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Showing papers by "Princeton Plasma Physics Laboratory published in 1996"


Journal ArticleDOI
TL;DR: In this paper, a set of nonlinear gyrofluid equations for simulations of tokamak turbulence are derived by taking moments of the nonlinear toroidal gyrokinetic equation.
Abstract: A set of nonlinear gyrofluid equations for simulations of tokamak turbulence are derived by taking moments of the nonlinear toroidal gyrokinetic equation The moment hierarchy is closed with approximations that model the kinetic effects of parallel Landau damping, toroidal drift resonances, and finite Larmor radius effects These equations generalize the work of Dorland and Hammett [Phys Fluids B 5, 812 (1993)] to toroidal geometry by including essential toroidal effects The closures for phase mixing from toroidal ∇B and curvature drifts take the basic form presented in Waltz et al [Phys Fluids B 4, 3138 (1992)], but here a more rigorous procedure is used, including an extension to higher moments, which provides significantly improved accuracy In addition, trapped ion effects and collisions are incorporated This reduced set of nonlinear equations accurately models most of the physics considered important for ion dynamics in core tokamak turbulence, and is simple enough to be used in high resolution

186 citations


Journal ArticleDOI
TL;DR: Turbulent fluctuations in plasmas with reversed magnetic shear investigated on the Tokamak Fusion Test Reactor are found to be consistent with the suppression of turbulence by the E x B velocity shear.
Abstract: Turbulent fluctuations in plasmas with reversed magnetic shear have been investigated on the Tokamak Fusion Test Reactor. Under intense auxiliary heating, these plasmas are observed to bifurcate into two states with different transport properties. In the state with better confinement, it has been found that the level of fluctuations is very small throughout most of the region with negative shear. By contrast, the state with lower confinement is characterized by large bursts of fluctuations which suggest a competition between the driving and the suppression of turbulence. These results are consistent with the suppression of turbulence by the $\mathbf{E}\ifmmode\times\else\texttimes\fi{}\mathbf{B}$ velocity shear.

173 citations


Journal ArticleDOI
TL;DR: Mc McGuire et al. as discussed by the authors showed that the amount of lithium on the limiter and the effectiveness of its action can be maximized through injecting four Li pellets into Ohmic plasmas of increasing major and minor radius.
Abstract: Wall conditioning in the Tokamak Fusion Test Reactor (TFTR) [K. M. McGuire et al., Phys. Plasmas 2, 2176 (1995)] by injection of lithium pellets into the plasma has resulted in large improvements in deuterium–tritium fusion power production (up to 10.7 MW), the Lawson triple product (up to 1021 m−3 s keV), and energy confinement time (up to 330 ms). The maximum plasma current for access to high‐performance supershots has been increased from 1.9 to 2.7 MA, leading to stable operation at plasma stored energy values greater than 5 MJ. The amount of lithium on the limiter and the effectiveness of its action are maximized through (1) distributing the Li over the limiter surface by injection of four Li pellets into Ohmic plasmas of increasing major and minor radius, and (2) injection of four Li pellets into the Ohmic phase of supershot discharges before neutral‐beam heating is begun.

168 citations


Journal ArticleDOI
TL;DR: In this article, the authors calculated the effective rate coefficient for plasma recombination taking into account the plasma chemical reactions with vibrationally excited molecules and showed that the large size of this rate coefficient and its specific dependence on plasma parameters may explain the anomalously fast plasma recombinations experimentally observed on many divertor tokamaks.

111 citations


Journal ArticleDOI
TL;DR: In this article, a set of nonlinear fluid equations for mirror-trapped electrons is developed which differs from conventional fluid equations in two main respects: (1) the trapped•fluid moments average over only two of three velocity space dimensions, retaining the full pitch angle dependence of the trapped electron dynamics, and (2) closure approximations include the effects of collisionless waveparticle resonances with the toroidal precession drift.
Abstract: A novel set of nonlinear fluid equations for mirror‐trapped electrons is developed which differs from conventional fluid equations in two main respects: (1) the trapped‐fluid moments average over only two of three velocity space dimensions, retaining the full pitch angle dependence of the trapped electron dynamics, and (2) closure approximations include the effects of collisionless wave‐particle resonances with the toroidal precession drift. Collisional pitch angle scattering is also included. By speeding up calculations by at least √mi/me, these bounce averaged fluid equations make possible realistic nonlinear simulations of turbulent particle transport and electron heat transport in tokamaks and other magnetically confined plasmas.

