Showing papers by "Princeton Plasma Physics Laboratory published in 1988"
TL;DR: In this article, it is shown that this limit may be caused by a dramatic deterioration in core particle confinement occurring as the density limit boundary is approached, which can help explain the disruptions and Marfes that are associated with density limit.
Abstract: While the results of early work on the density limit in tokamaks from the ORMAK and DITE groups have been useful over the years, results from recent experiments and the requirements for extrapolation to future experiments have prompted a new look at this subject. There are many physical processes which limit the attainable densities in tokamak plasmas. These processes include: (1) radiation from low Z impurities, convection, charge exchange and other losses at the plasma edge; (2) radiation from low or high Z impurities in the plasma core; (3) deterioration of particle confinement in the plasma core; and (4) inadequate fuelling, often exacerbated by strong pumping by walls, limiters or divertors. Depending upon the circumstances, any of these processes may dominate and determine a density limit. In general, these mechanisms do not show the same dependence on plasma parameters. The multiplicity of processes leading to density limits with a variety of scaling has led to some confusion when comparing density limits for different machines. The authors attempt to sort out the various limits and to extend the scaling law for one of them to include the important effects of plasma shaping, i.e. ;e = k, where ne is the line average electron density (1020 m−3), κ is the plasma elongation and (MAm−2) is the average plasma current density, defined as the total current divided by the plasma cross-sectional area. In a sense, this is the most important density limit since, together with the q-limit, it yields the maximum operating density for a tokamak plasma. It is shown that this limit may be caused by a dramatic deterioration in core particle confinement occurring as the density limit boundary is approached. This mechanism can help explain the disruptions and Marfes that are associated with the density limit.
682 citations
TL;DR: In this article, the wave-induced fluxes of energetic-trapped ions during ICRF heating of tokamak plasmas are calculated using quasilinear equations.
Abstract: The wave-induced fluxes of energetic-trapped ions during ICRF heating of tokamak plasmas are calculated using quasilinear equations. A simple single particle model of this transport mechanism is also given. Both a convective flux proportional to k/sub phi/vertical bar E/sub +/vertical bar/sup 2/ and a diffusive flux proportional to k/sub phi//sup 2/vertical bar E/sub +/vertical bar/sup 2/ are found. Here, k/sub phi/ is the toroidal wave number and E/sub +/ is the left-hand polarized wave field. The convective flux may become significant for large k/sub phi/ if the wave spectrum is asymmetric in k/sub phi/. But for the conditions of most previous experiments, these calculations indicate that radial transport driven directly by the ICRF wave is unimportant.
109 citations
TL;DR: A high-energy trapped-particle population is shown to have a strong stabilizing effect on the internal resistive kink mode of a tokamak plasma.
Abstract: Recent experiments involving high-power radio-frequency heating of a tokamak plasma show strong suppression of the sawtooth oscillation. A high-energy trapped-particle population is shown to have a strong stabilizing effect on the internal resistive kink mode. Numerical calculations are in reasonable agreement with experment.
90 citations
TL;DR: Substantial progress was made during the period 1981-1986 in plasma parameters, physics understanding, and improvement of the stellarator/heliotron concept as discussed by the authors, and the short-term direction of the program is clear; a number of new facilities that were designed to resolve these issues are about to come into operation or are in the final design stages.
Abstract: Substantial progress was made during the period 1981-1986 in plasma parameters, physics understanding, and improvement of the stellarator/heliotron concept. Recent advances include (1) substantial achievements in higher plasma parameters and currentless plasma operation, (2) new theoretical results with respect to higher beta limits, second stability region, effect of a helical axis, effect of electric fields on transport, and reduction of secondary currents; and (3) improvements to the reactor concept. The key issues have been further refined, and the short-term direction of the program is clear; a number of new facilities that were designed to resolve these issues are about to come into operation or are in the final design stages. This report summarizes these advances.
72 citations
TL;DR: Ion Bernstein wave heating (IBWH) has been investigated on PLT with up to 650 kW of rf power coupled to the plasma, exceeding the ohmic power of 550 kW.
