Showing papers by "Princeton Plasma Physics Laboratory published in 1995"
TL;DR: In this paper, a new tokamak confinement regime has been observed on the Tokamak Fusion Test Reactor (TFTR), where particle and ion thermal diffusivities drop precipitously by a factor of \ensuremath{\sim}40 to the neoclassical level for the particles and to much less than the NE value for the ions in the region with reversed shear.
Abstract: A new tokamak confinement regime has been observed on the Tokamak Fusion Test Reactor (TFTR) where particle and ion thermal diffusivities drop precipitously by a factor of \ensuremath{\sim}40 to the neoclassical level for the particles and to much less than the neoclassical value for the ions in the region with reversed shear. This enhanced reversed shear confinement mode allows the central electron density to rise from 0.45 \ifmmode\times\else\texttimes\fi{} ${10}^{20}$ ${\mathrm{m}}^{\ensuremath{-}3}$ to \ensuremath{\sim}1.2 \ifmmode\times\else\texttimes\fi{} ${10}^{20}$ ${\mathrm{m}}^{\ensuremath{-}3}$ with ${T}_{i}\ensuremath{\sim}24$ keV and ${T}_{e}\ensuremath{\sim}8$ keV. This regime holds promise for significantly improved tokamak performance.
594 citations
TL;DR: In this paper, a coordinate system for nonlinear fluid, gyrokinetic Vlasov, or particle simulations is presented that exploits the elongated nature of the turbulence by resolving the minimum necessary simulation volume: a long thin twisting flux tube.
Abstract: Turbulence in tokamaks is characterized by long parallel wavelengths and short perpendicular wavelengths. A coordinate system for nonlinear fluid, gyrokinetic ‘‘Vlasov,’’ or particle simulations is presented that exploits the elongated nature of the turbulence by resolving the minimum necessary simulation volume: a long thin twisting flux tube. It is very similar to the ballooning representation, although periodicity constraints can be incorporated in a manner that allows E×B nonlinearities to be evaluated efficiently with fast Fourier transforms (FFT’s). If the parallel correlation length is very long, however, enforcing periodicity can introduce artificial correlations, so periodicity should not necessarily be enforced in the poloidal angle at θ=±π. This method is applied to high resolution three‐dimensional simulations of toroidal ion temperature gradient (ITG) driven turbulence, which predict fluctuation spectra and ion heat transport similar to experimental measurements.
372 citations
TL;DR: In this paper, a first-principles model of anomalous thermal transport based on numerical simulations is presented, with stringent comparisons to experimental data from the Tokamak Fusion Test Reactor (TFTR).
Abstract: A first‐principles model of anomalous thermal transport based on numerical simulations is presented, with stringent comparisons to experimental data from the Tokamak Fusion Test Reactor (TFTR) [Fusion Technol. 21, 1324 (1992)]. This model is based on nonlinear gyrofluid simulations, which predict the fluctuation and thermal transport characteristics of toroidal ion‐temperature‐gradient‐driven (ITG) turbulence, and on comprehensive linear gyrokinetic ballooning calculations, which provide very accurate growth rates, critical temperature gradients, and a quasilinear estimate of χe/χi. The model is derived solely from the simulation results. More than 70 TFTR low confinement (L‐mode) discharges have been simulated with quantitative success. Typically, the ion and electron temperature profiles are predicted within the error bars, and the global energy confinement time within ±10%. The measured temperatures at r/a≂0.8 are used as a boundary condition to predict the temperature profiles in the main confinement ...
325 citations
92 citations
TL;DR: The first magnetic fusion experiments to study plasmas using nearly equal concentrations of deuterium and tritium have been carried out on the Tokamak Fusion Test Reactor (TFTR).
