External Heating and Current Drive Source Requirements towards Steady-state Operation in ITER
Authors: F.M. Poli, C.E. Kessel, P.T. Bonoli, D.B. Batchelor, R.W. Harvey and P.B. Snyder
Abstract:
Steady state scenarios envisaged for ITER aim at optimizing the bootstrap current, while maintaining sufficient confinement and stability to provide the necessary fusion yield. Non-inductive scenarios will need to operate with Internal Transport Barriers (ITBs) in order to reach adequate fusion gain at typical currents of 9 MA. However, the large pressure gradients associated with ITBs in regions of weak or negative magnetic shear can be conducive to ideal MHD instabilities, reducing the no-wall limit. The E Χ B flow shear from toroidal plasma rotation is expected to be low in ITER, with a major role in the ITB dynamics being played by magnetic geometry. Combinations of heating and current drive (H/CD) sources that sustain reversed magnetic shear profiles throughout the discharge are the focus of this work. Time-
dependent transport simulations indicate that a combination of electron cyclotron
(EC) and lower hybrid (LH) waves is a promising route towards steady state operation
in ITER. The LH forms and sustains expanded barriers with their foot at large radii,
while the EC deposition at mid-radius freezes the bootstrap current profile stabilizing
the barrier and leading to confinement levels 50% higher than typical H-mode energy
confinement times. Using LH spectra with parallel refractive index in the range of
1.75-1.85, the performance of these plasma scenarios is close to the ITER target of 9
MA non-inductive current and fusion gain Q = 5.
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Published in: Nuclear Fusion 54 073007 (April 2014)
doi:10.1088/0029-5515/54/7/073007
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