced the equivalent initial surface roughness for the imprinted foil. We verified the mitigation of initial imprinting with diamond from the quantitative evaluation. [Preview Abstract] |
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UP8.00099: A New Theory of Mix in Omega Capsule Implosions Dana Knoll, Luis Chacon, Rick Rauenzahn, Andrei Simakov, William Taitano, Leslie Welser-Sherrill We put forth a new mix model that relies on the development of a charge-separation electrostatic double-layer at the fuel-pusher interface early in the implosion of an Omega plastic ablator capsule. The model predicts a sizable pusher mix (several atom \%) into the fuel. The expected magnitude of the double-layer field is consistent with recent radial electric field measurements in Omega plastic ablator implosions. Our theory relies on two distinct physics mechanisms. First, and prior to shock breakout, the formation of a double layer at the fuel-pusher interface due to fast preheat-driven ionization. The double-layer electric field structure accelerates pusher ions fairly deep into the fuel. Second, after the double-layer mix has occurred, the inward-directed fuel velocity and temperature gradients behind the converging shock transports these pusher ions inward. We first discuss the foundations of this new mix theory. Next, we discuss our interpretation of the radial electric field measurements on Omega implosions. Then we discuss the second mechanism that is responsible for transporting the pusher material, already mixed via the double-layer deep into the fuel, on the shock convergence time scale. Finally we make a connection to recent mix motivated experimental data on [Preview Abstract] |
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UP8.00100: Numerical Investigation of a New Electrostatic Double-Layer Driven Kinetic Mix Mechanism for an Omega Plastic Ablator Capsule William Taitano, Dana Knoll, Luis Chacon, Andrei Simakov The primary mix mechanisms considered so far by the ICF community are hydrodynamic processes such as Rayleigh-Taylor and Richtmeyer-Meshkov instabilities. However, recent experiments on the Omega facility indicate that mix is happening both deeper and earlier than what the hydrodynamic models predict [1]. Additionally, there have been observations of a strong electric field within the ICF capsule on the Omega facility that cannot be explained by quasi-neutral fluid theory alone. A recent theoretical study of a new kinetic mix mechanism for an Omega plastic ablator capsule, based on an electrostatic double-layer field at the fuel-pusher interface has predicted a mix amount and electric field strength that are consistent with some experiments [2]. We have pursued a careful computational study to further refine and expand these theoretical results. We seek to obtain better estimates of the strength of the double-layer electric field and its effect on mix in an Omega plastic ablator capsule. We show numerically the existence of the postulated double-layer electric field, and quantify its impact on mix. We also show preliminary result of mix on an Omega plastic ablator capsule with titanium tracer.\\[4pt] [1] J.A.Baumgaertel et al., PoP,21, 052706, 2014\\[0pt] [2] D.A.Knoll et al., PRL,2014, under review [Preview Abstract] |
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UP8.00101: Implosion spectroscopy in Rugby hohlraums on OMEGA Franck Philippe, Veronique Tassin, Laurent Bitaud, Patricia Seytor, Charles Reverdin The rugby hohlraum concept has been validated in previous experiments on the OMEGA laser facility. This new hohlraum type can now be used as a well-characterized experimental platform to study indirect drive implosion, at higher radiation temperatures than would be feasible at this scale with classical cylindrical hohlraums. Recent experiments have focused on the late stages of implosion and hotspot behavior. The capsules included both a thin buried Titanium tracer layer, 0-3 microns from the inner surface, Argon dopant in the deuterium gas fuel and Germanium doped CH shells, providing a variety of spectral signatures of the plasma conditions in different parts of the target. X-ray spectroscopy and imaging were used to study compression, Rayleigh-Taylor instabilities growth at the inner surface and mix between the shell and gas. [Preview Abstract] |
