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Effects of orbit squeezing on ion transport processes close to magnetic axis

Description: It is shown that ion thermal conductivity close to the magnetic axis in tokamaks is reduced by a factor of {vert_bar}S{vert_bar}{sup 5/3} if (M{sub i}/M{sub e}){sup 2/3}(T{sub e}/T{sub i}){sup 4/3}/{vert_bar}S{vert_bar}{sup 5/3} {much_gt} 1. Here, S is the orbit squeezing factor, M{sub i}(M{sub e}) is the ion (electron) mass, and T{sub i}(Te{sub e}) is the ion (electron) temperature. The reduction reflects both the increase of the fraction of trapped particles by a factor of {vert_bar}S{vert_bar}{sup 1/3}, and the decrease of the orbit size in units of the poloidal flux {psi} by a factor of {vert_bar}S{vert_bar}{sup 2/3}.
Date: January 1997
Creator: Shaing, K. C.; Hazeltine, R. D. & Zarnstorff, M. C.
Partner: UNT Libraries Government Documents Department

Supershot performance with reverse magnetic shear in TFTR

Description: Discharges with large regions of reversed magnetic shear and good energy and particle confinement have been produced in the Tokamak Fusion Test Reactor. These plasmas were created by heating the plasma during a rapid plasma current increase. The stability of these discharges is dependent on the shape of the q profile, in particular the value and location of the minimum value of q. Control of the q profile by optimizing the plasma startup, prelude start time, the neutral-beam directionality during the prelude heating phase, and the plasma current ramp rate is demonstrated. High-performance discharges, created by injecting more than 18 to 25 MW of neutral beam power into a plasma with reverse shear, are also described.
Date: August 1, 1995
Creator: Batha, S.H.; Levinton, F.M.; Zarnstorff, M.C. & Schmidt, G.L.
Partner: UNT Libraries Government Documents Department

Improved confinement with reversed magnetic shear in TFTR

Description: Highly peaked density and pressure profiles in a new operating regime have been observed on the Tokamak Fusion Test Reactor (TFTR). The q-profile has a region of reversed magnetic shear extending from the magnetic axis to r/a {approximately}0.3-0.4. The central electron density rises from 0.45 x 10{sup 20} m{sup {minus}3} to nearly 1.2 x 10{sup 20} m{sup {minus}3} during neutral beam injection. The electron particle diffusivity drops precipitously in the plasma core with the onset of the improved confinement mode and can be reduced by a factor of {approximately}50 to near the neoclassical particle diffusivity level.
Date: July 1, 1995
Creator: Levinton, F.M.; Batha, S.H. & Zarnstorff, M.C.
Partner: UNT Libraries Government Documents Department

Introduction to Praxis

Description: Praxis is the practice of the programming art, science, and skill. It is a high-order language designed for the efficient programming of control and systems applications. It is a comprehensive, strongly typed, block-structured language in the tradition of Pascal, with much of the power of the Mesa and Ada languages. It supports the development of systems composed of separately compiled modules, user-defined data types, exception handling, detailed control mechanisms, and encapsulated data and routines. Direct access to machine facilities, efficient bit manipulation, and interlocked critical regions are provided within Praxis.
Date: July 1, 1980
Creator: Greenwood, J.R.; Evans, A. Jr.; Morgan, C.R. & Zarnstorff, M.C.
Partner: UNT Libraries Government Documents Department

Introduction to Praxis

Description: Praxis is the practice of the programming art, science, and skill. It is a high-order language designed for the efficient programming of control and systems applications. It is a comprehensive, strongly typed, block-structured language in the tradition of Pascal, with much of the power of the Mesa and Ada languages. It supports the development of systems composed of separately compiled modules, user-defined data types, exception handling, detailed control mechanisms, and encapsulated data and routines. Direct access to machine facilities, efficient bit manipulation, and interlocked critical regions are provided within Praxis.
Date: December 3, 1980
Creator: Greenwood, J.R.; Evans, A. Jr.; Morgan, C.R. & Zarnstorff, M.C.
Partner: UNT Libraries Government Documents Department