60 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated the resistive evolution of presheared magnetic arcades in a two-dimensional Cartesian geometry and found that there is a critical value of shear over which magnetic reconnection can take place in a magnetic arcade to create a magnetic island.
Abstract: The resistive evolution of presheared magnetic arcades in a two-dimensional Cartesian geometry is investigated. We find that there is a critical value of shear over which magnetic reconnection can take place in a magnetic arcade to create a magnetic island. The diffusion of the toroidal field eventually leads to thinning of the current layer for any amount of shear, whereas the diffusion of the poloidal field brings about current layer thinning only for shears above the critical value. The reconnection profiles are found to depend on spatial resistivity patterns. A fast reconnection with small shock angles can be achieved only when the resistivity is confined to a small volume. In this case, high-speed reconnection outflows can tear the magnetic island into a pair. The fast moving island system creates a fast shock or a steepened fast-mode structure, which resembles an observed coronal mass ejection (CME) frontal loop.

56 citations


Journal ArticleDOI
TL;DR: In this paper, Monte Carlo neutral transport simulations of hydrogen velocities in the Tokamak Fusion Test Reactor (TFTR) are compared with experiment using the Doppler-broadened Balmer-α spectral line profile.
Abstract: Monte Carlo neutral transport simulations of hydrogen velocities in the Tokamak Fusion Test Reactor (TFTR) [K. M. McGuire et al., Phys. Plasmas 2, 2176 (1995)] are compared with experiment using the Doppler‐broadened Balmer‐α spectral line profile. Good agreement is obtained under a range of conditions, validating the treatment of charge exchange, molecular dissociation, surface reflection, and sputtering in the neutral gas code DEGAS [D. Heifetz et al., J. Comput. Phys. 46, 309 (1982)]. A residual deficiency of 10–100 eV neutrals in most of the simulations indicates that further study of the energetics of H+2 dissociation for electron energies in excess of 100 eV is needed.

56 citations


Journal ArticleDOI
TL;DR: The first experimental demonstration that mode conversion from the fast magnetosonic wave to an ion Bernstein wave can efficiently heat electrons and drive current with low field side antennas in a tokamak plasma is reported.
Abstract: The first experimental demonstration that mode conversion from the fast magnetosonic wave to an ion Bernstein wave can efficiently heat electrons and drive current with low field side antennas in a tokamak plasma is reported. Up to 130 kA of current was noninductively driven, on and off axis, and the resultant current profiles were measured in the Tokamak Fusion Test Reactor. In heating experiments, 10 keV peak electron temperatures were produced with 3.3 MW of radio-frequency heating power. {copyright} {ital 1996 The American Physical Society.}

48 citations


Journal ArticleDOI
TL;DR: Evidence for fusion heating in the core of a deuterium-tritium (D-T) tokamak plasma is reported for the first time.
Abstract: Evidence for fusion heating in the core of a deuterium-tritium (D-T) tokamak plasma is reported for the first time. Electron temperature profile data were analyzed for differences between D-T, D, and T plasmas in the Tokamak Fusion Test Reactor. Data from D and D-T plasmas with similar plasma parameters were averaged to minimize isotopic effects. The electron temperature in D-T plasmas was systematically higher than in D or T plasmas. The temperature difference between D-T and D plasmas with similar confinement times is consistent with alpha-particle heating of electrons.

