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Main scientific results International collaboration Conferences held

Main scientific results (including results obtained before 1982 in the research group that became the basis of the department)

1967 – 1980
The foundations of physics of fusion-produced alpha particles and thermonuclear burn in plasmas were laid. A new class of instabilities of reactor plasmas was discovered. Now instabilities of this class are studied in many laboratories throughout the world both theoretically and experimentally. Pioneer works on the effect of self-heating of fusion plasmas were carried out, which gave a possibility to obtain a simple criterion of thermonuclear burn stability and investigate different regimes of the burn. These results were generally recognized and included to the review paper [Ya. I. Kolesnichenko, "The role of alpha particles in a tokamak reactor", Nuclear Fusion 20 (1980) 727 ], which is widely cited.
More detailed information are in next publications:

1983 – 1989
New methods of current drive in tokamaks were proposed. The near-axis current produced by alpha particles was predicted. The concept of the steady-state tokamak reactor with the current sustained by internal plasma processes was suggested. The steady-state current generation was made possible by the predicted near-axis seed current produced by alpha particles. This concept was further developed in the USA[K.C. Shaing et al., IAEA Fusion Energy-1998 Conference in Yokohama (IAEA, Vienna, 1999, on CD-ROM); Physics of Plasmas 4 (1997) 4331].

1990 – 1994
Ballooning flute modes in plasmas of toroidal systems were studied. The phenomenon of the ballooning modes stabilization by fast ions was discovered. The existence of kinetic ballooning modes was predicted. A stability criterion for ballooning modes in a plasma with an arbitrary pressure profile was obtained.

1992
An idea of a qualitatively new magneto¬hydro¬dynamic (MHD) process with reconnection of magnetic field lines was advanced, which is of importance for understanding of physical phenomena in laboratory and space plasmas. This process involves spitting magnetic flux surfaces. An explanation of important peculiarities of sawtooth oscillations in tokamaks was suggested. These results were included, in particular, into the book [R.B. White "The theory of toroidally confined plasmas", Imperial College Press, 2001].

1992 – 2000
Theory of energetic ion transport during sawtooth oscillations was developed. The sawtooth oscillations are a typical form of MHD-activity of tokamak plasmas, which is characterized by periodic relaxations of the plasma temperature, as well as soft X-ray and neutron emission. The existence of the critical energy of the ions was predicted: The ions with the energies above the critical energy are insensitive to the MHD-activity, whereas the ions with lower energies are expelled by the MHD-perturbations from the plasma core to the periphery. Later this prediction was confirmed experimentally on TFTR – the largest American tokamak [S. Medley et al., Nuclear Fusion 38 (1998) 1283]. The series of works "MHD phenomena and transport of high-energy ions in fusion plasmas" by Ya.I. Kolesnichenko, V.V. Lutsenko, and Yu.V. Yakovenko was awarded with the K.D. Synelnykov Prize of the National Academy of Sciences of Ukraine (2003 р.).

1995 – 2003
A three-dimensional Fokker-Planck model of fast ions in tokamaks in terms of constants of motion was developed, which was used to explain the behaviour of injected and fusion-produced fast ions in TFTR and JET, as well as for predictions of fast-ion effects in ІТЕR.

1997
The nature of superthermal ion cyclotron emission (ICE) from tokamak plasmas was clarified. It was shown that the ICE arises because of a magnetoacoustic instability enhanced by the toroidal drift of energetic ions. This explains a number of ICE frequency spectrum peculiarities observed in experiments on the European tokamak JET.

1998 – 2000
A mechanism of loss of partly thermalized fusion reaction products in the tokamak TFTR was proposed.

1999
It was shown that the fishbone instability – one of the most dangerous instabilities caused by energetic ions in tokamaks – can be stabilized in high-β plasmas of spherical tori. This conclusion was confirmed in experiments on the spherical torus MAST (UK) [M. P. Gryaznevich, S. E. Sharapov, Plasma Physics and Controlled Fusion 46 (2004) S15].

2001
A new classical (i.e., not associated with plasma instabilities) mechanism of the stochastic diffusion of energetic ions in stellarators was found. This mechanism is considered as the main one in the optimized stellarators of the Wendelstein line. It is associated with the presence of “transitioning” particles, which change the character of their orbits during collisionless motion

2005
Predictive calculations of the influence of the reversed magnetic shear in tokamaks on the spatial distribution of the neutron emission were carried out. The theory predictions were confirmed in experiments with injection of tritium beams into deuterium plasmas on JET.

1999 – 2007
Theory of Alfvén instabilities (instabilities which attract a great attention in current fusion research) in stellarator plasmas was developed. New types of Alfvén modes and resonances of the wave–particle interaction, which are caused by the lack of axial symmetry in stellarators, were predicted. In particular, the so-called Mirror-induced Alfvén eigenmodes (MAE) were discovered. It was shown that these modes and the Helicity-induced Alfvén eigenmodes (HAE) can be destabilized by ion beams. A new mechanism of anomalous heat conductivity of plasmas, which can take place also in space plasmas, was found. This mechanism was used to explain experiments on the German stellarator Wendelstein 7-AS, in which strong thermal crashes were observed. Conclusion of this theory were also confirmed in experiments on the largest stellarator LHD (Japan) [S. Yamamoto et al., Physical Review Letters 91 (2003) 245001]. In addition, they were used for the development of the conceptual project of the stellarator reactor Helias [C.D. Beidler et al., Nuclear Fusion 41 (2001) 1759].