Magnetic Field Line Tracing Calculations for Conceptual PFC Design in the National Compact Stellarator Experiment

Description: The National Compact Stellarator Experiment (NCSX) is a three-field period compact stellarator presently in the construction phase at Princeton, NJ. The design parameters of the device are major radius R=1.4m, average minor radius <a> = 0.32m, 1.2 {le} toroidal field (B{sub t}) {le} 1.7 T, and auxiliary input power up to 12 MW with neutral beams and radio-frequency heating. The NCSX average aspect ratio <R/a> of 4.4 lies well below present stellarator experiments and designs, enabling the investigation of high {beta} physics in a compact stellarator geometry. Also the NCSX design choice for a quasi-axisymmetric configuration aims toward the achievement of tokamak-like transport. In this paper, we report on the magnetic field line tracing calculations used to evaluate conceptual plasma facing component (PFC) designs. In contrast to tokamaks, axisymmetric target plates are not required to intercept the majority of the heat flux in stellarators, owing to the nature of the 3-D magnetic field footprint. The divertor plate design investigated in this study covers approximately one half of the toroidal extent in each period. Typical Poincare plots in Figure 1 illustrate the plasma cross-section at several toroidal angles for a computed NCSX high-beta equilibrium. The plates used for these calculations are centered in each period about the elongated cross-section shown in Figure 1a, extending to +/- {pi}/6 in each direction. Two methods for tracing the edge field line topology were used in this study. The first entails use of the VMEC/MFBE-2001 packages, whereas the second entails use of the PIES code with a post-processor by Michael Drevlak; the same field line integration routine was used to evaluate the equilibria for this comparison. Both inputs were generated based on the {beta}=4%, =iota=0.5 equilibrium computed from the final NCSX coil set. We first compare these two methods for a specific plate geometry, and ...
Date: June 12, 2006
Creator: Maingi, R; Kaiser, T; Hill, D N; Lyon, J F; Monticello, D & Zarnstorff, M C
Partner: UNT Libraries Government Documents Department

Electron temperature profiles in high power neutral-beam-heated TFTR (Tokamak Fusion Test Reactor) plasmas

Description: In 1986, the maximum neutral beam injection (NBI) power in the Tokamak Fusion Test Reactor (TFTR) was increased to 20 MW, with three beams co-parallel and one counter-parallel to I/sub p/. TFTR was operated over a wide range of plasma parameters; 2.5 < q/sub cyl/ < 10, and 2 x 10/sup 19/ < anti n/sub e/ < 7 x 10/sup 19/ m/sup -3/. Data bases have been constructed with over 600 measured electron temperature profiles from multipoint TV Thomson scattering which span much of this parameter space. We have also examined electron temperature profile shapes from electron cyclotron emission at the fundamental ordinary mode and second harmonic extraordinary mode for a subset of these discharges. In the light of recent work on ''profile consistency'' we have analyzed these temperature profiles in the range 0.3 < (r/a) < 0.9 to determine if a profile shape exists which is insensitive to q/sub cyl/ and beam-heating profile. Data from both sides of the temperature profile (T/sub e/(R)) were mapped to magnetic flux surfaces (T/sub e/(r/a)). Although T/sub e/(r/a), in the region where 0.3 < r/a < 0.9 was found to be slightly broader at lower q/sub cyl/, it was found to be remarkably insensitive to ..beta../sub p/, to the fraction of NBI power injected co-parallel to I/sub p/, and to the heating profile going from peaked on axis, to hollow. 10 refs., 8 figs.
Date: September 1, 1987
Creator: Taylor, G.; Grek, B.; Stauffer, F.J.; Goldston, R.J.; Fredrickson, E.D.; Wieland, R.M. et al.
Partner: UNT Libraries Government Documents Department

The effect of E{sub r} on MSE measurements of q, a new technique for measuring E{sub r}, and a test of the neoclassical electric field

