Alexander N. Saveliev

Alexander N. Saveliev
Ioffe Physical Technical Institute | ioffe · Laboratory of High Temperature Plasma Physics

Doctor of Sciences

About

94
Publications
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1,118
Citations
Additional affiliations
February 1979 - present
Ioffe Physical Technical Institute
Position
  • Senior Researcher

Publications

Publications (94)
Article
Full-text available
The Globus-M2 spherical tokamak is the considerably upgraded Globus-M facility. Its technical parameters were increased as much as possible to achieve the promising range of physical parameters (sub-fusion temperatures and collisionality of much less than unity). These parameters will be achieved in a compact magnetic configuration similar to that...
Article
We analyze the saturation of the low-threshold absolute parametric decay instability of an extraordinary pump wave leading to the excitation of two upper hybrid (UH) waves, only one of which is trapped in the vicinity of a local maximum of the plasma density profile. The pump depletion and the secondary decay of the localized daughter UH wave are t...
Article
In this paper we analyse low-threshold parametric decay instability (PDI) of the ordinary wave in first harmonic O-mode ECRH experiments at toroidal devices. The corresponding expressions for the PDI power threshold and its growth rate are derived analytically and evaluated numerically for the conditions of the ECRH experiments on the W7-A stellara...
Article
In experiments on lower hybrid current drive (LHCD) carried out at the FT-2 tokamak, a substantial increase in the central electron temperature Te(r = 0 cm) from 550 to 700 eV was observed. A complex simulation procedure is used to explain a fairly high LHCD efficiency and the observed additional heating, which can be attributed to a transition int...
Article
The Globus-M spherical tokamak has demonstrated practically all of the project objectives during the 15-year period of operation. The main factor limiting further progress in plasma performance is a relatively low toroidal magnetic field. The maximum toroidal magnetic field achieved on Globus-M was 0.4 T with the exception of a limited number of sh...
Article
Full-text available
A new one-dimensional approach to the lower hybrid current drive (LHCD) modelling in the presence of an inductive electric field is suggested in this paper. The approach is based on using time-dependent solutions of a well-known Fokker-Planck equation for the distribution function of fast electrons calculated concurrently with solving plasma transp...
Article
New results from MAST are presented that focus on validating models in order to extrapolate to future devices. Measurements during start-up experiments have shown how the bulk ion temperature rise scales with the square of the reconnecting field. During the current ramp up models are not able to correctly predict the current diffusion. Experiments...
Article
During the past decade, plasma physics research promoting the physics base of ITER and developing novel concepts such as a compact fusion neutron source has been conducted on the Globus-M spherical tokamak (ST) (R = 36 cm, a = 24 cm, I p ≤ 250 kA, B T ≤ 0.4 T). Tokamak reconstruction is imminent. The upgraded tokamak Globus-M2 will have the same va...
Article
Full-text available
To analyze factors influencing the limiting value of the plasma density at which lower hybrid (LH) current drive terminates, the isotopic factor (the difference in the LH resonance densities in hydrogen and deuterium plasmas) was used for the first time in experiments carried out at the FT-2 tokamak. It is experimentally found that the efficiency o...
Article
Full-text available
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 somewh...
Article
In this paper we present the fusion related activities of the Plasma Physics Division at the Ioffe Institute. The first experiments on lower hybrid current drive (LHCD) in a spherical tokamak performed at the Globus-M tokamak (R = 0.36 m, a = 0.24 m, Bt = 0.4 T, Ip = 200 kA) with a novel poloidally oriented grill resulted in an RF driven current of...
Article
Full-text available
First experiments on non-inductive current drive (CD) in the spherical tokamak using lower hybrid (LH) waves at 2.45 GHz are described. The basic characteristics of the new experimental approach utilizing poloidal LH wave slowing-down scheme obtained by modeling are presented at the beginning of the paper. The experimental results for a poloidal sl...
Article
Full-text available
The Mega Ampère Spherical Tokamak (MAST) programme is strongly focused on addressing key physics issues in preparation for operation of ITER as well as providing solutions for DEMO design choices. In this regard, MAST has provided key results in understanding and optimizing H-mode confinement, operating with smaller edge localized modes (ELMs), pre...
Article
Current drive by lower hybrid waves (LHCD) is the most effective method to sustain the plasma current, but it is feasible only at the plasma density not exceeding some density limit nDL. In the present work the main attention is paid to the investigation of this effect on the FT-2 (R = 0.55 m, a = 0.08 m, BT ≤ 3 T, Ipl = 19-40 kA, f0 = 920 MHz) tok...
