Recent results from the ATF torsatron

Abstract

Recent experiments in the Advanced Toroidal Facility (ATF) torsatron [Plasma Physics and Controlled Nuclear Fusion Research 1990 (IAEA, Vienna, in press)] have emphasized the role of magnetic configuration control in transport studies. Long-pulse plasma operation up to 20 sec has been achieved with electron cyclotron heating (ECH). With neutral beam injection (NBI) power of ≥1 MW, global energy confinement times of 30 msec have been obtained with line-average densities up to 1.3×1020 m−3. The energy confinement and the operational space in ATF are roughly the same as those in tokamaks of similar size and field. The empirical scaling observed is similar to gyro-reduced Bohm scaling with favorable dependences on density and field offsetting an unfavorable power dependence. The toroidal current measured during ECH is identified as the bootstrap current. The observed currents agree well with predictions of neoclassical theory in magnitude and in parametric dependence. Variations of the magnetic configuration in discharges heated by ECH alone and by NBI change plasma transport and plasma profiles. Magnetic fluctuations respond to the concomitant pressure profile variations. Comparative studies of edge fluctuations in the Texas experimental tokamak (TEXT) [Plasma Physics and Controlled Nuclear Fusion Research 1990 (IAEA, Vienna, in press)] and the ATF stellarator showed remarkable similarity in the levels of fluctuations and the existence of a velocity shear layer.

Assessment of Plasma Performance in a Magnetic Configuration with Reduced Poloidal Coils for a Helical DEMO Reactor FFHR-d1

“…In both cases of the circular and vertically elongated configurations, the upper data of β 0 are on a curve proportional to n 0.6 e0 . This is consistent with the gyro-Bohm model, where β 0 ∝ n 0.6 e0 [5][6][7][8][9]. There observed no clear difference between the two configurations in this figure. A clear difference is recognized in the Shafranov shift as shown in Fig.…”

Phase-space dynamics of runaway electrons in tokamaks

“…In tokamaks, relativistic runaway electrons are often observed during and after a plasma disruption or during a fast plasma shutdown [1][2][3][4]. The growth-rate of avalanche runaway electron induced by knock-on process, synchrotron radiation and magnetic fluctuations has been studied extensively [5][6][7].…”

Formularization of the confinement enhancement factor as a function of the heating profile for FFHR-d1 core plasma design

“…(aB) and ν * are the Bohm energy confinement time, the normalized ion gyro radius and the collisionality, respectively. Using the definition of τ E ∝ nT a 2 R/P , the gyro-Bohm energy confinement time, τ GB , is derived as τ GB ∝ a 2.4 R 0.6 B 0.8 P −0.6 n 0.6 [11,12,15]. According to this model, the scale factor of τ E is given by…”

“…However, there is a large degree of freedom in determining the radial profiles and the confinement enhancement factor, which causes a large ambiguity in the core plasma design. Recently, the direct profile extrapolation (DPE) method has been developed to predict the radial profiles in a reactor [10], where radial profiles observed in the experiment are directly extrapolated to the reactor condition using the gyro-Bohm model [11,12]. The gyro-Bohm-type parameter dependence is what is recognized in typical energy confinement scalings for magnetically confined toroidal plasmas of ISS04, ISS95, and H-mode scalings for tokamaks [13].…”