ECRH current drive studies in the CLEO tokamak

Abstract

Non-inductive current drive using second harmonic ECRH at both 28 GHz and 60 GHz has been studied in the CLEO tokamak. At 60 GHz, RF driven currents of up to 5 kA have been observed at n e = 4 x 10 18 rn~3 for 185 kW of injected power, indicating an efficiency of rj = IVJRFRO/PRF = 0 0 °l ( i o 2 ° m ~3. A > m > w ~' ) -T n e R F driven current scaled linearly with total plasma current in the range of 5-15 kA and was maximized when the cyclotron resonance was located near to the centre of the plasma. Sawtooth activity was normally strongly affected and transient sawtooth stabilization was often observed. With detailed theoretical studies it is possible to reproduce both the high absorption efficiencies and the scaling of RF driven current with resonance position seen in the 60 GHz experiments. However, the magnitude of the observed current is a factor of about three below that theoretically predicted. At 28 GHz, no evidence of RF driven current could be detected. Possible reasons for this are discussed.

Radial Transport and Electron-Cyclotron-Current Drive in the TCV and DIII-D Tokamaks

“…The role of radial transport on high energy electrons, particularly regarding radiofrequency (rf ) experiments, has been examined extensively ( [5][6][7][8][9][10][11], and references therein). Unique features in this Letter are that the TCV tokamak is entirely driven by EC power, removing ambiguities of Ohmic current and runaway electron current, and that the CQL3D numerical model for EC absorption and current drive has been extensively benchmarked against the well-diagnosed DIII-D tokamak.…”

Derek Robinson. 27 May 1941 — 2 December 2002

“…it was found that the stellarator had the best confinement time, τ e , but the tokamak achieved the best 'performance product', βτ e (26). in experiments led by Dr brian Lloyd with Dr A. C. (Tony) riviere and others, the device was also used to demonstrate non-inductive current drive by electron cyclotron current drive (eCCD) (32). To model such eCrH experiments, Derek encouraged Martin o'brien to develop a Fokker-Planck code, bAnDiT-3D (o'brien et al 1986), which has been used widely since.…”

Effects of radial transport on current drive in tokamaks

“…The use of lower hybrid heating (LHH) and electron cyclotron resonance heating (ECRH) to drive currents in tokamaks has received much theoretical and experimental attention (see, for example, Refs [1][2][3][4][5]). Two main uses of these schemes have been proposed and investigated: bulk current drive to reduce the voltsecond requirements of Ohmic heating and, particularly for electron cyclotron current drive (ECCD), control of the current profile to improve magnetohydrodynamic stability [6,7].…”

“…Two main uses of these schemes have been proposed and investigated: bulk current drive to reduce the voltsecond requirements of Ohmic heating and, particularly for electron cyclotron current drive (ECCD), control of the current profile to improve magnetohydrodynamic stability [6,7]. However, it has been recognized both theoretically [8][9][10] and experimentally [5,11] that radial transport of the current carrying electrons can lead to both a broadening of the driven current profile and a reduction of the total driven current. In this letter we present the results of a numerical investigation of these effects.…”

“…In the absence of radial transport, the code reproduces the classical Spitzer resistivity for Ohmic heating, as well as the current drive efficiencies for both ECRH and LHH given by CES [3] and others. We consider first the effects of transport on LHCD and then model the ECCD experiments in the CLEO tokamak [5] in which the discrepancy between driven and predicted currents was attributed to these transport effects [9].…”