Reduced ﬁeld Scenario with X3 heating in W7-X

Marushchenko, N. B.; Aleynikov, P.; Beidler, C. D.; Dinklage, A.; Geiger, J.; Helander, P.; Laqua, H. P.; Maaßberg, H.; Turkin, Y.

doi:10.1051/epjconf/201920301006

Cited by 11 publications

(10 citation statements)

References 16 publications

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“…The ICRF heating scenario, if successful, could be used for reduced field operation at 1.7 T in Wendelstein 7-X (W7-X) stellarator [18] with a hydrogen minority in deuterium working gas (heating frequency is f ≈ 26 MHz). This scenario has successfully been demonstrated at U-2M, only, which is notably smaller than LHD and W7-X.…”

Section: Introductionmentioning

confidence: 99%

First experiments on plasma production using field-aligned ICRF fast wave antennas in the large helical device

et al. 2021

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The results of the first experimental series to produce a plasma using the ion cyclotron range of frequency (ICRF) in the large helical device (LHD) within the minority scenario developed at Uragan-2M (U-2M) are presented. The motivation of this study is to provide plasma creation in conditions when an electron cyclotron resonance heating start-up is not possible, and in this way widen the operational frame of helical machines. The major constraint of the experiments is the low RF power to reduce the possibility of arcing. No dangerous voltage increase at the radio-frequency (RF) system elements and no arcing has been detected. As a result, a low plasma density is obtained and the antenna-plasma coupling is not optimal. However, such plasmas are sufficient to be used as targets for further neutral beam injection (NBI) heating. This will open possibilities to explore new regimes of operation at LHD and Wendelstein 7-X (W7-X) stellarator. The successful RF plasma production in LHD in this experimental series stimulates the planning of further studies of ICRF plasma production aimed at increasing plasma density and temperature within the ICRF minority scenario as well as investigating the plasma prolongation by NBI heating.

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Section: Introductionmentioning

confidence: 99%

First experiments on plasma production using field-aligned ICRF fast wave antennas in the large helical device

et al. 2021

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“…The importance of nonlinear wave-particle interaction during plasma initiation was previously demonstrated for a plane-wave approximation (Jaeger, Lichtenberg & Lieberman 1972;Carter et al 1986), and in a homogeneous magnetic field for a Gaussian beam structure (Farina & Pozzoli 1991;Seol, Hegna & Callen 2009;Farina 2018). Therefore, it is instrumental to understand the nonlinear interaction when designing and optimising reactor startup scenarios, such as ECRH-assisted startup in the International Thermonuclear Experimental Reactor (ITER), and higher-harmonic startup in Wendelstein 7-X (W7-X) (Marushchenko et al 2019). In particular, Farina (2018) highlights the difficulty of using the third harmonic (X3) for startup, demonstrating that, in a homogeneous background field, the interaction is too weak to support a startup using modern gyrotrons.…”

Section: Introductionmentioning

confidence: 99%

“…Therefore, it is instrumental to understand the nonlinear interaction when designing and optimising reactor startup scenarios, such as ECRH-assisted startup in the International Thermonuclear Experimental Reactor (ITER), and higher-harmonic startup in Wendelstein 7-X (W7-X) (Marushchenko et al. 2019). In particular, Farina (2018) highlights the difficulty of using the third harmonic (X3) for startup, demonstrating that, in a homogeneous background field, the interaction is too weak to support a startup using modern gyrotrons.…”

Section: Introductionmentioning

confidence: 99%

Electron cyclotron resonance during plasma initiation

Johansson,

Aleynikov

2024

J. Plasma Phys.

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Electron-cyclotron resonance heating (ECRH) is the main heating mechanism in the Wendelstein 7-X (W7-X) stellarator. Although second-harmonic ECRH (X2) has been used routinely for plasma startup, startup at third harmonic (X3) is known to be much more difficult. In this work, we investigate the energy gain of particles during nonlinear wave–particle interaction for conditions relevant to second- and third-harmonic startups in W7-X. We take into account both the beam and the ambient magnetic field inhomogeneities. The latter is shown to significantly increase the mean energy gain resulting from a single wave–particle resonant interaction. In W7-X-like conditions, the improvement in maximum gained energy is up to 4 times the analogous uniform magnetic field case. However, this improvement is not enough to ensure X3 startup. The optimal magnetic field inhomogeneity length scale for average energy gain and start up in W7-X-like conditions is found to be in the range of $1$ to $3\ {\rm km}^{-1}$ . A possibility of using multiple beams with neighbouring resonances is also considered. A considerable enhancement of the energy gain is demonstrated.

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“…The scenario could be considered for use at Wendelstein 7-X (W7-X) at 1.7 T magnetic field [14] with the hydrogen light ion species (heating frequency is about 26 MHz). In-depth studies of this scenario at U-2M could be a background for such a project, but a small size of U-2M and low magnetic field impose some uncertainties.…”

Section: Introductionmentioning

confidence: 99%

ICRF plasma production at hydrogen minority regime in LHD

Kovtun,

Kasahara,

Moiseenko

et al. 2023

Nucl. Fusion

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his study aim is to develop further an ion cyclotron range of frequencies (ICRF) method of plasma production in stellarators based on the minority heating. The previous studies demonstrate production of low density plasma (9.5×1017 m−3) at low power of up to 0.2 MW. The higher ICRF heating power experiments become possible after introducing a programmable ICRF power ramp up at the front of the ICRF pulse. With this trick, all the shots went with the antenna voltage within the safe range. Increase of the ICRF power predictably results in increase of the density of produced plasma. Without pre-ionization the plasma density achieved was 6×1018 m-3 which is 6 times higher than in previous experiments. However, the electron temperature was not high, the light impurities were hot fully stripped, and there were no recombination peaks after termination of the ICRF pulse. Plasma density is too low to provide good conditions for efficient plasma heating. For the reference, the ICRF heating of high density cold plasma prepared by electron cyclotron resonance heating (ECRH) is performed. Both electrons and ions were heated to high temperatures, and this plasma state is sustained. The antenna-plasma coupling was much better which result in larger heating power with the lower antenna voltage.

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Reduced ﬁeld Scenario with X3 heating in W7-X

Cited by 11 publications

References 16 publications

First experiments on plasma production using field-aligned ICRF fast wave antennas in the large helical device

First experiments on plasma production using field-aligned ICRF fast wave antennas in the large helical device

Electron cyclotron resonance during plasma initiation

ICRF plasma production at hydrogen minority regime in LHD

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