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Showing papers by "Princeton Plasma Physics Laboratory published in 1989"


Journal ArticleDOI
TL;DR: A sharp transport barrier, accompanied by a bifurcated poloidal rotation and a radial electric field, is formed at the plasma edge by driving a radial current across the outer magnetic surfaces of a tokamak.
Abstract: A sharp transport barrier, accompanied by a bifurcated poloidal rotation and a radial electric field, is formed at the plasma edge by driving a radial current across the outer magnetic surfaces of a tokamak. A decrease in particle transport is observed for negative radial E fields. When the radial current is turned off, the E field and the rotation damp on a time scale comparable with the ion-ion collision time.

527 citations


Journal ArticleDOI
TL;DR: Polarimetry measurements of the Doppler-shifted H{sub {alpha}} emission from a neutral hydrogen beam on the PBX-M tokamak have been employed in a novel technique for obtaining {ital q}({ital r}) and magnetic field pitch-angle profiles using the Stark effect.
Abstract: Polarimetry measurements of the Doppler-shifted H{sub {alpha}} emission from a neutral hydrogen beam on the PBX-M tokamak have been employed in a novel technique for obtaining {ital q}({ital r}) and magnetic field pitch-angle profiles using the Stark effect. The resulting {ital q}({ital r}) profile is very broad and its central value, {ital q}(0), is significantly below 1, which has important implications for theoretical models of sawteeth.

332 citations


Journal ArticleDOI
TL;DR: In this paper, the atomic processes involved in the stopping (or effective ionization) of the neutral beam atoms were studied in detail for the energy range from 10 keV/u to 10 MeV/U.
Abstract: The efficiency of neutral beam heating and current drive depends crucially on the deposition of the energy and momentum of the beam in the plasma. This deposition is determined by the atomic processes involved in the stopping (or effective ionization) of the neutral beam atoms. These processes have been studied in detail for the energy range from 10 keV/u to 10 MeV/u. The processes considered include both the ground state and the excited state of the beam atoms, thus allowing for the multistep ionization of the beam in collisions with the plasma constituents and impurities. The effective beam stopping cross-section has been calculated for a wide variety of beam and plasma parameters. The atomic database necessary for these calculations has been documented using the best data available at present. The stopping cross-section data are also given in terms of a convenient analytic fit, which can be used either in computer calculations or for simpler analytic estimates of neutral beam penetration.

134 citations


Journal ArticleDOI
TL;DR: Central ion temperatures up to 30 keV and rotation speeds up to 8/times/10/sup 5/ m/sec have been confirmed with new diagnostic measurements in the TFTR hot-ion enhanced-confinement regime, and the ion thermal diffusivity is found to be non-neoclassical and comparable to the anomalous electron thermal diffuse.
Abstract: Central ion temperatures up to 30 keV and rotation speeds up to 8/times/10/sup 5/ m/sec have been confirmed with new diagnostic measurements in the TFTR hot-ion enhanced-confinement regime, and the ion thermal diffusivity is found to be non-neoclassical and comparable to the anomalous electron thermal diffusivity. The dominant effect of strong rotation is the down-shifting of the neutral beam energies in the plasma frame, which results in reduced ion and electron heating on axis, and the presence of off-axis ion heating from viscous damping of the plasma rotation.

59 citations


Journal ArticleDOI
TL;DR: In this article, the authors present the history, state of the art, and the plans and prospects for antennas and transmission lines for RF heating in fusion devices, and evaluate the information needed to develop realistic antenna designs for a reactor environment.
Abstract: RF power is widely used as an auxiliary heating method in fusion devices. This paper reviews the relevant theoretical considerations for the ion cyclotron, lower hybrid and electron cyclotron ranges of frequency, and presents the history, the state of the art, and the plans and prospects for antennas and transmission lines for RF heating. Reactor-relevant concerns are discussed, and the information needed to develop realistic antenna designs for a reactor environment is assessed.