2008 – 2010
A theory of low frequency wave phenomena in toroidal systems is developed, which takes into account effects of finite diamagnetic frequency and plasma compressibility. Using this theory and observations on the stellarator Wendelstein 7-AS, it is found that there exist drift-sound eigenmodes and a new kind of drift-Alfvén eigenmodes. It is shown that Alfvén waves can be destabilized by a magnetic island. Two new types of fishbone mode are predicted: the resonance continuum mode (RCM) and non-resonance gap mode (NGM); frequencies of these modes well exceed the frequency of the conventional fishbone instabilities.

2010
A new phenomenon caused by energetic (superthermal) ions in plasmas - spatial channeling of the energy and momentum during energetic-ion-driven instabilities - is discovered. It is shown that waves (eigenmodes) destabilized by energetic ions can provide an efficient mechanism of the energy and momentum transfer from one plasma region to another one. The efficiency of the energy / momentum transfer due to the channeling can well exceed that due to heat conductivity and heat convection. For instance, this phenomenon may take place in toroidal fusion devices, where Alfvén eigenmodes are destabilized by beam ions injected for plasma heating.

 

2012
It is found that features of the spectrum of Alfvén oscillations drastically change in tokamaks with high beta and large safety factor (q). In particular, it is shown that conventional expressions for the frequencies of the Geodesic Acoustic Mode and the gaps in the Alfvén continuum of toroidal plasmas are valid only when the plasma pressure is rather low. Expressions for these frequencies in high beta / high-q plasmas are obtained. It is found that the Alfvén continua in the plasma core of the tokamaks with hollow current and the spherical tori with high beta are described by Mathieu's equation, from which it follows that the continuum gaps in the mentioned cases occupy almost all the frequency range.

 

2013
The nature of the sawtooth crashes with partial reconnection of magnetic field lines in tokamaks is considered. It is shown that joint action of effects of frozen-in magnetic field lines and satellite harmonics of the magnetic perturbation can lead to wide-spread stochasticity; the stochasticity occupies, in particular, the near-axis region - which is a necessary condition for drops of the central plasma temperature during the crashes.


Horizontal polarization of the plasma during electron cyclotron resonance heating (ECRH) is capable to suppress the so-called “Alfven cascades” – a plasma instability excited by energetic ions. The suppression mechanism consists in the formation of a potential “hill” for the cascade modes when the peak of the ECRH deposition is slightly shifted inside of the mode location, consistent with experiment on the tokamak DIII-D (USA).
A set of MHD equations describing the Geodesic Acoustic Mode (GAM / E-GAM) in tokamak plasmas with energetic ions and high pressure is derived. It is shown that that conditions for the GAM / EGAM instability to arise are mildest in the case of counter-injection of energetic ions with certain pitch angles, which explains experimental observations. It is found that the mode Fourier harmonics coupling caused by the plasma pressure and the field line curvature can determine the radial structure of the modes.

2014
It is found that (i) the destabilization of global Geodesic Acoustic modes (GAM or E-GAM) by passing energetic ions in tokamaks can be accompanied by a considerable energy transfer from these ions to the mode; (ii) the mode-induced slowing down of the energetic ions leads to a radial outward / inward shift of the ions moving in the counter- / co- direction to the plasma current, although the canonical angular momentum of the particles is conserved during GAMs. Some practical consequences of these phenomena are discussed.


It is shown that infernal modes can lead to convection of well passing energetic ions deposited in the core by fusion reactions and/or neutral injection. The convection mechanism consists in slowing down of the energetic ions trapped in the Doppler-precession resonance with a finite-amplitude infernal mode. The convection rate can reach 5-10 m/s in modern spherical tori. This mechanism can be responsible for the fast-ion pump-out by infernal modes in the spherical torus MAST (UK).

2015
Predictive 3D Fokker–Planck modelling of phase space distributions of fusion alpha particles for basic ITER scenarios is carried out. The poloidal profiles of the alpha induced current as well as of the fusion power deposition to bulk plasma electrons are simulated. It is demonstrated that anisotropy of the velocity distributions of alphas results in a rather strong alpha-driven current that makes up about 10–15% of the equilibrium plasma current density in the steady-state ITER scenario. The impact of the alpha-driven current on the ITER magnetic configuration is investigated. In the steady-state scenario the fusion alphas are shown to result in nearly 15% enhancement of the rotational transform and in about 11% enlargement of the Shafranov shift of magnetic flux surfaces.


The so-called “bucket transport” of energetic ions - the spatial mixing of these ions due to spatial displacement of resonances - is studied with special attention to quasi-steady-state magnetic perturbations. A Hamiltonian formalism suitable to the case when the resonance displacement results from the collisional slowing down of the particles and the temporal evolution of the safety factor profile is suggested. The energy flux produced due to the bucket transport is shown to be considerable in configurations with low shear.
A theory of electrodeless electric propulsion systems based on the use of the solenoid magnetic field and the rotating electromagnetic field produced by antennas is developed, which includes a study of the plasma acceleration by the Radio Frequency field and the concomitant thrust. The obtained results can be used for the optimization of particular experiments aimed to create a new thruster for long-time space missions.

2016
A theory is developed which describes the influence of the beam-driven Geodesic Acoustic Mode (E-GAM) on the energetic ions and concomitant change of the neutron emission in a beam-plasma system. This theory was used to clarify physical mechanisms responsible for large (10-15%) drops of the neutron emission that were observed in NBI experiments on the DIII-D tokamak (USA) during bursts of E-GAM instability


It is found that modes of Alfvénic character affected by plasma compressibility and having equal poloidal and toroidal mode numbers (named "isomon modes") can exist in Wendelstein 7-X. The energetic ions produced by neutral-beam injection (having the energy 55–60 keV) interact resonantly with large-scale isomon modes, which tends to lead to instabilities extending over a large part of the plasma cross section.

 

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