Description: Previous analysis of motional-Stark Effect (MSE) data to measure the q-profile ignored contributions from the plasma electric field. The MSE measurements are shown to be sensitive to the electric field and require significant corrections for plasmas with large rotation velocities or pressure gradients. MSE measurements from rotating plasmas on the Tokamak Fusion Test Reactor (TFTR) confirm the significance of these corrections and verify their magnitude. Several attractive configurations are considered for future MSE-based diagnostics for measuring the plasma radial electric field. MSE data from TFTR is analyzed to determine the change in the radial electric field between two plasmas. The measured electric field quantitatively agrees with the predictions of neoclassical theory. These results confirm the utility of a MSE electric field measurement.
Date: October 1, 1996
Creator: Zarnstorff, M.C.; Synakowski, E.J.; Levinton, F.M. & Batha, S.H.
Partner: UNT Libraries Government Documents Department

Physics Basis for High-Beta, Low-Aspect-Ratio Stellarator Experiments

Description: High-beta, low-aspect-ratio (compact) stellarators are promising solutions to the problem of developing a magnetic plasma configuration for magnetic fusion power plants that can be sustained in steady-state without disrupting. These concepts combine features of stellarators and advanced tokamaks and have aspect ratios similar to those of tokamaks (2-4). They are based on computed plasma configurations that are shaped in three dimensions to provide desired stability and transport properties. Experiments are planned as part of a program to develop this concept. A beta = 4% quasi-axisymmetric plasma configuration has been evaluated for the National Compact Stellarator Experiment (NCSX). It has a substantial bootstrap current and is shaped to stabilize ballooning, external kink, vertical, and neoclassical tearing modes without feedback or close-fitting conductors. Quasi-omnigeneous plasma configurations stable to ballooning modes at beta = 4% have been evaluated for the Quasi-Omnigeneous Stellarator (QOS) experiment. These equilibria have relatively low bootstrap currents and are insensitive to changes in beta. Coil configurations have been calculated that reconstruct these plasma configurations, preserving their important physics properties. Theory- and experiment-based confinement analyses are used to evaluate the technical capabilities needed to reach target plasma conditions. The physics basis for these complementary experiments is described.
Date: November 1, 1999
Creator: Brooks, A.; Reiman, A.H.; Neilson, G.H.; Zarnstorff, M.C. & al, et
Partner: UNT Libraries Government Documents Department

Physics Design of the National Compact Stellarator Experiment

Description: Compact quasi-axisymmetric stellarators offer the possibility of combining the steady-state low-recirculating power, external control, and disruption resilience of previous stellarators with the low-aspect ratio, high beta-limit, and good confinement of advanced tokamaks. Quasi-axisymmetric equilibria have been developed for the proposed National Compact Stellarator Experiment (NCSX) with average aspect ratio approximately 4.4 and average elongation approximately 1.8. Even with bootstrap-current consistent profiles, they are passively stable to the ballooning, kink, vertical, Mercier, and neoclassical-tearing modes for b &gt; 4%, without the need for external feedback or conducting walls. The bootstrap current generates only 1/4 of the magnetic rotational transform at b = 4% (the rest is from the coils). Transport simulations show adequate fast-ion confinement and thermal neoclassical transport similar to equivalent tokamaks. Modular coils have been designed which reproduce the physics properties, provide good flux surfaces, and allow flexible variation of the plasma shape to control the predicted MHD stability and transport properties.
Date: February 21, 2002
Creator: Neilson, G.H.; Zarnstorff, M.C.; Lyon, J.F. & Team, the NCSX
Partner: UNT Libraries Government Documents Department

Comparison of measured electron density rise and calculated neutral beam particle deposition in the TFTR tokamak

