Showing papers by "Princeton Plasma Physics Laboratory published in 1987"
TL;DR: A variety of methods have been proposed to provide continuous current, including methods that utilize particle beams or radio-frequency waves in any of several frequency regimes as mentioned in this paper, and experimentation in these techniques has now involved major tokamak facilities worldwide.
Abstract: The continuous operation of a tokamak fusion reactor requires, among other things, a means of providing continuously the toroidal current. Such operation is preferred to the conventional pulsed operation, where the plasma current is induced by a time-varying magnetic field. A variety of methods have been proposed to provide continuous current, including methods that utilize particle beams or radio-frequency waves in any of several frequency regimes. Currents as large as half a mega-amp have now been produced in the laboratory by such means, and experimentation in these techniques has now involved major tokamak facilities worldwide.
826 citations
TL;DR: The role of shear in determining the ideal MHD stability properties of tokamaks is discussed in this article, where the effects of low shear within the plasma upon pressure driven modes are assessed.
Abstract: The role of shear in determining the ideal MHD stability properties of tokamaks is discussed. In particular, the effects of low shear within the plasma upon pressure driven modes are assessed. The standard ballooning theory is shown to break down as the shear is reduced, and the growth rate is shown to be an oscillatory function of n, the toroidal mode number, treated as a continuous parameter. The oscillations are shown to depend on both the pressure profile and the safety factor profile. When the shear is sufficiently weak, the oscillations can result in bands of unstable n-values, which are present even when the standard ballooning theory predicts complete stability. These instabilities are named 'infernal modes'. The occurrence of these instabilities at integer n is shown to be a sensitive function of the q-axis, raising the possibility of a sharp onset as the plasma parameters evolve.
152 citations
TL;DR: In this article, a non-variational approach for determining the ideal MHD stability of axisymmetric toroidal confinement systems is presented, which employs cubic B -spline finite elements and Fourier expansion in a general flux coordinate (ψ, φ, ζ) system.
150 citations
TL;DR: A tokamak discharge has been formed and maintained through helicity injection, by use of only an external dc low-energy electron beam, and strong central peaking occurs and inward pinching is indicated for both density and current.
Abstract: A tokamak discharge has been formed and maintained through helicity injection, by use of only an external dc low-energy electron beam. The discharge, in a 5-kG toroidal field, evolved to a steady-state circular cross section with q(a)=10, q(0)=4, which was maintained for more than 400 L/R periods, the time (60 msec) limited by the cathode bias supply. The density profile reached a line-averaged n${\ifmmode\bar\else\textasciimacron\fi{}}_{e}$=2\ifmmode\times\else\texttimes\fi{}${10}^{13}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$, while ${T}_{e}$=25 eV and ${T}_{i}$=15 eV. Strong central peaking occurs and inward pinching is indicated for both density and current.
77 citations
TL;DR: A field-aligned eigenode analysis of compressional Alfven instabilities has been performed for a two component anisotropic plasma in a dipole magnetic field as discussed by the authors, where the eigenmode equations are derived from the gyrokinetic equations in the long wavelength (k rho < 1) and low frequency (..omega.. <..omega../sub b/) limits.
Abstract: A field-aligned eigenode analysis of compressional Alfven instabilities has been performed for a two component anisotropic plasma in a dipole magnetic field. The eigenmode equations are derived from the gyrokinetic equations in the long wavelength (k rho < 1) and low frequency (..omega.. < ..omega../sub b/) limits, where rho is the hot particle gyroradius and ..omega../sub b/ is the hot particle bounce frequency. Two types of compressional instabilities are identified. One is the drift mirror mode which has an odd parity compressional magnetic component with respect to the magnetic equator. The other is the drift compressional mode with an even parity compressional magnetic component. For typical storm time plasma parameters neargeosynchronous orbit, the drift mirror mode is most unstable and the drift compressional mode is stable. The storm time compressional Pc 5 waves, observed by multiple satellites during November 14-15, 1979 (Takahashi et al., 1987), can be explained by the drift mirror instability.