Article
In this paper we report on simulations of lower hybrid current drive (LHCD) in JET closely comparing the simulation results to the available experimental data. The simulations are performed all over the relevant discharge duration by ASTRA. The LHCD module, FRTC, is based on a standard ray-tracing Fokker–Planck model. The purpose of the paper is to...
Article
A possibility of 3D electron Bernstein wave trapping in intensive magnetic field aligned density fluctuation or blob in toroidal plasma is demonstrated. Semi-analytic approach for description of associated plasma cavity is developed. A mechanism of low-threshold parametric decay instability driven by 2nd harmonic extraordinary pump microwave and le...
Article
Results of comparative experimental studies of the efficiency of lower hybrid current drive (LHCD) and lower hybrid heating (LHH) in the FT-2 tokamak in hydrogen and deuterium plasmas are presented. In the new comparative experimental runs in deuterium/hydrogen plasmas suppression of the LHCD and beginning of the interaction of LH waves with ions...
Conference Paper
Full-text available
Abstract. Start-up technique reported here relies on a double mode conversion (MC) for electron Bernstein wave (EBW) excitation. It consists of MC of the ordinary (O) mode, entering the plasma from the low field side of the tokamak, into the extraordinary (X) mode at a mirror-polarizer located at the high field side. The X mode propagates back to t...
Article
The possibility of 3D electron Bernstein wave trapping in intensive magnetic field aligned density fluctuation or blobs in toroidal plasma is demonstrated. A semi-analytic approach for the description of associated plasma cavity is developed. A mechanism of low-threshold parametric decay instability driven by extraordinary pump microwave and leadin...
Article
Full-text available
New diagnostic, modelling and plant capability on the Mega Ampère Spherical Tokamak (MAST) have delivered important results in key areas for ITER/DEMO and the upcoming MAST Upgrade, a step towards future ST devices on the path to fusion currently under procurement. Micro-stability analysis of the pedestal highlights the potential roles of micro-tea...
Article
Full-text available
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,...
Article
The experimental conditions that facilitate the excitation of parametric decay instabilities upon the electron cyclotron resonance heating of a plasma at the second harmonic extraordinary wave in tokamaks and stellarators and, as a result, make anomalous absorption of microwave power possible have been analyzed. It has been shown that, in the case...
Article
Full-text available
In the paper the possibility of total 3D trapping of electron Bernstein (EB) waves in the tokamak equatorial plane in the vicinity of the local density maximum produced by electron pump-out-effect is demonstrated. Thresholds and growth rates of the associated absolute (temporally growing) parametric decay instability (PDI) leading to anomalous abso...
Article
Full-text available
On MAST studies of the profile evolution of the electron temperature (Te), electron density (ne), radial electric field (Er) as well as novel measurements of the ion temperature (Ti) and toroidal current density (j) in the pedestal region allow further insight into the processes forming and defining the pedestal such as the H-mode access conditions...
Article
Major developments on the Mega Amp Spherical Tokamak (MAST) have enabled important advances in support of ITER and the physics basis of a spherical tokamak (ST) based component test facility (CTF), as well as providing new insight into underlying tokamak physics. For example, L–H transition studies benefit from high spatial and temporal resolution...
Article
Full-text available
Angular scanning of electron Bernstein wave emission (EBE) has been conducted in MAST. From EBE measurements over a range of viewing angles, the angular position and orientation of the B-X-O mode conversion (MC) window can be estimated, giving the pitch angle of the magnetic field in the MC layer. The radial position of the corresponding MC layer i...
Article
Full-text available
Angular scanning of EBW emission (EBE) has been conducted in MAST. From EBE measurements over a range of viewing angles the angular position and orientation of the B-X-O mode conversion (MC) window can be estimated giving the pitch angle of the magnetic field in the MC layer. The radial position of the corresponding MC layer is found from Thomson s...
Article
Simulations predict LH driven current about 100 kA for existing Globus-M plasma parameters and poloidal grill orientation. Increased magnetic field, plasma current and temperature in modernized Globus-M will permit to drive LH current about 200 kA for poloidal grill orientation and about 460 kA for toroidal one. Both grill orientations will be poss...
Article
Full-text available
Abstract Since the last IAEA Conference JET has been in operation for one year with a programmatic focus on the qualification of ITER operating scenarios, the consolidation of ITER design choices and preparation for plasma operation with the ITER-like wall presently being installed in JET. Good progress has been achieved, including stationary ELMy...