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UP8.00102: Proving diamonds under ultra-high pressure with sound velocity measurements Keisuke Shigemori, Katsuya Shimizu, Yasuhiro Asakura, Tatsuhiro Sakaiya, Tadashi Kondo, Yoichiro Hironaka, Tetsuo Irifune, Hitoshi Sumiya, Toshihiko Kadono, Hiroshi Azechi Diamond under terapascal (TPa) regime is of great interest on its phase transition to a post diamond phase. Many experimental works have been done on the diamond at the TPa regime by measuring the shock parameters (shock velocity, particle velocity). We measured sound velocities of shock-compressed diamond under several pressures by means of x-ray backlighting technique. Experiments were done on GEKKO-HIPER laser irradiation facility at Institute of Laser Engineering, Osaka University. We obtained sound velocities at a pressure of 0.4 - 2.0 TPa by changing the laser intensity. The experimental sound velocity suggests that a clear discontinuity at around 0.7 TPa where the melting of the diamond starts. The sound velocity drops then slightly increases with increasing pressure. The slope of the sound velocity over 1 TPa is lower than that under 0.7 TPa, indicating the melting of the diamond. [Preview Abstract] |
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UP8.00103: Surface current density distribution measurements of an electrically exploded foil via B-dot probe array data inversion E.L. Ruden, D.J. Amdahl, R.H. Cooksey, P.R. Robinson, F.T. Analla, D.J. Brown, M.R. Kostora, J.F. Camacho Measurements are presented of the current per unit length as a function of the transverse distance from the center of a water-tamped 80~$\mu $m Al foil that narrows to a central width of 15.2~cm as it explodes into warm dense matter by Ohmic heating. Current is delivered by the discharge of a 36~$\mu $F capacitor bank charged to 30~kV and discharged to a peak current of 342~kA in 2.0~$\mu $s. The distribution is calculated by the linear regularized inversion of signals from an array of B-dot probes distributed along the foil's central half-width. The probes are far enough away from the foil (1~cm) be noninvasive and mechanically undisturbed during the time of interest. These results are compared to 3-D MHD ALEGRA simulations of the geometry driven by an external coupled two-loop lumped circuit model which accurately represents the driver. The goal of the effort is to test, in conjunction with other diagnostics, ab initio models of the equation of state and electrical conductivity of matter under conditions encountered in single-shot pulsed power devices (1 - 10~eV and 0.1 - 1~$\times$ solid density). [Preview Abstract] |
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UP8.00104: Spectroscopic Analysis and Thomson Scattering Diagnostics of Wire Produced Plasma Christopher Plechaty, Vladimir Sotnikov, Daniel Main, James Caplinger, Austin Wallerstein, Tony Kim The Lower Hybrid Drift Instability (LHDI) in plasma is driven by the presence of inhomogeneities in density, temperature, or magnetic field (Krall 1971, Davidson 1977), and occurs in systems where the electrons are magnetized and the ions are effectively unmagnetized. The LHDI is thought to occur in magnetic reconnection (Huba 1977), and has also been investigated as a mitigation technique which can allow for communications to take place through the plasma formed around hypersonic aircraft (Sotnikov 2010). To further understand the phenomenology of the LHDI, we plan to carry out experiments at the Air Force Research Laboratory, in the newly formed Plasma Physics Sensors Laboratory. In experiment, a pulsed power generator is employed to produce plasma by passing current through single, or dual-wire configurations. To characterize the plasma, a Thomson scattering diagnostic is employed, along with a visible spectroscopy diagnostic. Huba, J. D., et al., grl, 4, 125-128 (1977). Davidson, R. C., et al., Phys. of Fluids 20, 301-310 (1977). Krall, N., Phys. Rev. A 4, 2094 (1971). Sotnikov, V. I., AGU Fall Meeting Abstracts. Vol. 1. 2010. [Preview Abstract] |
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UP8.00105: Characterization of Turbulent Non-Uniform Exploding Wire Plasma Using High Resolution Interferometry, Schlieren and Shadowography Imaging J. Caplinger, G. Sarkisov, A.J. Wallerstein, V. Sotnikov, J. Lundberg, Z. Reed High resolution interferogram, Schlieren, and shadowgraph imaging has been used to characterize an exploding wire plasma. Using an 80 kV high voltage pulse generator with a rise time of 5 ns, exploding wire plasmas are created in aluminum, gold, tin, stainless steel, platinum and silver wires. The plasma is probed over a period of 3-7 ns using a 532 nm frequency doubled Nd:YAG Q-switched laser. The resulting laser radiation is imaged as an interferogram using an air-wedge interferometer, a shadowgraph and as a Schlieren image using two CCDs. Calculations resulting from the interferograms reveal ionizations between 10-20{\%} for Aluminum wires at atmospheric pressure. This is confirmed by the Schlieren images as the refraction caused by neutrals is dominant. Single wire, two parallel wires, and other two wire configurations are investigated. Additionally, influence of chamber pressure on plasma uniformity, shock wave propagation velocity and instabilities is presented. [Preview Abstract] |
