Alexander Ovsyannikov

Globus-M results as the basis for a compact spherical tokamak with enhanced parameters Globus-M2

The targeted plasma parameters of the compact spherical tokamak (ST) Globus-M have basically been achieved. The reasons that prevent further extension of the operating space are discussed. The operational limits of Globus-M together with an understanding of the limiting reasons form the basis for defining the design requirements for the next-step, Globus-M2. The recent experimental and theoretical results achieved with Globus-M are discussed, the operational problems and the research programme are summarized and finally, the targeted Globus-M2 parameters are presented. The magnetic field and plasma current in Globus-M2 will be increased to 1?T and 0.5?MA, respectively. The plasma dimensions will remain unchanged. With auxiliary heating at a high average plasma density, the temperatures will be in the keV range and the collisionality parameter with ?*???1 will define the operational conditions. Noninductive current drive will be a major element of the programme. The engineering design issues of Globus-M2 tokamak are discussed and the technical tokamak parameters are confirmed by thermal load and stress analysis simulations. The experimental results obtained on Globus-M2 and the limits of its performance should clarify the feasibility of an ST-based super compact neutron source.

Mathematical methods of plasma vertical stabilization in modern tokamaks

The paper presents the application of modern computational methods for tokamak plasma control system analysis. Several different approaches for feedback controller synthesis are described. General positions of the modern robust analysis theory are briefly formulated. The technique of robust features comparative analysis for feedback controllers is presented. The application of these computational methods is illustrated by the example of the MAST tokamak plasma vertical feedback control system.

OPTIMIZATION OF A RADIAL MATCHING SECTION

Optimization approach to define geometry (parameters) of the radial matching section in an RFQ accelerator is suggested. This approach gives wider opportunities for the design of the radial matching section because it does not have certain prescribed laws of variation of focusing strength along the section.

ON THE BEAM DYNAMICS OPTIMIZATION PROBLEM

The problem of dynamics optimization for charged particle beams in RFQ accelerators is discussed in this article. The problems of the optimization of particle capture into the acceleration mode are analyzed. Accelerators with low injection energies are considered.

The LIDOS.RFQ.Designer development

The LIDOS.RFQ.Designer code package gives users the possibility to proceed successfully from input data up to RFQ channel design and space-charge-dominated beam simulation. The codes main feature is that it displays the maximum scientific visualization for each calculation step. The package contains codes with three levels of mathematical model complexity. The first-level codes not only make a preliminary choice of the main parameter arrays on the basis of a simplified physical model but also choose the design optimization. The case of high-current CW RFQ radiation purity (minimum of lost particles) is considered as the main optimization criteria. The second-level codes are used for RF field calculations, taking into account the real shape of the RFQ vanes. The third-level codes are based on complex PIC-models that are needed for beam simulation in the chosen channel version.

BDO-RFQ code and optimization models

The software complex for step-by-step beam dynamics optimization of charged particles in RFQ structure is developed using MATLAB. The RFQ accelerating structure is one of the most common linear accelerators in the world for forming and accelerating high-current beams of charged particles at low injection energies.

Review of Globus-M spherical tokamak results

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. Alfven 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 Alfven eigenmodes is presented. Preliminary experiments on the isotopic effect influence on global confinement in the ohmic heating (OH) regime are described. Scrape-off layer (SOL) parameters were measured and compared with results from self-consistent integrated transport modelling. Results showed that SOL width scales inversely proportional to plasma current. The behaviour of an a priori damaged tungsten divertor plate mock-up exposed to plasma flows was investigated. Preliminary conclusions are that the initial damage gives rise to a loose layer formation with low thermal conductivity right beneath the surface. Finally, engineering design issues of the next step—Globus-M2 (1 T, 500 kA) and the status of component manufacture are described.

On optimization of the initial plasma stage in ITER

The optimization of initial development of the plasma discharge in ITER is considered. To solve this problem the variation approaches are suggested.

Numerical simulations of the radial electron flow formation for the triode type source

The problem of intensity electron beam formation in triode type source is considered. The presence of reflected or oscillating electrons results in changing emission current density and source operation parameters. We consider the variation algorithm based on current density function parameterization to determine a self-consistent distribution. Numerical results of beam dynamics simulation for vacuum electron source are presented.

Program for scientific and educational investigations on the base of small spherical tokamak Gutta

In Saint-Petersburg state University the modernization of spherical Gutta tokamak is carried out. The aim of the program is to build the research device to study plasma position, shape and current control problems in the tokamak, as well as to assist the scientific and educational programs on various plasma physics problems. Such feature of this device as a relatively small thickness of the vacuum vessel wall made as momentless shell allows changes in the magnetic field in plasma region, to measure the plasma parameters with a minimum delay using electromagnetic diagnostics and changes in toroidal field as necessary.