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Diffusion of Zonal Variables Using Node-Centered Diffusion Solver

Description: Tom Kaiser [1] has done some preliminary work to use the node-centered diffusion solver (originally developed by T. Palmer [2]) in Kull for diffusion of zonal variables such as electron temperature. To avoid numerical diffusion, Tom used a scheme developed by Shestakov et al. [3] and found their scheme could, in the vicinity of steep gradients, decouple nearest-neighbor zonal sub-meshes leading to 'alternating-zone' (red-black mode) errors. Tom extended their scheme to couple the sub-meshes with appropriate chosen artificial diffusion and thereby solved the 'alternating-zone' problem. Because the choice of the artificial diffusion coefficient could be very delicate, it is desirable to use a scheme that does not require the artificial diffusion but still able to avoid both numerical diffusion and the 'alternating-zone' problem. In this document we present such a scheme.
Date: August 6, 2007
Creator: Yang, T B
Partner: UNT Libraries Government Documents Department

Green (2(omega)) Laser Beam propagation in high-temperature Hohlraum Plasmas

Description: We demonstrate propagation and small backscatter losses of a frequency-doubled (2{omega}) laser beam interacting with inertial confinement fusion hohlraum plasmas. The electron temperature of 3.3 keV, approximately a factor of two higher than achieved in previous experiments with open geometry targets, approaches plasma conditions of high-fusion yield hohlraums. In this new temperature regime, we measure 2{omega} laser beam transmission approaching 80% with simultaneous backscattering losses of less than 10%. These findings suggests that good laser coupling into fusion hohlraums using 2{omega} light is possible.
Date: October 26, 2007
Creator: Niemann, C; Berger, R; Divol, L; Froula, D H; Jones, O S; Kirkwood, R K et al.
Partner: UNT Libraries Government Documents Department

X-ray Spectral Measurements and Collisional Radiative Modeling of Hot, High-Z Plasmas at the Omega Laser

Description: M-Band and L-Band Gold spectra between 3 to 5 keV and 8 to 13 keV, respectively, have been recorded by a photometrically calibrated crystal spectrometer. The spectra were emitted from the plasma in the laser deposition region of a 'hot hohlraum'. This is a reduced-scale hohlraum heated with {approx} 9 kJ of 351 nm light in a 1 ns square pulse at the Omega laser. The space- and time-integrated spectra included L-Band line emission from Co-like to Ne-like gold. The three L-Band line features were identified to be the 3s {yields} 2p, 3d{sub 5/2} {yields} 2p{sub 3/2} and 3d{sub 3/2} {yields} 2p{sub 1/2} transitions at {approx}9 keV, {approx}10 keV and {approx}13 keV, respectively. M-Band 5f {yields} 3d, 4d {yields} 3p, and 4p {yields} 3s transition features from Fe-like to P-like gold were also recorded between 3 to 5 keV. Modeling from the radiation-hydrodynamics code LASNEX, the collisional-radiative codes FLYCHK and SCRAM, and the atomic structure code FAC were used to model the plasma and generate simulated spectra for comparison with the recorded spectra. Through these comparisons, we have determined the average electron temperature of the emitting plasma to be {approx} 6.5 keV. The electron temperatures predicted by LASNEX appear to be too large by a factor of about 1.5.
Date: February 20, 2008
Creator: May, M J; Schneider, M B; Hansen, S B; Chung, H; Hinkel, D E; Baldis, H A et al.
Partner: UNT Libraries Government Documents Department

Ultrasfast Dynamics in Dense Hydrogen Explored at Flash

Description: The short pulse duration and high intensity of the FLASH (Free-electron LASer in Hamburg) allows us to generate and probe homogeneous warm dense non-equilibrium hydrogen within a single extreme ultraviolet (EUV) light pulse. By analyzing the spectrum of the 13.5 nm Thomson scattered light we determine the plasma temperature and density. We find that classical models of this interaction are in good agreement with our dense plasma conditions. In a FEL-pump FEL-probe experiment droplets of liquid hydrogen and their scattering behavior for different pump-probe setups were observed under 20{sup o} and 90{sup o}. We find that the scattering behavior of the scattered intensity depends on the scattering angle.
Date: August 1, 2011
Creator: Hilbert, V; Zastrau, U; Neumayer, P; Hochhaus, D; Toleikis, S; Harmand, M et al.
Partner: UNT Libraries Government Documents Department

