| 1. |
- Kazakov, Ye.O., et al.
(författare)
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Effect of plasma shaping and resonance location on minority ion temperature anisotropy in tokamak plasmas heated with ICRH
- 2012
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Ingår i: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 401:1, s. 012011-
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Tidskriftsartikel (refereegranskat)abstract
- Poloidal asymmetries of the impurity distribution, which are observed in tokamaks, may influence the impurity cross-field transport. Low field side ion cyclotron resonance heating (ICRH) often results in an inboard accumulation of impurities, which may in turn lead to an outward convective impurity flux. The temperature anisotropy of the ICRH-heated minority ions is identified to be one of the main parameters governing the impurity asymmetry strength. In the present work we analyze the effect of plasma shaping and the ICRH resonance location on the minority temperature anisotropy by means of the TORIC-SSFPQL modelling. We find that ellipticity reduces the anisotropy level due to the wave defocussing and broader absorption regions for the elongated plasmas. The temperature anisotropy decrease in case of the resonance layers located closer to the edge is caused by the significant reduction in heating power densities due to geometrical reasons.
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| 2. |
- Kazakov, Ye O., et al.
(författare)
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Poloidal asymmetries due to ion cyclotron resonance heating
- 2012
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 54:10, s. 105010-
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Tidskriftsartikel (refereegranskat)abstract
- The poloidal density asymmetry of impurity ions in ion cyclotron resonance heated (ICRH) discharges is calculated. The link between the asymmetry strength and ICRH and plasma parameters is quantified. The main parameter governing the asymmetry strength is identified to be the minority ion temperature anisotropy. Through numerical simulations with the full-wave TORIC code coupled to the Fokker-Planck quasilinear solver SSFPQL, the dependence of the anisotropy on various parameters, such as ICRH power, background density and temperature, minority and impurity concentration and toroidal wavenumber has been investigated. An approximate expression for the poloidal asymmetry of impurities as a function of plasma parameters, resonance location and ICRH power is given. A quantification of the link of the impurity asymmetry and ICRH heating is valuable not only for understanding the changes in the cross-field transport but also for the possibilities to use the asymmetry measurements as diagnostics.
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| 3. |
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| 4. |
- KOVTUN, Yurii V., et al.
(författare)
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ICRF Plasma Production with the W7-X Like Antenna in the Uragan-2M Stellarator
- 2022
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Ingår i: Plasma and Fusion Research. - : Japan Society of Plasma Science and Nuclear Fusion Research. - 1880-6821. ; 17:0
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Tidskriftsartikel (refereegranskat)abstract
- The results of the plasma start-up with ICRH of U-2M RF discharges in H2+He mixture with newly implemented controlled gas H2 concentration are presented. The W7-X like ICRH antenna operated in monopole phasing with applied RF power of ∼ 100 kW. We investigated plasma start-up in the pressure range p = 6×10−4 - 9 × 10−2 Pa. Plasma production with an average density of up to Ne ∼ 1013 cm−3 was observed at frequencies the fundamental harmonic of the hydrogen cyclotron frequency.
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| 5. |
- Van Eester, D., et al.
(författare)
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Minority and mode conversion heating in (He-3)-H JET plasmas
- 2012
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 54:7, s. 074009-
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Tidskriftsartikel (refereegranskat)abstract
- Radio frequency (RF) heating experiments have recently been conducted in JET (He-3)-H plasmas. This type of plasmas will be used in ITER's non-activated operation phase. Whereas a companion paper in this same PPCF issue will discuss the RF heating scenario's at half the nominal magnetic field, this paper documents the heating performance in (He-3)-H plasmas at full field, with fundamental cyclotron heating of He-3 as the only possible ion heating scheme in view of the foreseen ITER antenna frequency bandwidth. Dominant electron heating with global heating efficiencies between 30% and 70% depending on the He-3 concentration were observed and mode conversion (MC) heating proved to be as efficient as He-3 minority heating. The unwanted presence of both He-4 and D in the discharges gave rise to 2 MC layers rather than a single one. This together with the fact that the location of the high-field side fast wave (FW) cutoff is a sensitive function of the parallel wave number and that one of the locations of the wave confluences critically depends on the He-3 concentration made the interpretation of the results, although more complex, very interesting: three regimes could be distinguished as a function of X[He-3]: (i) a regime at low concentration (X[He-3] < 1.8%) at which ion cyclotron resonance frequency (ICRF) heating is efficient, (ii) a regime at intermediate concentrations (1.8 < X[He-3] < 5%) in which the RF performance is degrading and ultimately becoming very poor, and finally (iii) a good heating regime at He-3 concentrations beyond 6%. In this latter regime, the heating efficiency did not critically depend on the actual concentration while at lower concentrations (X[He-3] < 4%) a bigger excursion in heating efficiency is observed and the estimates differ somewhat from shot to shot, also depending on whether local or global signals are chosen for the analysis. The different dynamics at the various concentrations can be traced back to the presence of 2 MC layers and their associated FW cutoffs residing inside the plasma at low He-3 concentration. One of these layers is approaching and crossing the low-field side plasma edge when 1.8 < X[He-3] < 5%. Adopting a minimization procedure to correlate the MC positions with the plasma composition reveals that the different behaviors observed are due to contamination of the plasma. Wave modeling not only supports this interpretation but also shows that moderate concentrations of D-like species significantly alter the overall wave behavior in He-3-H plasmas. Whereas numerical modeling yields quantitative information on the heating efficiency, analytical work gives a good description of the dominant underlying wave interaction physics.
