The thesis describes the Charge-eXchange Recombination Spectroscopy (CXRS) diagnostics setup and its application to the ion temperature determination in the NBI-heated discharges in the Globus-M ...spherical tokamak. Measurements of the spectral line shape of the radiation emitted by the hydrogen-like carbon ion CVI (5290.5 Å) are presented. Comparison of CXRS and Neutral Particle Analyser (NPA) data demonstrates good agreement.
The article presents research on neutral beam current drive in Globus-M compact spherical tokamak. The experiments were performed in the plasma current range of 0.17–0.20 MA with a 0.4- or 0.5‑T ...toroidal magnetic field. The injection impact parameter was 33 cm. The variable parameters included compositions of plasma and the heating beam (hydrogen, deuterium), plasma density, and vertical displacement of the plasma column. The simultaneous increase in the plasma current and drop in the loop voltage were used to determine the neutral beam current drive. The injection of a hydrogen/deuterium beam into deuterium or hydrogen plasma resulted in a significant and reproducible drop in the loop voltage (up to 0.5 V). In order to process the obtained data, the authors developed an ASTRA code-based model, which allows one to calculate the neutral beam-driven current and bootstrap current. The share of noninductive currents as a function of plasma density during the injection of a hydrogen beam (28 keV, 0.5 MW) into the deuterium plasma was calculated. The authors analyze the results of experiments on off-axis beam injection achieved by vertical displacement of the plasma column and the effect of increasing the toroidal magnetic field on the consumption of the poloidal magnetic flux in discharges with atomic beam injection.
We consider synthesis and modeling of hierarchical robust magnetic control systems for plasma in tokamaks with adaptation of the magnetic axis’ vertical position. The studies were done for ITER ...(Cadarache, France) and Globus-M (St. Petersburg, Russia) tokamaks. Our original synthesis method ensures an improvement in performance for the shape of the plasma by resolving the contradiction between position and plasma shape via adaptation in a hierarchical system. Numerical modeling of synthesized control systems on multivariable linear models of plasma and nonlinear plasma-physics code DINA that unites basic equations of plasma dynamics in a magnetic field has shown the efficiency of the proposed approach and a possibility to apply it in a physical experiment.
A fast scanning probe which can penetrate inside the separatrix during discharge was developed for Globus-M2. The probe has been designed to move various sensor pins into the scrape-off layer. The ...driving force is provided by a crank-slider mechanism which is ensured maximum linear speed about 4 m/s. The paper presents probe head and drive system description.
The results from calculations of the anisotropic fast particle distribution function in the Globus-M/M2 spherical tokamaks are presented. The calculations were performed using the NUEBAM code, the ...reasons for the anisotropy occurrence are discussed (injection geometry, low toroidal magnetic field and plasma current, presence of neutral particles). It is shown that the anisotropy decreases with increasing toroidal magnetic field and plasma current: the density of the slowed down fast ions with energies of E < 4 keV almost doubles and the averaged perpendicular velocity of fast ions increases.
Analysis of stability of the peeling-ballooning modes in the edge plasma of the Globus-M tokamak is presented. Studies were performed using the ideal 3D MHD code written in the BOUT++ framework. The ...edge localized modes which are frequently observed in the Globus-M plasma could be described using MHD theory. It was found that the parameters of the Globus-M edge plasma are in the range of stability for the peeling-ballooning modes. The instability modes with a toroidal number of n = 12 and typical distances between filaments of approximately ∼12 cm were found to be the most unstable. This statement agrees with the Doppler backscattering measurements. It was also considered whether the plasma in the Globus-M2 tokamak will be stable against the PB instability.
Experimental study of thermal energy confinement in magnetic confinement devices is one of the fundamental problems in plasma physics. The data processing technique covering kinetic and magnetic ...measurements performed for the Globus-M tokamak is described. A zero-dimensional code has been developed on the basis of this approach making it possible to calculate important discharge parameters during the experiment (between discharges): the electron and ion stored thermal energy content, plasma effective charge, and confinement time. Good agreement of the zero-dimensional calculations and ASTRA modeling indicates that this approach can be applied for routine data processing in Globus-M in view of the specifics of the device.
A method of plasma boundary location based on last closed magnetic surface position detection as a maximum of electrostatic potential measured using Langmuir probes is presented. It is demonstrated ...that the method can be used for an absolute calibration of magnetic diagnostics of plasma position (TUMAN-3M) and as an independent diagnostic tool (Globus-M).
A high-energy counter-NBI has been applied for the first time on the Globus-M spherical tokamak. An ELM-free H-mode has been obtained. However, no significant increase in the ion temperature and ...plasma energy content compared to ELMy H-mode has been observed. This is due to a high level of the fastion losses. Neither increase in the plasma current nor an increase in plasma-wall distance resulted in an increase in NB heating efficiency as it occurred during the co-NBI experiments.
Conditions of the excitation of toroidal Alfvén eigenmodes (TAEs) and their inf luence on the confinement of fast particles into the Globus-M spherical tokamak have been studied by KINX code ...calculations of the magnetohydrodynamic spectra of reconstructed divertor equilibrium configurations with stability margin
q
0
> 1 on the magnetic axis. The sensitivity of the frequencies of TAE modes with toroidal wavenumber
n
= 1 to the type of boundary conditions and choice of boundary surface has been studied. It has been established that the frequencies of modes with dominating poloidal harmonics
m
= 1 and 2 in the gap of continuum are significantly higher than those observed in the spectra of signals measured in the Mirnov coil probes, especially under the assumption of free plasma boundary with allowance for its compressibility. The TAE modes with lower frequencies and higher poloidal wavenumbers localized near the plasma boundary may be responsible for the oscillations observed in the experiment. However, these modes are characterized by the interaction with continuum and, probably, exhibit related damping.
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