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- Glazunov, G.P., et al.
(author)
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Vacuum-plasma properties of stainless steel after impact of combined glow-microwave discharges in argon atmosphere
- 2021
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In: Problems of Atomic Science and Technology. - : Problems of Atomic Science and Technology. ; 27:1, s. 50-56
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Journal article (peer-reviewed)abstract
- The experiments were carried out to determine the vacuum-plasma characteristics (mainly erosion and outgassing rate in a vacuum) of the stainless steel 12X18H10T before and after processing the walls of the vacuum chamber with the glow discharge and combined, glow-microwave plasma discharges in argon atmosphere. The current-voltage characteristics, the electron density and electron temperature were measured. It was observed that the discharge voltage in the combined regime is significantly lower than in glow discharges. In some modes, this voltage decrease can be up to 200 V. It was shown that erosion of stainless steel 12X18H10T in the combined discharges is 70 %, less than in the glow discharges. Measurements were made of the outgassing rate of 12X18H10T stainless steel with the thermal desorption probe in situ in the DSM-1 vacuum chamber. It was shown that cleaning the chamber wall by the glow discharge during 5 h leads to a decrease in the outgassing rate from 5.5·10-5 to 1·10-5 (Torr.l)/(s.cm2) . When the chamber wall is treated with GM discharge starting from nearly the same initial conditions the outgassing rate decreased to 3·10-6 (Torr.l)/(s.cm2). Spectral measurements of the plasma radiation of a glow and combined discharges show a decrease in the ratio of the peaks of argon ions and neutrals during the transition from a glow discharge to a combined one.
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- Kamio, S., et al.
(author)
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First experiments on plasma production using field-aligned ICRF fast wave antennas in the large helical device
- 2021
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In: Nuclear Fusion. - : Institute of Physics (IOP). - 0029-5515 .- 1741-4326. ; 61:11
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Journal article (peer-reviewed)abstract
- 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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- Kotenko, V.G., et al.
(author)
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Heliotron magnetic system of a fusion neutron source
- 2021
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In: Problems of Atomic Science and Technology. - : Problems of Atomic Science and Technology. ; 27:1, s. 15-18
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Journal article (peer-reviewed)abstract
- Numerical calculations have been carried out on magnetic field of heliotron magnetic system with a region of stellarator and mirror-type magnetic field superposition. Formation of a region of magnetic field superposition takes place in the gap between two helical coil sections which have reduced pitch length L in comparison with pitch length L0 of the heliotron helical coils, L=L0/3.
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- Kovtun, Yurii, et al.
(author)
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Development of Technology for Vacuum Surface Conditioning by RF Plasma Discharge Combined With DC Discharge
- 2021
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In: Science and Innovation. - : National Academy of Sciences of Ukraine. - 2409-9066 .- 2413-4996. ; 17:4, s. 33-43
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Journal article (peer-reviewed)abstract
- Introduction: It is important to decrease light and heavy impurities influxes towards the plasma volume during the high temperature plasma experiments in fusion devices. This is why the conditioning of the wall inner vacuum surfaces is a basic part of the fusion device operation.Problem Statement: The conventional inner vacuum chamber surface conditioning methods has a significant drawback: sputtering materials in a vacuum chamber. The inner vacuum surfaces can be also conditioned with radio-frequency (RF) discharge plasma, but the conditioning effectiveness is limited by low ion energy.Purpose: The purpose of this research is to develop vacuum surface conditioning technology by the radio frequency plasma combined with DC discharge.Materials and Methods: The noncontact passive method of optical plasma spectroscopy has been used to estimate ion plasma composition. The stainless steel outgassing has been determined in situ with the thermodesorption probe method. The sputtering of the samples has been measured with the weight loss method.Results: The studies of combined discharge have shown that: the anode voltage of combined discharge is lower than in case of the glow discharge; the stainless steel 12Kh18N10T erosion coefficient is about 1.5 times less in the case of combined discharge than in the glow one; the thermal desorption diagnostic of wall conditions in the DSM-1 experimental device has shown better efficiency with the combined discharge as compared with the glow discharge. The proposed technology is an original one and has no analogs.Conclusions: The reported research results have shown good prospects for the combined discharge usage for plasma walls conditioning and opportunities for using the combined discharge technology for big fusion machines.
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| 8. |
- Kovtun, Yu.V., et al.
(author)
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Design and application of glow discharge cleaning at Uragan-2M stellarator
- 2021
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In: Problems of Atomic Science and Technology. - : Charkov Institute of Physics and Technology. ; 27:1, s. 19-24
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Journal article (peer-reviewed)abstract
- For the Uragan-2M stellarator, a glow discharge cleaning (GDC) system is developed. An overview of the GDC system design is presented. The first experimental studies of GDC in an argon atmosphere have been carried out. The dependence of the breakdown voltage on the argon pressure is determined. The current-voltage characteristics of the gas discharge were measured as a function of the working gas pressure also in presence of a magnetic field.
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| 9. |
- Kovtun, Yu.V., et al.
(author)
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ICRF plasma production in gas mixtures in the Uragan-2M stellarator
- 2023
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In: Fusion engineering and design. - : Elsevier BV. - 0920-3796 .- 1873-7196. ; 194
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Journal article (peer-reviewed)abstract
- This paper summarizes previous results and presents new studies on the ICRF plasma creation both in pure gases and gas mixtures. In all the experiments, the two-strap antenna was operated in monopole phasing with applied RF power of ∼100 kW. The research for plasma creation was carried out at RF frequencies near the fundamental hydrogen cyclotron harmonic.
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| 10. |
- Kovtun, Yurii, V, et al.
(author)
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ICRF Plasma Production with Hydrogen Minority Heating in Uragan-2M and Large Helical Device
- 2023
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In: Plasma and Fusion Research. - : Japan Society of Plasma Science and Nuclear Fusion Research. - 1880-6821. ; 18:2402042
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Journal article (peer-reviewed)abstract
- This report compares results ion-cyclotron range of frequencies (ICRF) plasma production at hydrogen mi-nority regime in Uragan-2M (U-2M) and Large Helical Device (LHD). The condition of the presence of the fundamental harmonic ion cyclotron resonance zone for the hydrogen inside the plasma column should be ful-filled for this method. The scenario is successful at both machines and weakly sensitive to the variation of the hydrogen concentration in the H2+He gas mixture. It should be noted that at LHD the start up is slower than at U-2M. The comparison of plasma production in ICRF with hydrogen minority at U-2M and LHD indicate that this scenario can be scaled to larger stellarator devices. The experiments made are the base for the proposal for usage this scenario for plasma production in ICRF at Wendelstein 7-X at magnetic field reduced to 1.7 T.
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