47 citations


Journal ArticleDOI
TL;DR: In this article, the ideal MHD evolution of a single magnetic arcade undergoing footpoint motions in a two-dimensional Cartesian geometry is investigated using numerical simulation, and force-free states of the same arcade are constructed with the use of a magnetofrictional method.
Abstract: The ideal MHD evolution of a single magnetic arcade undergoing footpoint motions in a two-dimensional Cartesian geometry is investigated using numerical simulation. Also, force-free states of the same arcade are constructed with the use of a magnetofrictional method, which is formulated differently from those used in previous studies. In MHD simulations, no instability or nonequilibrium is found to the value of shear 100 times as large as the footpoint separation in the potential field. The evolutionary sequence is composed of three distinct phases. The first phase is characterized by the increase of the toroidal field strength and the second phase by a sort of self-similar expansion. In the third phase, the formation and growth of a central current layer are conspicuous. With increasing shear, the maximum current density increases, the width of the current layer decreases, and the feet of the current layer, which bifurcates above the bottom boundary, get closer to each other. The field lines in the current layer tend to thread the bottom boundary nearly horizontally for a large shear. From our results, it is inductively inferred that the magnetic arcade in a two-dimensional Cartesian geometry approaches an open field as the shear increases indefinitely.

42 citations


Journal ArticleDOI
TL;DR: Transitions in heliumlike krypton (Kr{sup 34+}) have been made on the Electron Beam Ion Trap (EBIT) facility at the Lawrence Livermore National Laboratory and the results are in good agreement with recent theoretical predictions.
Abstract: Measurements of the 1s2${\mathit{p}}^{1}$${\mathit{P}}_{1}$\ensuremath{\rightarrow}1${\mathit{s}}^{2\mathrm{}1}$${\mathit{S}}_{0}$, 1s2${\mathit{p}}^{3}$${\mathit{P}}_{2}$\ensuremath{\rightarrow}1${\mathit{s}}^{2\mathrm{}1}$${\mathit{S}}_{0}$, 1s2${\mathit{p}}^{3}$${\mathit{P}}_{1}$\ensuremath{\rightarrow}1${\mathit{s}}^{2\mathrm{}1}$${\mathit{S}}_{0}$, and 1s2${\mathit{s}}^{3}$${\mathit{S}}_{1}$\ensuremath{\rightarrow}1${\mathit{s}}^{2\mathrm{}1}$${\mathit{S}}_{0}$ transitions in heliumlike krypton (${\mathrm{Kr}}^{34+}$) have been made on the Electron Beam Ion Trap (EBIT) facility at the Lawrence Livermore National Laboratory. The measurements were performed using a high-resolution crystal spectrometer and an accuracy of about 30 ppm was achieved. Unlike earlier measurements, our results are in good agreement with recent theoretical predictions. \textcopyright{} 1996 The American Physical Society.

Journal ArticleDOI
TL;DR: The National Spherical Tokamak Experiment (NSTX) as mentioned in this paper is an ultra low aspect ratio device with a plasma current of 1 MA, which is designed for an experimental pulse length that will demonstrate quasi-steady state non-inductively driven advanced tokamak operation.
Abstract: The National Spherical Tokamak Experiment (NSTX) is an ultra low aspect ratio device with a plasma current of 1 MA. The tokamak features auxiliary heating and current drive with a close-fitting conducting shell to maximize the plasma pressure. NSTX is designed for an experimental pulse length that will demonstrate quasi-steady state non-inductively driven advanced tokamak operation. The design also takes maximum advantage of existing facilities and components from previous Princeton devices to reduce the overall program costs.

