For plasma heating and stabilization in open magnetic traps, the high-power neutral beam injector with tunable beam energy was developed at Budker Institute of Nuclear Physics. The initial energy of the beam particles is 15 keV, and it can be subsequently increased to 40 keV. In this case, the neutral beam power increases from 1.7 to 3.5 MW. A distinctive feature of this injector is the fact that, as the accelerating voltage considerably changes, the ion beam current remains constant. The injectors based on the ion sources with tunable energy are used in experiments at the C-2W open trap (USA).

The spatial structure of electromagnetic plasma-induced waves has been defined in the high-energy content regime of the Gas Dynamic Trap operation. The waves with the smallest non-axisymmetric azimuthal mode m = 1 propagating in the direction of ion-diamagnetic drift current have been observed. Polarization of the excited waves changes their direction from that of ion gyration to that of electron gyration as the distance from the symmetry axis is increased. These data confirm the assumption that the instability observed is the Alfven ion-cyclotron one. The longitudinal velocity range of particles responsible for the instability excitation has been obtained from the experiment. This range is consistent with the theory.

The development of fusion energy will require materials resilient to harsh bombardment by energetic neutrons and plasma. The Gas Dynamic Trap (GDT) concept in Novosibirsk is proposed as a neutron and plasma source to test and validate appropriate materials. Recent results showed plasma beta of 0.6, provide a solid basis for extrapolating to a fusion relevant neutron source. Relative to previous magnetic mirror neutron sources, the GDT concept operates with simpler axisymmetric magnets and at higher efficiency. Plasma in the GDT device operating at the present time in the Budker Institute includes two ion components: 250 eV maxwellian warm ions and anisotropic hot ion population produced by 25 keV 5 MW oblique neutral beam injection.

Plasma generated electromagnetic oscillations at the frequency an order ion-cyclotron have been investigated in the high energy content regimes of GDT operation. That waves are found to be an Alfven ion-cyclotron instability. The microinstability threshold scaling law has been defined: with increase of the plasma column radius to Larmor radius ratio the threshold value of the diamagnetism in the midplane decreases. It qualitatively matches the theoretical calculations.

ЭКСПЕРИМЕНТЫ ПО АМБИПОЛЯРНОМУ УДЕРЖАНИЮ ПЛАЗМЫ В УСТАНОВКЕ ГДЛА.В.Аникеев

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.

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 E-h approximate to 9 keV and the maximum density of energetic ions n(h)approximate to 5.10(19)m(-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 n(w)approximate to 2.10(19)m(-3). Local plasma beta 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.

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.

A new vacuum-insulated tandem accelerator capable of producing a 5-mA proton beam with energy up to 2 MeV was used to produce a mono-energetic beam of 9.17-MeV gamma rays from the resonant production reaction, 13C(p,γ)14N, at 1.76 MeV. A graphite target enriched with 13C capable of withstanding the proton beam power was designed and fabricated. The 9.17-MeV gamma rays were subsequently resonantly absorbed in 14N via the inverse reaction, 14N(γ,p)13C. The data acquisition system to measure the resonance absorption in nitrogen includes a BGO detector and a goniometer and collimator assembly that rotate around the axis produced by the intersection of the proton beam and the production target. The accuracy of rotation of the detector around the target is approximately 0.1°. The results of the resonance gamma ray absorption measurements are presented to demonstrate the feasibility of the method to sensitively and selectively detect high concentrations of nitrogen, comparable to those found in most explosives.

The results of experiments on generating of resonance gamma-quanta using vacuum insulation tandem accelerator (VITA) are presented. The accelerator is able to produce proton beam with particles energy up to 2 MeV and 5 mA current. The resonance gammas have generated in the carbon target enriched with C-13 isotope with help of C-13(p,gamma)N-14 nuclear reaction. Registration of resonance gamma-quantas is carried out by goniometer and collimator assembly, that capable to be rotated around the target with 0.1 degrees accuracy. The experimental results on absorption of resonance gamma-quanta with energy 9.17 MeV are presented.