57 citations


Journal ArticleDOI
TL;DR: In this article, the STEP code predicts global unstable modes numerically, where D I is the Mercier parameter whose shear stabilization term is normalized as -1/4. And the relation between the MERCIER stability criterion and low-n stability limit with respect to pressure driven modes is clarified, where n is a toroidal mode number.
Abstract: Two-dimensional MHD equilibrium and stability codes based on the stellarator expansion provide a good description of the properties of three-dimensional stellarator configurations. Improvements and extensions of the two-dimensional stellarator expansion of such codes with a particular emphasis on the STEP code are discussed. Three-dimensional equilibria of the ATF Torsatron at zero and finite beta are given. The relation between the Mercier stability criterion and low- n stability limit with respect to pressure driven modes is clarified, where n is a toroidal mode number. Whenever \(D_{I}{\gtrsim}0.2\), the STEP code predicts global unstable modes numerically, where D I is the Mercier parameter whose shear stabilization term is normalized as -1/4. The second stability regime is realized by controlling the magnetic axis position by the vertical field in an l =2 and M =12 torsatron/heliotron configuration, where l is a pole number and M is a helical period number of the magnetic field.

42 citations


Journal ArticleDOI
TL;DR: In this paper, graphite bumper limiter tiles and metal surfaces have been studied to understand material transport by the plasma in the TFTR tokamak, and the correlation of limiter deposits with the type of discharges in TFTR indicates that the material composition depth distribution was determined by the TOKAMAK operational history.

33 citations


Journal ArticleDOI
TL;DR: In this paper, a distinct ion mode (i.e., density fluctuations propagating in the ion diamagnetic drift direction) is observed in the microturbulence spectra.
Abstract: For high density Ohmic discharges in the TEXT tokamak, a distinct ion mode (i.e. density fluctuations propagating in the ion diamagnetic drift direction) is observed in the microturbulence spectra. The magnitude and spectral characteristics of the mode are identified. A microinstability based transport model is used for the purpose of interpreting anomalous confinement properties. Onset of the ion feature occurs at plasma densities where a clear saturation is evident in the global energy confinement time τE. When the ion feature in the fluctuation spectra is strongest, agreement between predictions from the transport model and experimentally measured values of the global energy confinement time is realized if anomalous ion effects due to the ion pressure gradient driven (ηi) instability are included. By injecting pellets, a high density plasma is created in which the density profile is sharply peaked. Under these conditions the ion feature in the fluctuation spectra is suppressed. A possible connection between this experimentally observed ion mode and the theoretically predicted properties of the ηi instability is explored.

32 citations


Journal ArticleDOI
TL;DR: In this article, the authors derived Hamiltonian equations for the gyrophase-averaged nonrelativistic motion of charged particles in a perturbed dipole magnetic field.
Abstract: In order to study nonlinear wave-particle interactions in the Earth's magnetosphere we have derived Hamiltonian equations for the gyrophase-averaged nonrelativistic motion of charged particles in a perturbed dipole magnetic field. We assume low frequency (less than the proton gyrofrequency) fully electromagnetic perturbations, and we retain finite Larmor radius effects. Analytic and numerical results for the stochastic threshold of energetic protons ({approx gt}100 keV) in compressional geomagnetic pulsations in the Pc 5 range of frequencies 150--600 seconds are presented. These protons undergo a drift-bounce resonance with the Pc 5 waves which breaks the second (longitudinal) and third (flux) adiabatic invariants, while the first invariant (the magnetic moment) and the proton energy are approximately conserved. The proton motion in the observed spectrum of waves is found to be strongly diffusive, due to the overlap of neighboring primary resonances. {copyright} American Geophysical Union 1989

29 citations


Journal ArticleDOI
TL;DR: Gain measurements in C VI at 18.22 nm for a soft-x-ray amplifier produced by a line-focused glass laser (1.053 microm) on a solid carbon target are presented.
Abstract: We present recent gain measurements in C VI at 18.22 nm for a soft-x-ray amplifier produced by a line-focused glass laser (1.053 microm) on a solid carbon target. The maximum gain measured was 8 +/- 2 cm(-1) in the recombining plasma column, with additional radiation cooling, with additional radiation cooling by iron impurities.