Description: The initial rate of rise of the central electron density during {approximately}100 keV deuterium neutral beam injection is found to agree well with calculations of the beam deposition rate. The best agreement is with beam deposition calculations using older tabulations of the atomic cross-sections; the effects of using new tabulations or including multi-step ionization processes appear to approximately cancel. The neutral-beam deposition profile is a strong function of both the magnitude and the shape of the target plasma density. Peaked heating profiles can be achieved at high target densities only from peaked target density profiles. 15 refs., 4 figs.
Date: December 1, 1991
Creator: Park, H.; Budny, R.; McCune, D.; Taylor, G.; Zarnstorff, M. C. & Barnes, C. W.
Partner: UNT Libraries Government Documents Department

Stabilization and onset of sawteeth in TFTR

Description: Measurements from the Tokamak Fusion Test Reactor (TFTR) of the q-profile using motional Stark effect (MSE) polarimetry and the pressure profiles have allowed detailed comparison of both supershots and L-mode discharges to theoretical models describing the stability of sawteeth. In TFTR supershots sawteeth are usually absent, whereas in L-mode discharges they are generally present, and in both cases q(O) is less than one. It has been found that the {omega}*-stabilization criterion of the two-fluid collisionless m=l reconnection mode agrees very well with the presence or absence of sawteeth in TFTR and no beta limits to the sawtooth stabilization have been observed.
Date: March 1, 1994
Creator: Levinton, F. M.; Batha, S. H.; Zakharov, L.; Manickam, J. & Zarnstorff, M. C.
Partner: UNT Libraries Government Documents Department

Core Poloidal Rotation and Internal Trnasport Barrier Formation in TFTR

Description: Impurity poloidal rotation velocities have been measured in the core of TFTR plasmas using a new spectroscopic diagnostic. Two types of transitions to enhanced confinement in reversed shear plasmas are examined. A bifurcation in carbon poloidal rotation is observed to occur before the transition to enhanced confinement for one of these types, while other measured plasmas parameters remain constant. A narrow radial region with reversed poloidal rotation and rotational shear is established 60-100 ms before the transition, and is associated with a large negative radial electric field.
Date: January 1, 1998
Creator: Synakowski, E.J.; Levinton, F.M.; Zarnstorff, M.C.; Bell, R.E.; Batha, S.H. & al, et
Partner: UNT Libraries Government Documents Department

Local tests of parallel electrical resistivity in the Tokamak Fusion Test Reactor

Description: The motional Stark effect (MSE) polarimeter measures the local magnetic field pitch angle, proportional to the ratio of the poloidal to toroidal magnetic fields, in the Tokamak Fusion Test Reactor (TFTR). The authors have used the polarimeter to measure the temporal evolution of the local value of the magnetic field pitch angle during large changes in the current profile such as during a current ramp or discharge initiation. The measured evolution is compared to the evolution predicted by classical and neoclassical resistivity models. The neoclassical resistivity model is a better predictor of the local pitch angle temporal evolution than the classical model.
Date: January 1, 1997
Creator: Batha, S.H.; Levinton, F.M.; Ramsey, A.T.; Schmidt, G.L. & Zarnstorff, M.C.
Partner: UNT Libraries Government Documents Department

Physics Issues in the Design of Low Aspect-Ratio, High-Beta, Quasi-Axisymmetric Stellarators

Description: Compact stellarators have the potential to combine the best features of the stellarator and the advanced tokamak, offering steady state operation without current drive and potentially without disruptions at an aspect ratio similar to tokamaks. A quasi-axisymmetric stellarator is developed that is consistent with the boot-strap current and passively stable to the ballooning, kink, Mercier, vertical, and neoclassical tearing modes at b=4.1 % without need for conducting walls or external feedback. The configuration has good flux surfaces and fast ion confinement. Thermal transport analysis indicates that the confinement should be similar to tokamaks of the same size, allowing access to the b-limit with moderate power. Coils have been designed to reproduce the physics properties. Initial analysis indicates the coils have considerable flexibility to manipulate the configuration properties. Simulations of the current evolution indicate the kink-mode can remain stable during the approach to h igh-beta.
Date: November 16, 2000
Creator: Zarnstorff, M.C.; Berry, L.A.; Boozer, A.; Brooks, A.; Cooper, W.A. & al, et
Partner: UNT Libraries Government Documents Department