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| 6. |
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| 7. |
- Joffrin, E., et al.
(författare)
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Overview of the JET preparation for deuterium-tritium operation with the ITER like-wall
- 2019
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 59:11
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Forskningsöversikt (refereegranskat)abstract
- For the past several years, the JET scientific programme (Pamela et al 2007 Fusion Eng. Des. 82 590) has been engaged in a multi-campaign effort, including experiments in D, H and T, leading up to 2020 and the first experiments with 50%/50% D-T mixtures since 1997 and the first ever D-T plasmas with the ITER mix of plasma-facing component materials. For this purpose, a concerted physics and technology programme was launched with a view to prepare the D-T campaign (DTE2). This paper addresses the key elements developed by the JET programme directly contributing to the D-T preparation. This intense preparation includes the review of the physics basis for the D-T operational scenarios, including the fusion power predictions through first principle and integrated modelling, and the impact of isotopes in the operation and physics of D-T plasmas (thermal and particle transport, high confinement mode (H-mode) access, Be and W erosion, fuel recovery, etc). This effort also requires improving several aspects of plasma operation for DTE2, such as real time control schemes, heat load control, disruption avoidance and a mitigation system (including the installation of a new shattered pellet injector), novel ion cyclotron resonance heating schemes (such as the three-ions scheme), new diagnostics (neutron camera and spectrometer, active Alfven eigenmode antennas, neutral gauges, radiation hard imaging systems...) and the calibration of the JET neutron diagnostics at 14 MeV for accurate fusion power measurement. The active preparation of JET for the 2020 D-T campaign provides an incomparable source of information and a basis for the future D-T operation of ITER, and it is also foreseen that a large number of key physics issues will be addressed in support of burning plasmas.
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| 8. |
- Kazakov, Yevgen, 1984, et al.
(författare)
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Effect of impurities on the transition between minority ion and mode conversion ICRH heating in (3He)–H tokamak plasmas
- 2013
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 53:5, s. 053014-
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogen majority plasmas will be used in the initial non-activated phase of ITER operation. Optimizing ion cyclotron resonance heating (ICRH) in such scenarios will help in achieving H-mode in these plasmas. Past JET experiments with the carbon wall revealed a significant impact of intrinsic impurities on the ICRH performance in (3He)–H plasmas relevant for the full-field initial ITER phase. High plasma contamination with carbon impurities resulted in the appearance of a supplementary mode conversion layer and significant reduction in the transition concentration of 3He minority ions, defined as the concentration at which the change from minority heating to the mode conversion regime occurs. In view of the installation of the new ITER-like wall at JET, it is important to evaluate the effect of Be and W impurities on ICRH scenarios in (3He)–H plasmas. In this paper, an approximate analytical expression for the transition concentration of 3He minority ions is derived as a function of plasma and ICRH parameters, and accounting for typical impurity species at JET. The accompanying 1D wave modelling supports the analytical results and suggests a potential experimental method to reduce the 3He level needed to achieve a specific heating regime by puffing a small amount of 4He ions additionally to (3He)–H plasma.
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| 9. |
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| 10. |
- Kazakov, Yevgen, 1984, et al.
