Gas Dynamic Trap Research Articles

Auxiliary ECR heating system for the gas dynamic trap

Physics aspects of a new system for electron cyclotron resonance heating (ECRH) at the magnetic mirror device Gas Dynamic Trap (GDT, Budker Institute, Novosibirsk) are discussed. This system based on two 400 kW/54.5 GHz gyrotrons is aimed at increasing the electron temperature up to the range 250–350 eV for improved energy confinement of hot ions. The key physical issue of the GDT magnetic field topology is that conventional ECRH geometries are not accessible. The proposed solution is based on a peculiar effect of radiation trapping in inhomogeneous magnetized plasma. Under specific conditions, oblique launch of gyrotron radiation results in generation of right-hand-polarized (R) electromagnetic waves propagating with high N|| in the vicinity of the cyclotron resonance layer, which leads to effective single-pass absorption of the injected microwave power. In the present paper, we investigate numerically an optimized ECRH scenario based on the proposed mechanism of wave propagation and discuss the design of the ECRH system, which is currently under construction at the Budker Institute.

Axisymmetric Magnetic Mirror Applications – Divertor Test Stand to Fusion Power Plant

Axisymmetric mirrors can be MHD-stabilized by end losses. Neutral-beam-sustained operation to β~0.6, and Te~0.2 keV, with 5 ms 5 MW neutral beams on the Gas Dynamic Trap (GDT) has been demonstrated at the Budker Institute in Novosibirsk, Russia. Applications of this concept can reduce risks in the fusion program. A GDT-scale facility could test plasma-material interactions (PMI) at up to 400 MW/m2 and 5 s pulse duration for divertor development. Extrapolation of the GDT to a Dynamic Trap Neutron Source, DTNS, provides a DT-fusion neutron flux of 2 MW/m2 over 1 m2, at a power-plant efficiency of Q ~ 0.07. (A DTNS enables development and testing of materials and sub-component structures, for fusion power plants, MFE or IFE. A DTNS functions regardless of whether the tested components work. These developments would reduce risks for a tokamak Fusion Nuclear Science Facility (FNSF)). Further extrapolation to 0.2 ≤ Q ≤ 10 single-cell or tandem mirror yields several fusion-fission hybrid applications. Further extension to a pure-fusion axisymmetric-tandem-mirror power plant, requires Q>10. Tandem mirrors demand the use of different stabilization techniques that are not dependent on out-flowing plasma, a number of which have been proposed, and could be experimentally tested on the GDT.

Hybrid systems in the nuclear fuel cycle. Principles of operation and applications

The problem of utilization of nuclear fuel cycle waste is one of the main problems of modern nuclear energetics. In the Institute of Nuclear Physics of the Siberian Branch of the Russian Academy of Sciences (RAS) in cooperation with the Nuclear Safety Institute of the RAS, a model of a subcritical hybrid system with a plasma neutron driver based on an open gas-dynamic trap is being developed to solve this problem. Modeling of the plasma behavior in the source was carried out using the zero-dimensional GENESYS code, which takes into account the processes of capturing of injected atoms by ions and the processes of Coulombic interactions with warm plasma. This code also contains a module for calculating the linear power of neutron emission along the axis of the trap using the Monte Carlo method. As a template for the fuel blanket, a homogenized blanket of the EFIT system was used. The calculation of neutron-physical characteristics was carried out using a static NMC code which uses a method of direct modeling of neutron trajectories. The article presents the results of optimization of parameters of this system. In particular, the optimal length of the source emission zone was determined and the dependence of the multiplication factor on the thickness of the buffer zone of the subcritical blanket was determined.

Note: Multi-point measurement of |B| in the gas-dynamic trap with a spectral motional Stark effect diagnostic

An upgraded spectral motional Stark effect diagnostic has been installed on the gas-dynamic trap (GDT) experiment to enable spatially resolved measurement of |B|. A new low-noise charge-coupled device detector, combined with enhancements of the diagnostic neutral beam, allows single-shot profile measurements. Previously only single-point motional Stark effect measurements were possible, and detector noise severely limited measurement precision, requiring multi-shot averaging. The plasma pressure profile in GDT is derived from the measured diamagnetic modification of |B| and used to examine the conditions of stable plasma confinement at high plasma pressure.

Low-Frequency Oscillations of Plasma in the Gas Dynamic Trap

Vortex confinement is a new and effective method of convective losses suppression in gas-dynamic trap. Low frequency oscillations of radial magnetic field were observed during study of plasma MHD activity. Experimental data confirm the main statements of the vortex confinement theory. We also observed displacement of fast ions turning point. It can be explained by high beta equilibrium effects.

Neutral Beam System of the Gas Dynamic Trap

Within this report we summarize the technical and experimental effort made on high power neutral beam injector system (NBI) and diagnostics neutral beam injector (DINA-5M) which was installed at Gas Dynamic Trap device (GDT) last year. Basic components of NBI-systems and DINA are reviewed. Recent experimental results support the concept of the neutron source based on the gas dynamic trap.

