P. A. Bagryansky

EXPERIMENTAL STUDY OF CURVATURE-DRIVEN FLUTE INSTABILITY IN THE GAS-DYNAMIC TRAP

A curvature‐driven flute instability will be excited in the magnetized plasmas if the magnetic field lines curve toward the entire plasma boundary. Conditions under which it can be effectively stabilized in axisymmetric geometry have been experimentally studied in a gas‐dynamic trap (GDT) at Novosibirsk. Flexible design of the experimental device and the availability of neutral beams and ion cyclotron heating enabled the pressure‐weighted curvature to be varied over a wide range. The stability limits were thus measured and compared with those predicted by the modified Rosenbluth–Longmire criterion. Characteristics of unstable curvature‐driven flute modes were also measured and found to conform to a theory including finite ion Larmor radius (FLR) effects. Stable operation during neutral beam injection was achieved with a cusp end cell, resulting in an increase in Te to 45 eV, limited by end losses rather than anomalous power losses.

Observation of magnetohydrodynamic stability limit in a cusp-anchored gas-dynamic trap

In this paper, the observation of magnetohydrodynamic (MHD) stability limit in a fully axisymmetric gas-dynamic trap is reported. Transition through the stability boundary was studied by varying the plasma pressure in the stabilizing cusp end cell and simultaneously measuring the particle and energy lifetimes in the central cell. Energy and particle balance of the neutral beam heated plasma was measured and compared in unstable and stable regimes of operation. It was observed that if the calculations based on the energy principle predicted the plasma to be stable, experimentally measured transverse losses appeared to be smaller than the longitudinal ones. In the opposite case, the transverse losses were dominant thus indicating transition through the MHD stability boundary in the cusp-anchored gas-dynamic trap.

Spatial profiles of fusion product flux in the gas dynamic trap with deuterium neutral beam injection

Recently, a plasma with energetic deuterons has been produced in the gas dynamic trap (GDT) experiment under skew injection of 4 MW, 15–17 keV deuterium neutral beams. The GDT is a long, axially symmetric magnetic mirror device with a high mirror ratio. The deuterium neutral beams have been injected at the mid-plane of the device under 45° to the axis. High anisotropy of the fast ion angular distribution results in a strong peaking of the fast ion density at the turning points near the end mirrors. The axial profile of DD fusion product fluxes has been measured and found to be strongly peaked in the same regions. The characteristics of the profiles are consistent with the classical mechanism of fast ion relaxation caused by two-body Coulomb collisions with plasma particles. This observation validates an approach used in a GDT based neutron source, in which the regions of high neutron flux would be surrounded by the testing zones for fusion material irradiations.

Novosibirsk Project of Gas-Dynamic Multiple-Mirror Trap

Development of a new linear device for confinement of fusion plasmas is under way in the Budker Institute of Nuclear Physics, Novosibirsk. The new device combines features of existing GOL-3 and GDT traps, namely, the central GDT-like cell with sloshing ions produced by intense neutral beam injection, and the multiple-mirror end sections for suppression of axial plasma losses. It is designed as a prototype of an energy-efficient neutron source and a testbed for development of mirror-based fusion reactors.

Progress in Mirror-Based Fusion Neutron Source Development

The Budker Institute of Nuclear Physics in worldwide collaboration has developed a project of a 14 MeV neutron source for fusion material studies and other applications. The projected neutron source of the plasma type is based on the gas dynamic trap (GDT), which is a special magnetic mirror system for plasma confinement. Essential progress in plasma parameters has been achieved in recent experiments at the GDT facility in the Budker Institute, which is a hydrogen (deuterium) prototype of the source. Stable confinement of hot-ion plasmas with the relative pressure exceeding 0.5 was demonstrated. The electron temperature was increased up to 0.9 keV in the regime with additional electron cyclotron resonance heating (ECRH) of a moderate power. These parameters are the record for axisymmetric open mirror traps. These achievements elevate the projects of a GDT-based neutron source on a higher level of competitive ability and make it possible to construct a source with parameters suitable for materials testing today. The paper presents the progress in experimental studies and numerical simulations of the mirror-based fusion neutron source and its possible applications including a fusion material test facility and a fusion-fission hybrid system.

First results of an auxiliary electron cyclotron resonance heating experiment in the GDT magnetic mirror

The axially symmetric magnetic mirror device gas-dynamic trap (GDT, Budker Institute, Novosibirsk) has recently demonstrated a tangible increase in plasma electron temperature. According to laser scattering, a value of 0.4xa0keV has been achieved (a twofold increase). In addition to standard machine operation, utilizing a 5xa0MW neutral beam injection, a newly installed electron cyclotron resonance heating (ECRH) system was employed (54.5xa0GHz, 0.4xa0MW). The reported progress in electron temperature, along with previous experiments, which demonstrated plasma confinement at beta as high as 60%, is a significant advancement towards an energy efficient fusion neutron source based on GDT physics.

Formation of a Narrow Radial Density Profile of Fast Ions in the GDT Device

The radial density profile of fast ions with a mean energy of 10 keV is measured in experiments with a two-component high-β plasma in the GDT device. Fast ions are produced by injecting neutral beams into a warm plasma. The measured fast-ion density profile is found to be narrower than that calculated with allowance for the neutral beam trapping and Coulomb scattering. Special experiments with a movable limiter have indicated that the formation of a narrow fast-ion density profile in GDT cannot be attributed to the loss of fast ions. Possible mechanisms responsible for this effect are discussed.

Mirror based fusion neutron source: Current status and prospective

The paper presents a recent progress in experimental studies and status of numerical simulations of the mirror based fusion neutron source developed by the Budker Institute of Nuclear Physics (Novosibirsk, Russia) and its possible applications including a fusion material test facility and a fusion-fission hybrid system. Current research activity is supported by the Russian Science Foundation (project N 14-50-00080).

Project of the GDT-based steady-state experiment

In recent years, significant success in a plasma stabilization, heating and confinement in Gas Dynamic Trap (GDT) has been acheived. However, transition processes such as fast ions buildup, ion and electron temperature growth, etc., are still underway until the end of plasma heating. Thus, heating sources worktime (around 5u2005ms) is too short for plasma parameters to become stationary. In this work we propose a project of GDT-based stationary plasma experiment with pulse length long enough to finish all transition processes. The implemetation of the project will allow us to test GDT stabilization, heating and confinement methods to stationary conditions and to scale the methods to reactor-sized devices. Features of the project include a superconducting magnetic system with 15 T magnetic mirror field, 30u2005ms plasma pulse and mixed neutral particle and ECR heating. Results of numerical simulations of such experiment using DOL code are also presented.

Study of Microinstabilities in Anisotropic Plasmoid of Thermonuclear Ions

Abstract The following work presents the results of investigation of microinstabilities in the anisotropic synthesized hot ion plasmoid (SHIP). Plasmoid is located in a small mirror section that is installed at one side of the GDT facility, which is an axially symmetric magnetic mirror device of gas dynamic trap type. To define the type and the parameters of the developing microinstability a set of high-frequency electrostatic and magnetic probes was used. The microinstability observed in the additional section of GDT is the Alfven ion cyclotron instability (AIC), because of small azimuthal wave numbers, magnetic field vector rotating in the direction of ion gyration and oscillation frequency below the actual ion cyclotron frequency. AIC instability threshold was registered at the following plasma parameters: fast ion density n > 3 × 1013 cm-3, ratio of ion pressure to magnetic field pressure β ≈ 0.02, anisotropy A = 40, ai/Rp ≈ 0.23, where ai is the ion gyroradius and Rp is the plasmoid radius.