Study of Globus-M Tokamak Poloidal System and Plasma Position Control

In order to provide efficient performance of tokamaks with vertically elongated plasma position, control systems for limited and diverted plasma configuration are required. The accuracy, stability, speed of response, and reliability of plasma position control as well as plasma shape and current control depend on the performance of the control system. Therefore, the problem of the development of such systems is an important and actual task in modern tokamaks. In this study, the measured signals from the magnetic loops and Rogowski coils are used to reconstruct the plasma equilibrium, for which linear models in small deviations are constructed. We apply methods of the H∞-optimization theory to the synthesize control system for vertical and horizontal position of plasma capable to working with structural uncertainty of the models of the plant. These systems are applied to the plasma-physical DINA code which is configured for the tokamak Globus-M plasma. The testing of the developed systems applied to the DINA code with Heaviside step functions have revealed the complex dynamics of plasma magnetic configurations. Being close to the bifurcation point in the parameter space of unstable plasma has made it possible to detect an abrupt change in the X-point position from the top to the bottom and vice versa. Development of the methods for reconstruction of plasma magnetic configurations and experience in designing plasma control systems with feedback for tokamaks provided an opportunity to synthesize new digital controllers for plasma vertical and horizontal position stabilization. It also allowed us to test the synthesized digital controllers in the closed loop of the control system with the DINA code as a nonlinear model of plasma.     

Tearing Mode Behavior in the Globus-M Spherical Tokamak Plasma

Physics of Atomic Nuclei - The 2/1 tearing mode instability during the plateau phase of the plasma current time evolution has been observed since the start of the Globus-M spherical tokamak...     

A Study of the Near-Wall Plasma of the Globus-M Tokamak Using an Array of Divertor Langmuir Probes

Technical Physics - An array of ten built-in divertor probes was installed on the lower dome of the Globus-M spherical tokamak. It was used to measure the profiles of the floating potential,...     

Theoretical Study of ECRH Heating Of HL-2A Tokamak Plasma

Electron cyclotron resonance heating （ECRH） is one of the main auxiliary heating schemes for the HL-2A tokamak. Routinely, the ohmic heating can provide a heating power about 300-450 kW in this device （ estimated from that the total toroidal current is about 300 kA while the totoidal voltage is 1-1.5 V）. The total power for the ECRH now is 1 MW and in future 2 MW.     

Spectroscopic Diagnostic of the Peripheral Plasma in the Globus-M2 Tokamak with the Injection of Neutral Helium

JETP Letters - The diagnostic of the peripheral plasma parameters in terms of the relation of lines of neutral helium is included in the diagnostic complex of the tokamak Globus-M2. The first...     

Energy Confinement Dynamics and Soft X-Ray Spectra in Experiments on ECR Plasma Heating in the L-2M Stellarator at Heating Powers to 1 MW

Bulletin of the Lebedev Physics Institute - The shape of soft X-ray spectra and energy confinement dynamics is studied in experiments on central ECR heating with a power to 1 MW using the L-2M...     

First Heat and Particles Transport Study in the Globus-M2 Spherical Tokamak with Neutral Beam Injection at the Current Ramp-Up

Technical Physics - The article presents the results of studying the transfer of heat and particles in the Globus-M2 spherical tokamak in discharges with neutral injection at the current ramp up....     

Study of Plasma MHD Equilibrium in HL-2A Tokamak

1 Introduction In an axisymmetric toroidal system, the MHD equilibrium G-S equation can be written as：     

Study of Plasma MHD Equilibrium in HL-2A Tokamak

In an axisymmetric toroidal system, the MHD equilibrium Grad-Shafranov equation can be written as     

Study of Density Behavior During LHCD and IBW Heating in the HT-7 Superconducting Tokamak

A new method using special shape parameters has been introduced to study density behavior with synergy of lower hybrid current drive (LHCD) and ion Bernstein wave (IBW) heating in the HT-7 superconducting tokamak. During the synergy of the LHCD and IBW heating an improved confinement plasma was achieved, and the electron density was increased and peaked.     

Low-Threshold Parametric Excitation of Electron Plasma Waves Localized in the Edge Transport Barrier of a Tokamak during Electron Cyclotron Resonance Heating of a Plasma

JETP Letters - The possibility of the localization of longitudinal waves in the intermediate frequency range in the edge transport barrier of a toroidal nuclear fusion facility is discovered. It is...     

Numerical Study of Plasma Discharges in KTM Tokamak in Autumn Campaign 2019

Physics of Atomic Nuclei - The work presents some simulation results of discharge scenarios at the KTM facility during the autumn campaign 2019. The parameters for providing the plasma breakdown...     

On an Unconventional Approach to the Improvement of Plasma Confinement in Tokamaks

JETP Letters - A conceptual proposal has been suggested to improve the confinement of a turbulent plasma in tokamaks with the use of discharges with large safety factors qL at the plasma...     

Spectroscopic Study of Laser-Induced Cu Plasma With and Without the Confinement of a Substrate

Optical emission spectroscopic studies have been carried out on the laser-induced copper plasma generated in the process of laser-driven flyer (with the substrate confinement). The copper plasma in the air (without the substrate confinement) has also been researched in order to know the differences between the plasma with the confinement and that without the confinement. The plasma is assumed to be in local thermodynamic equilibrium. The result shows that, under the same laser fluence, the plasma exists a longer time with the confinement. The time-resolved electron temperature and density with the confinement are higher than those with no confinement. The substrate deposited with Cu foil plays an important role in enhancing the temperature and the density of the plasma. The electron temperature and density with confinement increase with a larger scope as the laser fluence increases than that with no confinement.      

First Observation of Neoclassical Tearing Modes in the HL-2A Tokamak

The m/n = 2/1 neoclassical tearing modes are first observed in HL-2A low density, low beta plasma with central electron cyclotron resonance heating. The neoclassical tearing modes （NTMs） are triggered by a sawtooth crash with m/n = 1/1 precursors, which are toroidal coupled with a small scale m/n = 2/1 mode. The time history of the island width is compared with the prediction of the NTM theory, showing a good agreement between theory and experiment.     

Electronically and Calorimetrically Measured Energy Balances of a Thermal Induction Plasma

The plasma efficiency is one of the most important factors for industrial applications of thermal induction plasmas. An analysis of all the terms contributing to the energy balance of the rf-generator and the induction plasma is presented. In order to measure the plasma power faster than with usual calorimetric methods, a new approach to the instantaneous measurement of electric power was developed, which allowed power measurements at several Megahertz in the oscillator circuit of a self-excited induction generator. Systematic measurements under 26 different operating conditions were carried out on a 12 kW, 5 MHz argon induction plasma and were checked by parallel calorimetric energy balances. The agreement of both methods is within an accuracy of 5%. The total plasma efficiency is over 50% of the plate power. It varies only slightly with the operating parameters (plate voltage and gas flow rates). The measurements indicate clearly where modifications of the system would improve the overall efficiency.