Confinement of Hot Ion Plasma with β = 0.6 in the Gas Dynamic Trap

A so called vortex confinement of plasma in axially symmetric mirror device was studied. This recently developed approach enables to significantly reduce transverse particle and heat losses typically caused by MHD instabilities which can be excited in this case. Vortex confinement regime was established by application of different potentials to the radial plasma limiters and end-plates. As a result, the sheared plasma flow at periphery appears which wraps the plasma core. Experiments were carried out on the gas dynamic trap device, where hot ions with a mean energy of Eh ≈ 9 keV and the maximum density of energetic ions nh ≈ 5·1019m-3 were produced by oblique injection of deuterium or hydrogen neutral beams into a collisional warm plasma with the electron temperature up to 250 eV and density nw ≈ 2·1019m-3. Local plasma β approaching 0.6 was measured. The measured transverse heat losses were considerably smaller than the axial ones. The measured axial losses were found to be in a good agreement with the results of numerical simulations. Recent experimental results support the concept of the neutron source based on the gas dynamic trap.

DD Product Yield in the GDT Central Cell

The report presents the recent results of experiments with deuterium neutral beam injection in the Gas Dynamic Trap (GDT) device. Neutron scintillation detector and single particle proton detector near fast ions mirror point allow to control DD activity in each shot. A system for spatial measurements of fusion protons is prepared. DD reaction yield measurements are needed to compare with the predictions of the theory based on two-body Coulomb collisions.

Extrapolation of GDT Results to a Neutron Source for Fusion Materials Testing

The achievement of 60% beta and near classical confinement in the Russian Gas Dynamic Trap (GDT) provides a basis for extrapolating to a 2 MW neutron source with 2 MW m-2 of 14 MeV neutron flux over an area of ~1 m2. Such a source is needed for fusion materials development and qualification. We consider two axisymmetric configurations: a single mirror cell Deuterium-Tritium Dynamic-Trap Neutron Source (DTNS) and a Tandem-mirror Neutron Source (TNS). Compared to earlier US neutron source concepts, neither configuration utilizes complex minimum-B magnets or thermal barriers. In this paper we describe extrapolations from GDT with the same physical size, and the same dimensionless plasma parameters, but with higher magnetic field as well as higher neutral beam energy and power.

Perspectives of Development of Magnetic Mirror Traps in Novosibirsk

The paper reviews the characteristic features of a volumetric neutron source based on the gas dynamic trap and the results of current experiments at GDT device on modeling of the operational regimes of the neutron source. Some limiting factors in the current experiments and possible next steps towards more comprehensive modeling in future experimental device are discussed. Also discussed are the recent findings in the GOL-3 experiment and their consequences for the next step experimental device.

Numerical Model of the Fusion-Fission Hybrid System Based on Gas Dynamic Trap for Transmutation of Radioactive Wastes

The paper presents a 3D numerical model of the neutron source for the transmutation of long-lived radioactive waste in spent nuclear fuel. The projected plasma type neutron source is based on the Gas Dynamic Trap (GDT) which is a special magnetic mirror system for the plasma confinement. A new improved version of the GDT type fusion neutron source is numerically simulated by use different numerical methods. New physical phenomena such as a vortex confinement, improved axial confinement, low radial transport, high β etc. were included in these simulations. The experimental and theoretical foundations of these phenomena were obtained in the GDT-U experimental facility in the Budker Institute. In result the proposed neutron source has two n-zones of 2 m length with a neutron power of 1.6 MW/m and a neutron production rate up to 1.5x1018 n/s each. This source can be used for application to a fusion driven system for the burning of MA in spent nuclear fuel.

The GDT Based Neutron Source as a Driver in a Sub-Critical Burner of Radioactive Wastes

Transmutation of long-lived radioactive nuclear waste, including plutonium, minor actinides and fission products, represents a highly important problem of fission reactor technology and is presently studied worldwide in large-scale. Sub-critical systems seem to be a promising option for efficiently burning plutonium and minor actinides provided a sufficiently high-intense neutron source is available. For a number of years the Budker Institute of Nuclear Physics (Russia) in collaboration with the Russian and European organizations developed the project of a 14 MeV neutron source for fusion material irradiation and other applications. The projected plasma type neutron source is based on the Gas Dynamic Trap (GDT) which is a special magnetic mirror system for the plasma confinement. This poster presents different version of the GDT-based neutron source for hybrid fusion-fission sub-critical system for the transmutation of the long-live radioactive waste in spent nuclear fuel.

