Fast-ion phase-space tailoring with RF wave fields to minimize AE transport

Fast-ions from neutral beam injection (NBI) or radio-frequency (RF) can resonantly interact with the background plasma exciting Alfvénic eigenmodes (AEs), leading to losses and damage to the reactor vessel. Combined RF-NBI heating shows mixed effected on the Alfvénic activity at NSTX(-U) sometimes mitigating or exciting the modes [1-3]. At the ASDEX-Upgrade tokamak, combined RF-NBI heating shows a reduced AE-induced fast-ion losses [4]. An accurate knowledge of the RF–NBI interplay is crucial for future devices, such as ITER.

This study uses the updated ORBIT-RF code [5, 6] to investigate the physics observed in NSTX(-U) and ASDEX Upgrade. The ORBIT-RF code, a Hamiltonian guiding-center following code, can import the AE modes from NOVA [7] code and RF wave field from TORIC [8] to track the particles’ evolution. We plan on making phase-space resonant power maps, that will inform strategies to mitigate particle transport by instabilities. We will examine how the phase-space stochasticity due to RF fields can be used to change the nonlinear evolution of the AEs, and specifically, we study whether the convective transport during AE frequency chirping could be suppressed using RF waves.

[1] W. W. Heidbrink et al., Plasma Phys. and Control. Fus.48 (2006)

[2] E. D. Fredrickson et al., Nucl. Fus. 55 (2015)

[3] M. Podestà et al., Nucl. Fus. 52 (2012)

[4] J. Galdon-Quiroga et al., in preparation

[5] R. B. White and M. S. Chance, Phys. Fluids 27 (1984)

[6] M. Choi et al., Phys. Plasmas 17 (2010)

[7] C.Z. Cheng et al., J. Comp. Phys. 71 (1987)

[8] M. Brambilla, Plasma Phys. and Control. Fus. 41 (1999)