Journal ArticleDOI
TL;DR: The validity of the analytic large aspect ratio, high-β equilibria developed by Cowley et al. as mentioned in this paper was extended to include finite aspect ratio with q2≫1, where q is the safety factor.
Abstract: The validity of the analytic large aspect ratio, high‐β equilibria developed by Cowley et al. [Phys. Fluids B 3, 2066 (1991)] is extended to include finite aspect ratio equilibria with q2≫1, where q is the safety factor. These high‐β equilibria have two regions. Most of the volume lies in the ‘‘core region,’’ where ψ=ψ(R). The flux surfaces close in the ‘‘boundary layer region,’’ which has thickness δ. The solutions are valid when δ/a∼O (√e/βq2) is small, where a is the minor radius. Thus, finite e is allowed when q2 is large. The equilibria are completely specified by the midplane profiles of pressure p(R) and poloidal magnetic field BP(R) and the shape of the plasma boundary, all of which can be measured experimentally. Note the departure from customary specification of p(ψ), q(ψ), or F(ψ). A fast numerical code, requiring a few seconds to execute, has been written to compute and illustrate the analytic high‐β equilibria. The qualitative features of high‐βP tokamaks are discussed in detail.

Journal ArticleDOI
TL;DR: In this paper, the importance of the flow shear in various enhanced confinement regimes is discussed in terms of the turbulence suppression criterion in general toroidal geometry, which is then further generalized to include the poloidal angle dependence of the equilibrium electrostatic potential.
Abstract: The importance of the flow shear in various enhanced confinement regimes is discussed in terms of the turbulence suppression criterion in general toroidal geometry. This criterion is then further generalized to include the poloidal angle dependence of the equilibrium electrostatic potential. The implication of the recently observed in - out asymmetry in the fluctuation behaviour in DIII-D VH-mode is discussed.

Journal ArticleDOI
TL;DR: In this article, a high-tokamak with a resistive shell was used to simulate VDEs induced by a strong collapse in a vertically elongated, high-tekamak, and it was shown that the VDE rate depends strongly on the magnitude of the collapse and the n-index of the equilibria.
Abstract: Extremely fast vertical displacement events (VDEs) induced by a strong collapse were found in a vertically elongated , high tokamak with a resistive shell through computer simulations using the tokamak simulation code. Although the plasma current quench which has been shown to be the prime cause of VDEs in a relatively low tokamak (Nakamura Y et al 1996 Nucl. Fusion 36 643), was not observed during the VDE evolution, the observed growth rate of VDEs was almost five times faster than the growth rate of the usual positional instability . The essential mechanism of the -collapse-induced VDE was clarified to be the intense enhancement of positional instability due to a large and sudden degradation of the magnetic field decay n-index in addition to the significant destabilization due to a reduction in the stability index . The radial shift of the magnetic axis caused by the collapse induces eddy currents on the resistive shell, and these eddy currents produce a large degradation of the n-index. It is pointed out that the shell geometry characterizes the VDE dynamics, and that the VDE rate depends strongly both on the magnitude of the collapse and the n-index of the equilibria just before the collapse occurs. The JT-60U vacuum vessel is shown to possess the capability of preventing -collapse-induced VDEs.

Journal ArticleDOI
TL;DR: In this article, the energy distributions and radial density profiles of the fast confined trapped alpha particles in DT experiments on TFTR are measured in the energy range 0.5 - 3.5 MeV using the pellet charge exchange (PCX) diagnostic.
Abstract: The energy distributions and radial density profiles of the fast confined trapped alpha particles in DT experiments on TFTR are being measured in the energy range 0.5 - 3.5 MeV using the pellet charge exchange (PCX) diagnostic. A brief description of the measurement technique which involves active neutral particle analysis using the ablation cloud surrounding an injected impurity pellet as the neutralizer is presented. This paper focuses on alpha and triton measurements in the core of MHD quiescent TFTR discharges where the expected classical slowing-down and pitch angle scattering effects are not complicated by stochastic ripple diffusion and sawtooth activity. In particular, the first measurement of the alpha slowing-down distribution up to the birth energy, obtained using boron pellet injection, is presented. The measurements are compared with predictions using either the TRANSP Monte Carlo code and/or a Fokker - Planck Post-TRANSP processor code, which assumes that the alphas and tritons are well confined and slow down classically. Both the shape of the measured alpha and triton energy distributions and their density ratios are in good agreement with the code calculations. We can conclude that the PCX measurements are consistent with classical thermalization of the fusion-generated alphas and tritons.

