Modeling of solenoid-free start-up using 2nd harmonic electron cyclotron heating and current drive in QUEST

Ono, M.; Bertelli, N.; Idei, H.; Hanada, K.; Onchi, Takumi; Kojima, Shinichiro; Elserafy, Hatem

doi:10.1063/5.0013966

Cited by 8 publications

(2 citation statements)

References 10 publications

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“…We also see that the X-mode have better absorption than O-mode, and the second order 2ω cH resonant is also stronger than that of O-mode. These high energy electron effects are similar to the recently reported [21] QUEST experimental and theoretical analysis results. We can also see from Fig.…”

Section: St Ecw Under Multi-fluid Equilibriumsupporting

confidence: 90%

BORAY: An Axisymmetric Ray Tracing Code Supports Both Closed and Open Field Lines Plasmas

Xie,

Debabrata,

Bai

et al. 2021

Preprint

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Ray tracing codes are useful to study the electromagnetic wave propagation and absorption in the geometrical optics approximation. In magnetized fusion plasma community, most ray tracing codes assume the plasma density and temperature be functions of the magnetic flux and study waves only inside the last closed flux surface, which are sufficient for the present day tokamak. However, they are difficult to be used for configurations with open magnetic field line plasmas, such as mirror machine and field-reversed-configuration (FRC). We develop a ray tracing code in cylindrical coordinates (r, φ, z) to support arbitrary axisymmetric configurations with both closed and open field lines plasmas. For wave propagation, the cold plasma dispersion relation is usually sufficient, and we require the magnetic field B(r, z) and species densities n s0 (r, z) profiles as input. For wave absorption, we require a further temperature T s0 (r, z) profile to solve a hot kinetic plasma dispersion relation. In difference to other ray tracing codes which calculate the imaginary part of wave vector k ⊥,i for wave absorption, we calculate the imaginary part of wave frequency ω i , which is shown to be equivalent with the former technique under weak damping approximation. The code can use either numerical or analytical equilibrium. Examples and benchmarks with electron cyclotron wave, lower hybrid wave and ion cyclotron wave for tokamak, spherical tokamak (ST), FRC and mirror machine are shown.

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Section: St Ecw Under Multi-fluid Equilibriumsupporting

confidence: 90%

BORAY: An Axisymmetric Ray Tracing Code Supports Both Closed and Open Field Lines Plasmas

Xie,

Debabrata,

Bai

et al. 2021

Preprint

View full text Add to dashboard Cite

show abstract

“…The single-pass absorption amount and the current driven by the ECCD were calculated using the RT-4 ray-tracing code developed in PPPL by Ono et al [54]. The RF absorption was calculated based on the hot-dispersion relationship.…”

Section: Discussionmentioning

confidence: 99%

Observation of second harmonic electron cyclotron resonance heating and current-drive transition during non-inductive plasma start-up experiment in QUEST

Kojima¹,

Hanada²,

Idei³

et al. 2021

Plasma Phys. Control. Fusion

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Noninductive plasma current start-up using 2nd harmonic electron cyclotron resonance heating (ECRH) with oblique radio frequency (RF) injection is demonstrated in a Q-shu University experiment with steady-state spherical tokamak. A strong transition was observed in the heating and plasma current ramp-up. The initial bulk electron heating regime exhibits T ebulk ∼ 140 eV and no hard x-ray (HXR) emission with a low I p of ∼15 kA; it abruptly transitions to a regime that exhibits a low T ebulk of ∼10 eV and a strong HXR emission with a high I p of ∼50 kA. This behavior is distinctly different from that observed in previous fundamental ECRH experiments. The mechanism of the heating and current drive transition are investigated considering wave power absorption and plasma power balance. The results indicate that the transition is caused by the favorable heating of tail electrons where the RF power absorption at the 2nd harmonic increases nearly linearly with T etail , while the power transfer from the tail electrons to the bulk electrons decreases with 1/T etail 0.5 . This causes a rapid transition to a state with high T etail while reducing T ebulk towards colder ion temperature. The understanding of the transition mechanism helps to consider plasma current start-up using 2nd harmonic ECRH for tokamak reactors such as JT-60 SA and ITER.

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Non-inductive plasma current ramp-up through oblique injection of harmonic electron cyclotron waves on the QUEST spherical tokamak

et al. 2021

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The plasma current is ramped up primarily by a 28 GHz electron cyclotron wave (ECW) in the Q-shu University experiment Steady-State Spherical Tokamak (QUEST), with multiple harmonic resonance layers from the second to the fourth stay in the plasma core. A steering antenna comprising two quasi-optical mirrors enhances the power density of ECWs. The ECW beam is injected obliquely from the low-field side where the parallel refractive index is N∥ = 0.75 at the second-harmonic resonance layer. Analysis of the resonance condition has found that energetic electrons moving forward along the magnetic field resonate more effectively than those moving backward. Such symmetry breaking is consistent with the results of the current ramp-up experiment. The peak plasma current reaches Ip>70 kA, constantly injecting a beam of radio frequency power of 100 kW. Ray-tracing by the TASK/WR code demonstrates that the power of the 28 GHz extraordinary mode is absorbed by energetic electrons via single-pass cyclotron absorption.

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Modeling of solenoid-free start-up using 2nd harmonic electron cyclotron heating and current drive in QUEST

Cited by 8 publications

References 10 publications

BORAY: An Axisymmetric Ray Tracing Code Supports Both Closed and Open Field Lines Plasmas

BORAY: An Axisymmetric Ray Tracing Code Supports Both Closed and Open Field Lines Plasmas

Observation of second harmonic electron cyclotron resonance heating and current-drive transition during non-inductive plasma start-up experiment in QUEST

Non-inductive plasma current ramp-up through oblique injection of harmonic electron cyclotron waves on the QUEST spherical tokamak

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