Article
The current ramp-up phase of ITER demonstration discharges, performed at JET, is analysed and the capability of the empirical L-mode Bohm–gyroBohm and Coppi–Tang transport models as well as the theory-based GLF23 model to predict the temperature evolution in these discharges is examined. The analysed database includes ohmic (OH) plasmas with variou...
Article
Full-text available
The problem of lower hybrid (LH) wave excitation and current drive (CD) in tokamaks with a small aspect ratio (spherical tokamaks) is discussed. It is proposed to solve this problem by exciting the waves slowed down in the poloidal rather than the toroidal direction. As a result, due to the strong poloidal inhomogeneity of the magnetic field in sph...
Article
Full-text available
Electron Bernstein wave (EBW) assisted plasma current start-up has been demonstrated for the first time in a tokamak. It was shown that plasma currents up to 17 kA can be generated non-inductively by 100kW of RF power injected. With optimized vertical field ramps, plasma currents up to 33 kA have been achieved without the use of solenoid flux. It i...
Article
Full-text available
Electron Bernstein waves (EBW) have the potential to provide highly localized heating and current drive (CD). EBWs are predominantly electrostatic and they damp on electrons near electron cyclotron harmonics without momentum injection into the plasma. These features represent a powerful tool for understanding transport and stability phenomena by l...
Article
The paper pays the main attention to the LHCD efficiency in experiments on the FT‐2 tokamak. LH wave spectra P(N z ) excited by the grill computed by GRILL3D code are presented. Physical processes responsible for termination of the CD with density rise are discussed for lower and higher plasma currents that are for relatively cold and relative...
Article
Full-text available
Several improvements to the MAST plant and diagnostics have facilitated new studies advancing the physics basis for ITER and DEMO, as well as for future spherical tokamaks (STs). Using the increased heating capabilities PNBI ≤ 3.8 MW H-mode at Ip = 1.2 MA was accessed showing that the energy confinement on MAST scales more weakly with Ip and more s...
Article
Full-text available
A new approach treating a real narrow microwave beam as a superposition of wide 'virtual' beams unaffected by diffraction within the plasma volume is proposed. A solution thus found describes propagation of a microwave beam in a plasma volume taking into account diffraction, absorption and refraction in the framework of a single procedure. In contr...
Article
A new approach treating an actual narrow microwave beam as a superposition of wide "virtual" beams unaffected by diffraction within a plasma volume is proposed. A solution thus found describes propagation of the microwave beam in the plasma volume taking into account the beam's diffraction, absorption and refraction in the framework of a single pro...
Article
EBW current drive assisted plasma current start-up has been demonstrated for the first time in a tokamak. It was shown that plasma currents up to 17 kA can be generated non-inductively by 100 kW of RF power injected. With optimized vertical field ramps, plasma currents up to 33 kA have been achieved without the use of solenoid flux. With limited so...
Conference Paper
Full-text available
Several improvements to the MAST plant and diagnostics have facilitated new studies advancing the physics basis for ITER and DEMO, as well as for future spherical tokamaks. Using the increased heating capabilities P NBI ≤ 3.8 MW H-mode at I p = 1.2 MA was accessed showing that the energy confinement on MAST scales more weakly with I p and more stro...
Article
A conceptual design of the lower hybrid current drive (LHCD) system for the upgraded T-15 tokamak (RNC Kurchatov Institute, Moscow) is presented. A tentative theoretical analysis, including extensive numerical simulations of different antenna types and LH wave propagation as well as estimation of LHCD efficiency, is carried out. The analysis has sh...
Article
Steady state operation is preferable for fusion reactors. The possibility of extending the pulse length in ITER is considered taking into account the capabilities of the planned electron-cyclotron current drive (ECCD) and low-hybrid current drive (LHCD). The ECCD efficiency for current drive at different locations is assessed. The possibility of ex...
Article
Full-text available
There is a comprehensive, closely-interlinked electron Bernstein wave (EBW) programme on MAST covering heating experiments, plasma start-up studies, plasma emission measurements, theory and modelling. In this paper we report on proof-of-principle EBW heating experiments conducted on MAST with a 60 GHz, 1 MW gyrotron complex. A 28 GHz (200 kW) EBW s...