24 citations


Journal ArticleDOI
TL;DR: In this article, a two-dimensional emissivity profile was reconstructed from the soft X-ray data using a tomography technique, and it was found that the soft x-ray fluctuations reflect the relaxation mechanism of the RFP plasma.
Abstract: Soft X-ray measurements have been made with surface barrier diode (SBD) arrays in the REPUTE-1 RFP device (R/a = 82/22 cm). Arrays of seven and eleven SBDs are arranged so that they view a minor cross-section of the plasma from the vertical and horizontal diagnostic ports, respectively. Applying the tomography technique to the soft X-ray data, a two-dimensional emissivity profile can be reconstructed. In the sustainment phase of the RFP discharge, the soft X-ray emissivity profile exhibits a periodic peaking and a subsequent large crash across the minor cross-section. The fluctuation period is in the range of 60–150 μs, whereas the duration of the large crash is always about 30 μs (corresponding to ~ 100 × τA, where τA is the Alfven transit time). The soft X-ray emission is due to two modes: one is a dominantly m = 0 mode, which corresponds to the axisymmetric increase or decrease of the soft X-ray emissivity profile, and the other is an m = 1 mode. The toroidal correlation length of the m = 0 mode ranges from 20° to 80°, while the m = 1 mode has a high toroidal mode number. In the crash process, an m = 1 distortion of the emissivity profile, which indicates reconnection of the flux surfaces, can be observed. The magnetic fluctuations observed simultaneously are well correlated with the soft X-ray fluctuations. It is found that the soft X-ray fluctuations reflect the relaxation mechanism of the RFP plasma. This phenomenon is considered to be driven by global MHD activity.

Journal ArticleDOI
TL;DR: A zero-dimensional transport code formulated with theoretical drift wave models having an ad hoc q-dependence is used to estimate ignition conditions for the proposed Compact Ignition Tokamak (CIT).
Abstract: A zero-dimensional transport code formulated with theoretical drift wave models having an ad hoc q-dependence is used to estimate ignition conditions for the proposed Compact Ignition Tokamak (CIT). The theoretical models are normalized to tokamak confinement time data over a wide range of density, field and size (ISX, TFTR, DIII, DIII-D, JET) for L- and H-modes. The fit coefficient for the dissipative trapped electron (DTE) mode is fixed by low density Ohmic discharges and the coefficient for the ion temperature gradient (ITG) mode is fixed by beam heated discharges. While the theoretical models are almost indistinguishable from the standard (Kaye-Goldston) empirical model in fitting the available data, they have significant quantitative and qualitative differences on projection to ignition. The empirical model fails to account for the unfavourable temperature scaling of the DTE mode masked in Ohmic heating and the favourable density scaling of the ITG mode masked by beam penetration and impurity line radiation effects in the present experiments. The ignition conditions are analysed with explicit formulas for the minimum required auxiliary power Pm and a figure of merit FM given essentially by the radio of ?MHD to the minimum beta on the ignition curve BM[FM = BM5/6, QM = 5 FM/(1 - FM)] Both Pm and BM have strong favourable scaling with size (a) and field (B) and depend sensitively on the normalization of confinement time within the scatter of the data, f = ?exp/?model: BM?1 (BMDTE)?1 + (BMITG)?1 where BMDTE = 1.47 (a/55 cm)2 (B/100 kG)3 fOH1.2 and BMITG = 1.14 (a/55 cm)4 ? (B/100 kG)5 faux2.5 (?/2.5)2.5 for the standard CIT broad density profile case parameters, ? = ?H/?L corresponds to the factor 2.5 improvement in H over L confinement time. Clearly, when ITG dominates, BMJ ~ O(10) BML. The minimum ignition densities nm are typically in excess of Ohmic density limits scaling with current density, but it is demonstrated that sufficient auxiliary power can burn out line radiation, allowing operation at higher densities.