Abstract: After many years of fusion research, the conditions needed for a D–T fusion reactor have been approached on the Tokamak Fusion Test Reactor (TFTR) [Fusion Technol. 21, 1324 (1992)]. For the first time the unique phenomena present in a D–T plasma are now being studied in a laboratory plasma.The first magnetic fusion experiments to study plasmas using nearly equal concentrations of deuterium and tritium have been carried out on TFTR. At present the maximum fusion power of 10.7 MW, using 39.5 MW of neutral‐beam heating, in a supershot discharge and 6.7 MW in a high‐βp discharge following a current rampdown. The fusion power density in a core of the plasma is ≊2.8 MW m−3, exceeding that expected in the International Thermonuclear Experimental Reactor (ITER) [Plasma Physics and Controlled Nuclear Fusion Research (International Atomic Energy Agency, Vienna, 1991), Vol. 3, p. 239] at 1500 MW total fusion power. The energy confinement time, τE, is observed to increase in D–T, relative to D plasmas, by 20% and the ni(0) Ti(0) τE product by 55%. The improvement in thermal confinement is caused primarily by a decrease in ion heat conductivity in both supershot and limiter‐H‐mode discharges. Extensive lithium pellet injection increased the confinement time to 0.27 s and enabled higher current operation in both supershot and high‐βp discharges. Ion cyclotron range of frequencies (ICRF) heating of a D–T plasma, using the second harmonic of tritium, has been demonstrated. First measurements of the confined alpha particles have been performed and found to be in good agreement with TRANSP [Nucl. Fusion 34, 1247 (1994)] simulations. Initial measurements of the alpha ash profile have been compared with simulations using particle transport coefficients from He gas puffing experiments. The loss of alpha particles to a detector at the bottom of the vessel is well described by the first‐orbit loss mechanism. No loss due to alpha‐particle‐driven instabilities has yet been observed. D–T experiments on TFTR will continue to explore the assumptions of the ITER design and to examine some of the physics issues associated with an advanced tokamak reactor.
84 citations
TL;DR: Three dimensional MHD simulations of high-{beta} plasmas show that toroidally localized high-n ballooning modes can be driven unstable by the local pressure steepening which arises from the evolution of low-n modes.
Abstract: Three dimensional MHD simulations of high-{beta} plasmas show that toroidally localized high-n ballooning modes can be driven unstable by the local pressure steepening which arises from the evolution of low-n modes. Nonlinearly, the high-n mode becomes even more localized and produces a strong local pressure bulge which destroys the flux surfaces resulting in a thermal quench. The flux surfaces then recover temporarily but now contain large magnetic islands. This scenario is supported by experimental data.
78 citations
TL;DR: Gyrokinetic-magnetohydrodynamic hybrid simulations have been carried out to study the nonlinear saturation of the torodicity-induced Alfv\'en eigenmode driven by energetic particles in a tokamak plasma, and wave-particle trapping is shown to be excited by the energetic particles.
Abstract: Gyrokinetic-magnetohydrodynamic hybrid simulations have been carried out to study the nonlinear saturation of the torodicity-induced Alfv\'en eigenmode driven by energetic particles in a tokamak plasma It is shown that wave-particle trapping is the nonlinear saturation mechanism for the parameters considered The corresponding density profile flattening of the hot particles is observed The saturation amplitude is proportional to the square of the linear growth rate In addition, a new $n\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1,m\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0$ global Alfv\'en eigenmode is shown to be excited by the energetic particles
76 citations
TL;DR: A simple model for the nonlinear evolution of a short-pulse free-electron laser oscillator in the small gain regime is derived and the analytical and numerical results are compared with the experimental observations from the Free-Electron Laser for Infrared eXperiments experiment.
Abstract: A simple model for the nonlinear evolution of a short-pulse free-electron laser oscillator in the small gain regime is derived. An analysis of the linearized system allows the definition and calculation of the eigenmodes characterizing the small signal regime. An arbitrary solution of the nonlinear system can then be expanded in terms of these supermodes. In the single-supermode approximation, the system reduces to a Landau-Ginzburg equation, which allows the efficiency and saturated power to be obtained as functions of cavity detuning and cavity losses. In the limit of small cavity detuning, electrons emit superradiantly, with an efficiency inversely proportional to the number of radiation wavelengths within the optical pulse, and power proportional to the square of the bunch charge. In the multisupermode regime, limit cycles and period doubling behavior are observed and interpreted as a competition between supermodes. Finally, the analytical and numerical results are compared with the experimental observations from the Free-Electron Laser for Infrared eXperiments experiment.
70 citations
TL;DR: First measurements of the fast confined $\ensuremath{\alpha}$-particle energy distribution in a fusion plasma are reported, and stochastic ripple effects are responsible for steepening the energy distribution outside the plasma core.
Abstract: This Letter reports the first measurements of the fast confined $\ensuremath{\alpha}$-particle energy distribution in a fusion plasma. The pellet charge exchange technique shows the fusion generated $\ensuremath{\alpha}$'s in the core of the Tokamak Fusion Test Reactor plasma slow down classically, and appear to be well confined. Preliminary indications are that stochastic ripple effects are responsible for steepening the energy distribution outside the plasma core $(r/a\ensuremath{\gtrsim}0.35)$. Sawteeth mixing of fast $\ensuremath{\alpha}$'s is suggested in data during the post-beam-heating plasma decay.
