The Effects of Parallel Inhomogeneity in Lower Hybrid Current Drive RF Heating Experiments*

The effect of parallel inhomogeneity in the magnetic field on cyclotron wave damping in magnetic confinement fusion experiments has long been recognized [1,2]. Introduction of inhomogeneity broadens resonances and induces non-local energy transfer. This effect has been included for cyclotron damping in spectral full-wave codes for many years [3]. However, only recently has parallel inhomogeneity’s influence on Landau damping been calculated [4]. We extend previous analyses of parallel inhomogeneity induced broadening to arbitrary distribution functions and derive an explicit Landau resonance broadening function. We then integrate the function into TORLH full wave tokamak current drive simulations to determine the influence of inhomogeneity in lower hybrid current drive experiments. We also consider the inclusion of the effects of parallel inhomogeneity in the formulation of the quasi-linear diffusion coefficient (DQL) using a modified version of the bounced averaged DQL from [5].

[1] D.W. Faulconer, PPCF 29, 433 (1987)

[2] D. Smithe, P. Colestock, T. Kammash, R. Kasuba, PRL 60, 801 (1988)

[3] M. Brambilla, Phys. Lett. A 188, 376 (1994)

[4] L. Berry, et. al. PoP 23, 102504 (2016)

[5] J.P. Lee, D. Smithe, J.C. Wright, P.T. Bonoli PPCF 60 025007 (2018)