Lower hybrid heating and current drive on the Alcator C-Mod tokamak

On the Alcator C-Mod tokamak, lower hybrid current drive (LHCD) is being used to modify the current profile with the aim of obtaining advanced tokamak (AT) performance in plasmas with parameters similar to those that would be required on ITER. To date, power levels in excess of 1 MW at a frequency o...

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Bibliographic Details
Published in:Nuclear fusion 2009-11, Vol.49 (11), p.115015-115015 (8)
Main Authors: Wilson, J.R, Parker, R, Bitter, M, Bonoli, P.T, Fiore, C, Harvey, R.W, Hill, K, Hubbard, A.E, Hughes, J.W, Ince-Cushman, A, Kessel, C, Ko, J.S, Meneghini, O, Phillips, C.K, Porkolab, M, Rice, J, Schmidt, A.E, Scott, S, Shiraiwa, S, Valeo, E, Wallace, G, Wright, J.C
Format: Article
Language:English
Subjects:
Current drive
helicity injection
Exact sciences and technology
Laser-plasma interactions
Magnetic confinement and equilibrium
Physics
Physics of gases, plasmas and electric discharges
Physics of plasmas and electric discharges
Plasma heating by radiofrequency fields
icr, icp, helicons
Plasma production and heating
Tokamaks
X-ray, gamma-ray and particle generation
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Summary:On the Alcator C-Mod tokamak, lower hybrid current drive (LHCD) is being used to modify the current profile with the aim of obtaining advanced tokamak (AT) performance in plasmas with parameters similar to those that would be required on ITER. To date, power levels in excess of 1 MW at a frequency of 4.6 GHz have been coupled into a variety of plasmas. Experiments have established that LHCD on C-Mod behaves globally as predicted by theory. Bulk current drive efficiencies, n 20 I lh R / P lh ∼ 0.25, inferred from magnetics and MSE are in line with theory. Quantitative comparisons between local measurements, MSE, ECE and hard x-ray bremsstrahlung, and theory/simulation using the GENRAY, TORIC-LH CQL3D and TSC-LSC codes have been performed. These comparisons have demonstrated the off-axis localization of the current drive, its magnitude and location dependence on the launched n ∥ spectrum, and the use of LHCD during the current ramp to save volt-seconds and delay the peaking of the current profile. Broadening of the x-ray emission profile during ICRF heating indicates that the current drive location can be controlled by the electron temperature, as expected. In addition, an alteration in the plasma toroidal rotation profile during LHCD has been observed with a significant rotation in the counter-current direction. Notably, the rotation is accompanied by peaking of the density and temperature profiles on a current diffusion time scale inside of the half radius where the LH absorption is taking place.
ISSN:0029-5515
1741-4326
DOI:10.1088/0029-5515/49/11/115015