Journal ArticleDOI
TL;DR: The experimentally determined transition energies were compared to the transition energies calculated using the multiconfiguration Dirac-Fock technique and find significant discrepancies between the experimental and calculated transition energies.
Abstract: The 4${s}_{1/2}$-4${p}_{1/2}$ and 4${s}_{1/2}$-4${p}_{3/2}$ transitions in the Cu-like ions of the elements Sn, Xe, La, Nd, Eu, Gd, Dy, and Yb (atomic numbers Z=50, 54, 57, 60, 63, 64, 66, and 70) have been observed in the spectra from the Princeton Large Torus tokamak. The experimentally determined transition energies were compared to the transition energies calculated using the multiconfiguration Dirac-Fock technique. By including previously published observations, the experimental and calculated transition energies were compared for the entire Cu i isoelectronic sequence from Ru (Z=44) to U (Z=92). Contrary to the conclusion of Cheng and Wagner [Phys. Rev. A 36, 5435 (1987)], we find significant discrepancies between the experimental and calculated transition energies. The discrepancies are attributable to electron correlation corrections that are not accounted for in the calculation.

Journal ArticleDOI
TL;DR: In this paper, a two-step tokamak regression procedure was applied to L-mode confinement data and the resulting scaling expression for?E: is similar to other published scaling expressions.
Abstract: The authors apply a two-step tokamak regression procedure to L-mode confinement data. The resulting scaling expression for ?E: is similar to other published scaling expressions. Using the random coeffcient model, tokamak-to-tokamak variations are included in the estimate of the uncertainty. The uncertainty factor in the predicted confinement times is calculated to be 19% for ITER and 35% for CIT. The confinement uncertainties are dominated by the propagation of uncertainties arising from the tokamak-to-tokamak variation in scalings with q and n to the second-step regression and, for CIT, by the lack of high magnetic field, moderate size devices in the L-mode database.

Journal ArticleDOI
TL;DR: The quenching of Einstein {ital A} coefficients was observed by measuring the branching ratio of visible and extreme-ultraviolet line intensities for C IV, C III, and N V ions.
Abstract: The quenching of Einstein {ital A} coefficients was observed by measuring the branching ratio of visible and extreme-ultraviolet line intensities for C IV, C III, and N V ions.

Journal ArticleDOI
TL;DR: The primary purpose of the Maintenance Manipulator is to provide a means of remotely performing certain defined maintenance and inspection tasks inside the vacuum torus so as to minimize personnel exposure to radiation.

Journal ArticleDOI
TL;DR: In this paper, a coupled forward-adjoint algorithm, employing both the deterministic and Monte Carlo sampling methods, was presented to model the neutron transport in the complex tokamak and detector geometries.
Abstract: Neutron transport simulations have been carried out to calculate the absolute detection efficiency of a moderated /sup 235/U neutron detector which is used on the TFTR as a part of the primary fission detector diagnostic system for measuring fusion power yields. Transport simulations provide a means by which the effects of variations in various shielding and geometrical parameters can be explored. These effects are difficult to study in calibration experiments. The calculational model, benchmarked against measurements, can be used to complement future detector calibrations, when the high level of radioactivity resulting from machine operation may severely restrict access to the tokamak. We present a coupled forward-adjoint algorithm, employing both the deterministic and Monte Carlo sampling methods, to model the neutron transport in the complex tokamak and detector geometries. Sensitivities of the detector response to the major and minor radii, and angular anisotropy of the neutron emission are discussed. A semi-empirical model based on matching the calculational results with a small set of experiments produces good agreement (+-15%) for a wide range of source energies and geometries. 20 refs., 6 figs., 4 tabs.

Journal ArticleDOI
TL;DR: Although the total radiated power in the Tokamak Fusion Test Reactor is often as high as 70% of the heating power, most of the radiation is concentrated near the surface of the plasma, and the inte...
Abstract: Although the total radiated power in the Tokamak Fusion Test Reactor is often as high as 70% of the heating power, most of the radiation is concentrated near the surface of the plasma, and the inte...

Journal ArticleDOI
TL;DR: In this article, the authors investigated plasma-material interaction processes that will affect this first tritium-fueled tokamak and derived estimates of the in-vessel inventory for the Tokamak Fusion Test Reactor (TFTR).

Journal ArticleDOI
TL;DR: In this paper, the effect of releasing carbon and methane into TFTR was modeled using the DEGAS code and the carbon neutral transport at the boundary of the plasma boundary layer.

