Showing papers by "Princeton Plasma Physics Laboratory published in 1993"
TL;DR: In this article, a status report on developments in the gyrofluid approach to simulating tokamak turbulence is given, with a detailed description of toroidal ITG-driven toroidal turbulence simulations.
Abstract: A status report is given on developments in the gyrofluid approach to simulating tokamak turbulence. 'Gyrofluid' (r 'gyro-Landau fluid') equations attempt to extend the range of validity of fluid equations to a more collisionless regime typical of tokamaks, by developing fluid models of important kinetic effects such as Landau-damping and gyro-orbit averaging. The fluid moments approach should converge if enough moments are kept, though this may require a large number of moments for some processes. Toroidal gyrofluid equations have been extended from 4 to 6 moments, and to include the mu Del B magnetic mirroring force. An efficient field-line coordinate system for toroidal turbulence simulations (useful for both particle and fluid simulations) is presented. Nonlinear 3-D simulations of toroidal ITG-driven turbulence indicate that turbulence-generated sheared flows play an important role in the development and saturation of the turbulence. There is a strong enhancement of the flows when the electrons are assumed adiabatic on each flux surface, which is partially offset by toroidal drift effects which reduce the flows.
289 citations
TL;DR: This work reports the first successful use of the weighted algorithms in particle codes for the nonlinear simulation of plasmas, and makes it possible to regulate the weights of the fast-moving particles and, in turn, to eliminate the associated high frequency oscillations.
157 citations
TL;DR: An anisotropic wave-number spectrum is observed, and estimates of the turbulence-driven transport are comparable to the anomalous transport observed in tokamaks.
Abstract: Long-wavelength (${\mathit{k}}_{\mathrm{\ensuremath{\perp}}}$${\mathrm{\ensuremath{\rho}}}_{\mathit{i}}$1) density turbulence has been measured with good spatial localization in the core region of a high temperature tokamak plasma with auxiliary heating. Density fluctuations of n\ifmmode \tilde{}\else \~{}\fi{}/ng0.5% exist for ${\mathit{k}}_{\mathrm{\ensuremath{\perp}}}$2 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ with radial and poloidal correlation lengths typically 1--2.5 cm in the confinement region, corresponding to ${\mathit{k}}_{\mathrm{\ensuremath{\perp}}}$${\mathrm{\ensuremath{\rho}}}_{\mathit{i}}$\ensuremath{\approxeq}0.1--0.3. An anisotropic wave-number spectrum is observed, and estimates of the turbulence-driven transport are comparable to the anomalous transport observed in tokamaks.
145 citations
TL;DR: In contrast to earlier expectations, it is estimated that generation of runaway electrons from close collisions of existing runaways with cold plasma electrons can be significant even for small electric fields, whenever runaways can gain energies of about 20 MeV or more as discussed by the authors.
115 citations
TL;DR: A localized transition zone is observed between turbulent, long-wavelength density fluctuations in the core and edge of beam-heated discharges in TFTR, suggesting that distinct modes are responsible for turbulence in the two regions and that only the core mode is directly related to global confinement.
Abstract: A localized transition zone is observed between turbulent, long-wavelength density fluctuations (${\mathit{k}}_{\mathrm{\ensuremath{\perp}}}$2 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$) in the core and edge of beam-heated discharges in TFTR. The core turbulence is unimodal while the edge has two counterpropagating modes, both of which are spectrally distinct from the core fluctuations. The fluctuation amplitude in the core scales with the global energy confinement time while in the edge it does not. These observations suggest that distinct modes are responsible for turbulence in the two regions and that only the core mode is directly related to global confinement.
42 citations
TL;DR: The report on the IAEA Technical Committee Meeting held at Montreal, Quebec, Canada, 15-17 June 1992 as mentioned in this paper, was the only paper that addressed the issue of nuclear power.
Abstract: Report on the IAEA Technical Committee Meeting held at Montreal, Quebec, Canada, 15-17 June 1992.
15 citations
TL;DR: The required pump-laser intensity is calculated and found to be attainable with current lasers, and the propagation of the pump through the ``gas'' of spheres is considered and the problems arising from pump scattering by the spheres are discussed.