Journal ArticleDOI
01 Sep 1996-Chaos
TL;DR: A set of difference equations (maps) is derived for the nonrelativistic particle motion limit and numerically study them to elucidate the various aspects of the phase space dynamics.
Abstract: We study the dynamics of charged particles in the presence of two electrostatic waves propagating obliquely to an ambient magnetic field. The presence of a second wave makes the problem a two‐dimensional and time‐dependent one with a complicated phase space behavior. We derive a set of difference equations (maps) for the nonrelativistic particle motion limit and numerically study them to elucidate the various aspects of the phase space dynamics. For the general case of oblique propagation, we observe synergistic effects leading to the lowering of the stochasticity threshold and the concomitant reduction in electric field amplitudes for particle heating applications. These results can be understood in terms of the resonance structures associated with the two waves and we obtain approximate analytic expressions for the thresholds. For the degenerate case of ω1=nΩ,ω2=mΩ (where ω1,ω2 are the frequencies of the two waves, Ω is the cyclotron frequency and n,m are integers) and strictly perpendicular propagation, the problem simplifies to a one‐and‐one‐half‐dimensional one. We observe the presence of stochastic webs in this situation.

Journal ArticleDOI
TL;DR: In this article, the ratio of energy-dependent fluence to total fusion yield is calculated using a fully three-dimensional Monte Carlo calculation with the Monte Carlo code for neutron and photon transport (MCNP).
Abstract: The most accurate determination of neutron yields from fusion reactors may be obtained from neutron activation measurements of elemental foils. On the Tokamak Fusion Test Reactor (TFTR), a re-entrant irradiation end has been installed to provide a low-scattering environment close to the plasma for neutron activation measurements. The ratio of energy-dependent fluence to total fusion yield is calculated using a fully three-dimensional Monte Carlo calculation with the Monte Carlo code for neutron and photon transport (MCNP). Corrections to the `virgin` fluence from attenuation and scattering are only 10 to 20% for deuterium-tritium (D-T) reactions and 30 to 40% for deuterium-deuterium reactions. A total 1-sigma accuracy of {+-}8% is achieved for D-T neutron yields over a wide dynamic range. This paper documents the response coefficients (hits per source neutron, where hits are activated nuclei per target nuclei) for use by the neutron activation system on TFTR; describes the possible systematic corrections needed (such as major radial variations or the impact of ion temperature on reactions with high-energy thresholds); and estimates uncertainties in the response coefficients. Results from in situ use of a D-T neutron generator are also analyzed using the MCNP modeling as an approximate benchmarking experiment; only 20% accuracy inmore » the comparison is possible because of poor counting statistics in the calibration experiment. 21 refs., 9 figs., 3 tabs.« less