63 citations
TL;DR: In this article, the authors review the progress that has been made in the line identification program, paying particular attention to the high-Z members of the isoelectronic sequences of the second period.
Abstract: Spectral lines emitted from the different ionization stages of various elements present (either naturally occuring or deliberately added) in high-temperature tokamak plasmas may be used for localized diagnostics of such plasmas. This fact has motivated a search for transitions suitable for these purposes. Such transitions are of essentially two types: Δn = 0 resonance transitions (in particular of one- and two-valence electron systems) and magnetic dipole transitions arising within the ground configurations of ions of highly-ionized, high-Z elements. The latter transitions are peculiar to the fairly low-density, quasisteady plasmas prevailing in tokamaks – and to celestial plasmas. In this paper we review the progress that has been made in the line identification program, paying particular attention to the high-Z members of the isoelectronic sequences of the second period. For these sequences, critical examinations of measured data and comparisons with theoretical calculations have been carried out by Professor Bengt Edlen, resulting in highly accurate wavelength predictions.
35 citations
TL;DR: In this paper, it was shown that the TFTR electron temperature profile shapes are even more constrained than previous models of profile consistency suggested, and the profile shapes, Te(r)/Te(a/2), are found to be invariant (for r > 0.4 a) for a wide range of parameters, including q(a).
Abstract: Electron heat transport on TFTR and other tokamaks is several orders of magnitude larger than neoclassical calculations predict. Despite considerable effort, there is still no clear theoretical understanding of this anomalous transport. The electron temperature profile, Te(r), has shown a marked consistency on many machines for a wide range of plasma parameters and heating profiles. This could be an important clue as to the process responsible for this enhanced thermal transport. In the first section of the paper the result is presented that TFTR electron temperature profile shapes are even more constrained than previous models of profile consistency suggested. The profile shapes, Te(r)/Te(a/2), are found to be invariant (for r > 0.4 a) for a wide range of parameters, including q(a). In the second section, an experiment is discussed which uses a fast current ramp to transiently decouple the current density profile, J(r), and the Te(r) profiles. From this experiment, it has been determined that the J(r) profile can be strongly modified with no measurable effect on the electron temperature profile shape. Thus, while the electron temperature profile is apparently constrained, the current profile is not.
35 citations
TL;DR: In this article, the authors measured the efflux of neutral hydrogen in the energy range from 10 to 2000 eV as a function of plasma parameters in the steady-state portion of ohmically heated discharges in PLT.
31 citations
TL;DR: In this article, the edge turbulence in TFTR is characterized by several diagnostics, including Langmuir probes and D-alpha imaging, and it is shown that large amplitude, small-scale, broadband density fluctuations in the scrape-off region near the wall are detected by small-angle microwave scattering and magnetic pickup loops.
27 citations
TL;DR: In this paper, a detailed discussion of the use of an impurity transport model to infer absolute impurity densities and radiative losses from line intensity and visible continuum measurements is given.
Abstract: Quantitative spectroscopic measurements of Zeff, impurity densities and radiated power losses have been made for ohmically heated and neutral beam heated TFTR discharges at a plasma current of 2.2 MA and a toroidal field of 4.7 T. Variations in these quantities with line average plasma density (e) and beam power up to 5.6 MW are presented for discharges on a movable graphite limiter. A detailed discussion of the use of an impurity transport model to infer absolute impurity densities and radiative losses from line intensity and visible continuum measurements is given. These discharges were dominated by low-Z impurities, with carbon having a considerably higher density than oxygen, except in high e Ohmic discharges where the densities of carbon and oxygen were comparable. Metallic impurity concentrations and radiative losses were small, resulting in hollow radiated power profiles and fractions of the input power radiated being 30–50% for Ohmic heating and 30% or less for beam heating. Spectroscopic estimates of the radiated power were in good agreement with bolometrically measured values. Because of an increase in the carbon density, Zeff rose from 2.0 to 2.8 as the beam power increased from 0 to 5.6 MW, pointing to a potentially serious dilution of the neutron producing plasma ions with increasing beam power. Both the low-Z and the metallic impurity concentrations were approximately constant with minor radius, indicating no central impurity accumulation in these discharges.