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UP8.00106: Electron density and effective atomic number (Z$_{\mathrm{eff}})$ determination through x-ray Moir\'{e} deflectometry Maria Pia Valdivia Leiva, Dan Stutman, Michael Finkenthal Talbot-Lau based Moir\'{e} deflectometry is a powerful density diagnostic capable of delivering refraction information and attenuation from a single image, through the accurate detection of X-ray phase-shift and intensity. The technique is able to accurately measure both the real part of the index of refraction $\delta $ (directly related to electron density) and the attenuation coefficient $\mu$ of an object placed in the x-ray beam. Since the atomic number Z (or Zeff for a composite sample) is proportional to these quantities, an elemental map of the effective atomic number can be obtained with the ratio of the phase and the absorption image. The determination of Zeff from refraction and attenuation measurements with Moir\'{e} deflectometry could be of high interest in various fields of HED research such as shocked materials and ICF experiments as Zeff is linked, by definition, to the x-ray absorption properties of a specific material. [Preview Abstract] |
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UP8.00107: Characterization of spatially resolved high resolution x-ray spectrometers for HEDP and light-source experiments K.W. Hill, M. Bitter, L. Delgado-Aparicio, P. Efthimion, N. Pablant, J. Lu, P. Beiersdorfer, H. Chen, E. Magee A high resolution 1D imaging x-ray spectrometer concept comprising a spherically bent crystal and a 2D pixelated detector is being optimized for diagnostics of small sources such as high energy density physics (HEDP) and synchrotron radiation or x-ray free electron laser experiments. This instrument is used on tokamak experiments for measurement of spatial profiles of Doppler ion temperature and plasma flow velocity, as well as electron temperature. Laboratory measurements demonstrate a resolving power, E/$\Delta $E of 10,000 and spatial resolution better than 10 $\mu$m. Good performance is obtained for Bragg angles ranging from 23 to 63 degrees. Initial tests of the instrument on HEDP plasmas are being performed with a goal of developing spatially resolved ion and electron temperature diagnostics. [Preview Abstract] |
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UP8.00108: Measurements of X-ray spectra from irradiated gold foils at the OMEGA Laser facility Joshua Davis, Paul Keiter, Paul Drake, Sallee Klein, Jeff Fein In many HED systems high intensity x-rays can be used to measure plasma properties such as density and temperature. At the OMEGA laser facility, these X-rays are produced by irradiating a metal foil with high-intensity lasers, which heats the foil and causes it to act as a quasi-continuum x-ray source for radiography or absorption spectroscopy. As this emission is quasi-continuous and the transmission of x-rays through a material varies with photon energy a well-characterized x-ray source is vital. Therefore, in order to optimize diagnostics reliant upon x-rays it is necessary to gain a better understanding of how the x-ray emission from these targets varies over time and varying beam energy. We will present experimental results studying the effect that beam energy and pulse length have on M-band and sub-keV x-ray emission generated from a 5$\mu$m thick gold disk using time-resolved spectroscopy and a Henway crystal spectrometer. This work is~funded by the U.S. Department of Energy, through the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, grant number~DE-NA0001840, and the National Laser User Facility Program, grant number~DE-NA0000850, and through the Laboratory for Laser Energetics, University of Rochester by the NNSA/OICF under Cooperative Agreement No. DE-FC52-08NA28302. [Preview Abstract] |