Journal ArticleDOI
12 Apr 1996-Science
TL;DR: The letters from Stix et al .
Abstract: Letters from: [ Paul H. Rutherford ][1] [ Charles C. Baker ][1] Thomas H. Stix et al . take issue with the present course of the International Thermonuclear Experimental Reactor (ITER) initiative (Letters, 16 Feb., p. 891). ITER is a fusion research facility based on the highly successful “tokamak” approach to plasma confinement, now being designed under an international agreement executed in 1992 by the European Union, Japan, the Russian Federation, and the United States. ITER seeks to achieve, for the first time ever in controlled fusion research, a self-heated “burning” deuterium-tritium plasma. Plasma burn has been widely endorsed as a critically important and appropriate next step for fusion. Stix et al . question combining this step with three other “giant steps”: large size, long pulse, and superconducting magnets. The size of the ITER plasma is dictated by the requirement to provide sufficient energy confinement to reach the burning state; this is determined from size-scaling relationships derived from experiments on tokamaks with plasma volumes spanning two orders of magnitude; the largest of these tokamaks already operate at plasma densities and temperatures similar to those expected in ITER. Confinement in a tokamak is determined primarily by the magnitude of the plasma current: ITER's plasma current is about four times larger than that in the Joint European Torus. The step in pulse length is derived from the additional physics requirement to sustain the burn over times long compared with those characteristic of the evolution of plasma profiles. The step from copper to superconducting magnets has been found to be the most practical way of achieving the required pulse lengths. Superconducting magnets have already been used in tokamaks, including one of the size of Princeton's successful Tokamak Fusion Test Reactor. The long pulse and the superconducting magnets are also essential for ITER to advance fusion engineering objectives. The engineering features of ITER are generic to any fusion reactor; in ITER, they can be tested together in an integrated facility, made possible only by international partnership. Stix et al . also question the capability of the ITER design to achieve its stated technical objectives. Recognizing the need for broad technical consensus, a Technical Advisory Committee (TAC) was formed which, on a continuing basis, reports to the ruling ITER Council on the adequacy of the ITER design and its physics basis. The TAC's 16 members are drawn equally from all four partners, but they serve as individuals, independent of both the design team and their respective governmental agencies. Last July, the TAC completed a review of the “Interim Design” and, with unanimity, concluded that the design can fully meet ITER's mission and technical objectives. # {#article-title-2} The letters from Stix et al ., Ernesto Mazzucato, and William E. Parkins (16 Feb., p. 891) have two common themes, namely, that we should postpone or even cancel the ITER project and that we do not know how to make an attractive fusion reactor. Stix et al . and Mazzucato correctly note the tremendous progress that has been made in fusion research and that we are in a period where our expectations of continued progress are high. This is used as an argument to suggest that a commitment to the construction of ITER be postponed. I would argue just the opposite. We need to build on our excellent progress and take advantage of the unique opportunity offered by participation in ITER to move forward with fusion science and energy development. Projects like ITER are always faced with the idealistic argument that we should wait for better results. Such logic would have postponed most major undertakings that have lead to significant scientific and technological progress. The letters raise valid technical issues (including improved plasma confinement, control of disruptions, and engineering and materials development). These issues have been clearly recognized by fusion researchers, in general, and ITER, in particular. They are being responsibly addressed in the ITER research and development and base program activities. [1]: /lookup/doi/10.1126/science.272.5259.179e

Journal ArticleDOI
TL;DR: In this paper, the authors investigated vertical displacement events (VDEs) in tokamaks using the Tokamak Simulation Code and showed that disruption events such as a sudden plasma pressure drop (β p collapse) and the subsequent plasma current quench (I p quench) can accelerate VDEs due to the adverse destabilizing effect of the resistive shell.
Abstract: Vertical displacement events (VDEs), which are frequently observed in disruptive discharges of elongated tokamaks, are investigated using the Tokamak Simulation Code. We show that disruption events such as a sudden plasma pressure drop (β p collapse) and the subsequent plasma current quench (I p quench) can accelerate VDEs due to the adverse destabilizing effect of the resistive shell, which has previously been thought to stabilize VDEs. In a tokamak with a surrounding shell which is asymmetric with respect to the geometric midplane, the I p quench also causes an additional VDE acceleration due to the vertical imbalance of the attractive force. While the shell-geometry characterizes the VDE dynamics, the growth rate of VDEs depends strongly on the magnitude of the β p collapse, the speed of the I p quench and the n-index of the plasma equilibrium just before the disruption. An amelioration of I p quench-induced VDEs was experimentally established in the JT-60U tokamak by optimizing the vertical location of the plasma just prior to the disruption. The JT-60U vacuum vessel is shown to be suitable for preventing the β p collapse-induced VDE.

Journal ArticleDOI
TL;DR: In this paper, the authors present evidence that the fast-ion diffusion coefficient changes across the TFTR plasma column and compare the results from the transport simulation code TRANSP with the results obtained from measurements and simulation.
Abstract: We present evidence that the fast-ion diffusion coefficient changes across the TFTR plasma column. Two MHD quiescent discharges are analysed: a high power D - T plasma heated with 21 MW of deuterium and tritium beams, and an ohmic plasma into which a 10 MW, 20 ms deuterium beam pulse was injected. The localized charge-exchange measurements in the ohmic plasma, and the neutron flux measurements in the D - T plasma are compared with predictions from the transport simulation code TRANSP. We have modified the code to allow modelling with arbitrary fast-ion diffusion profiles . Significant improvement in the agreement between measurement and simulation is obtained with a profile that has low values in the inner half of the plasma column and then rises rapidly towards the plasma periphery. This suggests a common underlying mechanism of enhanced beam ion transport in the two discharges, such as stochastic ripple diffusion.

