Development of helium electron cyclotron wall conditioning on TCV

Douai, D.; Goodman, T. P.; Isayama, A.; Fukumoto, M.; Wauters, T.; Sozzi, C.; Coda, S.; Blanchard, P.; Figini, L.; Garavaglia, S.; Miyata, Yasumitsu; Moro, A.; Ricci, D.; Silva, M.; Theiler, C.; Vartanian, S.; Verhaegh, K.

doi:10.1088/1741-4326/aa9d2b

Cited by 18 publications

(14 citation statements)

References 15 publications

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“…Discharge parameters in the experiment in TCV were tuned in order (i) to minimize the absorption of stray radiation by in-vessel components by minimizing the time for ECRH plasma breakdown, and maximizing the absorption of ECRH power over the duration of the discharge, (ii) to improve the discharge homogeneity, by extending the discharge vertically and radially, and wall coverage, in particular of inboard surfaces where JT-60SA plasmas will be initiated [43], and (iii) to improve the efficiency of He-ECWC to deplete carbon-based PFC from fuel. For all above purposes, the application of a vertical field component of about 0.5% of the toroidal field is found to be critical [40]. It reduces the breakdown time and increases the achievable density by compensating the vertical × ∇ drift by a vertical pitch angle [37], [45].…”

Section: Electron Cyclotron Wall Conditioning In Tcvmentioning

confidence: 99%

Wall conditioning in fusion devices with superconducting coils

Wauters¹,

Borodin

Brakel

et al. 2020

Plasma Phys. Control. Fusion

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Wall conditioning is essential in tokamak and stellarator research to achieve plasma performance and reproducibility. This paper presents an overview of recent conditioning results, both from experiments in present devices and modelling, in view of devices with superconducting coils, with focus on W7-X, JT-60SA and ITER. In these devices, the coils stay energised throughout an experimental day or week which demands for new conditioning techniques that work in presence of the nominal field, in addition to the proven conditioning methods such as baking, glow discharge conditioning (GDC) and low-Z wall coating through GDC-plasma, which do not work under such condition. The discussed techniques are RF conditioning without plasma current, both in the ion cyclotron and electron cyclotron range of frequencies, and diverted conditioning plasmas with nested magnetic flux surfaces.

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Section: Electron Cyclotron Wall Conditioning In Tcvmentioning

confidence: 99%

Wall conditioning in fusion devices with superconducting coils

Wauters¹,

Borodin

Brakel

et al. 2020

Plasma Phys. Control. Fusion

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“…This lead to H becoming the minority species as the He partial pressure was continuously increased. While it is less common to operate optical Penning gauges with H as the minority species, it has been used to study hydrogen coming off the wall during He wall conditioning at TCV 16 . This could lead to a different operation regime, since the ionization of He is providing the…”

Section: Gas Dependence Of Ion Current Measurementmentioning

confidence: 99%

Wisconsin In Situ Penning (WISP) gauge: A versatile neutral pressure gauge to measure partial pressures in strong magnetic fields

Kremeyer

Flesch

Schmitz

et al. 2020

Review of Scientific Instruments

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A new type of in-vessel Penning gauge, the Wisconsin In-Situ Penning (WISP) gauge, has been developed and successfully operated in the Wendelstein 7-X (W7-X) island divertor baffle and vacuum vessel. The capacity of the quantitative measurements of the neutral reservoir for light impurities, in particular helium, is important for tokamaks as well as stellarator divertors in order to avoid fuel dilution and radiative energy loss. Penning gauges assisted by spectroscopy are a powerful tool to obtain the total neutral pressure as well as fractional neutral pressures of specific impurities. The WISP gauge is a miniaturized Penning gauge arrangement, which exploits the ambient magnetic field of magnetic confinement fusion experiments to establish the Penning discharge. Then, in-situ spectroscopy is conducted to separate the fractional neutral pressures of hydrogen, helium and possibly also other impurities. The WISP probe head was qualified using the magnetic field of the Magnetized Dusty Plasma Experiment, MDPX, at Auburn University between 0.25 T and 3.5 T [E. Thomas, Journal of Plasma Physics 81 ( 2015)]. The in-depth quantitative evaluation for hydrogen and helium will be shown as well as an exploration of nitrogen, argon and neon. A power law scaling between current I and pressure p: I = f (Gas,V) • p n(Gas, B) was shown. The factor f is gas and anode potential dependent, while n is gas and magnetic field strength dependent. Pressure measurements from 0.1 mbar and down to 1 × 10 −5 mbar were achieved, demonstrating a reliable operation range for relevant pressure levels in the divertor and main vessel regions in current and future fusion devices, with a time resolution of up to 1 kHz. The lowest achievable pressure measurement increases with increasing B and can be shifted with the anode potential V .At Wendelstein 7-X the WISP probe head was mounted on an immersion tube set up that reaches through the cryostat and places the probe head close to the plasma. Two probe heads were positioned in the different divertor pump gaps, top and bottom, and one close to the plasma on the mid-plane in one module. The gauges were in-situ calibrated together with the ASDEX pressure gauges [G. Haas and H. Bosch, Vacuum 51, 39 (1998)]. Data was taken during the entire operation phase 1.2b (OP1.2b) and measurements were coherent with other neutral gas pressure gauges. For the spectroscopic partial pressure measurements, channels of a spectroscopic detection system based on photo-multipliers, so-called Filterscope [R. Colchin, Review of scientific instruments 74, 2068 (2003)] provided by Oak Ridge National Lab (ORNL) were used.