Abstract: Ion Bernstein wave heating (IBWH) has been investigated on PLT with up to 650 kW of rf power coupled to the plasma, exceeding the ohmic power of 550 kW. Plasma antenna loading of 2 ..cap omega.. has been observed, resulting in 80 to 90% of the rf power being coupled to the plasma. An ion heating efficiency of ..delta..T/sub i/(0)n/sub e//P/sub rf/ = 6 x 10/sup 13/ eV cm/sup -3//kW, without high energy tail ions, has been observed up to the maximum rf power. The deuterium particle confinement during high power IBWH increases significantly (as much as 300%). Associated with it, a longer injected impurity confinement time, reduced drift wave turbulence activity, frequency shifts of drfit wave turbulence, and development of a large negative edge potential were observed. The energy confinement time, however, shows some degradation from the ohmic value, which can be attributed to the enhanced radiation loss observed during IBWH. The ion heating and energy confinement time are relatively independent of plasma current.
60 citations
TL;DR: In this paper, high-resolution spectra of the elements Fe, Ni, Zn, Ge, Se, and Mo injected into the Princeton Large Torus tokamak were recorded by the 2m Schwob-Fraenkel soft-x-ray multichannel spectrometer.
Abstract: High-resolution spectra of the elements Fe, Ni, Zn, Ge, Se, and Mo injected into the Princeton Large Torus tokamak were recorded by the 2-m Schwob–Fraenkel soft-x-ray multichannel spectrometer. Spectra were recorded every 50 msec during the times before and after injection. The spectral lines of the injected element were very strong in the spectrum recorded immediately after injection, and the transitions in the injected element were easily distinguished from the transitions in the intrinsic elements (C, O, Ti, Cr, Fe, and Ni). An accurate wavelength scale was established using well-known reference transitions in the intrinsic elements. The spectra recorded just before injection were subtracted from the spectra recorded after injection, and the resulting spectrum was composed almost entirely of transitions from the injected element. A large number of Δn = 0 transitions between the ground and the first excited configurations in the Li i through K i isoelectronic sequences of the injected elements were identified in the wavelength region 60 to 345 A.
32 citations
TL;DR: In this paper, the wavelengths of the 3s2 1S0-3s3p3P1 transition for the magnesium-like ions Zn18+, Ge20+, Se22, Mo30+, Sn38+, and Xe42+ have been measured in spectra from the Princeton Large Torus tokamak.
Abstract: The wavelengths of the 3s2 1S0–3s3p3P1 transition for the magnesiumlike ions Zn18+, Ge20+, Se22+, Mo30+, Sn38+, and Xe42+ have been measured in spectra from the Princeton Large Torus tokamak. When we compare these and other recently available observations with wavelengths calculated using Grant’s multiconfiguration Dirac–Fock program, wavelengths are predicted for the ions Fe14+ through Nd48+.
29 citations
TL;DR: In this article, the axisymmetric inner wall limiter, constructed of graphite tiles, is described, including the necessary conditioning procedures needed for impurity and particle control of high power (≤ 20 MW) neutral injection experiments.
23 citations
TL;DR: In this paper, the authors investigated the validity of ideal MHD theory in explaining the low qψ disruptions in PBX discharges, specifically the characteristics of the pre-disruption MHD activity in these low-q discharges.
Abstract: Princeton Beta Experiment (PBX) discharges run at the lowest q and highest βt always terminated in a hard disruption. The discharges, with βt values of up to 5.5% and q-values down to 2.2, were obtained by employing large current ramps and large gas feed rates during neutral beam injection. Previous work has indicated that the achieved βt values were consistent with the limit imposed by the n = l ideal external kink with a conducting wall at b/a = 2. The authors of the paper investigate further the validity of ideal MHD theory in explaining the low qψ disruptions. In particular, the characteristics of the pre-disruption MHD activity in these low-q discharges, specifically the time-scale of growth and internal and external mode structures, are compared with those determined from theoretical calculations. The results of these comparisons indicate that non-ideal effects must be considered in order to obtain detailed agreement between theory and experiment.
