A. S. Krivenko

First experimental results from 2 MeV proton tandem accelerator for neutron production.

A 2 MeV proton tandem accelerator with vacuum insulation was developed and first experiments are carried out in the Budker Institute of Nuclear Physics (Novosibirsk). The accelerator is designed for neutron production via reaction (7)Li(p,n)(7)Be for the boron neutron-capture therapy of the brain tumors, and for explosive detection based on 9.1724 MeV resonance gamma, which are produced via reaction (13)C(p,gamma)(14)N, absorption in nitrogen.

Hall current layer formation in arc discharge across magnetic field and transfer of fast ions out of discharge

In the work presented here the geometry of the Hall current layer in a plasma of the vacuum arc discharge in the transverse magnetic field are analyzed. The extraction of an intense pure flux of fast ions generated in the cathode spots with the help of the Hall layer is discussed. Experiments on the arc source of carbon fast ions are described. The anode geometry adequate to the mechanism of the arc current passage through the transverse magnetic field is found out experimentally. Up to 70% of fast ions are extracted out of the arc discharge in the arched magnetic field. In experiments, the Hall current layer formation in the vacuum arc discharge across magnetic field is confidently confirmed.

Production and Study of a High-Temperature Plasma in the Central Solenoid of the AMBAL-M Device

Results are presented from experiments on the production and study of a hot dense plasma in the central solenoid of the AMBAL-M fully axisymmetric ambipolar magnetic confinement system. The hot plasma in the solenoid and end cell is produced by filling the system with a thermally insulated current-carrying plasma stream with developed low-frequency turbulence. The plasma stream is generated by a gas-discharge plasma source placed upstream from the magnetic mirror of the solenoid. As a result, an MHD-stabilized plasma with a length of 6 m, a diameter of 40 cm, a density of 2×1013 cm−3, an ion energy of 250 eV, and an electron temperature of 60 eV is produced in the central solenoid. It is found that, in the quiescent decay phase, transverse plasma losses from the solenoid due to low-frequency oscillations and nonambipolar transport are rather small and comparable with the classical diffusion losses.

Neutral Beam Dump Utilizing Cathodic ARC Titanium Evaporation

Abstract Unlike tokamaks, where the neutral beam shine through is rarely an issue, open magnetic systems with neutral beam injection oftentimes suffer from incomplete beam capture, which necessitates the handling of the shine through power load and beam particle recycling. The cathodic arc gettering, which provides high evaporation rate coupled with a fast time response, is a powerful and versatile technique for depositing clean getter films in vacuum. A compact neutral beam dump utilizing the titanium arc gettering was developed for a field-reversed configuration plasma sustained by 1 MW, 20–40 keV neutral hydrogen beams. The beam dump is capable of handling large, pulsed gas loads, has a high sorption capacity, and is robust and reliable. The beam recycling coefficient, measured under the beam particle flux density of 5 × 1017 H/(cm2s) sustained for 3–10 ms, is ~ 0.7. The use of the beam dump allows to reduce the recycling of the shine through neutral beam by factor of 3–5, as well as to improve the vacuum conditions in the machine.

Neutral beam dump with cathodic arc titanium gettering

An incomplete neutral beam capture can degrade the plasma performance in neutral beam driven plasma machines. The beam dumps mitigating the shine-through beam recycling must entrap and retain large particle loads while maintaining the beam-exposed surfaces clean of the residual impurities. The cathodic arc gettering, which provides high evaporation rate coupled with a fast time response, is a powerful and versatile technique for depositing clean getter films in vacuum. A compact neutral beam dump utilizing the titanium arc gettering was developed for a field-reversed configuration plasma sustained by 1 MW, 20-40 keV neutral hydrogen beams. The titanium evaporator features a new improved design. The beam dump is capable of handling large pulsed gas loads, has a high sorption capacity, and is robust and reliable. With the beam particle flux density of 5 × 10(17) H∕(cm(2) s) sustained for 3-10 ms, the beam recycling coefficient, defined as twice the ratio of the hydrogen molecular flux leaving the beam dump to the incident flux of high-energy neutral atoms, is ∼0.7. The use of the beam dump allows us to significantly reduce the recycling of the shine-through neutral beam as well as to improve the vacuum conditions in the machine.

ICR heating in an axisymmetric solenoid

The density and diameter of plasma obtained In the central solenoid of the fully axisymmetric ambipolar mirror trap AMBAL-M are sufficient enough for ioncyclotron 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 semiloop 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.

Gas Puffing into the AMBAL-M Solenoid Plasma

The central solenoid of AMBAL-M was filled with a turbulent plasma stream generated by a source located outside the entrance magnetic throat, the plasma ~0.4 m in diameter, with density ~1.5·1013 cm-3, electron temperature ~50 eV and ion energy ~200 eV was obtained. Additional hydrogen puffing allowed plasma density increase. The plasma with a cold component from ionized gas and charge exchange ions was heated by electrostatic oscillations produced by the working source. At optimized gas puffing the plasma density was increased to 5·1013 cm-3 without substantial reduction of the ion temperature. No big differences in plasma properties were found between gas puffing through a gas-box and a ceramic tube. The plasma density increment was shown to depend only on the total amount of the injected gas. The experimental optimization was made for different values of solenoid magnetic field taking the diamagnetism into account. Neutral hydrogen distribution in the solenoid vacuum chamber and recycling rate were estimated from data of fast inverse magnetron gauges constructed in BINP.

Behavior of the initial plasma in AMBAL-M

Recent experimental results on the initial plasma behavior in the AMBAL-M solenoid are reported. Attempts of forced destabilization and stabilization of the solenoid plasma by varying magnetic field structure in the solenoid to create a local mirror trap and divertor are described. Observations of unstable MHD plasma behavior after cut-off of the essentially stabilizing plasma gun are presented.

Stripping Target of 2.5 MeV 10 mA Tandem Accelerator

An electrostatic tandem‐accelerator with 2.5 MeV 10 mA proton beam is under development at BINP. One of the important accelerator parts is a target that converts the half energy accelerated negative hydrogen ions into the proton beam. In the tandem accelerator an argon stripping target with 1 cm tube diameter and 40 cm tube length will be used. To reduce argon flux from the target to accelerator gaps a gas recirculation by turbomolecular pump installed in high voltage electrode is provided. Processes of plasma production and ultraviolet emission due to target ionization by fast ions and stripped electrons are considered in the report.

Experiments on the AMBAL-M Central Solenoid

Experimental studies of a high-β plasma in a long solenoid of the axisymmetric mirror trap AMBAL-M are being continued. 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 β enhancement were performed. Another way of increasing β consists in forming 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 β-values. A preliminary result on the local-mirror-trap experiment is presented. Further steps on β increase in the solenoid are proposed and discussed.