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UP8.00109: Calibration of the LLNL Imaging Proton Spectrometer A.M. Rasmus, M.J.-E. Manuel, C.C. Kuranz, S. Klein, P.X. Belancourt, J.R. Fein, M.J. MacDonald, R.P. Drake, A.U. Hazi, B.B. Pollock, J. Park, G.J. Williams, H. Chen Ultra intense short pulse lasers incident on solid targets (e.g. Au foil) produce well collimated, broadband proton beams. These proton beams can be used to characterize magnetic fields in high-energy-density systems. The Imaging Proton Spectrometer (IPS) was previously designed and built (H. Chen 2010, RSI) for use with such laser produced proton beams. The IPS has an energy range of 50keV-40MeV with a resolving power (E/dE) of about 250 at 0.5 MeV and 350 at 2 MeV, as well as a single spatial imaging direction. In order to better characterize the imaging capability of this diagnostic, a 3D FEA solver has been used to calculate the magnetic field of the IPS. Particle trajectories are then obtained via numerical integration to calibrate the imaging axis of the IPS. Experiments using alpha sources will be used to verify the calculated calibration. This work is funded by the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, grant number DE-NA0001840. Work by LLNL was performed under the auspices of U.S. DOE under contract DE-AC52-07NA27344. [Preview Abstract] |
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UP8.00110: Characterization of argon cluster targets in high-density, continuous gas jets Donggyu Jang, Yong Sing You, Yan Tay, Luke Hahn, Howard Milchberg, Hyyong Suk, Ki-Yong Kim We have developed a simple all-optical method for characterizing the average cluster size, number of clusters per unit volume (density), and mass fraction of clusters in gas jets. In this technique, we combine three optical diagnostics---forward/backward Mie scattering detection, 90 degree scattering imaging, and neutral gas interferometry. We also demonstrate its use in characterizing a continuous gas jet. In particular, we have investigated the spatial variation of cluster parameters for continuous cluster jets produced by cryogenic cooling. This technique, in principle, can serve as an in-situ diagnostic for characterizing cluster jets prior to injecting high-intensity laser pulses for driving intense laser-cluster interactions. In particular, our cryogenically-cooled, continuous cluster source can produce relatively large clusters ($\sim$ 70 nm), favorable in many laser-cluster experiments including plasma waveguide generation, with a moderate clustering ratio ($\sim$ 20{\%}). Such a cluster source can be used as a potential target for intense, high-repetition-rate (\textgreater kHz) laser pulses. [Preview Abstract] |
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UP8.00111: Preliminary results of equation of state measurements using imaging x-ray Thomson spectrometer Patrick Belancourt, Wolfgang Theobald, Paul Keiter, Timothy Collins, Mark Bonino, Pawel Kozlowski, Paul Drake Understanding the equation of state of materials under shocked conditions is important for laboratory astrophysics and high-energy-density physics experiments. The goal of the experiments discussed here is to create a platform for equation of state measurements in shocked foams on Omega EP. The target of interest for these experiments is shocked carbonized resorcinol formaldehyde foam with an initial density of 0.34 g/cc. Lasers irradiate an ablator, driving a shock into the foam. Plasma conditions ahead of the shock, at the shock and behind the shock are diagnosed using the imaging x-ray Thomson spectrometer (IXTS). The IXTS is capable of spectrally resolving the scattered x-ray beam while imaging in one spatial dimension. Preliminary results from these experiments will be shown. This work is funded by the U.S. Department of Energy, through the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, grant number DE-NA0001840, and the National Laser User Facility Program, grant number DE-NA0000850, and through the Laboratory for Laser Energetics, University of Rochester by the NNSA/OICF under Cooperative Agreement No. DE-FC52-08NA28302. [Preview Abstract] |
(Author Not Attending)
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UP8.00112: Level shifting in intense KrF laser-xenon cluster interactions Kenneth Whitney, Jack Davis, Tzvetelina Petrova A variety of experiments\footnote{Borisov A. B., et. al., J. Phys. B,\textbf{ 41, }105602 (2008).} were carried out in which gases composed of xenon clusters were irradiated with 230 fs pulses of 248 nm wavelength laser radiation at intensities, 10$^{19}$ W/cm$^{2}$. At these intensities, the laser pulses self-focused and amplified x-ray emissions occurred in the plasma channels that were formed. A significant feature of these emissions was the irreproducibility of their wavelengths, i.e., amplification was seen at wavelengths of 2.71, 2.804, 2.86, and 2.88 Angstroms. A theoretical model of a cluster's expansion and ionization dynamics was subsequently constructed that identified the atomic transition involved in this x-ray amplification, i.e., it was able to reproduce the observed gains. However, the ionization model did not attempt to calculate the observed line shifts. A laser intensity dependent level shift calculation will be described in this talk that, when added to the theoretical model, will allow a comparison to the experimental data to be made. [Preview Abstract] |