17 citations
Abstract: Various aspects of MHD stability are studied for a high current, high beta tokamak. Included is a study of kink and ballooning mode beta limits as a function of current and safety factor at the plasma edge (qs). These studies were carried out with pressure profiles optimized with respect to ballooning and ohmically consistent current profiles whereby the ⋅/⋅∇ profile is specified. The effect of current profile shaping is studied. Current profiles with steep edge gradients are more unstable to kink instabilities at high beta. This is particularly true for values of qs near an integer value on edge where the kink mode beta limit can fall off steeply. For a less steep edge current gradient, the ballooning modes are more unstable at high beta. The effect of elongation and triangularity are also considered. Improvement in the beta limit is observed for increasing elongation, up to κ = 2.0, after which beta drops off. A modest increase in triangularity does not improve the overall beta limits.
17 citations
TL;DR: In this paper, the authors derived the central ion temperature from deuterium neutral beam charge exchange spectra above the neutral beam injection energy using Fokker-Planck simulations of the TFTR energetic ion mode discharges.
Abstract: Fokker-Planck simulations of the Tokamak Fusion Test Reactor (TFTR) energetic ion mode discharges were performed to evaluate the utility of deriving the central ion temperature Ti from deuterium neutral beam charge exchange spectra above the neutral beam injection energy. The Ti values obtained from fitting the calculated spectra obtained from sightlines nearly tangent to the neutral beam injection radius reproduce the central ion temperature within ±10% over the full range of TFTR energetic ion mode parameters. The code simulations demonstrate that the ion temperature obtained from the high energy tangential deuterium charge exchange spectrum is insensitive to variations in plasma density, Zeff, plasma current, loop voltage, and injected neutral beam power and energy. The use of this method to reduce charge exchange data from TFTR energetic ion mode plasmas is demonstrated.
TL;DR: In this article, self-consistent equilibrium effects on tokamak magnetic field ripple have been calculated using a three-dimensional equilibrium code and the effects are found to be large enough that they should be included in tokak ignition experiment designs.
Abstract: Self-consistent equilibrium effects on tokamak magnetic field ripple have been calculated using a three-dimensional equilibrium code. The effects are found to be large enough that they should be included in tokamak ignition experiment designs. Even the modification of the well depth associated with the flow of force-free plasma current along rippled field lines is substantial. An analysis of the results separates the contribution of the Shafranov shift to the ripple modification from the contributions of other finite-pressure effects. 5 refs., 10 figs., 1 tab.
TL;DR: Alpha particle parameters in sub-ignited D-T tokamaks like TFTR can be optimized in a high temperature ''alpha storage regime '' in which the alpha particle thermalization time /tau//sub ..cap alpha../ is long and can be used to provide a strong (but transient) alpha heating pulse.
Abstract: Alpha particle parameters in sub-ignited D-T tokamaks like TFTR can be optimized in a high temperature ''alpha storage regime '' in which the alpha particle thermalization time /tau//sub ..cap alpha../ is long (approx.1.0 sec) and in which the alpha particle source rate S/sub ..cap alpha../ is enhanced due to a beam-target and beam-beam reactions (by a factor of approx.2-3). Near reactor-level alpha instability parameters ..beta../sub ..cap alpha../(0) approx. n/sub ..cap alpha../(0)/n/sub e/(O) approx. 1% are predicted by simulation codes when Q approx. 0.5-1, while present TFTR ''supershots'' already have ..beta../sub ..cap alpha../(O) approx. n/sub /alpha/(O)/n/sub e/(O) /approx/ 0.1-0.2%. Plasmas in this regime can be used to test theories of collective alpha instabilities for the first time, and can be used to provide a strong (but transient) alpha heating pulse. An experimental scenario to exploit this regime is described. 28 refs., 5 figs., 5 tabs.,
TL;DR: In this paper, two dimensional calculations of impurtiy transport in a high recycling divertor scrape-off region have been made with an updated version of the ZTRANS Monte Carlo computer code.