Journal ArticleDOI
TL;DR: The PBX-M Neutral Probe Beam Project was initiated to design, fabricate, acceptance-test, install, and commission an 80 kV, 2.7 GHz neutral probe beam for use in q-profile measurements as discussed by the authors.
Abstract: The PBX-M Neutral Probe Beam Project was initiated to design, fabricate, acceptance-test, install, and commission an 80 kV, 2.7 A neutral probe beam for use in PBX-M q-profile measurements. The 100 ms, H° output beam is modulated at 1 kHz and has a pulse repetition rate of 3 min. The beam has a divergence of 0.5° and a focal length of 400 cm. The injection angle can be varied about 25°, from near perpendicular to outboard tangential. The beamline is shielded from magnetic fields and interfaces to the existing mechanical, electrical, and control systems of PBX-M.

Journal ArticleDOI
TL;DR: In this paper, the performance of atmospheric detritiation systems and possible ways for improving their performance were investigated, and small-scale experiments demonstrated that system performance is strongly dependent on catalyst bed temperature.
Abstract: An investigation of the performance of atmospheric detritiation systems and of possible ways for improving their performance was undertaken. Small-scale experiments demonstrated that system performance is strongly dependent on catalyst bed temperature. That may be helped by addition of protium to the process gas stream, but added protium at constant temperature does not increase conversion to HTO. Collection of the HTO on dry sieve with residual HTO fraction of less than one part in 10/sup 7/ was observed. Ways suggested for improvement in collection of HTO on molecular sieve beds include adding H/sub 2/O to the stream entering the molecular sieve and premoistening of the sieve with H/sub 2/O. While these improvement schemes may reduce HTO emissions they increase the amount of tritiated waste that must be handled.

Journal ArticleDOI
TL;DR: By simulating data numerically, the authors can estimate the informative worth of data prior to obtaining it, and tractable a statistical analysis that compares essentially all parameter sets that might possibly explain the transient signal.
Abstract: A brief, deliberate, perturbation of hot tokamak electrons produces a transient, synchrotron radiation signal, in frequency-time space, with impressive informative potential on plasma parameters; for example, the dc toroidal electric field, not available by other means, may be measurable. Very fast algorithms have been developed, making tractable a statistical analysis that compares essentially all parameter sets that might possibly explain the transient signal. By simulating data numerically, we can estimate the informative worth of data prior to obtaining it.

Journal ArticleDOI
TL;DR: Tritium retention noted in graphite tiles underscores the significance of material selection in present and future 3H-fueled fusion devices.
Abstract: The Princeton Plasma Physics Laboratory (PPPL) began fusion experiments in 1951. In the early years, the major health physics concerns were associated with x radiation produced by energetic electrons in the plasma. Within the past year, neutron and 3H production from 2H-2H (represented hereafter as D-D) reactions has increased significantly on the larger fusion devices. Tritium retention noted in graphite tiles underscores the significance of material selection in present and future 3H-fueled fusion devices. This paper reports on operational health physics radiation measurements made on various PPPL machines over the past 10 y.

Journal ArticleDOI
TL;DR: The theory of carbon transport in a plasma boundary layers is important for understanding the impurity penetration, and carbon and hydrogen recycling, in tokamaks using carbon compounds as limiters and as wall coatings.
Abstract: The theory of carbon transport in a plasma boundary layers is important for understanding the impurity penetration, and carbon and hydrogen recycling, in tokamaks using carbon compounds as limiters and as wall coatings. Neutral carbon kinetics and transport at the edge of plasma devices where chemical release is a source of carbon are modeled. Plasma reactions with carbon and hydrocarbons are important for such modeling, and these collisional processes are summarized. Combining the reaction schemes and kinetics in the DEGAS code makes it possible to treat the neutral transport at the plasma boundary layer. Results of such modeling of the atomic carbon and methane distribution at the edge are presented for comparison with recent carbon probe experiments performed on the Divertor and Injection Tokamak Experiment (DITE).