27 citations
TL;DR: The nonlinear saturated state of the m = 1, n = 1 ideal MHD instability is calculated for a large--aspect-ratio tokamak and may be related to the steady-state oscillations seen when sawteeth are suppressed by lower-hybrid current drive.
Abstract: The nonlinear saturated state of the m = 1, n = 1 ideal MHD instability is calculated for a large--aspect-ratio tokamak. When the q(r) profile is nonmonotonic with ..delta..q = (q/sub min/-1)>0, the amplitude xi of the nonlinear state is given by xi/sup 2/q''/..delta..q = 7.9((..delta..q/sub c//..delta..q)/sup 3//sup ///sup 2/-1), where ..delta../sup q//sub c/ is the critical value of ..delta..q at which the system is marginally stable. This nonlinear state is similar to that seen during the sawtooth crash in large tokamaks and may be related to the steady-state oscillations seen when sawteeth are suppressed by lower-hybrid current drive.
TL;DR: In this article, high-resolution spectra from the Princeton Large Torus plasma have been recorded by a 2m Schwob-Fraenkel soft-x-ray multichannel spectrometer.
Abstract: High-resolution spectra from the Princeton Large Torus plasma have been recorded by a 2-m Schwob–Fraenkel soft-x-ray multichannel spectrometer. Spectra covering a wavelength range of approximately 50 A were recorded every 50 msec, and the spectra were normalized and added together to produce composite spectra covering the region 80–340 A. Several well-known reference lines were used to establish an absolute wavelength scale, and transition wavelengths were measured to an accuracy of approximately 0.02 A. By subtracting spectra recorded at various times throughout the discharge, transitions from ions formed in the cooler and hotter plasmas were easily distinguished, and blends between hot and cold transitions were resolved. Wavelengths of transitions in C, O, Ti, Cr, Mn, Fe, and Ni have been measured.
TL;DR: The Compact Ignition Tokamak (CIT) as discussed by the authors is a modest-size ignition experiment designed to study the physics of alpha particle heating, and the basic concept is to achieve ignition by using a high plasma density to achieve nT{sub E} {approx} 2 x 10{sup 20}s/m{sup 3} required for ignition.
Abstract: The Compact Ignition Tokamak (CIT) is a proposed modest-size ignition experiment designed to study the physics of alpha particle heating. The basic concept is to achieve ignition in a modest-size minimum cost experiment by using a high plasma density to achieve nT{sub E} {approx} 2 x 10{sup 20}s/m{sup 3} required for ignition. The high density requires a high toroidal field (10 T). The high toroidal field allows a large plasma current (10 MA) which provides a high level of ohmic heating, improves the energy confinement, and allows a relatively high beta ({approx} 6%). The present CIT design also has a high degree of elongation (k {approx} 1.8) to aid in producing the large plasma current. A double null poloidal divertor and pellet injection are part of the design to provide impurity and particle control, improve the confinement, and provide flexibility for improving the plasma profiles. Auxiliary heating is expected to be necessary to achieve ignition, and 10-20 MW of ICRF is to be provided.
TL;DR: In this paper, the first absolute measurements of the ionization source in the Tandem Mirror Experiment Upgrade (TMX-U) plasma have been obtained, which have permitted the determination of the magnitude of ambipolar radial transport from the particle balance.
Abstract: Ambipolar radial transport (equal ion and electron flux) is not directly measured in tandem mirror experiments because the particle flow does not produce a net electrical current. The first absolute measurements of the ionization source in the Tandem Mirror Experiment Upgrade (TMX-U) plasma have been obtained. These have permitted the determination of the magnitude of ambipolar radial transport from the particle balance. Furthermore, comparisons of the source measurements with a Monte Carlo neutral transport code have shown reasonable agreement. Measurements of the particle balance under several operating conditions are presented. For some of these cases, the ambipolar radial transport is smaller than the other measured losses.