Confinement of Hot Ion Plasma with = 0.6 in the Gas Dynamic Trap

Confinement of Hot Ion Plasma with = 0.6 in the Gas Dynamic Trap

Line Plasma Density Measurement in the Gas Dynamic Trap with Dispersion Interferometer

Plasma consists of two components in the Gas Dynamic Trap facility: a relatively cold and dense collisional plasma and a population of fast anisotropic ions which oscillate between mirror points. Peaks of fast ion density are made closely to the mirror points. It formes an ambipolar potential difference between these points and the center of the facility. The ambipolar potential restricts a plasma flow through the mirror region, so it influences on the plasma confinement. The ambipolar potential value can be found from the line plasma density in the central facility region. The dispersion interferometer, which is based on a CO2-laser with wavelength l = 9.57 ¼m, has been made for this purpose. The minimal line plasma density measurable with the dispersion interferometer is (nel) ~ 1013 cm-2, the time resolution is 100 ¼s. The fast ion line density is 4 times higher than the warm ion line density in the mirror region. The ambipolar potential value is eϕ » 0.7 Te in electron temperature units. Also the flute instability restriction opportunity with gradient of local electric field has been observed. The limiter voltage satisfying the condition U ~ Te is boundary for stabilization of plasma behavior.

Possible Further Steps for Upgrading the GDT Device

Recent upgrade of the neutral beam system has resulted in considerable improvement of the plasma parameters in the gas dynamic trap experiment. With injection of 5 ms, 20 keV, 4.5 MW neutral beams the electron temperature approaching 250 eV was obtained. At the same time maximal plasma beta attained about 60%. Further progress in plasma temperature and pressure could only be possible with considerable increase of the magnetic field in the central solenoid and re-optimization of its profile to improve stability of high-beta plasma, as well as with extension of the neutral beam pulse. Possible steps in this direction are considered in this paper.

Study of Microinstabilities in Anisotropic Plasmoid of Thermonuclear Ions

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.

Modern magnetic mirrors and their fusion prospects

This paper reviews the most important findings from recent experiments on modern magnetic mirrors, apart from tandem mirrors and rotating plasma devices. These modern magnetic mirrors are represented by a multiple mirror device GOL-3 and a gas dynamic trap, experiments on which are carried out in Novosibirsk. Both devices are characterized by axial symmetry and improved axial confinement of plasma compared with conventional mirror machines. Recent findings from experiments enable us to more practically consider applications of the gas dynamic trap as a high-flux 14 MeV neutron source for fusion materials testing, and possibly as a driver for fusion–fission hybrids. They also indicate that effective axial plasma confinement in a multiple mirror can be obtained with a smaller plasma density compared with theory and β < 1. This is beneficial from the point of view of the technical realization of a multiple mirror reactor.

High Beta Experiments in the GDT Axisymmetric Magnetic Mirror

This paper reports recent results from the Gas Dynamic Trap magnetic mirror device. Achieving plasma betas up to 60% provides a basis for extrapolating this concept to a fusion relevant 14 MeV neutron source for testing and validating materials applicable to fusion systems.

Formation of a magnetic hole above the mirror-instability threshold in a plasma with sloshing ions

Within the framework of paraxial approximation it is shown that in an anisotropic plasma with sloshing ions confined an open-ended system a magnetic hole is formed near the turning point of the sloshing ions above the threshold of the mirror instability. The magnetic field experiences a jump at the hole boundary from the side of the magnetic mirror. For a small excess over the mirror instability threshold, the surface of the discontinuity has the shape of a truncated paraboloid, and the magnitude of the magnetic field jump at the system axis is proportional to the radius of the hole and gradually decreases to zero away of the axis. It is argued that disappearance of the magnetic hole because of the widening of the sloshing ions angular spread in the course of the neutral beam injection results in abrupt anticorrelated changes of the diamagnetic signals measured near the turning point of the sloshing ions and near the midplane of the gas-dynamic trap.

Results of Recent Experiments on GDT Device After Upgrade of Heating Neutral Beams

The status of the experiments on the axially symmetric magnetic mirror device gas dynamic trap (GDT) is discussed. The plasma has been heated by skewed injection of 20-keV, 3.5-MW, 5-ms deuterium/hydrogen neutral beams at the center of the device, which produces anisotropic fast ions. Neither enhanced transverse losses of the plasma nor anomalies in the fast ion scattering and slowing down were observed. Extension of neutral beam injection pulse duration from 1 to 5 ms resulted in an increase in the on-axis transverse beta (ratio of the transverse plasma pressure to magnetic field pressure) from 0.4 at the fast ion turning points near the end mirrors to about 0.6. The measured beta value is rather close to or even higher than that expected in different versions of the GDT-based 14-MeV neutron source for fusion materials testing. The density of fast ions with the mean energy of 10 to 12 keV reached 5 × 1019 m−3 near the turning points. The electron temperature at the same time reached ≈200 eV. The radial plasma losses were suppressed by sheared plasma rotation in the periphery driven by biasing of end wall segments and the radial limiter in the central solenoid.