(författare)
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Enhanced ICRF (ion cyclotron range of frequencies) mode conversion efficiency in plasmas with two mode conversion layers
- 2010
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 1361-6587 .- 0741-3335. ; 52:11
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Tidskriftsartikel (refereegranskat)abstract
- The ICRF (ion cyclotron range of frequencies) mode conversion regime efficiently provides local electron heating. The efficiency of mode conversion could be enhanced due to the interference between the reflected waves (Fuchs V et al 1995 Phys. Plasmas 2 1637–47). Plasmas of large-scale tokamaks can include multiple mode conversion layers which results in a complicated picture of mode conversion. The 1D theory of mode conversion in plasmas with two ion–ion hybrid resonance layers is presented. Using the phase-integral method the analytical expression for the conversion coefficient is derived within a cold plasma model. The possible enhancement of the mode conversion coefficient in such plasmas is shown. The developed theory is used to analyze the role of carbon ions in the (3He)H scenario of ICRF heating. As hot plasma effects may decrease the amount of power ultimately ending up on mode converted waves, a brief discussion of numerically obtained results but relying on a hot plasma model is included.
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| 11. |
- Kazakov, Yevgen, 1984, et al.
(författare)
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Influence of impurities on the transition from minority to mode conversion heating in (3He)–H plasmas
- 2014
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Ingår i: AIP Conference Proceedings. - : American Institute of Physics. - 0094-243X .- 1551-7616. - 9780735412101 ; 1580, s. 302-305
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Konferensbidrag (refereegranskat)abstract
- Ion cyclotron resonance heating (ICRH) is one of the main auxiliary heating systems used in present-day tokamaks and is planned to be installed in ITER. In the initial full-field phase of ITER operating with hydrogen majority plasmas, fundamental resonance heating of helium-3 ions is one of a few ICRH schemes available. Past JET experiments with the carbon wall revealed a significant impact of impurities on the ICRH performance in (3He)–H plasmas. A significant reduction of the helium-3 concentration, at which the transition from minority ion to mode conversion heating occurs, was found to be due to a high plasma contamination with carbon ions. In this paper we discuss the effect of Be and another impurity species present at JET after the installation of a new ITER-like wall on the transition helium-3 concentration in (3He)–H plasmas. We suggest a potential method for controlling helium-3 level needed for a specific ICRH regime by puffing an extra helium-4 gas to the plasma.
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| 12. |
- Kazakov, Yevgen, 1984, et al.
(författare)
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Kazakov and Fülöp Reply
- 2014
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 113:8, s. 089502-
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Tidskriftsartikel (refereegranskat)abstract
- A Reply to the Comment by Kim and Johnson.
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| 13. |
- Kazakov, Yevgen, 1984, et al.
(författare)
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Mode Conversion of Waves in the Ion-Cyclotron Frequency Range in Magnetospheric Plasmas
- 2013
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 111:12, s. 125002-
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Tidskriftsartikel (refereegranskat)abstract
- Waves in the ion-cyclotron range of frequencies with linear polarization detected by satellites can beuseful for estimating the heavy ion concentrations in planetary magnetospheres. These waves areconsidered to be driven by mode conversion (MC) of the fast magnetosonic waves at the ion-ion hybridresonances. In this Letter, we derive analytical expressions for the MC efficiency and tunneling of wavesthrough the MC layer. We evaluate the particular parallel wave numbers for which MC is efficient forarbitrary heavy ion/proton ratios and discuss the interpretation of the experimental observations.
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| 14. |
- Kazakov, Yevgen, 1984, et al.
(författare)
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Mode Conversion Study in Plasmas with Two Ion-Ion Hybrid Resonances
- 2009
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Ingår i: Proceedings of the 18th Topical Conference: RADIO FREQUENCY POWER IN PLASMAS. ; AIP 1187, s. 617-620
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Konferensbidrag (refereegranskat)abstract
- The ICRF mode conversion regime provides the effective local electron heating. The efficiency of the mode conversion could be enhanced due to the interference between thereflected waves [1]. The ID theoretical model is presented for the case of two ion-ion hybrid resonances in the plasma. The role of the carbon impurities in the inverted ICRF (3He)H scenario is studied. The optimal range of the helium and carbon concentrations for the enhanced mode conversion is estimated.
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| 15. |
- Kazakov, Yevgen, 1984, et al.
