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| 2. |
- Moiseyenko, Volodymyr, et al.
(författare)
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First experiments on ICRF discharge generation by a W7-X-like antenna in the Uragan-2M stellarator
- 2020
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Ingår i: Journal of Plasma Physics. - : Cambridge University Press (CUP). - 0022-3778 .- 1469-7807. ; 86:5
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Tidskriftsartikel (refereegranskat)abstract
- In support of the ICRF experiments planned on the Wendelstein 7-X (W7-X) stellarator, i.e. fast ion generation, wall conditioning, target plasma production and heating, a first experimental study on plasma production has been made in the Uragan-2M (U-2M) stellarator using W7-X-like two-strap antenna. In all the experiments, antenna monopole phasing was used. The W7-X-like antenna operation with launched radiofrequency power of ~100 kW have been performed in helium (p = (4–14) × 10−2 Pa) with the vacuum vessel walls pre-loaded with hydrogen. Production of plasma with a density higher than 1012 cm−3 was observed near the first harmonic of the hydrogen cyclotron frequency. Operation at first hydrogen harmonic is feasible in W7-X future ICRF experiments.
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| 4. |
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| 5. |
- Buermans, J., et al.
(författare)
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Characterization of ECRH plasmas in TOMAS
- 2024
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 31:5
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Tidskriftsartikel (refereegranskat)abstract
- To improve the plasma performance and control the density and plasma quality during the flat top phase, wall conditioning techniques are used in large fusion devices like W7-X and in JT60-SA. To study the performance of electron cyclotron wall conditioning, numerous experiments were performed on the TOroidally MAgnetized System, which is operated by LPP-ERM/KMS at the FZ-Jülich. It is a facility designed to study plasma production, wall conditioning, and plasma-surface interactions. The produced electron cyclotron resonance heating plasmas are characterized in various conditions by density and temperature measurements using a movable triple Langmuir probe in the horizontal and the vertical direction, complemented by video and spectroscopic data, to obtain a 2D extrapolation of the plasma parameters in the machine. A way to calibrate the triple Langmuir probe measurements is also investigated. These data can be used to determine the direction of the plasma drift in the vessel and identify the power absorption mechanisms. This will give more insight in the plasma behavior and improve the efficiency of wall conditioning and sample exposure experiments.
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| 6. |
- Goriaev, A., et al.
(författare)
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The upgraded TOMAS device : A toroidal plasma facility for wall conditioning, plasma production, and plasma-surface interaction studies
- 2021
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Ingår i: Review of Scientific Instruments. - : AMER INST PHYSICS. - 0034-6748 .- 1089-7623. ; 92:2
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Tidskriftsartikel (refereegranskat)abstract
- The Toroidal Magnetized System device has been significantly upgraded to enable development of various wall conditioning techniques, including methods based on ion and electron cyclotron (IC/EC) range of frequency plasmas, and to complement plasma-wall interaction research in tokamaks and stellarators. The toroidal magnetic field generated by 16 coils can reach its maximum of 125 mT on the toroidal axis. The EC system is operated at 2.45 GHz with up to 6 kW forward power. The IC system can couple up to 6 kW in the frequency range of 10 MHz-50 MHz. The direct current glow discharge system is based on a graphite anode with a maximum voltage of 1.5 kV and a current of 6 A. A load-lock system with a vertical manipulator allows exposure of material samples. A number of diagnostics have been installed: single- and triple-pin Langmuir probes for radial plasma profiles, a time-of-flight neutral particle analyzer capable of detecting neutrals in the energy range of 10 eV-1000 eV, and a quadrupole mass spectrometer and video systems for plasma imaging. The majority of systems and diagnostics are controlled by the Siemens SIMATIC S7 system, which also provides safety interlocks.
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| 7. |
- Kovtun, Yu, et al.