TL;DR: Etude du transport dans des stellarators optimises aux faibles frequences de collision, par une methode numerique de resolution de l'equation de Fokker-Planck.
Abstract: Etude du transport dans des stellarators optimises aux faibles frequences de collision, par une methode numerique de resolution de l'equation de Fokker-Planck
TL;DR: The basic fusion driver requirements of a toroidal materials production reactor are considered in this article, and the tokamak, stellarator, bumpy torus, and reversed field pinch are compared with regard to their demonstrated performance, probable near-term development, and potential advantages and disadvantages if used as reactors for materials production.
Abstract: The basic fusion driver requirements of a toroidal materials production reactor are considered. The tokamak, stellarator, bumpy torus, and reversed-field pinch are compared with regard to their demonstrated performance, probable near-term development, and potential advantages and disadvantages if used as reactors for materials production. Of the candidate fusion drivers, the tokamak is determined to be the most viable for a near-term production reactor. Four tokamak reactor concepts (TORFA/FED-R, AFTR/ZEPHYR, Riggatron, and Superconducting Coil) of approximately 500-MW fusion power are compared with regard to their demands on plasma performance, required fusion technology development, and blanket configuration characteristics. Because of its relatively moderate requirements on fusion plasma physics and technology development, as well as its superior configuration of production blankets, the TORFA/FED-R type of reactor operating with a fusion power gain of about 3 is found to be the most suitable tokamak candidate for implementation as a near-term production reactor.
TL;DR: In this paper, measured wavelengths of the lithiumlike Se xxxii resonance lines and the berylliumlike Se xxi resonance and intercombination line were compared with the isoelectronic extrapolations by Edlen.
Abstract: Measured wavelengths of the lithiumlike Se xxxii resonance lines and the berylliumlike Se xxxi resonance and intercombination line are compared with the isoelectronic extrapolations by Edlen. Also, a number of other transitions from oxygenlike Se xxvii to boronlike Se xxx are identified.
TL;DR: In this article, the eddy current induced on the Tokamak Fusion Test Reactor vacuum vessel during compression experiments is estimated based on a cylindrical model, which produces an error magnetic field that generates an error current.
Abstract: The eddy current induced on the Tokamak Fusion Test Reactor vacuum vessel during compression experiments is estimated based on a cylindrical model. It produces an error magnetic field that generate...
TL;DR: In this article, a deuterium-tritium (D-T) neutron point source simulating the extended fusion plasma neutron source in the Tokamak Fusion Test Reactor (TFTR) at the Princeton Plasma Physics Laboratory is reported.
Abstract: Spectral distributions of high-energy neutrons (0.9 less than or equal to E/sub n/ less than or equal to 14.5 MeV) and of high-energy gamma rays (0.4 less than or equal to E/sub ..gamma../ less than or equal to 9.4 MeV) due to a deuterium-tritium (D-T) neutron point source simulating the extended fusion plasma neutron source in the Tokamak Fusion Test Reactor (TFTR) at the Princeton Plasma Physics Laboratory are reported. A D-T neutron generator was positioned inside the vacuum vessel at ten different locations around the torus. Neutrons and gamma rays were detected by a liquid-scintillator-based detector (4.65-cm diam X 4.22 cm high) with electronic pulse-shape discrimination to differentiate between events in the detector due to incident neutrons and those due to incident gamma rays. The detector was placed on the median plane of the reactor at 8.85 m from the geometric center of the TFTR. Two spectral distributions, one for neutrons and the other for gamma rays, were obtained for each of 18 measurements. The neutron data exhibit a high-energy peak dominated by uncollided primary-energy neutrons and a low-energy contribution from the scattered neutrons. The gamma-ray data exhibit a high-energy contribution due to neutron capture gamma rays and amore » low-energy contribution due to gamma rays following neutron inelastic scattering reactions.« less
TL;DR: In this article, the important impurities in TFTR plasmas are carbon and oxygen, and the impurity concentration as a function of edge electron temperature is compared with a simple sputtering model, which shows the importance of C-C and O-C sputtering at the limiter in addition to fuel gas sputtering in explaining the observed carbon concentration.