60 citations
TL;DR: It is shown that nonlinear ponderomotive force produced by TAE's interaction drives sound-wave-like density fluctuation with low phase velocity which can resonantly interact with the bulk ion parallel motion.
Abstract: The nonlinear interactions of high mode number toroidal Alfven eigenmodes (TAE), mediated via Compton scattering off the bulk ions, are investigated. It is shown that nonlinear /I[ital J][sub [perpendicular]] [times]/I[ital B][sub [perpendicular]] ponderomotive force produced by TAE's interaction drives sound-wave-like density fluctuation with low phase velocity which can resonantly interact with the bulk ion parallel motion. Consequently, fluctuation energy of TAE's is transferred to lower frequency and eventually absorbed by linearly stable TAE's near the lower shear Alfven continuum, leading to nonlinear saturation. An explicit expression for the saturated magnetic fluctuation amplitude is derived.
59 citations
TL;DR: The complete channelling of energy from alpha particles is likely to be realized only through the excitation of a variety of waves, rather than by one wave alone as mentioned in this paper, even at the expense of less restrictive motion of the alpha particles.
Abstract: The complete channelling of energy from alpha particles is likely to be realized only through the excitation of a variety of waves, rather than by one wave alone. While one wave constrains more firmly the direction of the energy transfer, the necessary wave characteristics are far more easily achieved through a combination of waves, even at the expense of less restrictive motion of the alpha particles
TL;DR: The toroidicity-induced Alfven eigenmodes (TAE) are found to be stable in the Tokamak Fusion Test Reactor (TFTR) deuterium-tritium plasmas and a core localized TAE mode is shown to exist near the center of the plasma at small magnetic shear and finite plasma beta.
Abstract: The toroidicity-induced Alfven eigenmodes (TAE) are found to be stable in the Tokamak Fusion Test Reactor (TFTR) deuterium-tritium plasmas. The dominant stabilizing mechanisms are beam ion Landau damping and radiative damping. A core localized TAE mode is shown to exist near the center of the plasma at small magnetic shear and finite plasma beta, which can be destabilized by energetic alpha particles in future TFTR DT experiments. With additional instability drive from fast minority ions powered by ion cyclotron radio frequency, both the global and core localized TAE modes can be readily destabilized.
TL;DR: In this paper, the authors measured the helium ash production and transport in TFTR deuterium-tritium plasmas using charge exchange recombination spectroscopy and showed that the ash confinement time is dominated by edge pumping rates rather than core transport.
Abstract: Helium ash production and transport have been measured in TFTR deuterium-tritium plasmas using charge-exchange recombination spectroscopy. The helium ash confinement time, including recycling effects, is 6-10 times the energy confinement time and is compatible with sustained ignition in a reactor. The ash confinement time is dominated by edge pumping rates rather than core transport. The measured evolution of the local thermal ash density is consistent with modeling based on previously measured helium transport coefficients and classical slowing down of the alpha particles.
TL;DR: In this article, high frequency MHD activities observed during second harmonic ICRF heating are identified to be toroidicity-induced Alfven eigenmodes (TAE) driven by MeV protons produced by ICRFs.
TL;DR: Experiments have been performed on the TFTR to study rf wave heating of a D-T plasma by way of the second-harmonic tritium cyclotron resonance, where the majority of the rf power is found to damp on thetritium ions.
Abstract: Experiments have been performed on the TFTR to study rf wave heating of a D-T plasma by way of the second-harmonic tritium cyclotron resonance. The addition of tritium ions to a deuterium plasma allows for absorption of the rf waves at the tritium cyclotron harmonics and by electron damping of a mode converted ion Bernstein wave. Competing mechanisms include direct electron damping and damping at the fundamental cyclotron resonance of deuterium, $\ensuremath{\alpha}$ particles, and ${}^{3}$He ions. The contribution of each is estimated from a series of plasma discharges where various plasma parameters are varied. The majority of the rf power is found to damp on the tritium ions.
TL;DR: Three-dimensional fluid and kinetic models are being used to simulate the turbulent confinement of energy and plasma in the core of tokamaks, and these simulations represent a qualitative improvement in the realism with which they model large toKamak experiments.
TL;DR: In this paper, the Nordman-Weiland model is combined with models for transport driven by pressure gradients to compute the coefficients for the transport of ion heat, hydrogen ions, and electron heat.