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UP8.00113: Bright X-ray Source Development at the National Ignition Facility M.J. May, K.B. Fournier, J.D. Colvin, M.A. Barrios, K. Widmann, H. Chen, M. Schneider, Y.P. Opachich, S.P. Regan High x-ray conversion efficiency (XRCE) K-shell and L-shell sources are being developed for High Energy Density (HED) experiments for use as backlighters and for the testing of materials exposed to high x-ray fluences. Sources with high XRCE in the Xe L-shell and Mo, Fe and Kr K-shell have been investigated at the National Ignition Facility. These targets were either 4.1 mm in diameter and 4 mm tall hollow tubes lined with $\sim$3 $\mu$m of metal or similarly sized gas pipes pressurized to 1 - 1.5 atm. The target walls were $\sim$50 $\mu$m thick. Either 160 or 192 beams of the NIF laser were used to deposit between 350 - 1330 kJ of 3$\omega$ light into the target in 3.3 to 14 ns pulses. The absolute x-ray emission of the source was measured by two calibrated Dantes, which are filtered x-ray spectrometers. Time resolved images filtered for the L- and K-shell were recorded to understand the heating of the target. Time resolved and time integrated high resolution (E/dE $\sim$100) spectra were recorded. Details of the experiment and XRCE's will be discussed. This work was done under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
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UP8.00114: Synthetic Spectra for Krypton Filled/Germanium Doped Pipes as a Laser Driven K-shell Source John Giuliani, Nicholas Ouart, Arati Dasgupta, Kevin Fournier, John Apruzese, Robert Clark Recent results from Kr filled pipes on the National Ignition Facility have demonstrated 1.6 kJ/sr of Kr K-shell, or 20 kJ into 4*pi [1]. The observed Kr He-alpha and Ly-alpha lines indicate a temperature of 6 - 8 keV, but the strong underlying continuum emission is characterized by a significantly lower temperature ($\sim$ 1keV). Using radiation-hydrodynamic modeling we consider a similar target but with a germanium dopant on the inside of the epoxy pipe. After partial absorption of the laser energy by the Kr fill, the remaining energy in the beam is deposited onto the inner pipe wall. The resultant inward ablation leads to a structured, multi-component plasma. Radially resolved spectra are calculated for various density and temperature profiles of the Ge/Kr mix within the target. The Ge K-shell line emission is between 10 keV and its cold K-edge absorption at 11.1 keV. The He-alpha line of Kr is at 13.1 keV. The objective is to develop a diagnostic for the strong continuum observed in [1]. If this feature arises from a cold envelope surrounding the Kr hot spot, then the Ge K-shell lines may enable measurement of its radial extent and temperature. \\[4pt] [1] K.B. Fournier, M. J. May, J.D. Colvin, et al., Phys. Rev. E, 88, 033104, 2013. [Preview Abstract] |
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UP8.00115: Characterization of ultrashort pulse laser-produced miniature hohlraum XUV sources Andrew McKelvey, Anthony Raymond, Calvin Zulick, Anatoly Maksimchuk, John Nees, Victor Yanovsky, Vladimir Chvykov, Alexander Thomas, Karl Krushelnick Experiments at the National Ignition Facility (NIF) allow the radiative~properties of dense, high-temperature matter to be studied at previously~unreachable regimes, but are limited by cost and system availability. A~scaled down system using ultra-short laser pulses and delivering energy to a~much smaller hohlraum could be capable of reaching comparable energy~densities by depositing the energy in a significantly smaller volume before~ablation of the wall material closes the cavity. The laser is tightly~focused through the cavity and then expands to illuminate the wall with an~intensity closer to that of a long pulse laser. Experiments were performed~on a number of short-pulse Ti:sapphire tabletop laser systems.~Targets include cavities machined in bulk material using low laser powers, and~then shot in situ with a single full power pulse as well as micron scale pre-fabricated~targets. Spectral characteristics were measured using a flat-field soft X-ray spectrometer and a seven channel filtered photo cathode array.~These broadband EUV sources may allow opacity and atomic physics measurements with plasma and~radiation temperatures comparable to NIF type hohlraums, but with a~significantly higher repetition rate and in a university scale system. [Preview Abstract] |