(författare)
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Modelling of the ion cyclotron resonance heating scenarios for W7-X stellarator
- 2014
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Ingår i: AIP Conference Proceedings. - : American Institute of Physics. - 1551-7616 .- 0094-243X. - 9780735412101 ; 1580, s. 342-345
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Konferensbidrag (refereegranskat)abstract
- The construction of the world largest superconducting stellarator Wendelstein 7-X (W7-X) has reached the final stage. One of the main scientific objectives of the W7-X project is to prove experimentally the predicted good confinement of high-energy ions. Ion cyclotron resonance heating (ICRH) system is considered to be installed in W7-X to serve as a localized source of high energy ions. ICRH heating scenarios relevant for hydrogen and deuterium phases of W7-X operation are summarized. The heating efficiency in (3He)-H plasmas is qualitatively analyzed using a modified version of the 1D TOMCAT code able to account for stellarator geometry. The minority ion absorption is shown to be maximized at the helium-3 concentration ~2% for the typical plasma and ICRH parameters to be available during the initial phase of W7-X.
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| 16. |
- Kazakov, Yevgen, 1984
(författare)
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Progress in theoretical models of the ICRF mode conversion
- 2011
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Ingår i: Nukleonika. - 1508-5791 .- 0029-5922. ; 57:1, s. 31-35
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Tidskriftsartikel (refereegranskat)abstract
- The technique of heating the plasma with the electromagnetic waves in the ion cyclotron range of frequencies (ICRF) has many important applications that may lead to improved performance of tokamaks. Recently the heating efficiency of the ICRF mode conversion scenarios characterized by a narrow power deposition profiles received much attention. This paper highlights progress in the theoretical models of the ICRF mode conversion that allowed to achieve a successful experimental realisation of these scenarios in present-day tokamaks.
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| 17. |
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| 18. |
- Kazakov, Yevgen, 1984, et al.
(författare)
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Search for Ion Heating Scenarios in Burning D-T Plasmas with ICRH.
- 2011
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Ingår i: Proceedings of 12th Technical Meeting on Energetic Particles in Magnetic Confinement Systems, p. P1.14.
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Konferensbidrag (refereegranskat)abstract
- Various ICRH scenarios relevant for the D-T phase of the JET tokamak operation are studied. It is known that an enhancement of the heating efficiency in the mode conversion regime (when the concentrations of D and T species are comparable) is possible due to the constructive interference of the reflected fast waves. Such a heating enhancement in D-T plasma is investigated first for the JET-like conditions for both dipole and +π/2 ICRH antenna phasings, and for T concentration varied from 0 to 100%. It is shown that most of the considered scenarios suffer from the parasitic absorption caused by the presence of fusion-born alpha-particles and NBI-produced fast particles. It is found that thermal ion heating becomes dominant in tritium-rich plasmas with T concentration ~80%. This scenario is compared with the alternative 3He minorityICRH scenario in D:T=50:50 plasmas.
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| 19. |
- Kazakov, Yevgen, 1984, et al.
(författare)
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Study of ICRH scenarios for thermal ion heating in JET D–T plasmas
- 2012
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 52:9
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Tidskriftsartikel (refereegranskat)abstract
- Various ion cyclotron resonance heating (ICRH) scenarios relevant for the D–T phase of the JET tokamak are studied. Recent ICRH experiments in JET (3He)–D and (3He)–H plasmas confirmed the possibility of electron heating enhancement in the mode conversion (MC) regime due to the constructive interference of the reflected fast waves. Such a heating enhancement in D–T plasma is investigated first for JET-like conditions for both dipole and +π/2 ICRH antenna phasing, and for T concentration varied from 0% to 100%. It is shown that most of the MC scenarios at comparable concentrations of D and T species suffer from a parasitic absorption by fusion-born alpha-particles and NBI-produced fast ions whereas the impact of such fast ions in the minority heating (MH) ICRH schemes is substantially smaller. A possibility of ion heating enhancement due to the interference effect is shown for the MH scenarios. It is found that thermal ion heating becomes dominant in tritium-rich plasmas with T concentration ~80%. The efficiency of ion heating in such a scenario is compared with the alternative 3He minority ICRH scenario in D:T=50:50 plasmas.
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| 20. |
- Kazakov, Yevgen, 1984, et al.
(författare)
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Test particle modelling of impurity collisional transport in tokamaks
- 2012
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Ingår i: 39th EPS Conference on Plasma Physics 2012, EPS 2012 and the 16th International Congress on Plasma Physics; Stockholm; Sweden; 2 July 2012 through 6 July 2012; Code 96757. - 9781622769810 ; 1, s. 229-232
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Konferensbidrag (refereegranskat)
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| 21. |
- Kazakov, Yevgen, 1984, et al.