TL;DR: In this paper, the authors observed that high Ip, high ne TFTR discharges exhibit a strong density increase throughout most of the period of 0.5 s neutral beam pulses.
01 Jul 1987
TL;DR: In this article, it was shown that the D-T fusion reaction can be modified by polarizing the nuclear spins and the ways in which this improves reactor performance are mentioned and the feasibility of the process of spin polarization of magnetic fusion is discussed.
Abstract: It is shown that the D-T fusion reaction can be modified by polarizing the nuclear spins. The ways in which this improves reactor performance are mentioned and the feasibility of the process of spin polarization of magnetic fusion is discussed.
TL;DR: The tandem mirror and tokamak are being considered as candidate fusion drivers for a materials production reactor that could be implemented in the 1990s, and their performance characteristics are compared with the present state of the art.
Abstract: The tandem mirror and tokamak are being considered as candidate fusion drivers for a materials production reactor that could be implemented in the 1990s. This report considers, in detail, the required performance characteristics of the fusion plasma and the major technological subsystems for each fusion driver. These performance characteristics are compared with the present state of the art, corresponding development needs are identified, and technology program requirements, in addition to those now being supported by the Department of Energy, are pointed out. The tandem mirror and tokamak fusion drivers are also compared with regard to their required advancements in plasma performance and technology development.
TL;DR: In this article, a computer code, DSTAR, has been developed to quantitify the surface erosion and induced forces that can occur during major tokamak plasma disruptions, and a disruption analysis has been performed with DSTAR for the TFCX device.
01 Jul 1987
TL;DR: The D-3He reaction has the same spin dependence as the d-t reaction and it produces no neutrons so that if the D-d reactivity could be reduced it would lead to a neutron-clean reactor.
Abstract: The D-3He reaction has the same spin dependence as the d-t reaction. It produces no neutrons so that if the d-d reactivity could be reduced it would lead to neutron-clean reactor. The current understanding of the possible suppression of the d-d reactivity by spin polarization is discussed. The question as to whether a suppression is possible is still unresolved. Other advanced fuel reactions are briefly discussed.
TL;DR: The complement of CAMAC hardware systems and components that comprise the interface for tokamak control and measurement instrumentation, and communication with the central instrumentation control and data acquisition (CICADA) system are described and discussed.
Abstract: Princeton's tokamak fusion test reactor (TFTR) utilizes Computer Automated Measurement and Control (CAMAC) to provide instrumentation for real and quasi real time control, monitoring, and data acquisition systems. This paper describes and discusses the complement of CAMAC hardware systems and components that comprise the interface for tokamak control and measurement instrumentation, and communication with the central instrumentation control and data acquisition (CICADA) system. It also discusses CAMAC reliability and calibration, types of modules used, a summary of data acquisition and control points, and various diagnostic maintenance tools used to support and troubleshoot typical CAMAC systems on TFTR.
TL;DR: In this paper, a stainless steel vacuum vessel and a chromium sublimation source were assembled to simulate the arrangement in TFTR and the results indicated that the residual effects of the chromium film on the vacuum are due to reduced outgassing of the stainless steel surface.
TL;DR: In this article, the simulation of auroral double layers with realistic particle-in-cell models is presented, and an early model simulated weak DLs formed in a self-consistent circuit but under conditions subject to the ion-acoustic instability.
Abstract: Work on the simulation of auroral double layers (DLs) with realistic particle-in-cell models is presented. An early model simulated weak DLs formed in a self-consistent circuit but under conditions subject to the ion-acoustic instability. Recent work has focused on strong DLs formed when currentless jets are injected into a dipole magnetic field.