High-beta injection experiments on the ISX-B tokamak

Abstract

Neutral-beam injection of up to 2.5 MW into plasmas in the ISX-B tokamak (R0 = 0.93 m, a = 0.27 m, BT = 0.9–1.5 T, Ip = 70–210 kA, n̄e = 2.5–10×1013 cm−3) has created plasmas with volume-averaged beta of up to ∼ 2.5%, peak beta values of up to ∼ 9%, and root-mean-square beta values of up to ∼ 3.5%. Energy confinement time is observed to decrease by about a factor of two as beam power goes from 0 to 2.5 MW; the decrease is caused predominantly by the electron confinement time falling below the predictions of ‘Alcator scaling’ by a factor of 3–4 at high beam power. An empirical relationship of the form fits our measurements over a wide range of plasma parameters. The function f(Pb), where Pb is the beam power, is linear for Pb ≤ 1.2 MW but tends to saturate for 1.2 MW ≤ Pb ≤ 2.5 MW. Although the equilibria attained in ISX-B are predicted to be above the threshold for the ideal magnetohydrodynamic (MHD) ballooning instability, no evidence of these modes is observed.

Optimization of Steady-State Beam-Driven Tokamak Reactors

“…On the other hand, a driven reactor would require a higher power handling capability in the burn-control mechanism; in addition, independent control of both the electron and ion temperatures is desirable in order to maintain each temperature near its optimum. The needed burn control processes have yet to be demonstrated experimentally, but ISX-B results [42] suggest that the expected high-(5 MHD instabilities may provide effective control if they manifest themselves through increased transport rather than catastrophic failure of equilibrium.…”

“…The neoclassical bootstrap current would be very bem-icial; a discovery of the conditions necessary to produce the bootstrap current could be invaluable. Finally, the study of the effects of fast-ion pressure and fast-ion driven currents on MHD equilibria and stability [42,43] should be extended to higher values of p. (a) J(x,y) > 0.9 J(x max ,y) for x_ < x < x+ Fig. 1 The effective ionization cross section, a , for neutral deuterium err In a hydrogen plasma with Z e ff = 2 due to Argon Impurities.…”

Magnetohydrodynamic Instability with Neutral-Beam Heating in the ISX-BTokamak

“…^Qn assignment from Nuclear Division, Computer Sciences, Union Carbide Corporation, Oak Ridge, There has been considerable recent interest in the nature of the liquid-solid transition in two dimensions, 1 spurred by the development of a beautiful and detailed dislocation unbinding theory due to Halperin and Nelson 2 (and also Young 2 ) based on the ideas of Kosterlitz and Thouless. 3 Many experiments and computer experiments have been carried out 1,4 to test its novel predictions, e.g., that there is a hexatic phase be- tween the solid and the isotropic liquid, and that the transitions are thermodynamically continuous, Most recent computer simulations, e.g., on the Lennard-Jones system at constant pressure, 5 and r~n systems with n = 12, 6 » 7 n = 3, 8 ' 9 and w = l, 10 show a first-order transition and no hexatic phase. Freezing parameters such as the entropy change (AS/k B ) 6 " 10 and the structure factor peak near freezing 7 ' 9,n * 12 are close to 0.3 and 5.0, re-…”

Highβpplasma formation using off-axis ECCD in Ohmic heated plasma in the spherical tokamak QUEST

“…This transformation is a consequence of high β p formation. We evaluate β p from the generalized Shafranov equation for radial force balance for the equilibrium vertical magnetic field [15] ‫ܤ‬ ‫ݖ‬ = (1) where ‫ܤ‬ ߠ (ܽ) = ߤ 0 ‫ܫ‬ ‫‬ /2ߨܽ is the poloidal magnetic field at the boundary r = a. l i is the internal inductance assumed here to be unity and not varying. β p * = β p +l i /2 evaluated from this method shows that it started increasing from 3 during OH phase to over 5 in RF phase.…”

“…Here I p is the driven plasma current having plasma minor radius a and toroidal magnetic field B 0 at the axis. For attaining a high β p plasma, it is known to utilize an external source to heat the bulk Maxwellian component of the plasma [1,2] or to create a confined anisotropic population of energetic particles [3,4]. It is also proposed to operate in a shaped configuration to increase β p [5].…”