ECRF experiments for local heating and current drive by fundamental O-mode launch from the low-field side on JT-60U

Abstract

An electron cyclotron range of frequency (ECRF) program has been initiated to study the local heating and current drive in JT-60U. A frequency of 110 GHz was adopted to couple the fundamental O-mode from the low-field side with an oblique toroidal injection angle for the current drive. Experiments were performed at an injection power of ~1.5 MW by using three gyrotrons, each of which has generated the output power up to ~0.8 MW for 3 seconds. A strongly peaked T e profile was observed and the central electron temperature increased up to ~15 keV when the O-mode was absorbed on the axis. The local electron heating clarified the significant difference in the heat pulse propagation between in the plasmas with internal transport barrier (ITB) and without. The driven current estimated by the Motional Stark Effect (MSE) diagnostic showed that the electron cyclotron (EC) waves drove the plasma current up to ~0.2 MA for an injected power of ~1.3 MW at the local electron temperature and density of T e ~6 keV, n e ~0.7×1019 m-3. The measured driven current near the axis was consistent with the theoretical prediction using a Fokker-Planck code. In the case of co-electron cyclotron current drive (ECCD), the sawtooth activity in neutral beam (NB) heated plasma was completely suppressed for 1.5 s with the deposition at the inversion radius, while the sawtooth was enhanced for counter-ECCD at the same deposition condition.

Chapter 6: Steady state operation

“…The non-inductive current fraction reaches 90%. Work on JT-60U has shown [112,113] the maintenance of an electron transport barrier in discharges with high electron heating by a combination of ECH and negative ion based neutral beam heating as a means of simulating the strong electron heating which takes place in a burning plasma. These discharges showed excellent global confinement with 55% of the power heating electrons and T e > T i .…”

Sawtooth control using electron cyclotron current drive in the presence of energetic particles in high performance ASDEX Upgrade plasmas

“…Control of the sawtooth period with ECCD has been demonstrated on a number of tokamaks [16][17][18][19][20][21][22], and consequently has been included in the design of the sawtooth control system for ITER [23,24]. The history of sawtooth control using current drive is reviewed in [25].…”

Sawtooth control and the interaction of energetic particles

“…a crash can be triggered) by enhancing s 1 (through localized current drive, for example), or through δW reduction or reversal. For instance, current driven by electron cyclotron resonance heating has been used to control sawtooth periods in ASDEX Upgrade [11], TCV [12], JT-60U [13] and TEXTOR [14]. Furthermore, recent initial results in TORE-SUPRA [15] suggest that electron cyclotron current drive (ECCD) can be used to destabilize long-period sawteeth stabilized by a population of fast ions resulting from simultaneous ion cyclotron resonance heating (ICRH).…”