(författare)
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Comparative analysis of the plasma parameters of ECR and combined ECR plus RF discharges in the TOMAS plasma facility
- 2021
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 63:12
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Tidskriftsartikel (refereegranskat)abstract
- The toroidal magnetized system (TOMAS) plasma facility aims at complementary research on wall conditioning methods, plasma production and plasma-surface interaction studies. This paper explores for the first time the parameters in helium electron-cyclotron resonance (ECR) plasma and combined ECR + radio-frequency (RF) discharges in TOMAS. The ECR discharge in this work, at 2.45 GHz and 87.6 mT, is the main one for creating and maintaining the plasma, while the addition of RF power at 25 MHz allows to broaden the achievable electron temperature and density at a given gas flow, as evidenced by triple Langmuir probe measurements. This effect of the combined ECR + RF discharge provides flexibility to study particular aspects of wall conditioning techniques relevant to larger devices, or to approach plasma conditions relevant to fusion edge plasmas for particular surface interaction studies.
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| 8. |
- Buermans, J., et al.
(författare)
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Triple Langmuir probe calibration in TOMAS ECRH plasma
- 2023
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 13:5
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Tidskriftsartikel (refereegranskat)abstract
- In the TOMAS device, a triple Langmuir probe is used to measure the electron temperature and density. The accuracy of this measurement depends on correct determination of the effective collecting area of the probe, which depends on complex plasma transport processes. The probe can be calibrated by electron cyclotron resonance heating experiments using the cut-off density of the ordinary wave (O-wave). This threshold only depends on the frequency of the injected wave, and the occurrence of this phenomenon is clearly visible in the temperature evolution. The value of density is consequently known at this point and can be used to calibrate the density measurements of the triple Langmuir probe.
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| 9. |
- Buermans, Johan, et al.
(författare)
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X-mode electron cyclotron heating scenarios beyond the cut-off density
- 2023
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Ingår i: 24th Topical Conference on Radio-Frequency Power in Plasmas. - : AIP Publishing.
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Konferensbidrag (refereegranskat)abstract
- Electron Cyclotron Heating (ECH) at the fundamental resonance in X-mode is limited by a low cut-off density. Electromagnetic waves cannot propagate in the region between this cut-off and the Upper Hybrid Resonance (UHR) and cannot reach the Electron Cyclotron Resonance (ECR) position. Higher harmonic heating is hence preferred in nowadays ECH plasma heating scenarios to overcome this problem. However, if this evanescent region is small compared to the wavelength of the waves, additional power deposition mechanisms can occur to increase the plasma density. This includes collisional losses in the evanescent region, tunneling of the X-wave with resonant coupling at the ECR, and conversion to the Electron Bernstein Wave (EBW) with resonant coupling. Several ECH plasma production experiments were performed on the TOMAS device with simple toroidal magnetic field to identify these additional heating regimes and to study the influence of the heating power on the ECH plasma parameters and the power deposition. Density and temperature profiles were measured with Langmuir Probes. Measurements of the forwarded and reflected power allow to estimate the coupling efficiency. The results help to understand ECH plasma production for tokamak plasma breakdown assistance and Electron Cyclotron Wall Conditioning (ECWC).
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| 10. |
- Crombé, K., et al.
(författare)
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Radio frequency plasma production on the TOMAS device
- 2023
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Ingår i: 24th Topical Conference on Radio-Frequency Power in Plasmas. - : AIP Publishing.
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Konferensbidrag (refereegranskat)abstract
- The study of discharge initiation by an Ion Cyclotron Range of Frequency (ICRF) antenna is of importance for operational scenarios at low magnetic field in e.g., ITER and Wendelstein 7-X. At low magnetic fields ohmic breakdown is difficult because of relatively short connection lengths and the electron cyclotron (EC) systems cannot assist because of a low-density cut-off. In that case ion cyclotron (IC) start-up, with waves in the Radio Frequency (RF) wavelength range, can be a good alternative solution. To explore in more detail the processes at play during the initial breakdown phase and to test measurement requirements, the diagnostic's capabilities of the TOMAS experimental device are being enlarged to allow for IC breakdown studies. A first set of IC breakdown experiments has been performed and data was taken by a newly installed spectrometer and a horizontal triple Langmuir probe. Limitations were found in pressure, ICRF power, and hydrogen concentration. Further diagnostic's upgrades and extensions of the experimental sessions will allow for a more complete study in support of modelling and experiments on other machines.