Abstract: Transport simulations of TFTR temperature and density profiles have been carried out with the Nordman-Weiland transport model for ηi and trapped electron modes (including impurities and finite Larmor radius effects) combined together with resistive ballooning mode and neoclassical transport models. The Nordman-Weiland model is combined together with models for transport driven by pressure gradients to compute the coefficients for the transport of ion heat, hydrogen ions, and electron heat. The predictions of this model are compared with the experimentally observed profiles for TFTR L-mode and supershot plasmas.
TL;DR: In this paper, a new reversed magnetic shear regime is investigated with reduced core transport and a higher predicted stability limit, which is currently limited by MHD stability. But this regime is not suitable for TFTR.
Abstract: Routine tritium operation in TFTR has permitted investigations of alpha particle physics in parameter ranges resembling those of a reactor core. ICRF wave physics in a DT plasma and the influence of isotopic mass on supershot confinement have also been studied. Continued progress has been made in optimizing fusion power production in TFTR, using extended machine capability and Li wall conditioning. Performance is currently limited by MHD stability. A new reversed magnetic shear regime is being investigated with reduced core transport and a higher predicted stability limit.
03 May 1995-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: In this paper, the authors used Fabry-Perot interferometry to study visible lines from highly-charged ions created and trapped within an electron beam ion trap (EBIT), and showed that the Doppler-broadened 1 A line width is consistent with an expected ion temperature of less than 1 keV.
Abstract: We are using Fabry-Perot interferometry to study visible lines from highly-charged ions created and trapped within an electron beam ion trap (EBIT). The 3d 4 5 D 2 – 5 D 3 titanium-like barium (Ba 34+ ) line at 3932(2) A was recently measured in Ref. [1] (C.A. Morgan et al., Phys. Rev. Lett. 74 (1995) 1716) using a grating monochromator. We present preliminary Fabry-Perot spectra of this line with significantly improved resolution. The Doppler-broadened 1 A line width is consistent with an expected ion temperature of less than 1 keV. We discuss the possibility of resolving Zeeman splittings, and of using these visible lines as a diagnostic in high temperature, low density plasmas, like those that exist in tokamaks and the EBIT itself.
TL;DR: In this article, high-precision measurements are presented of an excellent resonance between the 3s1/2 → 2p3/2 (J = 1) transition in neonlike La47+ and the 1s2 1S0-1s2p 1P1 line in heliumlike Ti20+.
Abstract: High-precision measurements are presented of an excellent resonance between the 3s1/2 → 2p3/2 (J = 1) transition in neonlike La47+ and the 1s2 1S0-1s2p 1P1 line in heliumlike Ti20+. The measurements were carried out with a high-resolution crystal spectrometer on the PLT tokamak. Neonlike La47+ and heliumlike Ti20+ were produced and shown to coexist under the same plasma conditions. The difference between the two transitions was found to be 96 ± 38 ppm. This value is several times less than the width of each transition expected from thermal broadening. The resonance can be used for selective modification of the kinetics of a proposed 57 A laser based on neonlike La47+.
TL;DR: In this paper, a theoretical model of flux-surface-averaged radial transport in tokamaks has been tested and calibrated against a well-documented set of temperature and density profiles from a pre-defined set of discharges from seven different discharges.
Abstract: A theoretical model of flux-surface-averaged radial transport in tokamaks has been tested and calibrated against a well-documented set of temperature and density profiles from a pre-defined set of discharges from seven tokamaks. The transport theory includes neoclassical, drift/ηi, circulating electron mode, kinetic ballooning, neoclassical MHD, and resistive ballooning effects. Allowing for no explicitly adjustable free parameters, the nominal theory results are compared with experimental density and temperature profiles from the reference set of discharges from Alcator-C, ASDEX, ISX-B, TFTR, DIII-D, and JET. Profile results are also given for an additional set of six discharges including Alcator-C, ASDEX, DIII-D, TFTR, JET, and JFT-2M in addition to five TFTR discharges as part of a ρ* and β scan. Employed is a statistical model of calibration/modeling and measurement variances allowing detailed analysis of results and further calibration of the model along with a well defined procedure for setting the time dependent boundary conditions at an appropriate location just inside the inner-most "closed" magnetic flux surface.
TL;DR: It is determined that the planned annual TFTR neutron production of 1 × 1021 D-T neutrons is consistent with the design objective of limiting the total dose-equivalent at the property line, from all radiation sources and pathways, to less than 10 mrem per year.