The paper summarizes recent results obtained in the gas dynamic trap experiment. Gas dynamic trap (GDT) is a mirror device where Maxwellian plasma component and fast anisotropic ions are confined in the axially symmetric central cell with outboard MHD anchor cell. The GDT NB heating system is capable of providing six focused 20-25 keV hydrogen or deuterium beams. The total beam power delivered to the central cell plasma reached 4 MW in the 5 ms pulse. Two additional focused 25 keV beams provide up to 1.2 MW in the compact mirror cell attached at the end of the GDT central cell. Comparison of the experimental data on global energy and particle balance with the results of the Monte-Carlo modeling of the plasma equilibrium parameters indicates that the two-component plasma in GDT reaches steadystate within 5ms shot. The characteristic plasma lifetimes are 4 5 times shorter than the pulse duration. In these experiments peripheral gas-puff near the end mirror is used to maintain plasma radial profile during the NB injection. Peak density of anisotropic ions with the mean energy of 10 keV exceeded 4x10 19 m -3 near their turning points, that is close to main plasma density in the reported experiments. Accordingly, in these experiments the maximal beta value was increased from 0.4, which was reported previously, to about 0.6. Electron temperature of plasma was also significantly increased from ~100eV up to about 160 eV in the steady state regime and exceeded 200eV in transient regimes with somewhat smaller density. The stability against MHD interchange modes was established using the set of biased radial limiters and segmented end wall. The new results of experiments with the compact mirror cell attached to the GDT central cell are be also presented in the paper. In particular, micro-instability limits in extremely anisotropic hot ion plasmoid were

The density and diameter of plasma obtained In the central solenoid of the fully axisymmetric ambipolar mirror trap AMBAL-M are sufficient enough for ion-cyclotron heating using fast waves, which provides plasma heating at the axis. At present the experiment on such ICR heating of the solenoid plasma is under preparation. The heating will be carried out two semi-loop antennas installed in the end of the solenoid For protection from the impact of the edge plasma, the antennas are equipped with Faraday shields and graphite limiters with slanted slits.

Experimental studies of a high-beta plasma in a long solenoid of the axisymmetric mirror trap AMBAL-M are being continued [1]. In order to increase the density of the initial warm plasma generated by a plasma source, additional gas puffing was used. Optimization of gas puffing through a gas-box and reduction of magnetic-field in the solenoid aimed at beta enhancement were performed. Another way of increasing beta consists informing a small local mirror-trap in the solenoid where the plasma volume is much smaller than that of the whole solenoid plasma, and it is easier to achieve high beta-values. A preliminary result on the local-mirror-trap experiment is presented Further steps on beta increase in the solenoid are proposed and discussed.

Investigation of the hot initial plasma created in an axisymmetric end system of the ambipolar trap AMBAL-M has been completed. In the end mirror we obtained the MHD stable plasma with the electron temperature of 50 eV, ion temperature 200 eV, and density about 10 13 cm -3 . In an MHD anchor - the semicusp a transverse profile of the plasma pressure favorable for the MHD stability was obtained. Pulsed injection of fast atoms with the current of 100 A demonstrated sufficient accumulation rate of the ion population trapped into the initial plasma. The first experiments with ICR-heating of the initial plasma were carried out. Two atomic injectors of the end mirror were prepared for work. In these injectors four quasistationary proton beams were obtained with the energy of 25 keV and current of up to 50 A per beam. After their charge-exchange the atomic beams were passed through an MHD stabilizing shell and the target plasma. Principal vacuum units of the 2-nd stage of the installation were tested and prepaired for assembly. One-half of the magnet-vacuum system of the AMBAL-M central solenoid was assembled and tested for vacuum.

The experience with an ion source for our atomic injector have been described. Ion beams with a current of 50 A, energy of 30 keV, and pulse duration of 0.1 s are extracted from a rectangular plasma emitter with dimensions 24×12 cm2. The beams have small angular divergence. Geometrical focusing through the extraction system provides the size of the beam to less than 24 cm at a distance 4 m from the ion source. The beam current density distribution has been measured by light emission. The power supply can be operated in multibreakdown mode with time periods of 0.4–2 ms. The control and the operating functions of the power supply are integrated into the computer. The data are transferred to the computer through both fiber optic channels and cable channels.