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| 11. |
- Goriaev, A., et al.
(författare)
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First studies of local ion fluxes in radio frequency plasmas for ion cyclotron wall conditioning applications in the TOMAS device
- 2023
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Ingår i: AIP Conference Proceedings. - : American Institute of Physics Inc..
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Konferensbidrag (refereegranskat)abstract
- To measure the local ion energy distribution functions for support of Ion Cyclotron Wall Conditioning (ICWC) application studies in the TOMAS device, a Semion Retarding Field Energy Analyzer (RFEA) by Impedans Ltd. has been installed in the sample load-lock system. The RFEA system has been commissioned in hydrogen Radio-Frequency (RF) plasmas. The first studies have been performed on the influence of the neutral hydrogen pressure, the input power, the magnetic field and the location on the average ion energy and ion flux density.
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| 12. |
- Kovtun, Yu, et al.
(författare)
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Measurement of hydrogen plasma parameters of the combined ECR+RF discharge in the TOMAS facility
- 2023
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Ingår i: 24TH TOPICAL CONFERENCE ON RADIO-FREQUENCY POWER IN PLASMAS. - : AIP Publishing.
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Konferensbidrag (refereegranskat)abstract
- The plasma electron density and temperature were measured in hydrogen electron-cyclotron resonance (ECR) plasma and combined ECR + radio-frequency (RF) discharges in the TOMAS facility. The results of ECR and combined ECR+RF discharges studies are compared. With an addition of RF, it is possible to vary the plasma parameters around the values provided by the ECR discharge. The propagation of slow (SW) and fast (FW) waves in hydrogen plasma is analyzed. Depending on the plasma density and the parallel component of the wave vector three cases are possible: SW propagation only, SW and FW simultaneous propagation, and FW propagation only.
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| 13. |
- Kovtun, Yu., et al.
(författare)
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Overview of TOMAS plasma diagnostics
- 2023
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Ingår i: Journal of Instrumentation. - : IOP Publishing. - 1748-0221. ; 18:2
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents an overview of the TOMAS plasma diagnostics. The Langmuir probe method is employed to measure electron temperature, density and floating potential distributions. Two triple probes (horizontal and vertical distributions) and a single probe (horizontal distribution) are used. The measured plasma parameters by the triple and single probes are compared. The ion and neutral atom flux and energy distribution is respectively characterized with a Residual Field Energy Analyzer and a Time-of-Flight Neutral Particle Ana-lyzer. To determine the elemental/charge content of the plasma, the passive method of time-resolved optical emission spectroscopy is used. The time dependence of the integral flow of plasma emission from the discharge is registered by a photodetector. Using a filter allows the photodetector to measure spectral line intensities. To record a wide variety of plasma events several video diagnostics are used. It includes slow video cameras and one high-speed camera in the visible range including Hα.
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| 14. |
- López-Rodríguez, D., et al.
(författare)
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Characterisation of radio frequency plasmas in the upgraded TOMAS device
- 2023
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Konferensbidrag (refereegranskat)abstract
- To complement wall conditioning research in TOMAS, a characterisation of radio-frequency hydrogen plasmas has been performed using a radially movable triple Langmuir probe. Experimental measurements of electron temperature and density radial profiles at different magnetic field on axis strengths and neutral pressures have been performed. First results of simulations of the radial profiles with the code TOMATOR-1D can qualitatively reproduce the measurements of the diagnostic and may be used to understand the behaviour of the waves inside the plasma.
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