Enhanced loss of fast ions during mode conversion ion Bernstein wave heating in TFTR

Description: A strong interaction of fast ions with ion Bernstein waves has been observed in TFTR. It results in a large increase in the fast ion loss rate, and heats the lost particles to several MeV. The lost ions are observed at the passing/trapped boundary and appear to be either DD fusion produced tritons or accelerated D neutral beam ions. Under some conditions, enhanced loss of DT alpha particles is also seen. The losses provide experimental support for some of the elements required for alpha energy channeling.
Date: December 1, 1995
Creator: Darrow, D.S.; Majeski, R.; Fisch, N.J.; Heeter, R.F.; Herrmann, H.W.; Herrmann, M.C. et al.
Partner: UNT Libraries Government Documents Department

Enhanced loss of fusion products during mode conversion heating in TFTR

Description: Ion Bernstein waves (IBWS) have been generated by mode conversion of ion cyclotron range of frequency (ICRF) fast waves in TFTR. The loss rate of fusion products in these discharges can be large, up to 10 times the first orbit loss rate. The losses are observed at the passing/trapped boundary, indicating that passing particles are being moved onto loss orbits either by increase of their v{perpendicular} due to the wave, by outward transport in minor radius, or both. The lost particles appear to be DD fusion produced tritons heated to {approximately}1.5 times their birth energy.
Date: July 1, 1995
Creator: Darrow, D. S.; Majeski, R.; Fisch, N. J.; Heeter, R. F.; Herrmann, H. W.; Herrmann, M. C. et al.
Partner: UNT Libraries Government Documents Department

Eliminating Islands in High-pressure Free-boundary Stellarator Magnetohydrodynamic Equilibrium Solutions

Description: Magnetic islands in free-boundary stellarator equilibria are suppressed using a procedure that iterates the plasma equilibrium equations and, at each iteration, adjusts the coil geometry to cancel resonant fields produced by the plasma. The coils are constrained to satisfy certain measures of engineering acceptability and the plasma is constrained to ensure kink stability. As the iterations continue, the coil geometry and the plasma simultaneously converge to an equilibrium in which the island content is negligible. The method is applied with success to a candidate plasma and coil design for the National Compact Stellarator eXperiment [Physics of Plasma, 7 (2000) 1911].
Date: November 19, 2002
Creator: Hudson, S.R.; Monticello, D.A.; Reiman, A.H.; Boozer, A.H.; Strickler, D.J.; Hirshman, S.P. et al.
Partner: UNT Libraries Government Documents Department

Measurements of the heating beam deposition profile in TFTR (Tokamak Fusion Test Reactor)

Description: The calculated heating-beam deposition profile is experimentally verified for a variety of target plasma densities for the first time. The calculation of the heating-beam deposition is found to be consistent with the measurement for the discharges without MHD activity. It is also demonstrated that the radial electron flux is unchanged from the ohmic phase to the initial auxiliary heating phase ({le}100 msec).
Date: August 1, 1990
Creator: Park, H.K.; Budny, R.; Taylor, G.; Zarnstorff, M.C. (Princeton Univ., NJ (USA). Plasma Physics Lab.) & Barnes, C.W. (Los Alamos National Lab., NM (USA))
Partner: UNT Libraries Government Documents Department

Ballistic contributions to heat pulse propagation on TFTR (Tokamak Fusion Test Reactor)

