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Title: Confinement and power balance in the S-1 spheromak

Abstract

The confinement and scaling features of the S-1 spheromak have been investigated using magnetic, spectroscopic, and Thomson scattering data in conjunction with numerical modeling. Results from the multipoint Thomson scattering diagnostic shows that the central beta remains constant (/beta//sub to/ /approximately/ 5%) as the plasma current density increases from 0.68--2.1 MA/m/sup 2/. The density is observed to increase slowly over this range, while the central electron temperature increases much more rapidly. Analysis of the global plasma parameters shows a decrease in the volume average beta and energy confinement as the total current is increased. The power balance has been modeled numerically with a 0-D non-equilibrium time-dependent coronal model and is consistent with the experimental observations. 20 refs., 12 figs., 2 tabs.

Authors:
; ; ; ; ; ;
Publication Date:
Research Org.:
Princeton Univ., NJ (USA). Plasma Physics Lab.
OSTI Identifier:
5936208
Report Number(s):
PPPL-2636
ON: DE89014342
DOE Contract Number:
AC02-76CH03073
Resource Type:
Technical Report
Resource Relation:
Other Information: Portions of this document are illegible in microfiche products
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; SPHEROMAK DEVICES; PLASMA CONFINEMENT; CONFINEMENT TIME; CURRENT DENSITY; ELECTRIC CONDUCTIVITY; ELECTRON DENSITY; ELECTRON TEMPERATURE; PLASMA DIAGNOSTICS; POWER LOSSES; THOMSON SCATTERING; CLOSED PLASMA DEVICES; CONFINEMENT; ELECTRICAL PROPERTIES; ENERGY LOSSES; INELASTIC SCATTERING; LOSSES; PHYSICAL PROPERTIES; SCATTERING; THERMONUCLEAR DEVICES; TOKAMAK DEVICES; 700101* - Fusion Energy- Plasma Research- Confinement, Heating, & Production; 700102 - Fusion Energy- Plasma Research- Diagnostics

Citation Formats

Levinton, F.M., Meyerhofer, D.D., Mayo, R.M., Janos, A.C., Ono, Y., Ueda, Y., and Yamada, M. Confinement and power balance in the S-1 spheromak. United States: N. p., 1989. Web. doi:10.2172/5936208.
Levinton, F.M., Meyerhofer, D.D., Mayo, R.M., Janos, A.C., Ono, Y., Ueda, Y., & Yamada, M. Confinement and power balance in the S-1 spheromak. United States. doi:10.2172/5936208.
Levinton, F.M., Meyerhofer, D.D., Mayo, R.M., Janos, A.C., Ono, Y., Ueda, Y., and Yamada, M. Sat . "Confinement and power balance in the S-1 spheromak". United States. doi:10.2172/5936208. https://www.osti.gov/servlets/purl/5936208.
@article{osti_5936208,
title = {Confinement and power balance in the S-1 spheromak},
author = {Levinton, F.M. and Meyerhofer, D.D. and Mayo, R.M. and Janos, A.C. and Ono, Y. and Ueda, Y. and Yamada, M.},
abstractNote = {The confinement and scaling features of the S-1 spheromak have been investigated using magnetic, spectroscopic, and Thomson scattering data in conjunction with numerical modeling. Results from the multipoint Thomson scattering diagnostic shows that the central beta remains constant (/beta//sub to/ /approximately/ 5%) as the plasma current density increases from 0.68--2.1 MA/m/sup 2/. The density is observed to increase slowly over this range, while the central electron temperature increases much more rapidly. Analysis of the global plasma parameters shows a decrease in the volume average beta and energy confinement as the total current is increased. The power balance has been modeled numerically with a 0-D non-equilibrium time-dependent coronal model and is consistent with the experimental observations. 20 refs., 12 figs., 2 tabs.},
doi = {10.2172/5936208},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sat Jul 01 00:00:00 EDT 1989},
month = {Sat Jul 01 00:00:00 EDT 1989}
}

Technical Report:

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  • This note addresses the division of gun power and helicity between the open line volume and the closed flux surface volume in a steady state flux core spheromak. Our assumptions are that fine scale turbulence maintains each region close to an axisymmetric Taylor state, {mu}{sub o}j = {lambda}B. The gun region that feeds these two volumes surrounded by a flux conserver is shown topologically below. (The actual geometry is toroidal). Flux and current from the magnetized gun flow on open lines around the entire closed surface containing the spheromak. The gun current flows down the potential gradient, the potential differencemore » between the two ends of each line being the gun voltage. Here, the gun voltage excludes the sheath drops at each end. These volumes have different values of {lambda} in each region (open line volume V{sub 1} and closed spheromak volume V{sub 2}) and we want to calculate the efficiency of transferring the gun power to the spheromak to sustain the ohmic loss in steady state.« less
  • This note addresses the division of gun power and helicity between the open line volume and the closed flux surface volume in a steady state flux core spheromak. Our assumptions are that fine scale turbulence maintains each region close to a Taylor state, {mu}{sub o}J = {lambda}B. The gun region that feeds these two volumes surrounded by a flux conserver is shown topologically below. (The actual geometry is toroidal). Flux and current from the magnetized gun flow on open lines around the entire closed surface containing the spheromak. The gun current flows down the potential gradient, the potential difference betweenmore » the two ends of each line being the gun voltage. Here, the gun voltage excludes the sheath drops at each end. When these volumes have different values of {lambda} (ratio of {mu}{sub o}B{sup -2}j {center_dot} B in each region) in the open line volume V{sub 1} and the closed spheromak volume V{sub 2} the efficiency of transferring the gun power to the spheromak to sustain the ohmic loss is the {lambda}-ratio of these regions, in the limit V{sub 1} << V{sub 2}. This result follows immediately from helicity balance in that limit. Here we give an accounting of all the gun power, and do not assume a small edge (open line) region.« less
  • The local carbon diffusion coefficient was measured in the S - 1 spheromak by detecting the radial spread of injected carbon impurity. The radial impurity density profile is determined by the balance of ionization and diffusion. Using measured local electron temperature T/sub e/ and density n/sub e/, the ionization rate is determined from which the particle diffusion coefficient is inferred. The results found in this work are consistent with Bohm diffusion. The absolute magnitude of D/sub /perpendicular// was determined to be (4/approximately/6) /times/ D/sub Bohm/. 25 refs., 13 figs., 2 tabs.
  • The S-1 machine is part of the Magnetic Fusion Program. The goal of the Magnetic Fusion Program is to develop and demonstrate the practical application of fusion. S-1 is an experimental device which will provide an essential link in the research effort aiming at the realization of fusion power.
  • Experimental measurements of the equilibrium in the S-1 Spheromak by use of magnetic probes inside the plasma show that the final magnetic equilibrium is one which has relaxed close to the Taylor (minimum-energy) state, even though the plasma is far from that state during formation. The comparison is made by calculating the two-dimensional ..mu.. profile of the plasma from the probe data, where ..mu.. is defined as ..mu../sub 0/j/sub parallel//B. Measurements using a triple Langmuir probe provide evidence to support the conclusion that the pressure gradients in the relaxed state are confined to the edge region of the plasma.