Speaker
Description
Fast ions from neutral beam injection (NBI) or radiofrequency (RF) heating can resonantly interact with the background plasma and excite Alfvénic eigenmodes (AEs), leading to losses and potential damage to the reactor vessel [1]. Combined RF-NBI heating shows mixed effects on the Alfvénic activity at NSTX(-U) sometimes mitigating or exciting the modes [2-4]. An accurate knowledge of the RF–NBI interplay is crucial for reliable projections from present to future devices, such as ITER.
In spherical tokamaks (STs), typical scale-lengths for variations of the magnetic field can be comparable to -or smaller than- energetic particles gyro-radius and orbit width. Therefore, applicability of the GC approximation is questionable, particularly for highly energetic ions, such as the RF-accelerated ions and the full-orbit description should be used instead [6]. In this work, we will present the implementation of the full-orbit counterpart of the RF field in the ASCOT5 code [7]. The ASCOT5 code is a particle following code that can import the RF wavefields from TORIC [8]. We will show applications of the new feature of the ASCOT5 code in a conventional tokamak, using an AUG case [9], where the GC approximation is still within reasonable limits. Comparison with kick-based GC codes, like ORBIT-RF [10, 11] and ASCOT-RFOF [12, 13], will be conducted for cross-comparison and validation. We will study the applicability and limitations of those GC codes in a ST case, NSTX(-U), comparing it to the newly developed feature in ASCOT5.
We will apply the modeling to NSTX(-U) cases to determine the changes in the AE fast-ion drive, addressing the differences observed in experiments. 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, acting on the fast-ion population, 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.
This work has been supported by the US DOE, Office of Science, Office of Fusion Energy Sciences under contract DE-AC02-09CH11466. This work has been carried out within the framework of the EUROfusion Consortium, via the Euratom Research and Training Programme (Grant Agreement No 101052200 — EUROfusion) and funded by the Swiss State Secretariat for Education, Research and Innovation (SERI). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union, the European Commission, or SERI. Neither the European Union nor the European Commission nor SERI can be held responsible for them. This work was supported in part by the Swiss National Science Foundation.
[1] A. Loarte et al., Plasma Physics and Controlled Fusion 45 (2003) pp. 1549-1569
[2] W. W. Heidbrink et al., Plasma Physics and Controlled Fusion 48 (2006) pp. 1347-1372
[3] E. D. Fredrickson et al., Nuclear Fusion 55 (2015) pp. 013012
[4] M. Podestà et al., Nuclear Fusion 52 (2012) pp. 094001
[5] J. Galdon-Quiroga et al., in preparation
[6] A. Bierwage et al., Phys. Plasmas 29 (2022) pp. 113906.
[7] J. Varje et al., arXiv:1908.02482 (2019)
[8] M. Brambilla, Plasma Physics and Controlled Fusion 41 (1999) pp. 1-34
[9] M. Weiland et al., Nucl. Fusion 57 (2017) 116058
[10] R. B. White and M. S. Chance, Physics of Fluids 27 (1984) pp. 2455-2467
[11] M. Choi et al., Physics of Plasmas 17 (2010) pp. 056102
[12] T. Johnson et al., 19th Topical Conf. on Radio Frequency Power in Plasmas, AIP Conf. Proc. 1406 (2011) 373
[13] S. Sipila et al., Nucl. Fusion 61 (2021) 086026
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