Full Wave Simulation of Lower Hybrid Waves in ITER Plasmas Based on the Finite Element Method

Meneghini, O.; Shiraiwa, S.

doi:10.1585/pfr.5.s2081

Cited by 10 publications

(7 citation statements)

References 15 publications

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“…Spectrum spreading observed in the full-wave code is not important if the single pass absorption is strong. In fact, LHCD simulations using ray-tracing and LHEAF in an ITER plasma predicted almost identical power deposition and driven current profiles [40]. As for PDI, although its importance in the strong single pass absorption regime is still arguable, the result on Alcator C-Mod suggests that it may not be a major power loss mechanism.…”

Section: Velocity Space Synergymentioning

confidence: 99%

Progress towards steady-state regimes in Alcator C-Mod

et al. 2013

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Recent progress on lower hybrid current drive (LHCD) experiment and simulation towards steady-state (t ⩾ 3–5 × τr, where τr is the current relaxation time) regimes on Alcator C-Mod is presented. Highly non-inductive reversed shear plasmas are obtained with spontaneous generation of internal transport barriers at the density close to what is expected on ITER steady-state scenarios. Progress has been made to better understand and mitigate the unexpected degradation of LHCD efficiency at high densities, which poses an issue both for extending the non-inductive plasmas to advanced tokamak regimes (with a high bootstrap current fraction, fBS) on C-Mod and for predicting the performance of LHCD on future devices such as ITER. Several physics mechanisms that potentially contribute anomalous losses of LHCD power have been studied extensively. Numerical modelling of collisional absorption in cold scrape-off layer plasmas has been integrated into a ray-tracing code. The LHEAF full-wave code clarifies that full-wave effects move the power deposition profile closer to the separatrix than a calculation based on the WKB approximation, leading to a lower efficiency. Non-linear wave interactions were studied experimentally by LH wave spectral measurements using Langmuir probes, suggesting parametric decay instabilities to explain the remaining difference between experiments and simulations. An experimental demonstration of recovery of good LHCD efficiency at high densities is also reported. Improving the single pass absorption is proposed as a key to recover LHCD efficiency. A wave physics design of additional launcher (LH3) has been developed in order to demonstrate an improved LHCD performance by realizing high (∼80%) single pass absorption, in which the synergistic interaction in the velocity space with the existing launcher is maximized.

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Section: Velocity Space Synergymentioning

confidence: 99%

Progress towards steady-state regimes in Alcator C-Mod

et al. 2013

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“…HFS launch then both improves current drive efficiency which scales ∝ 1/N 2 [53] and enables off-axis LHCD in tokamak scenarios where it previously was not possible because waves launched at the low-field-side access limit would damp before reaching the top of an H-mode pedestal. Only one study verifying raytracing using full-wave simulation in reactor-relevant LHCD regimes has been performed previously [54], and a fullwave simulation of LH wave propagation and damping using HFS launchers has never been performed despite their importance in ARC reactor designs [14]. Finally, in the DIII-D HFS cases the rays propagate through a number of caustics even though they undergo strong single-pass damping.…”

Section: Diii-d Hfs Lhcdmentioning

confidence: 99%

An Assessment Of Full Wave Effects On Maxwellian Lower Hybrid Wave Damping

Frank¹,

Wright²,

Hutchinson³

et al. 2022

Preprint

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Lower-hybrid current drive (LHCD) actuators are important components of modern day fusion experiments as well as proposed fusion reactors. However, simulations of LHCD often differ substantially from experimental results, and from each other, especially in the inferred power deposition profile shape. Here we investigate some possible causes of this discrepancy; "full-wave" effects such as interference and diffraction, which are omitted from standard raytracing simulations and the breakdown of the raytracing near reflections and caustics. We compare raytracing simulations to state-of-the-art full-wave simulations using matched hot-plasma dielectric tensors in realistic tokamak scenarios for the first time. We show that differences between fullwave simulations and raytracing in previous work were primarily due to numerical and physical inconsistencies in the simulations, and we demonstrate that good agreement between raytracing and full-wave simulations can be obtained in reactor relevantscenarios with large ray caustics and in situations with weak damping.

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“…Spatial domain FEM codes have several advantages over spectral solvers for ICRF simulation, including the capability to include complex 3-D antenna structures and SOL details that play an important role in coupling and E generation. In addition, FEM generally produces numerically sparse matrices, an important consideration for the solution of large electromagnetic problems [30].…”

Section: Spatial Domain Cold Plasma Modelmentioning

confidence: 99%