Study of fast-ion losses in experiments on neutral beam injection on the Globus-M spherical tokamak

Чернышев, Ф. В.; Afanasyev, V. I.; Гусев, В. К.; Иванов, А. Е.; Курскиев, Г. С.; Melnik, A. D.; Минаев, В. Б.; Mironov, M. I.; Несеневич, В. Г.; Патров, М. И.; Петров, М. П.; Petrov, S. Ya.; Petrov, Yu. V.; Sakharov, N. V.; Tolstyakov, S. Yu.

doi:10.1134/s1063780x11060201

Cited by 20 publications

(16 citation statements)

References 10 publications

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“…Two codes utilizing different approaches were applied to analyse the experimental data. One is the NUBEAM code [20] and the other is a full 3D fast ion tracking algorithm [21] combined with the solution of the Boltzmann kinetic equation [22]. The algorithm [21] is designed for spherical tokamaks, where particle orbits are not well described by the guiding centre motion or drift approximation.…”

Section: Fast Ion Confinementmentioning

confidence: 99%

“…One is the NUBEAM code [20] and the other is a full 3D fast ion tracking algorithm [21] combined with the solution of the Boltzmann kinetic equation [22]. The algorithm [21] is designed for spherical tokamaks, where particle orbits are not well described by the guiding centre motion or drift approximation. An example of the calculation of the fast ion deposition (ionization profile) and density together with a typical ion orbit during an 18 keV H NBI is shown in figure 7.…”

Section: Fast Ion Confinementmentioning

confidence: 99%

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Review of Globus-M spherical tokamak results

et al. 2015

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The first experiments on noninductive current drive (CD) using lower hybrid waves in a spherical tokamak are described. Waves at 2.45 GHz were launched by a 10 waveguide grill with 120° phase shift between neighbouring waveguides. The experimental results for a novel poloidal slowing-down scheme are described. The CD efficiency is found to be somewhat larger than that predicted theoretically whilst at the same time being somewhat less than that for standard tokamak lower hybrid CD. Geodesic acoustic modes (GAM) have been discovered in Globus-M. GAMs are localized 2-3 cm inside the separatrix. The GAM frequency agrees with theory. The mode structures of plasma density and magnetic field oscillation at the GAM frequency have been studied. Fast particle confinement during neutral beam injection has been investigated and numerically simulated. Alfvén instabilities excited by fast particles were detected by a toroidal Mirnov probe array. Their excitation conditions are discussed and the dynamics of fast ion losses induced by Alfvén eigenmodes is presented. Preliminary experiments on the isotopic effect influence on global confinement in the ohmic Nuclear Fusion

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Section: Fast Ion Confinementmentioning

confidence: 99%

Section: Fast Ion Confinementmentioning

confidence: 99%

Review of Globus-M spherical tokamak results

et al. 2015

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“…The lower magnitude of losses for protons as compared to deuterons is probably related to a smaller width of the orbit, which is determined by the Larmor radii in the total and poloidal magnetic fields. Under the conditions of the experiments described above (B t = 0.4 T, I p = 200 kA), these radii for deuterons with an energy of 30 keV according to orbital calculations [5] are on the order of 10 and 25 cm, respectively (i.e., are comparable with the tokamak minor radius). In our experiments, these deuterons exhibited greater losses during TAE devel opment.…”

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confidence: 83%

The influence of toroidal Alfvén modes on the confinement of fast particles in the Globus-M spherical tokamak