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UP8.00116: Differential hard x-ray imaging of HED/ICF plasmas using Compton scattering Frederic Hartemann Tunable, narrow-bandwidth, picosecond x-ray pulses can be produced via Compton scattering. Such pulses can be used for high-contrast K-edge imaging of specific ions in a plasma. In addition, the K-edge shift due to ionization and screening could also be studied using such x-rays. Details of a Compton scattering x-ray source will be presented, along with methods for spectral resolution and imaging, and information retrieval of the ion states and plasma conditions. [Preview Abstract] |
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UP8.00117: The MIT Accelerator Laboratory for Diagnostic Development for OMEGA, Z and the NIF R. Petrasso, M. Gatu Johnson, E. Armstrong, D. Orozco, H.G. Rinderknecht, J. Rojas Herrera, M. Rosenberg, H. Sio, A. Zylstra, J. Frenje, C.K. Li, F.H. Seguin, K. Hahn, B. Jones, C.L. Ruiz, T.C. Sangster The MIT Linear Electrostatic Ion Accelerator\footnote{Sinenian \textit{et al.} RSI (2012)} generates D-D and D-3He fusion products, which are used for development of nuclear diagnostics for OMEGA, Z, and the NIF. Fusion reaction rates around 10$^{6}$ s$^{-1}$ are routinely achieved with this accelerator, and fluence and energy of the fusion products are accurately characterized. Diagnostics developed and calibrated at this facility include CR-39 based charged-particle spectrometers, neutron detectors, and the particle Time-Of-Flight (pTOF) CVD-diamond-based bang time detector. The accelerator is also a vital tool in the education of graduate and undergraduate students at MIT. This work was supported in part by SNL, DOE, LLE and LLNL. [Preview Abstract] |
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UP8.00118: Measuring radial profiles of nuclear burn in ICF implosions at OMEGA and the NIF using proton emission imaging F.H. Seguin, H.G. Rinderknecht, M. Rosenberg, A. Zylstra, J. Frenje, C.K. Li, R. Petrasso, F.J. Marshall, T.C. Sangster, N.M. Hoffman, P.A. Amendt, C. Bellei, S. Le Pape, S.C. Wilks Fusion reactions in ICF implosions of D$^{3}$He-filled capsules produce 14.7-MeV D$^{3}$He protons and 3-MeV DD protons. Measurements of the spatial distributions of the D$^{3}$He and DD reactions are studied with a penumbral imaging system\footnote{F. H. S\'{e}guin \textit{et al}., Rev. Sci. Instrum. \textbf{75}, 3520 (2004).}$^,$\footnote{F. H. S\'{e}guin \textit{et al}., Phys. Plasmas \textbf{13}, 082704 (2006).} that utilizes a CR-39-based imaging detector to simultaneously record separate penumbral images of the two types of protons. Measured burn profiles are useful for studying implosion physics and provide a critical test for benchmarking simulations. Recent implosions at OMEGA of CD capsules containing $^{3}$He gas fill\footnote{H. G. Rinderknecht \textit{et al}., Phys. Rev. Lett \textbf{ 112}, 135001 (2014).} and SiO$_{2}$ capsules containing low-pressure D$^{\mathrm{3}}$He gas\footnote{M. J. Rosenberg \textit{et al}., at this conference and Phys. Rev. Lett. \textbf{112}, 185001 (2014).} were expected to have hollow D$^{3}$He burn profiles (in the $^{3}$He-filled capsule, due to fuel-shell mix), but penumbral imaging showed that the reactions were centrally peaked due to enhanced ion diffusion. The imaging technique is to be implemented soon on the NIF. This work was supported in part by NLUF, DOE, and LLE. [Preview Abstract] |
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UP8.00119: Design of a compact, low-energy-charged-particle-spectrometer for stellar nucleosynthesis experiments at OMEGA and the NIF E. Armstrong, J. Frenje, M. Gatu Johnson, C.K. Li, H. Rinderknecht, M. Rosenberg, F.H. Seguin, H. Sio, A. Zylstra, R.D. Petrasso A compact ``Orange'' Spectrometer is being designed for measurements of alpha and proton spectra in the range of $\sim$ 1-5 MeV, produced in low-yield $^{3}$He$^{3}$He experiments at the OMEGA laser and at the National Ignition Facility (NIF). Particle ray-tracing through magnetic fields, modeled by COMSOL, were conducted with the code Python. The goal is to identify an optimal setup for a spectrometer to measure alpha particles at relatively low energies and at low yield. Ability to study the alpha particles in addition to the protons is essential for understanding the nuclear physics governing the final-state interactions between pairs of particles in the three-body final state. This work was supported in part by the U.S. DOE and NLUF. [Preview Abstract] |