Time-resolved Temperature Measurements in SSPX

Description: We seek to measure time-resolved electron temperatures in the SSPX plasma using soft X-rays from free-free Bremsstrahlung radiation. To increase sensitivity to changes in temperature over the range 100-300 eV, we use two photodiode detectors sensitive to different soft X-ray energies. The detectors, one with a Zr/C coating and the other with a Ti/Pd coating, view the plasma along a common line of sight tangential to the magnetic axis of the spheromak, where the electron temperature is a maximum. The comparison of the signals, over a similar volume of plasma, should be a stronger function of temperature than a single detector in the range of Te< 300 eV. The success of using photodiodes to detect changing temperatures along a chord will make the case for designing an array of the detectors, which could provide a time changing temperature profile over a larger portion of the plasma.
Date: August 14, 2006
Creator: Ludington, A R; Hill, D N; McLean, H S; Moller, J & Wood, R D
Partner: UNT Libraries Government Documents Department

Laser-Plasma Interactions in High-Energy Density Plasmas

Description: Laser-plasma interactions (LPI) have been studied experimentally in high-temperature, high-energy density plasmas. The studies have been performed using the Omega laser at the Laboratory for Laser Energetics (LLE), Rochester, NY. Up to 10 TW of power was incident upon reduced-scale hohlraums, distributed in three laser beam cones. The hot hohlraums fill quickly with plasma. Late in the laser pulse, most of the laser energy is deposited at the laser entrance hole, where most of the LPI takes place. Due to the high electron temperature, the stimulated Raman scattering (SRS) spectrum extends well beyond {omega}{sub 0}/2, due to the Bohm-Gross shift. This high-temperature, high-energy density regime provides a unique opportunity to study LPI beyond inertial confinement fusion (ICF) conditions.
Date: August 24, 2005
Creator: Constantin, C G; Baldis, H A; Schneider, M B; Hinkel, D E; Langdon, A B; Seka, W et al.
Partner: UNT Libraries Government Documents Department

Discrete Particle Noise in Particle-in-Cell Simulations of Plasma Microturbulence

Description: Recent gyrokinetic simulations of electron temperature gradient (ETG) turbulence with flux-tube continuum codes vs. the global particle-in-cell (PIC) code GTC yielded different results despite similar plasma parameters. Differences between the simulations results were attributed to insufficient phase-space resolution and novel physics associated with toroidicity and/or global simulations. We have reproduced the results of the global PIC code using the flux-tube PIC code PG3EQ, thereby eliminating global effects as the cause of the discrepancy. We show that the late-time decay of ETG turbulence and the steady-state heat transport observed in these PIC simulations results from discrete particle noise. Discrete particle noise is a numerical artifact, so both these PG3EQ simulations and the previous GTC simulations have nothing to say about steady-state ETG turbulence and the associated anomalous heat transport. In the course of this work we develop three diagnostics which can help to determine if a particular PIC simulation has become dominated by discrete particle noise.
Date: May 24, 2005
Creator: Nevins, W M; Dimits, A & Hammett, G
Partner: UNT Libraries Government Documents Department

Stochastic Transport Modeling of Resonant Magnetic Perturbations in DIII-D

Description: Three-dimensional two-fluid simulations of heat transport due to resonant magnetic perturbations of tokamaks have been computed by coupling the TRIP3D field line tracing code to the E3D edge transport code. The predicted electron temperature contours follow the new separatrix represented by the perturbed invariant manifold structure of the X-point in qualitative agreement with X-point TV observations. However, preliminary modeling predicts that the resulting stochastic heat transport is greater than that measured in low-collisionality ELM suppression experiments in DIII-D H-mode plasmas. While improved determination of transport coefficients is definitely required, possible explanations include plasma screening of resonant perturbations, invalid treatment of the edge as a fluid, or insufficient understanding of stochastic heat transport.
Date: June 1, 2006
Creator: Joseph, I; Moyer, R A; Evans, T E; Schaffer, M J; Runov, A M; Schneider, R et al.
Partner: UNT Libraries Government Documents Department

Laser-plasma interaction in ignition relevant plasmas: benchmarking our 3D modelling capabilities versus recent experiments