et al. 2014

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1136Our previous experiments with neutral beam injec tion into the Globus M spherical tokamak [1] at the early stage of discharge revealed the development of instabilities in a frequency range of 50-200 kHz, which have been previously identified as toroidal Alfvén eigenmodes (TAEs) [2]. In our last experi ments, we have studied the isotope effect using hydro gen and deuterium as the injected beam and the target plasma. Figure 1 shows the experimental spectra of signals from Mirnov probes, which reveal a different character of the mode behavior for various isotopes. In the case of deuterium injection (two upper spectra in Fig. 1), the mode develops as short spikes of 0.5 ms duration with fast drop in the frequency (so called chirping modes). This behavior is probably described by the "predator-prey" model, according to which the development of instability leads to the loss of fast par ticles responsible for its onset, so that the mode fre quency drops in order to retain effective energy trans fer from particles to the wave. In the case of hydrogen injection (two lower spectra in Fig. 1), the mode also appears as short spikes, but then usually converts into a long lived mode with approximately constant ampli tude. This behavior is probably explained by better confinement of protons as compared to deuterons and, accordingly, lower losses of protons during TAE development (see below). As can be seen from Fig. 1, the TAE frequency in all four cases remains in approx imately the same range of ~100 kHz, except for the hydrogen beam injection into hydrogen plasma, where the first spikes are observed at a significantly higher frequency. However, the main mode is develops at 100 kHz. A correlation analysis of signals from four fast mag netic probes showed that the perturbations developed in most cases have a single mode composition with toroidal number n = 1. This is consistent with the notions of the linear theory [3,4], according to which the maximum toroidal number of TAE in tokamaks is determined aswhere r is the minor radius and ω cf is the cyclotron fre quency. For the conditions in the Globus M spherical tokamak, n max = 1-1.5. Sometimes, a weak mode with n = 2 appears, the behavior of which differs from that of TAE. These modes (indicated in the two lower spec tra in Fig. 1) with frequencies increasing with time probably represent the Alfvén cascades. In separate strong spikes of TAE, it was possible to determine poloidal number m with the aid of a set of 26 probes with a poloidal arrangement. In all cases, this number proved to be n = 3. In the series of experiments under consideration, the improved temporal resolution of the diagnostics rω cf q 2 V A Abstract-Neutral beam injection into the Globus M spherical tokamak at the early stage of discharge leads to the development of instabilities in a frequency range of 50-200 kHz, which have been identified as toroidal Alfvén eigenmodes (TAEs) [1]. The influence of these modes on the confinement of fast particles has been studied with the aid of a neutral particle anal...

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“…To improve our understanding of the loss mechanism, a special 3D numerical code was developed to simulate 'direct' particle losses [18]. It includes programs in beam particle ionization and the calculation of the fast ion trajectory.…”

Section: Neutral Beam With Injection Of High Particle Energy and Fast...mentioning

confidence: 99%

“…The experimentally estimated value of the lost particle fraction agrees with the simulations. This experimental estimate was obtained from a comparison of the fast particle spectra recorded by the charge exchange (CX) neutral particle analyser (NPA) and the theoretical prediction of the slowing-down spectra based on the solution of the Fokker-Planck equation [1] and [18]. The 'direct' losses could reach 70-80% at a low density ( n e ∼ 1 × 10 19 m −3 ), decreasing with density rise.…”

Section: Neutral Beam With Injection Of High Particle Energy and Fast...mentioning

confidence: 99%

Investigation of beam– and wave–plasma interactions in spherical tokamak Globus-M

et al. 2011

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The experimental and theoretical results obtained in the last two years on the interaction of neutral particle beams and high-frequency waves with a plasma using the spherical tokamak Globus-M are discussed. The experiments on the injection of low-energy proton beam of ∼300 eV directed particle energy are performed with a plasma gun that produces a hydrogen plasma jet of density up to 3 × 1022 m−3 and a high velocity up to 250 km s−1. A moderate density rise (up to 30%) is achieved in the central plasma region without plasma disruption. Experiments on high-energy (up to 30 keV) neutral beam injection into the D-plasma are analysed. Modelling results on confinement of fast particles inside the plasma column that follows the neutral beam injection are discussed. The influence of the magnetic field on the fast particle losses is argued. A neutral beam injection regime with primary ion heating is obtained and discussed. The new regime with fast current ramp-up and early neutral beam injection shows electron temperature rise and formation of broad Te profiles until the q = 1 flux surface enters the plasma column. An energetic particle mode in the range of frequencies 5–30 kHz and toroidal Alfvén eigenmodes in the range 50–300 kHz are recorded in that regime simultaneously with the Te rise. The energetic particle mode and toroidal Alfvén eigenmodes behaviour are discussed. The toroidal Alfvén eigenmode spectrum appears in Globus-M as a narrow band corresponding to n = 1. The first experimental results on plasma start-up and noninductive current drive generation are presented. The experiments are carried out with antennae providing mostly poloidal slowing down of waves with a frequency of 920 MHz, which is higher than a lower hybrid one existing under the experimental conditions. The high current drive efficiency is shown to be high (of about 0.25 A W−1), and its mechanism is proposed. Some near future plans of the experiments are also discussed.

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Study of fast-ion losses in experiments on neutral beam injection on the Globus-M spherical tokamak

Cited by 20 publications

References 10 publications

Review of Globus-M spherical tokamak results

Review of Globus-M spherical tokamak results

The influence of toroidal Alfvén modes on the confinement of fast particles in the Globus-M spherical tokamak

Investigation of beam– and wave–plasma interactions in spherical tokamak Globus-M

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