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UP8.00120: Impact of x-ray dose on the CR-39 response to 1-9 MeV protons with application to proton spectroscopy at OMEGA and NIF J. Rojas-Herrera, H.G. Rinderknecht, M. Gatu Johnson, A. Zylstra, M. Rosenberg, H. Sio CR-39 is a clear plastic nuclear track detector utilized in many nuclear diagnostics fielded in large-scale inertial confinement fusion (ICF) facilities. Large x-ray fluences in ICF experiments may impact the CR-39 response to incident charged particles. A thick-target bremsstrahlung x-ray machine was used to expose CR-39 to various x-ray doses to determine their impact on the CR-39 response to protons. This x-ray machine emits Cu-$\alpha $ line-radiation at 8 keV and has been absolutely calibrated using radiochromic film. The CR-39 detectors were then exposed to D$^{3}$He-protons generated by the MIT Linear Electrostatic Ion Accelerator. The regions of the CR-39 exposed to x-rays showed a smaller track diameter than those not exposed to x-rays. For example, a dose of 60 $\pm$ 1.3 Gy results in a decrease of 53{\%} in the track diameter, while a dose of 5 $\pm$ 0.1 Gy causes a decrease of 7.5{\%} in the track diameter. Doses of approximately 5Gy are typical on CR-39 detectors used to diagnose ICF implosions at OMEGA and the NIF. The resulting data will be used to evaluate how x-ray doses received by CR-39 in OMEGA and NIF experiments affect the recorded data. This undergraduate research was supported in part by the U.S. DOE, NLUF, LLE, and LLNL. [Preview Abstract] |
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UP8.00121: Charged Particle Detection with CR-39 under High Yield Conditions in ICF Experiments D. Orozco, M. Rosenberg, M. Gatu Johnson, H. Sio, H.G. Rinderknecht, A. Zylstra, F.H. Seguin, R.D. Petrasso CR-39 is a solid-state nuclear track detector commonly used in Inertial Confinement Fusion (ICF) experiments for detecting individual charged particles. Under high yield conditions at OMEGA and NIF, detecting individual particle tracks becomes very difficult because of track overlap. The fluence on the CR-39 when this becomes a problem is approximately 10$^5$ tracks/cm$^2$. A scattering foil behind a pinhole aperture (``scattering pinhole'') can be added in front of the CR-39 in order to reduce the fluence on the CR-39 by a factor related to the pinhole size, scattering angle of the foil, distance from the implosion to the foil, and the distance from the foil to the CR-39. This has been. For example, 400 micron foil behind a 300 micron pinhole 9mm in front of a piece of CR-39 can reduce the fluence of 15MeV protons by a factor of $\sim$ 50. The scattering pinhole is also being used at OMEGA in order to detect alphas produced in D $+$ T and D $+$ 3He reactions. This work was supported in part by the U.S. DOE and NLUF. *Rosenberg \textit{et al. }RSI 85, 043302 [Preview Abstract] |
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UP8.00122: Studies of MCP Sensitivity to 250 eV to 25 keV x-rays: Comparisons of Monte Carlo Simulations and Experimental Results Ming Wu, Craig Kruschwitz, Ken Moy, Greg Rochau We present results of Monte Carlo simulations of microchannel plate (MCP) response to x-rays in the 250 eV to 25 keV energy range as a function of x-ray energy, impact angle, and x-ray flux. X-ray penetration through multiple MCP pore walls is increasingly important above 5 keV and the effect of this penetration on MCP performance is studied. In agreement with past measurements, it is found that the angular dependence of MCP sensitivity with angle changes from a cotangent dependence to angular independence as x-ray energy increases. It is also found that the MCP gain sensitivity with voltage decreases for higher x-ray energies. Finally, it is found that for x-rays incident at zero degrees relative to the MCP surface normal, spatial resolution shows little dependence on x-ray energy, but that spatial resolution degrades for higher x-ray energies as the angle of incidence relative to the surface normal increases. Dynamic range of MCP in this energy range is also examined. Simulation results are compared to recent experimental measurements for 6-25 keV x-rays. The experiments were performed on the X15 beamline at the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory. Agreement between simulations and experiments is generally very good. [Preview Abstract] |
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