Plasma Confinement Studies in the ISX-ATokamak

Abstract

The ISX-A (Impurity Study Experiment) tokamak operated with major radius R =92 cm, minor radius a =26 cm, and relatively low toroidal magnetic field B T < 15 kG. 1 * 2 Only Ohmic heating was appliedo Studies of plasma confinement in this device yielded unusually favorable results in comparison with empirical scaling formulas., For example, the gross-energy-confinement times, r E = !&[/(n e T e +W|Ti)dv]/Po m E. 9 exceeded the values expected from the scaling of Jassby et at? by factors of 1-3 (lo6 average) and were larger than the values predicted by the Hugill-Sheffield formula 4 [with scaling l-l] by factors of 1.5-4.5 (3.1 average). At line-average densities (n e ) above 10 13 cm" 3 , the ISX-.A data are closest to the scaling proposed by Mirnov, 5 r E = (3 x 1(T 9 )a(cm) x/(A)« e l72 sec (n e is given in units of 10 13 cm" 3 ), although they still exceed the expectations by an average value of 1.2. Also, the maximum value of n e achieved before a major disruption occurred was 7xl0 13 cm" 3 , a factor almost 4.5 times larger than that anticipated by B T /R 0 scaling. 6 The largest values of toroidal beta, P T (0) equal to No. GA-A14133, 1976 (to be published); see also Ref" 5, above. 7 G. R. Hopkins and John M. Rawls, Nucl. Technol. 36, 171 (1977), and references contained therein. 8 P

Energy confinement in Doublet III with high-Z limiters

“…The 13 -3 maximum line-average density obtained at 24 kG is approximately 5 x 10 em , a value which is comparable ( Fig. 9) to the limiting density in other recent circular tokamak experiments, including several operating with titanium gettering [5][6][7][8][9][10].…”

Anomalous thermal confinement in ohmically heated tokamaks

“…This has involved comparisons of results from different experiments and also confinement studies carried out on a single machine [4][5][6][7][8][9]. The data base from these studies, which have been recently summarized in Refs.…”

“…In particular, the experimental observation that the energy confinement time rg increases linearly with the average density [ 1 ] has stimulated attempts to explain this trend, and there were further investigations of possible scalings of rg with other key plasma parameters and with the size of the device [2,3]. This has involved comparisons of results from different experiments and also confinement studies carried out on a single machine [4][5][6][7][8][9]. The database from these studies, which have been summarized in Refs [10,11], indicates that at low density in Ohmic discharges, TE is rather well described by the 'Neo-Alcator' scaling, rg a n a 1 0 4 R 2 0 4 , where n is the line average density, a is the minor radius and R is the major radius.…”

Comments on experimental results of energy confinement of tokamak plasmas

“…Experiments show that in the otaiic heating regime with gas puffing at the plasma periphery as a means to increase the plasma density, the energy confinement time t£ of a steady-state tokamak plasma first increases linearly with density (the linear regime), but begins to deviate from the linear increase [8] beyond a certain electron density fi es . At higher densitiesc becomes independent of, or even to decrease with, density (the saturated regime).…”

“…II, the first density landmark delineating a change in confinement time is rL s , the density at which the energy confinement no longer increases linearly with density. In Fig, 1 we plot n es /j versus the toroidal field B h , the plasma current I_, the major radius RQ, the minor radius a, and the cylindrical safety factor q(a), based on results as reported for a number of tokamaks [1,[8][9][10][25][26][27][28][29][30][31][32][33][34] in the ohmic heating regime. n es /3 * 0.35 (10 20 /MA-m) and is nearly independent of all of the parameters.…”