Description: Measurements on the TFTR tokamak of the electron temperature profile evolution and soft x-ray emissivity on a fast (10 {mu}sec) time scale during a sawtooth crash, show that significant heat is deposited beyond the mixing (or reconnection) radius within 200 {mu}sec following a sawtooth crash. This extended region in which electron heat is redistributed during the sawtooth crash substantially complicates the determination of heat transport properties from the subsequent heat pulse propagation. It is shown that the relaxation of this extended perturbation is consistent with the power balance estimates of the local thermal diffusivity. 19 refs., 6 figs.
Date: July 1, 1990
Creator: Fredrickson, E.D.; McGuire, K.; Cavallo, A.; Budny, R.; Janos, A.; Monticello, D. et al.
Partner: UNT Libraries Government Documents Department

Fast current ramp experiments on TFTR

Description: Electron heat transport on TFTR and other tokamaks is several orders of magnitude larger than neoclassical calculations would predict. Despite considerable effort, there is still no clear theoretical understanding of this anomalous transport. The electron temperature profile T/sub e/(r), shape has shown a marked consistency on many machines, including TFTR, 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 this paper 'profile consistency' in TFTR is described and an experiment which uses a fast current ramp to transiently decouple the current density profile J(r), and the T/sub e/(r) profiles is discussed. From this experiment the influence of J(r) on electron temperature profile consistency can be determined.
Date: May 1, 1987
Creator: Fredrickson, E.D.; McGuire, K.; Goldston, R.J.; Bell, M.; Grek, B.; Johnson, D. et al.
Partner: UNT Libraries Government Documents Department

Parallel electric resistivity in the TFTR tokamak

Description: The average parallel resistivity and the location of the q = 1 surface are found to be consistent with the predictions of neoclassical transport theory and inconsistent with classical resistivity (uncorrected for toroidal effects) for ohmic plasmas in the TFTR tokamak, both in near-equilibrium and during ramping of the plasma current. These observations are incompatible with theories predicting anomalous parallel resistivity in concert with anomalous perpendicular transport. 41 refs., 9 figs., 1 tab.
Date: May 1, 1990
Creator: Zarnstorff, M.C.; McGuire, K.; Bell, M.G.; Grek, B.; Johnson, D.; McCune, D. et al.
Partner: UNT Libraries Government Documents Department

Ion thermal confinement in the TFTR enhanced confinement regime

Description: Measurements of the plasma ion temperature and toroidal rotation speed profiles have allowed the study of ion thermal transport in the TFTR hot ion enhanced confinement regime. Central ion temperatures up to 30 keV and rotation speeds up to 8 x 10/sup 5/ m/sec have been confirmed with new diagnostic measurements, and the ion thermal diffusivity is found to be non-neoclassical and comparable to the anomalous electron thermal diffusivity. The dominant effects of strong rotation are 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. 14 refs., 3 figs.
Date: December 1, 1988
Creator: Fonck, R.J.; Howell, R.; Jaehnig, K.; Roquemore, L.; Schilling, G.; Scott, S. et al.
Partner: UNT Libraries Government Documents Department

Progress Toward Attractive Stellarators

Description: The quasi-axisymmetric stellarator (QAS) concept offers a promising path to a more compact stellarator reactor, closer in linear dimensions to tokamak reactors than previous stellarator designs. Concept improvements are needed, however, to make it more maintainable and more compatible with high plant availability. Using the ARIES-CS design as a starting point, compact stellarator designs with improved maintenance characteristics have been developed. While the ARIES-CS features a through-the-port maintenance scheme, we have investigated configuration changes to enable a sector-maintenance approach, as envisioned for example in ARIES AT. Three approaches are reported. The first is to make tradeoffs within the QAS design space, giving greater emphasis to maintainability criteria. The second approach is to improve the optimization tools to more accurately and efficiently target the physics properties of importance. The third is to employ a hybrid coil topology, so that the plasma shaping functions of the main coils are shared more optimally, either with passive conductors made of high-temperature superconductor or with local compensation coils, allowing the main coils to become simpler. Optimization tools are being improved to test these approaches.
Date: January 5, 2011
Creator: Neilson, G. H.; Brown, T. G.; Gates, D. A.; Lu, K. P.; Zarnstorff, M. C.; Boozer, A. H. et al.
Partner: UNT Libraries Government Documents Department