Description: We have developed a new target platform to study Laser Plasma Interaction in ignition-relevant condition at the Omega laser facility (LLE/Rochester)[1]. By shooting an interaction beam along the axis of a gas-filled hohlraum heated by up to 17 kJ of heater beam energy, we were able to create a millimeter-scale underdense uniform plasma at electron temperatures above 3 keV. Extensive Thomson scattering measurements allowed us to benchmark our hydrodynamic simulations performed with HYDRA [1]. As a result of this effort, we can use with much confidence these simulations as input parameters for our LPI simulation code pF3d [2]. In this paper, we show that by using accurate hydrodynamic profiles and full three-dimensional simulations including a realistic modeling of the laser intensity pattern generated by various smoothing options, fluid LPI theory reproduces the SBS thresholds and absolute reflectivity values and the absence of measurable SRS. This good agreement was made possible by the recent increase in computing power routinely available for such simulations.
Date: September 27, 2007
Creator: Divol, L; Froula, D H; Meezan, N; Berger, R; London, R A; Michel, P et al.
Partner: UNT Libraries Government Documents Department

Ideal Laser Beam Propagation through high temperature ignition hohlraum plasmas

Description: We demonstrate that a blue (3{omega}, 351 nm) laser beam with an intensity of 2 x 10{sup 15} W-cm{sup -2} propagates within the original beam cone through a 2-mm long, T{sub e}=3.5 keV high density (n{sub e} = 5 x 10{sup 20} cm{sup -3}) plasma. The beam produced less than 1% total backscatter; the resulting transmission is greater than 90%. Scaling of the electron temperature in the plasma shows that the plasma becomes transparent for uniform electron temperatures above 3 keV. These results are consistent with linear theory thresholds for both filamentation and backscatter instabilities inferred from detailed hydrodynamic simulations. This provides a strong justification for current inertial confinement fusion designs to remain below these thresholds.
Date: September 20, 2006
Creator: Froula, D H; Divol, L; Meezan, N; Dixit, S; Moody, J D; Pollock, B B et al.
Partner: UNT Libraries Government Documents Department

A Collective Scattering System for Measuring Electron Gyroscale Fluctuations on the National Spherical Torus Experiment

Description: A collective scattering system has been installed on the National Spherical Torus Experiment (NSTX) to measure electron gyroscale fluctuations in NSTX plasmas. Up to five distinct wavenumbers are measured simultaneously, and the large toroidal curvature of NSTX plasmas provides enhanced spatial localization. Steerable optics can position the scattering volume throughout the plasma from the magnetic axis to the outboard edge. Initial measurements indicate rich turbulent dynamics on the electron gyroscale. The system will be a valuable tool for investigating the connection between electron temperature gradient turbulence and electron thermal transport in NSTX plasmas.
Date: February 13, 2009
Creator: D.R. Smith, E. Mazzucato, W. Lee, H.K. Park, C.W. Domier, and N.C. Luhmann, Jr.
Partner: UNT Libraries Government Documents Department

Verification of Gyrokinetic (delta)f Simulations of Electron Temperature Gradient Turbulence

Description: The GEM gyrokinetic {delta}f simulation code [Chen, 2003] [Chen, 2007] is shown to reproduce electron temperature gradient turbulence at the benchmark operating point established in previous work [Nevins, 2006]. The electron thermal transport is within 10% of the expected value, while the turbulent fluctuation spectrum is shown to have the expected intensity and two-point correlation function.
Date: May 7, 2007
Creator: Nevins, W M; Parker, S E; Chen, Y; Candy, J; Dimits, A; Dorland, W et al.
Partner: UNT Libraries Government Documents Department

Refractive and Relativistic Effects on ITER Low Field Side Reflectometer Design

Description: The ITER low field side reflectometer faces some unique design challenges, among which are included the effect of relativistic electron temperatures and refraction of probing waves. This paper utilizes GENRAY, a 3- D ray tracing code, to investigate these effects. Using a simulated ITER operating scenario, characteristics of the reflected RF waves returning to the launch plane are quantified as a function of a range of design parameters, including antenna height, antenna size, and antenna radial position. Results for edge/SOL measurement with both O- and X-modes using proposed antennas are reported.
Date: June 1, 2010
Creator: Wang, G.; Rhodes, T. L.; Peebles, W. A.; Harvey, R. W. & Budny, R. V.
Partner: UNT Libraries Government Documents Department