Abstract: We describe a scheme for obtaining very short wavelengths (\ensuremath{\lambda}\ensuremath{\sim}10 \AA{}) in recombination lasers. The rapid cooling rates necessary to achieve population inversion during recombination are attained by adiabatic expansion of submicrometer spheres. The lasing region is made up of many such spheres. The spheres are heated impulsively by a powerful picosecond laser. First, they ionize, then as they expand, they cool and recombine. We have calculated the optimum sphere size and initial temperature for maximum gain in the n=3 to 2 transition of hydrogenlike ions of elements with atomic numbers, Z, between 10 and 30. Gain of about 250 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ is calculated in aluminum at 38.8 \AA{}. Gain rapidly decreases with Z so that gain in titanium at 13.6 \AA{} is about 10 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. We have calculated the required pump-laser intensity and found it to be attainable with current lasers. The propagation of the pump through the ``gas'' of spheres is considered and the problems arising from pump scattering by the spheres are discussed.
9 citations
TL;DR: In this article, a survey of six large fusion devices [ASDEX, DIII-D, the Joint European Torus (JET), JT-60, the Tokamak Fusion Test Reactor (TFTR), Tore Supra], information was collected on PFC materials, cleaning and conditioning techniques, device operating temperatures and vacuum pumping system characteristics and on the surface conditions and partial pressures necessary to achieve high-purity plasma discharges in each device.
9 citations
TL;DR: A new two-time-scale model of strong Langmuir turbulence has been constructed, using higher-moment fluid equations with dissipative closures designed to better simulate Vlasov theory predictions of linear wave properties, and to treat collisionless heating of particles by waves.
Abstract: A new two-time-scale model of strong Langmuir turbulence has been constructed, using higher-moment fluid equations with dissipative closures designed to better simulate Vlasov theory predictions of linear wave properties, and to treat collisionless heating of particles by waves. Numerical solutions are carried out in a study of electron heating associated with collapse and burnout of a large-amplitude initial Langmuir wave and in a study of radiation-driven Langmuir turbulence interacting with ion-acoustic quasimodes in plasmas with ${\mathit{T}}_{\mathit{e}}$\ensuremath{\approxeq}${\mathit{T}}_{\mathit{i}}$.
8 citations
TL;DR: In this article, a comparison of results from the PIES code, which determines the equilibrium properties of three-dimensional toroidal configurations by direct integration along the magnetic field lines, with those from the VMEC code which uses an energy minimization in a flux representation to determine the equilibrium configuration, for two devices: the ATF stellarator at Oak Ridge and the TJ-II heliac which is being built in Madrid.
7 citations
TL;DR: In this article, a new post-processor was developed for use with output from the PEST tokamak stability code to take better advantage of the physical picture of the plasma instability which they can provide.
01 Jan 1993
TL;DR: The Steady State Advanced Tokamak (SSAT) as discussed by the authors is designed to develop and demonstrate optimized steady state operating modes for high-aspectratio plasmas with high bootstrap current fraction.
Abstract: The Steady State Advanced Tokamak is designed to develop and demonstrate optimized steady state operating modes. It will explore improvements in energy confinement and beta limit scaling in high-aspectratio plasmas with a high bootstrap current fraction. It will demonstrate advanced divertor operation techniques for steady state energy and particle removal. Key physics features include a plasma with strong shaping, a doublenull poloidal divertor, fully non-inductive current drive, and current profile control capability. The plasma heating and current drive systems includes neutral beams, ICRF, and lower hybrid. The engineering design incorporates a superconducting magnet system, actively cooled divertor and first wall systems, and in-vessel remote maintenance.
01 Jan 1993
TL;DR: The SSAT-S as discussed by the authors is a superconducting steady-state advanced tokamak that uses an ICCS design for steady state and long-pulse operation.
Abstract: The superconducting steady-state advanced tokamak (SSAT-S) proposes to perform advanced tokamak physics experiments in steady-state and long-pulse operation provided by a superconducting magnet system. The superconducting magnets use an advanced internally-cooled cabled superconductor (ICCS) design, developed in support of the International Thermonuclear Experimental Reactor (ITER). The toroidal field magnets provide 3.35 T at 2.25 m with a stored energy of 720 MJ. The poloidal field magnets provide 18.2 V-s to ohmically start and control long burns of a 1.85 MA plasma.
01 Jan 1993
TL;DR: An extensive numerical simulation of the Ignitor-Ult plasma dynamics has been carried out using both the free boundary equilibrium code TEQ and the transport and MHD free boundary code TSC.
Abstract: An extensive numerical simulation of the Ignitor-Ult plasma dynamics has been carried out using both the free boundary equilibrium code TEQ and the transport and MHD free boundary code TSC The stability behavior of the plasma - vacuum vessel - poloidal field coils - passive plate system has been analyzed for different machine and plasma configurations The response of several feedback systems has been studied taking into account the real characteristics of the power supply The converter and its controller behavior has been extensively studied by means of the simulation program CSMP that uses a lumped parameter model of the system The results show a good stability behavior over a wide operating range