Abstract: Two dimensional calculations of impurtiy transport in a high recycling divertor scrape-off region have been made with an updated version of the ZTRANS Monte Carlo computer code. The calculations use plasma parameters for the Doublet 3 divertor, as computed by the Planet Fluid Transport Code. The effects of electric field, particle drift velocities, and thermal forces are included in the calculations. For all impurity species studied, it is found that impurity transport is dominated by frictional forces, over most of the scrape-off region. Light impurities, however, impinge substantially closer to the divertor plate center than do heavy impurities, which tend to impinge at the outer plate boundary. 8 refs., 4 figs., 2 tabs.
01 Aug 1988-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: The question of the suppression of the D-D reaction by alignment of the nuclear spins of D is discussed in this article, and the arguments for and against the suppression are presented.
Abstract: The question of the suppression of the D-D reaction by alignment of the nuclear spins of the D is discussed. The arguments for and against the suppression are presented.
TL;DR: In the Tokamak Fusion Test Reactor (TFTR) vacuum vessel atmosphere in 1985, measurements indicated low levels of tritium oxide (HTO) as discussed by the authors, which was later increased to 1 MBq m/sup -3/ (28..mu..Ci m/Sup -3/) or approximately six times the DOE concentration guide value of 185 kBqm/m/sup −3/(5..mu.Cim m/SUP -3)/ (5 )
Abstract: Measurements within the Tokamak Fusion Test Reactor (TFTR) vacuum vessel atmosphere in 1985 indicated low levels of tritium oxide (HTO). From January to July 1987 approximately 3 x 10/sup 18/ D-D fusion neutrons were produced in TFTR operations. These reactions would be expected to produce a triton for each reaction or 5.4 GBq (145 milliCuries) of tritium. An HTO measurement made of the vessel on 7/10/87, five days after the last pulsing of the machine, but before the machine was let up to air, indicated and HTO level of 1 MBq m/sup -3/ (28 ..mu..Ci m/sup -3/) or approximately six times the DOE concentration guide value of 185 kBq m/sup -3/ (5 ..mu..Ci m/sup -3/). The ICRP 30 Derived Air Concentration (DAC) limit of 800 kBq m/sup -3/ (22 ..mu..Ci m/sup -3/) will become the limit when Draft DOE Order 5480.11 is implemented. A venting program for the vessel was set up with the objective of limiting the internal dose equivalent to personnel working inside the vacuum vessel. An HTO/HT measurement indicated a 57:1 ratio.
TL;DR: In this article, the time evolution of the 2D Marfe is followed and typical e-folding times and their variation with the poloidal and radial heat conductivities are determined.
Abstract: In the first part of this paper we present multifluid model calculations of marfe instabilities in a simple geometry. Assuming carbon as the dominant impurity, the time evolution of the 2D Marfe is followed and typical e-folding times and their variation with the poloidal and radial heat conductivities are determined. In part two of this paper we present a scrape-off layer simulation in a typical x-point geometry using a simplyfied hydrogen recycling model and again carbon as impurities. Other impurity species can be treated as well.
TL;DR: The local carbon particle diffusion coefficient was measured in the Proto S-1/C spheromak with use of a test-particle injection scheme and appears to be driven by correlations of the fluctuating electric field and density.
Abstract: The local carbon particle diffusion coefficient was measured in the Proto S-1/C spheromak with use of a test-particle injection scheme. When the plasma was not in a force-free Taylor state, and when there were pressure gradients in the plasma, the particle diffusion was 5 times that predicted by Bohm and was consistent with collisional drift-wave diffusion. The diffusion appears to be driven by correlations of the fluctuating electric field and density. During the decay of the discharge when the plasma was in the Taylor state, the diffusion coefficient of the carbon was classical.