Journal ArticleDOI
TL;DR: The titanium alloy Ti6Al-4V is currently the reference alloy for the vacuum vessel of the tokamak physics experiment (TPX), which will use D ǫ as fuel.

Journal ArticleDOI
TL;DR: In this article, a new nonlinear Raman instability in underdense plasma is investigated theoretically Unlike the usual linear Raman instabilities which grow exponentially in time, this instability takes a finite amount of time to diverge.
Abstract: A new nonlinear Raman instability in underdense plasma is investigated theoretically Unlike the usual linear Raman instabilities which grow exponentially in time, this instability takes a finite amount of time to diverge The explosion time t∞ depends on the initial level of the perturbation A general set of equations for spatio‐temporal evolution of the forward nonlinear Raman scattering is derived and its temporal evolution is studied in detail This new instability results in the generation of forward Raman radiation shifted by half the plasma frequency for laser intensities of order or exceeding 1018 W/cm2, something that has been recently observed [A Modena (private communication, 1995)]

Journal ArticleDOI
TL;DR: The use of discharge cleaning techniques and venting to remove the tritium was investigated in this paper, which resulted in a reduction in the in-vessel inventory from 16.4 kCi at the end of 1995 operation to 7.2 kCI at the start of the 1996 experimental program.
Abstract: Operation of the Tokamak Fusion Test Reactor (TFTR) with a mixture of deuterium and tritium fueling has permitted the opportunity to measure the retention of tritium in the graphite limiter and other internal hardware. The use of discharge cleaning techniques and venting to remove the tritium was investigated. The tritium was introduced into TFTR by neutral beam injection and by gas puffing. The graphite limiter is subject to erosion and codeposition. While short term retention was high, the retention averaged over the 1993-1995 D-T campaign was 52% {+-} 15%. The tritium removal techniques resulted in lowering the in-vessel inventory from 16.4 kCi at the end of 1995 operation to 7.2 kCi at the start of the 1996 experimental program. 14 refs., 3 figs., 1 tab.

Journal ArticleDOI
TL;DR: In this article, the poloidal field (PF) coils have been designed to produce a wide range of plasmas, and a new algorithm for shape control of a few critical plasma boundary points is described and used in simulations using the Tokamak Simulation Code.
Abstract: Control of the poloidal field (PF) in the Tokamak Physics Experiment (TPX) is critical to achieving its mission of advanced tokamak research. Extensive examination of the plasma equilibrium; plasma start-up; plasma position, shape, and current control; and plasma shape reconstruction have been performed as part of the design process. This paper reports the progress in this area. The PF coils have been designed to produce a wide range of plasmas. Plasma start-up can be achieved for multiple conditions. Fast plasma position control coils inside the vacuum vessel are used for short timescale control of the plasma vertical and radial position. Shape and total plasma-current control are provided by the PF coils over a slower timescale. A new algorithm for shape control of a few critical plasma boundary points is described and used in simulations using the Tokamak Simulation Code. Fast magnetostatic reconstruction of the plasma shape is examined to determine the impact of measurement locations and their quality.

Journal ArticleDOI
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 All-like charge state is proposed.

Journal ArticleDOI
TL;DR: In this article, a simple model for the nonlinear low gain evolution of a short pulse Compton free electron laser (FEL) oscillator is derived, and an analysis of the small signal regime allows the calculation of the shape of the produced optical pulse.
Abstract: A simple model for the nonlinear low gain evolution of a short pulse Compton free electron laser (FEL) oscillator is derived. An analysis of the small signal regime allows the calculation of the shape of the produced optical pulse. For small excess over threshold, a Landau-Ginzburg equation is obtained, which allows us to show that a strong superradiant efficiency enhancement occurs at small detuning. Furthermore, the knowledge of the eigenfrequencies in the small signal regime allows one to infer a scale law for the period of limit cycles occurring at larger excess over threshold. Theoretical results are compared to experimental results from FELIX.