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“…TCV has been used to test techniques anticipated for the successful operation of JT-60SA [49], which will also feature a carbon wall. Characterization of wall cleaning with ECRH, as a substitute for glow discharge cleaning (GDC), has continued from the previous campaign [50]. Additionally, experiments were performed on ECRH-assisted start-up at reduced loop voltage (electric field 0.7 V m −1 , consistent with JT-60SA) with residual gas and/or impurities, such as would be expected after a disruption or generally with a shortened shot cycle.…”

Section: Wall Cleaning and Start-up Assist With Ecrh In Support Of Jt...mentioning

confidence: 99%

Physics research on the TCV tokamak facility: from conventional to alternative scenarios and beyond

Coda

Agostini²,

Albanese

et al. 2019

Nucl. Fusion

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The research program of the TCV tokamak ranges from conventional to advanced-tokamak scenarios and alternative divertor configurations, to exploratory plasmas driven by theoretical insight, exploiting the device’s unique shaping capabilities. Disruption avoidance by real-time locked mode prevention or unlocking with electron-cyclotron resonance heating (ECRH) was thoroughly documented, using magnetic and radiation triggers. Runaway generation with high-Z noble-gas injection and runaway dissipation by subsequent Ne or Ar injection were studied for model validation. The new 1 MW neutral beam injector has expanded the parameter range, now encompassing ELMy H-modes in an ITER-like shape and nearly non-inductive H-mode discharges sustained by electron cyclotron and neutral beam current drive. In the H-mode, the pedestal pressure increases modestly with nitrogen seeding while fueling moves the density pedestal outwards, but the plasma stored energy is largely uncorrelated to either seeding or fueling. High fueling at high triangularity is key to accessing the attractive small edge-localized mode (type-II) regime. Turbulence is reduced in the core at negative triangularity, consistent with increased confinement and in accord with global gyrokinetic simulations. The geodesic acoustic mode, possibly coupled with avalanche events, has been linked with particle flow to the wall in diverted plasmas. Detachment, scrape-off layer transport, and turbulence were studied in L- and H-modes in both standard and alternative configurations (snowflake, super-X, and beyond). The detachment process is caused by power ‘starvation’ reducing the ionization source, with volume recombination playing only a minor role. Partial detachment in the H-mode is obtained with impurity seeding and has shown little dependence on flux expansion in standard single-null geometry. In the attached L-mode phase, increasing the outer connection length reduces the in–out heat-flow asymmetry. A doublet plasma, featuring an internal X-point, was achieved successfully, and a transport barrier was observed in the mantle just outside the internal separatrix. In the near future variable-configuration baffles and possibly divertor pumping will be introduced to investigate the effect of divertor closure on exhaust and performance, and 3.5 MW ECRH and 1 MW neutral beam injection heating will be added.

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Development of helium electron cyclotron wall conditioning on TCV

Cited by 18 publications

References 15 publications

Wall conditioning in fusion devices with superconducting coils

Wall conditioning in fusion devices with superconducting coils

Wisconsin In Situ Penning (WISP) gauge: A versatile neutral pressure gauge to measure partial pressures in strong magnetic fields

Physics research on the TCV tokamak facility: from conventional to alternative scenarios and beyond

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