18 Nov 1988
TL;DR: In this paper, a 30 meter long circular corrugated waveguide run with a corrugation period and depth of 250μ has been fabricated for low loss (<0.01 dB/m) multimode operation over the frequency range of 75-575 GHz.
Abstract: A 30 meter long circular corrugated waveguide run (i.d.=6.35 cm) with a corrugation period and depth of 250μ has been fabricated. It is designed for low loss (<0.01 dB/m) multimode operation over the frequency range of 75-575 GHz. It will be installed on TFTR (Tokamak Fusion Test Reactor) for use in electron cyclotron emission measurements. Results will be compared to those obtained using conventional tall rectangular C-band waveguide.
TL;DR: In this paper, the slow wave was revealed through the presence of its resonance cone, which was attributed to parasitic excitation, which is a linear mechanism involving electron × motion and charge separation in a density gradient.
Abstract: Excitation of the lower hybrid wave (slow wave) using a launcher designed for fast wave excitation has been observed under conditions where neither direct excitation nor mode conversion is expected to take place. The slow wave was revealed through the presence of its resonance cone. The experiment was performed with Ωi ω Ωe. The coupling of the fast wave into the slow wave is attributed to parasitic excitation, which is a linear mechanism involving electron × motion and charge separation in a density gradient. This process could be a significant loss mechanism for fast wave current drive in toroidal plasmas.
TL;DR: In this article, a model for the ion Bernstein wave heating experiment on the JIPPT-II-U tokamak has been developed, in which a resonance layer is formed by the third harmonic of deuterium-like ions, such as fully ionized carbon and oxygen ions near the plasma center.
Abstract: By using a transport code combined with an ion Bernstein wave tokamak ray tracing code, a modelling code for the ion Bernstein wave heting has been developed. With this code, the ion Bernstein wave heating experiment on the JIPPT-II-U tokamak has been analysed. It is assumed that a resonance layer is formed by the third harmonic of deuterium-like ions, such as fully ionized carbon, and oxygen ions near the plasma centre. As wave absorption mechanisms, electron Landau damping, ion cyclotron harmonic damping, and collisional damping are considered. The characteristics of the ion Bernstein wave heating experiment, such as an increase in ion temperature, a strong dependence of the quality factor on the magnetic field strength and a dependence of the ion temperature increment on the input power are well reproduced.
27 Apr 1988
TL;DR: In this article, a soft x-ray amplification in lithium-like ions in a CO 2 laser-produced recombining plasma confined in a magnetic field is presented, where a one-dimensional hydrodynamic code with a collisional-radiative atomic model is used to model the plasma and comparisons of theoretical results with experimental observation are discussed.
Abstract: We present recent experiments on soft x-ray amplification in lithium-like ions in a CO 2 laser-produced recombining plasma confined in a magnetic field. The maximum gain-length products observed are GL = 3 - 4 for the 154 A, 4f - 3d transition in Al XI and GL = 1 - 2 for the 129 A, 4f-3d transition in Si XII, respectively. A one-dimensional hydrodynamic code with a collisional-radiative atomic model was used to model the plasma and comparisons of theoretical results with experimental observation are discussed. Descriptions of both hydrodynamic and atomic physics code are given.
18 May 1988
TL;DR: In this article, the effect of density inhomogeneities on the degenerate four-wave mixing (DFWM) and phase conjugate properties of plasmas is investigated. And a comparison is made between DFWM in collisionless and collisional Plasmas.
Abstract: Plasmas have recently received considerable attention as poten-tially efficient long wavelength (infrared to microwave) phase con-jugators using degenerate four-wave mixing (DFWM). However, the current theory assumes an idealized isotropic, homogeneous, quies-cent plasma. In order to ascertain the suitability of plasmas for phase conjugation applications, a more complete theory of DFWM in the presence of plasma density inhomogeneities, turbulence, etc. is necessary. This paper focuses on the effect of density inhomogeneities on the DFWM and phase conjugate properties of plasmas. In addition, a comparison is made between DFWM in collisionless and collisional plasmas.