Journal ArticleDOI
TL;DR: In this article, a response to the Office of Energy Research of the US DOE from the Fusion Energy Advisory Committee on a review of alternate concepts for magnetic confinement devices was provided, and the committee was asked to specifically respond to the concept of sperical tokamaks, and to offer suggestions for investment strategies for funding alternate concepts.
Abstract: This article is a response to the Office of Energy Research of the US DOE from the Fusion Energy Advisory Committee on a review of alternate concepts for magnetic confinement devices. This response was solicited in response to one of the suggestions made as part of the advisory report `A Restructured Fusion Energy Sciences Program` submitted to the US DOE in early 1996. The committee was asked to specifically respond to the concept of sperical tokamaks, and to offer suggestions for investment strategies for funding alternate concepts.

Proceedings ArticleDOI
01 Feb 1996
TL;DR: The folded waveguide (FWG) antenna is an advanced ICRF launcher under development at ORNL that offers many significant advantages over current-strap type antennas as mentioned in this paper, particularly beneficial for reactor-relevant applications such as ITER and TPX.
Abstract: The folded waveguide (FWG) antenna is an advanced ICRF launcher under development at ORNL that offers many significant advantages over current‐strap type antennas. These features are particularly beneficial for reactor‐relevant applications such as ITER and TPX. Previous tests of a development folded waveguide with a low density plasma load have shown a factor of 5 increase in power capability over loop antennas into similar plasma conditions. The performance and reliability of a FWG with an actual tokamak plasma load must now be verified for further acceptance of this concept. A 58 MHz, 4 MW folded waveguide is being designed and built for the PBX‐M and TFTR tokamaks at Princeton Plasma Physics Laboratory. This design has a square cross‐section that can be installed as either a fast wave (FW) or ion‐Bernstein wave (IBW) launcher by 90° rotation. Two new features of the design are: a shorter quarter‐wavelength resonator configuration and a rear‐feed input power coupling loop. Loading calculations with a standard shorting plate indicate that a launched power level of 4 MW is possible on either machine. Mechanical and disruption force analysis indicates that bolted construction will withstand the disruption loads. An experimental program is planned to characterize the plasma loading, heating effectiveness, power capability, impurity generation and other factors for both FW and IBW cases. High power tests of the new configuration are being performed with a development FWG unit on RFTF at ORNL.

Journal ArticleDOI
TL;DR: The deuterium-tritium (D-T) experiments on the Tokamak Fusion Test Reactor (TFTR) have yielded unique information on the confinement, heating and alpha particle physics of reactor scale D-T plasmas as well as the first experience with tritium handling and D-Ts neutron activation in an experimental environment as discussed by the authors.
Abstract: The deuterium-tritium (D-T) experiments on the Tokamak Fusion Test Reactor (TFTR) have yielded unique information on the confinement, heating and alpha particle physics of reactor scale D-T plasmas as well as the first experience with tritium handling and D-T neutron activation in an experimental environment. The D-T plasmas produced and studied in TFTR have peak fusion power of 10.7 MW with central fusion power densities of 2.8 MWm−3 which is similar to the 1.7 MWm−3 fusion power densities projected for 1,500 MW operation of the International Thermonuclear Experimental Reactor (ITER). Detailed alpha particle measurements have confirmed alpha confinement and heating of the D-T plasma by alpha particles as expected. Reversed shear, highli and internal barrier advanced tokamak operating modes have been produced in TFTR which have the potential to double the fusion power to ∼20 MW which would also allow the study of alpha particle effects under conditions very similar to those projected for ITER. TFTR is also investigating two new innovations, alpha channeling and controlled transport barriers, which have the potential to significantly improve the standard advanced tokamak.