EFFECT OF PARTICLE SOURCES ON THE STRUCTURE OF THE H-MODE PEDESTAL

Description: Techniques of dimensional analysis have been applied to deuterium and hydrogen plasmas in DIII-D to test the postulate that the edge particle source plays a role in forming the edge H-mode density profile. These experiments show that the pedestal density scale length is typically a factor of two to three larger in hydrogen plasmas than in deuterium plasmas with dimensionally similar ion parameters. These results are in agreement with the postulate [1,2] that the density scale length is primarily determined by the local particle source, rather than by the shape of a hypothetical particle transport barrier. The electron temperature scale length displays a similar trend, albeit with a weaker density dependence. Thus the pedestal pressure gradient scale length is larger in hydrogen. It is also observed that the frequency of a coherent mode, localized within the pedestal, increases with the local density (i.e. inversely with the local density scale length) irrespective of the working gas species. This frequency is a factor of two lower in a hydrogen discharge than in a dimensionally similar deuterium plasma, a result which cannot be explained solely in terms of plasma physics variables.
Date: July 1, 2002
Creator: MAHDAVI, M.A.; R.J.GROEBNER; LEONARD, A.W.; LUCE, T.C.; McKEE, G.R.; MOYER, R.A. et al.
Partner: UNT Libraries Government Documents Department

Reciprocating and fixed probe measurements of n{sub e} and T{sub e} in the DIII-D divertor

Description: This paper describes divertor density and temperature measurements using both a new reciprocating Langmuir probe (XPT-RCP) which plunges vertically above the divertor floor up to the X-point height and swept, single, Langmuir probes fixed horizontally across the divertor floor. These types of measurements are important for testing models of the SOL and divertor which then are used to design plasma facing components in reactor size tokamaks. This paper presents an overview of the new divertor probe measurements and how they compare with the new divertor Thomson scattering system. The fast time response of the probe measurements allows detailed study of ELMs.
Date: November 1, 1996
Creator: Watkins, J.G.; Moyer, R.A.; Cuthbertson, J.W.; Buchenauer, D.A.; Carlstrom, T.N.; Hill, D.N. et al.
Partner: UNT Libraries Government Documents Department

The evidence for non-local transport in TEXT

Description: The electron temperature response of a tokamak to rapid edge cooling has characteristics difficult to reconcile with local transport analysis. The initial observations in TEXT have been extended to a wider range of plasma and perturbation parameters, including auxiliary heating, and the associated turbulence changes have been measured across the plasma radius. The fast edge temperature drops and core temperature increases are quantified by more extensive analysis. A perturbation complementary to edge cooling, edge heating by a fast current ramp, evokes a completely complementary plasma response.
Date: November 11, 1996
Creator: Gentle, K.W.; Bravenec, R.V. & Cima, G.
Partner: UNT Libraries Government Documents Department

A study of tearing modes via electron cyclotron emission from tokamak plasmas

Description: This thesis studies several tearing mode problems from both theoretical and experimental points of view. A major part of this thesis is to demonstrate that Electron Cyclotron Emission (ECE) is an excellent diagnostic for studying an MHD mode structure and its properties in a tokamak plasma. It is shown that an MHD mode can be detected from the electron temperature fluctuations measured by ECE. The amplitude and phase profiles of the fluctuations contain detailed information about the mode structure. The ECE fluctuation phase profile indicates the magnetic island deformation due to the combination of sheared flow and viscosity. A model is presented to relate qualitatively the observed phase gradient to the local magnetic field, flow velocity shear and viscosity in a 2D slab geometry, using an ideal Ohm`s law and the plasma momentum equation including flow and viscosity. Numerical solution of the resultant Grad-Shafranov-like equation describing the deformed island shows that the experimentally observed value of the phase gradient can be obtained under realistic parameters for the shear in the flow velocity and viscosity. A new approach to the tearing mode stability boundary and saturation level is also presented.
Date: July 1, 1998
Creator: Ren, C.
Partner: UNT Libraries Government Documents Department

Compact electron beam focusing column

Description: A novel design for an electron beam focusing column has been developed at LBNL. The design is based on a low-energy spread multicusp plasma source which is used as a cathode for electron beam production. The focusing column is 10 mm in length. The electron beam is focused by means of electrostatic fields. The column is designed for a maximum voltage of 50 kV. Simulations of the electron trajectories have been performed by using the 2-D simulation code IGUN and EGUN. The electron temperature has also been incorporated into the simulations. The electron beam simulations, column design and fabrication will be discussed in this presentation.
Date: July 13, 2001
Creator: Persaud, Arun; Leung, Ka-Ngo & Reijonen, Jani
Partner: UNT Libraries Government Documents Department

