Effect of toroidal Alfvén eigenmodes on fast particle confinement in the spherical tokamak Globus-M

Abstract

In experiments with neutral beam injection at the early stage of a Globus-M discharge, instabilities were observed that were excited by fast ions in the frequency range of 50–200 kHz, which were identified as toroidal Alfvén eigenmodes (TAE) (Petrov et al., Plasma Phys. Rep., vol. 37, 2011, pp. 1001–1005). In contradiction with the NSTX and MAST tokamaks, a regime of TAE generation was realized with strongly developed single modes. Magnetic measurements with fast Mirnov probes have shown that most of the modes have toroidal number $n=1$. The influence of the modes on the fast particle confinement was recorded by means of a tangentially directed neutral particle analyser (NPA) and neutron detector. Hydrogen and deuterium were used as target plasma and injected beam for study of the isotopic effect. At deuterium injection into the deuterium plasma, TAE led to the neutron rate dropping by 25 %, whereas NPA fluxes of high energy dropped by 75 %. At hydrogen injection, the drop in the measured NPA fluxes did not exceed 25 %.

Review of Advanced Implementation of Doppler Backscattering Method in Globus-M

“…The shift of the main TAE harmonic (i.e., with n = 1) to the inner plasma regions appears to be related to the increasing plasma current [73]. [68] Spectral peak width ∆f, kHz 80 the decrease of the TAE frequency is related to the slowing down of the Alfven wave Type continuous or burst dependent on the injected beam parameters [69] t lifetime (for burst type), ms~0.1-0.5 predator-prey model [69] Radial The four frequency DBS system was used to study turbulence in H-mode with and without ELMs. The experiments were performed in the Globus-M spherical tokamak operated in H-mode initiated by NBI.…”

“…The instability was observed either in the form of a short burst lasting from 0.1 up to 0.5 ms or as continuous oscillations of several ms. The length of the TAE burst apparently can be defined through a predator-prey model [69].…”

Analysis of toroidal Alfven eigenmode-induced fast ion losses in Globus-M2 spherical tokamak

“…In the experiments at Globus-M2 [9,21,22], where toroidal Alfven eigenmodes were found to arise during neutral beam injection, the first NBI with energy E NBI = 28 keV and beam power P beam about 0.85 MW was applied. ACORD-24M NPA was used to measure neutral flux and ACORD-12 analyzer was applied to measure ion temperature [23].…”

Анализ Потерь Быстрых Ионов, Вызванных Распространением Тороидальных Альфвеновских Мод В Плазме Сферического Токамака Глобус-М2

“…TAE в токамаке Глобус-М регистрировались в диапазоне параметров плазмы n e < 10 20 m −3 , I p = 180−250 kA, B T = 0.4−0.5 T как на стадии роста тока, так и на стадии плато [9]. В токамаке Глобус-М2 были достигнуты значения магнитного поля B T = 0.6−0.8 T и тока по плазме до 400 kA, что позволило проанализировать зависимость потерь быстрых ионов в более широком диапазоне параметров, а ранее полученная [21,22] зависимость была дополнена [24] соответствующими точками (рис. 5 в работе [21], рис.…”

“…Это увеличение тока по плазме и магнитного поля также повлияло и на нейтронный выход. Ранее для токамака Глобус-М была получена [22] зависимость числа зарегистрированных нейтронов от амплитуды TAE для поля 0.4 T и токов 180−230 kA по данным пропорционального счетчика нейтронов, заполненного 3 2 He, ранее использовавшегося на установке Глобус-М. В связи с тем что диагностика нейтронов была усовершенствована (вместо пропорционального счетчика используется коронный счетчик и нейтронный спектрометр), сравнение ранее полученных данных с новыми оказывается затруднительно.…”