TL;DR: In this paper, the saturation activities have been obtained and discussed with a view to characterizing the neutron energy spectra near three different kinds of penetrations on walls of TFTR test cell.
TL;DR: In this article, the authors discuss the present divertor design for the planned TPX tokamak, which will explore the physics and technology of steady-state (1000s pulses) heat and particle removal in high confinement (2--4{times} L-mode), high beta (sub N} {ge} 3) divertor plasmas sustained by non-inductive current drive.
TL;DR: In this article, a ΔE−E type proton recoil telescope, called COTETRA, was developed and is presently being applied to TFTR D•T fusion experiments, and two sets of COTetRA were prepared for this experiment.
Abstract: A ΔE‐E type proton recoil telescope, called COTETRA, was developed and is presently being applied to TFTR D‐T fusion experiments. Two types of COTETRA were prepared for this experiment. One set is used primarily for high‐resolution measurements of the neutron energy and uses Si diode as an E detector (set A), while another set (set B) uses a plastic scintillator to attain high count‐rate capability. Both sets of COTETRA have small physical dimensions and use fast NIM electronic modules for high neutron flux rate measurements. A data acquisition system has been developed for the TFTR CAMAC system. A calibration experiment has been performed using a D‐T neutron generator. Energy resolution of 4.0% is obtained for set A. Set B is expected to work at a count rate of up to 104 cps, which corresponds to a neutron flux rate of ∼109 (n/cm2)/s at the detector position. Currently, both of them are installed under the multichannel neutron collimator of TFTR.
TL;DR: The availability of high D-T fusion neutron yields at TFTR has provided a useful opportunity to measure directly D-Ts neutron-induced radioactivity in a realistic tokamak fusion reactor environment for materials of vital interest to ITER.
TL;DR: There have been many significant changes in the status of tritium activities in the US since the 4th Tritium Conference in October 1991 as mentioned in this paper, and many of the activities previously performed there have been transferred to Los Alamos and Savannah River.
Abstract: There have been many significant changes in the status of tritium activities in the US since the 4th Tritium Conference in October, 1991. The replacement Tritium Facility (RTF) at Savannah River Site and the Weapons Engineering Tritium Facility (WETF) at the Los Alamos National Laboratory are now operational with tritium. The Tokamak Fusion Test Reactor (TFTR) has initiated a highly successful experimental campaign studying DT plasmas, and has produced more than 10 Megawatts (MW) of fusion power in a D-T plasma. Sandia National Laboratory has ceased tritium operations at the Tritium Research Laboratory (TRL) and many of the activities previously performed there have been transferred to Los Alamos and Savannah River. The tritium laboratory at Lawrence Livermore National Laboratory has reduced the tritium inventory to <5 grams. The Tritium Systems Test Assembly (TSTA) at Los Alamos continues to be at the forefront of tritium technology and safety development for the fusion energy program.
TL;DR: In this article, real-time solid target boronization has been applied to PBX-M using the plasma erosion of solid target probes to optimize vaporization and minimize spallation.
TL;DR: In this article, the DEGAS Monte Carlo neutral transport code is applied to gas target divertor simulation experiments in the PISCEA-A linear plasma device to study the neutral gas dynamics in a well diagnosed environment.
01 Aug 1995
TL;DR: In this article, a model that takes into account the contribution to the MgI-like emission features from autoionizing levels of the adjacent AlIlike charge state is proposed.
Abstract: Radiative transitions with very different characteristic rates can serve as important diagnostics of local conditions in a plasma. Here, the observed intensity ratio of the 3s{sup 2} {sup 1}S{sub 0} - 3s3p {sup 1}P{sub 1} to the 3s{sup 2} {sup 1}S{sub 0} - 3s3p {sup 3}P{sub 1} transitions in MgI-like ions has always presented those who model plasma spectra with a challenge; the observed intensity of the intercombination line is always several times greater than what simple models predict. The authors offer a model that takes into account the contribution to the MgI-like emission features from autoionizing levels of the adjacent AlI-like charge state. Models in the present work, which include the effects of configuration interaction on ionic wavefunctions, and the contribution of both direct, impact ionization and autoionization channels from the AlI-like ion to the MgI-like ion, give good agreement with the observed resonant/intercombination (R/I) emission ratio only when a departure from ionization equilibrium is assumed. The authors also identify, for the first time, intercombination lines of the form 3s3p {sup 1}P{sub 1} - 3p{sup 2} {sup 3}P{sub 2} in several elements relevant to both astrophysical and magnetically-confined fusion plasmas.