Article
Full-text available
Burning plasma spherical tokamaks (STs) rely on off-axis current drive (CD) and nonsolenoid start-up techniques. Electron Bernstein waves (EBWs) may provide efficient off-axis heating and CD in high-density ST plasmas. EBWs may also be used in the plasma start-up phase because EBW absorption and CD efficiency remain high even in relatively cold pla...
Article
Full-text available
A new simple and accurate approximate electrostatic relativistic dispersion relation for electron Bernstein waves in a Maxwellian plasma has been obtained. The relativistic relation is valid for an arbitrary value of parallel refractive index. Comparisons with corresponding exact formulae are given.
Article
Full-text available
Substantial advances have been made on the Mega Ampère Spherical Tokamak (MAST). The parameter range of the MAST confinement database has been extended and it now also includes pellet-fuelled discharges. Good pellet retention has been observed in H-mode discharges without triggering an ELM or an H/L transition during peripheral ablation of low spee...
Article
Full-text available
Propagation and absorption of the electron Bernstein waves (EBWs) in spherical tokamaks (STs) have been intensively discussed in recent years because the EBWs coupled with an externally launched electromagnetic beam seem to be the only opportunity for microwave plasma heating and current drive in the electron cyclotron (EC) frequency range in the...
Conference Paper
Full-text available
Burning plasma spherical tokamak (ST) designs rely on off-axis current drive and non-solenoid start-up techniques. Electron Bernstein waves (EBW) may provide efficient off-axis heating and current drive (CD) in high density ST plasmas. EBW may also be used in the plasma start-up phase due to the fact that EBW absorption and CD efficiency remain hig...
Conference Paper
Full-text available
Substantial advances have been made on MAST. The parameter range of the MAST confinement database has been extended and it now also includes pellet-fuelled discharges. Good pellet retention has been observed in H-mode discharges without triggering an ELM or an H/L transition. Co-ordinated studies on MAST and DIII-D demonstrate a strong link between...
Conference Paper
Full-text available
Important advances have been made on MAST, aided by substantial developments to plasma control, diagnostics and heating systems. The parameter range of the MAST confinement database has been extended and it now also includes pellet-fuelled discharges. Co-ordinated studies on MAST and DIII-D provide a strong link between the aspect ratio and beta sc...
Article
Full-text available
Burning plasma spherical tokamak (ST) designs rely on off-axis current drive and non-solenoid start-up techniques. Electron Bernstein waves (EBW) may provide efficient off-axis heating and current drive (CD) in high density ST plasmas. EBW may also be used in the plasma start-up phase due to the fact that EBW absorption and CD efficiency remain hig...
Article
The recent success in coupling lower hybrid (LH) waves in high performance plasmas at JET together with the first demonstration on FTU of the coupling capability of the new passive active multijunction launcher removed major concerns on the possibility of using LH on ITER. LH exhibits the highest experimental current drive (CD) efficiency at low pl...
Article
The data in figures 6 and 13(a) were incorrectly plotted. Please see the pdf for the corrected versions.
Article
Full-text available
A new approximate electrostatic relativistic dispersion relation for electron Bernstein waves (EBWs) in a Maxwellian plasma has been derived. The relation is reasonably simple for analytical analysis and accurate enough for numerical applications. Comparisons with corresponding exact formulae are presented. Formulae for absorption of the EBWs based...
Article
Full-text available
Significant progress has been made on the Mega Ampere Spherical Tokamak (MAST) towards a fundamental understanding of transport, stability and edge physics and addressing technological issues for future large devices. Collaborative studies of the L–H transition with NSTX and ASDEX Upgrade confirm that operation in a connected double-null configurat...
Article
Full-text available
Low aspect ratio plasmas in devices such as the mega ampere spherical tokamak (MAST) are characterized by strong toroidicity, strong shaping and self fields, low magnetic field, high beta, large plasma flow and high intrinsic E × B flow shear. These characteristics have important effects on plasma behaviour, provide a stringent test of theories and...
Article
Full-text available
Many experiments have proved the effectiveness of lower hybrid waves for current drive (CD) and current density profile control in tokamaks. However, fusion generated α-particles may be accelerated well beyond their birth velocity and may damp the wave energy, thus reducing the CD efficiency. This effect is absent at high frequency (8 GHz), but suc...
Article
The Frascati Tokamak Upgrade (FTU) has been operating for more than 12 yr since its first plasma in 1990 and has played an important role in several aspects of the tokamak research. As the first paper of this special issue containing papers on all aspects of FTU, this paper briefly summarizes the main dates, the general description of the facility,...