Thomson scattering from laser plasmas

Description: Thomson scattering has recently been introduced as a fundamental diagnostic of plasma conditions and basic physical processes in dense, inertial confinement fusion plasmas. Experiments at the Nova laser facility [E. M. Campbell et al., Laser Part. Beams 9, 209 (1991)] have demonstrated accurate temporally and spatially resolved characterization of densities, electron temperatures, and average ionization levels by simultaneously observing Thomson scattered light from ion acoustic and electron plasma (Langmuir) fluctuations. In addition, observations of fast and slow ion acous- tic waves in two-ion species plasmas have also allowed an independent measurement of the ion temperature. These results have motivated the application of Thomson scattering in closed-geometry inertial confinement fusion hohlraums to benchmark integrated radiation-hydrodynamic modeling of fusion plasmas. For this purpose a high energy 4{omega} probe laser was implemented recently allowing ultraviolet Thomson scattering at various locations in high-density gas-filled hohlraum plasmas. In partic- ular, the observation of steep electron temperature gradients indicates that electron thermal transport is inhibited in these gas-filled hohlraums. Hydrodynamic calcula- tions which include an exact treatment of large-scale magnetic fields are in agreement with these findings. Moreover, the Thomson scattering data clearly indicate axial stagnation in these hohlraums by showing a fast rise of the ion temperature. Its timing is in good agreement with calculations indicating that the stagnating plasma will not deteriorate the implosion of the fusion capsules in ignition experiments.
Date: January 12, 1999
Creator: Moody, J D; Alley, W E; De Groot, J S; Estabrook, K G; Glenzer, S H; Hammer, J H et al.
Partner: UNT Libraries Government Documents Department

Summary of the experimental session EC-10 workshop

Description: This review summarizes a subset of the EC-10 presentations which had been assigned by the organizing committee identification tags beginning with EX. There were fourteen presentations in this group, seven oral and seven posters. Included among the oral presentations were two invited talks. With the exception of the review of plans for electron cyclotron waves in ITER, there were all reports of physics experiments or operational experience as opposed to accounts of hardware development.
Date: June 1, 1997
Creator: Lohr, J.
Partner: UNT Libraries Government Documents Department

Confinement and the safety factor profile

Description: The conjecture that the safety factor profile, q(r), controls the improvement in tokamak plasmas from poor confinement in the Low (L-) mode regime to improved confinement in the supershot regime has been tested in two experiments on the Tokamak Fusion Test Reactor (TFTR). First, helium was puffed into the beam-heated phase of a supershot discharge which induced a degradation from supershot to L-mode confinement in about 100 msec, far less than the current relaxation time. The q and shear profiles measured by a motional Stark effect polarimeter showed little change during the confinement degradation. Second, rapid current ramps in supershot plasmas altered the q profile, but were observed not to change significantly the energy confinement. Thus, enhanced confinement in supershot plasmas is not due to a particular q profile which has enhanced stability or transport properties. The discharges making a continuous transition between supershot and L-mode confinement were also used to test the critical-electron-temperature-gradient transport model. It was found that this model could not reproduce the large changes in electron and ion temperature caused by the change in confinement.
Date: December 1, 1995
Creator: Batha, S.H.; Levinton, F.M. & Scott, S.D.
Partner: UNT Libraries Government Documents Department

Development of critical surface diagnostic based on the ion acoustic decay instability in laser produced high density plasma

Description: We have developed a large angle, UV collective Thomson scattering (CTS) diagnostic for high density, hot plasma relevant to laser fusion. The CTS measured the basic parameters of the plasma waves (frequency, wave number), or the spectral density function for selected wave vectors of plasma waves, which were excited by the IADI (ion acoustic parametric decay instability). It is a good diagnostic tool for a local electron temperature measurement. The electron temperature was estimated by measuring either ion acoustic wave or electron plasma wave in the laser intensity window of 1<I{sub L}/I{sub th}<8. The CTS diagnostic is also useful to study important physics of plasma waves in laser produced high density plasma.
Date: December 31, 1994
Creator: Mizuno, K.; DeGroot, J.S.; Drake, R.P.; Seka, W.; Craxton, R.S. & Estabrook, K.G.
Partner: UNT Libraries Government Documents Department

Thermal effects in intense laser-plasma interactions

Description: We present an overview of a new warm fluid model that incorporates leading-order kinetic corrections to the cold fluid model without making any near-equilibrium assumptions. In the quasi-static limit we obtain analytical expressions for the momentum spread and show excellent agreement with solutions of the full time-dependant equations. It is shown that over a large range of initial plasma temperatures, the fields are relatively insensitive to the pressure force. We discuss implications of this work for model validation.
Date: October 22, 2004
Creator: Shadwick, B.A.; Tarkenton, G.M. & Esarey, E.H.
Partner: UNT Libraries Government Documents Department