(författare)
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Tunneling and mode conversion of fast magnetosonic waves in the magnetospheres of Earth and Mercury
- 2015
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Ingår i: Journal of Plasma Physics. - 0022-3778 .- 1469-7807. ; 81:2
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Tidskriftsartikel (refereegranskat)abstract
- Narrow-band linearly polarized waves, having a resonant structure and a peak frequency between the local cyclotron frequency of protons and heavy ions, have been detected in the magnetospheres of Earth and of Mercury. Some of these wave events have been suggested to be driven by linear mode conversion (MC) of the fast magnetosonic waves (FWs) at the ion–ion hybrid (IIH) resonances. Since the resonant IIH frequency is linked to the plasma composition, solving the inverse problem allows one to infer the concentration of the heavy ions from the measured frequency spectra. In this paper, we identify the conditions when the MC efficiency is maximized in the magnetospheric plasmas and discuss how this can be applied for estimating the heavy ion concentration in the magnetospheres of Earth and Mercury.
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| 22. |
- Kononenko, Zhanna, 1984, et al.
(författare)
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Test particle modelling of ion collisional transport in tokamaks
- 2011
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Ingår i: Nukleonika. - 1508-5791 .- 0029-5922. ; 57:1, s. 43-47
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Tidskriftsartikel (refereegranskat)abstract
- A numerical method is presented for evaluation of the radial diffusion coefficient, based on the full orbitmodelling of particle orbits in the tokamak geometry. The code solves the full orbit equations of motion for a set of test particles in an arbitrary equilibrium magnetic field. The effect of Coulomb collisions of test ions with background plasma particles is simulated by means of an equivalent Monte Carlo collision operator which scatters the pitch angle as well as the gyrophase of the particle. The radial diffusion coefficient is estimated by calculating the temporal dependence of the mean-square displacement of an ensemble of monoenergetic test particles. As an illustration of the method theeffect of magnetic islands on the impurity collisional transport is studied. It is shown that in presence of m = 2, n = 1 resonant magnetic perturbation (RMP) the diffusion coefficient for the tungsten ions (W28+, E = 1 keV) can increase by a factor of 5–10.
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| 23. |
- Kovtun, Yurii, et al.
(författare)
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ICRF production of plasma with hydrogen minority in Uragan-2M stellarator by two-strap antenna
- 2024
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Ingår i: Physics of Plasmas. - : American Institute of Physics (AIP). - 1070-664X .- 1089-7674. ; 31:4
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Tidskriftsartikel (refereegranskat)abstract
- The experiments on medium-size stellarator Uragan-2M (U-2M) in Kharkiv, Ukraine, are carried on in support of the Wendelstein 7-X (W7-X) experimental program. The scenario ion cyclotron frequency range (ICRF) plasma production at the hydrogen minority regime had been experimentally tested on U-2M and was qualified at the Large Helical Device (LHD). The paper presents the results of further research on the ICRF plasma production. The ICRF discharge studies were carried out in a H2 + He mixture with a controlled hydrogen concentration ranging from few percents to 75%. The two-strap like antenna mimicks the W7-X antenna operated in monopole phasing. The applied RF power was in the range of ∼100 kW. Relatively dense plasma of up to Ne ∼ 1019 m−3 was produced near the first harmonic of the hydrogen cyclotron frequency. The maximum temperature of the electrons and ions was not more than a few tens of electron volt. The characteristic features of RF plasma production and the propagation of electromagnetic waves in the experimental conditions are discussed. The experiments on U-2M and LHD indicate that the minority scenario of ICRF plasma production appears to be scalable and could be used in large stellarator machines. This is, in particular, important for the future experiments ICRF production of target plasma in W-7X in conditions where electron cyclotron resonance heating start-up is not possible.
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| 24. |
- Kovtun, Yurii V., et al.
(författare)
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ICRF plasma production at hydrogen minority regime in LHD
- 2023
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Ingår i: Nuclear Fusion. - : Institute of Physics Publishing (IOPP). - 0029-5515 .- 1741-4326. ; 63:10
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Tidskriftsartikel (refereegranskat)abstract
- This 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 × 1017m−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 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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| 25. |
- Kovtun, Yurii, V, et al.
(författare)
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ICRF Plasma Production with Hydrogen Minority Heating in Uragan-2M and Large Helical Device
- 2023
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Ingår i: Plasma and Fusion Research. - : Japan Society of Plasma Science and Nuclear Fusion Research. - 1880-6821. ; 18:2402042
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Tidskriftsartikel (refereegranskat)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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