Book ChapterDOI
TL;DR: The Tokamak Fusion Test Reactor (TFTR) vacuum vessel was opened in July, 1987 for a period of seven months in order to install and refurbish in-vessel hardware as discussed by the authors.
Abstract: The Tokamak Fusion Test Reactor (TFTR) vacuum vessel was opened in July, 1987 for a period of seven months in order to install and refurbish in-vessel hardware. The primary purpose of this shutdown was to install two ICRF antennas and reorient the neutral beam injectors for balanced injection at full power. The in-vessel work consisted of six major tasks. A vacuum leak in a vessel bellows segment designed to increase the toroidal resistance of the vessel was exposed and welded over. All 36 of the Surface Pumping System panels were removed from the vessel and rebuilt without the Zr/A1 pumping modules as the result of a flaking problem which compromised tritium compatability. The rebuilt panels were replaced in the machine to provide protection for the bellows. Most of the carbon tiles on the inner toroidal Bumper Limiter were removed, sanded clean of metal deposits, and replaced in the vessel. To protect the vacuum vessel from damage due to neutral beam shinethrough and faults, new first-wall protective plates were installed. In order to protect the new ICRF antennas, two new limiters fabricated from a carbon-carbon composite material were installed, replacing the Moveable Limiter which was removed. Extensive in-vessel diagnostic installation and calibration occurred. All of these activities were significantly complicated due to the in-vessel hardware having become radioactive by neutron activation during the previous run period and the presence in the vessel of removable tritium surface contamination exceeding 17 Bq/100 cm 2 (1000 dpm/100 cm 2 ).

Book ChapterDOI
TL;DR: The neutral beam permissive system on TFTR is designed to prevent damage to the protective plates during neutral beam injection as mentioned in this paper, which is used in conjunction with an administrative procedure to ensure appropriate settings of the thresholds for the requested power and duration.
Abstract: The neutral beam permissive system on TFTR is designed to prevent damage to protective plates during neutral beam injection. The protective plates shield the vacuum vessel from direct neutral beam bombardment. They are not capable of withstanding an unattenuated 3.2 MW, 35 MW/m 2 , 2-second duration pulse from a single source. An active measurement of the protective plate surface temperature was forgone in favor of a system based upon comparison of various plasma parameters to thresholds. This system is used in conjunction with an administrative procedure to ensure appropriate settings of the thresholds for the requested power and duration. The system is used to afford some protection to the RF limiters as well.

Journal ArticleDOI
TL;DR: In this paper, the authors estimate the deformation of magnetic surfaces during sawtooth crashes by comparing experimental observations of X-rays and ECE electron temperature with a simple simulation which calculates signals of line-integrated X-ray and local electron temperature assuming rigid rotation of the plasma.
Abstract: The m =1 island size or m =1 deformation of magnetic surfaces during sawtooth crashes is estimated on TFTR by comparing experimental observations of X-rays and ECE electron temperature with a simple simulation which calculates signals of line-integrated X-ray and local electron temperature assuming rigid rotation of the plasma. Sawteeth oscillations with a slow crash (τ crash ∼several ms) can be simulated by a Kadomtsev-type reconnection model in which an m =1 island grows to the size of the q =1 surface during the sawtooth crash. In the sawteeth which have a fast crash (50 µs∼τ crash ∼500 µs), the m =1 island size sometimes (not always) becomes ∼1/2 of the sawtooth inversion radius during the crash phase. The final structure, however, is hard to identify, because of the slow plasma rotation frequency. The “Hot Core” appears to move away from the plasma center in a Kadomtsev-type reconnection without causing very large transport or diffusion.

Journal ArticleDOI
TL;DR: In this paper, the authors describe the increased activities of the health physics staff in providing measurement techniques, contamination control, written procedural requirements, and the radiation training instituted for ensuring the safety of the employees.

Journal ArticleDOI
TL;DR: In this article, a computational procedure is developed to include the structure in the determination of coil current and voltage trajectories to achieve a specified equilibrium evolution and drive the required plasmas.
Abstract: A computational procedure is developed to include the structure in the determination of coil current and voltage trajectories to achieve a specified equilibrium evolution and drive the required pla