Speaker
Dr
Vitaly Astrelin
(Budker INP SB RAS)
Description
In the Institute of Nuclear Physics SB RAS on the open magnetic trap GOL-3 the experiments are carried out on an electron beam generation (up to 80 keV, 100 А, diameter up to 8 cm) in the multiaperture diode with plasma emitter [1]. The beam is formed in moderate (0.01-0.1 T) magnetic field and is injected into the trap along increasing magnetic field up to 0.3 T. A beam duration is limited due to electrical breakdown of diode which was observed in the experiment. One of possible causes of this limitation may be electrons reflected from input magnetic mirror and an appearance of the dense plasma on the back side of the anode, which then penetrates into the diode. The present paper considers reflection of electrons from magnetic mirror analytically and numerically, taking into account the volume charge of the beam.
Generation of beam in magnetic field is accompanied by the appearance of angular divergence of its electrons. Pitch angles of electrons in the diode may occur due to imperfect of its optics, due to the presence of the azimuthal magnetic and radial electric fields of the beam, resulted in transverse velocity of electrons. They can lead to reflection of electrons in increasing magnetic field due to rise in pitch angles, reduction of longitudinal velocity of the electrons and subsequent increase of space charge.
An analytical estimate of the vacuum beam current limit, taking into account the initial pitch angles of electrons and beam compression in magnetic field is made [2]. The case of the beam volume charge neutralization with pitch angles increasing in his radius is also considered.
The results of numerical simulation of transport and compression beam with non-uniform distribution in radius of current and pitch angles in the magnetic field under different conditions are considered. The values of currents are obtained, for which a reflection of electrons begins. The results of simulation are compared with the results of experiments in which similar reflection and diode breakdown are observed. They are in a good agreement.
The investigation is supported by RFBR Grant No. 16-08-00785-а
REFERENCES
[1] A. Burdakov, A. Arzhannikov, V. Astrelin, et al. Fusion Science and Technology 55, No.2T, p. 63 (2009).
[2] V.T. Astrelin, I.V. Kandaurov, V.M. Sveshnikov. Advances of Applied Physics 1, No 5, p. 574 (2013)
Primary author
Dr
Vitaly Astrelin
(Budker INP SB RAS)
Co-authors
Mr
Igor Kandaurov
(Budker INP SB RAS)
Mr
Victor Kurkuchekov
(Budker INP SB RAS)
Prof.
Victor Sveshnikov
(ICM MG SB RAS)
Mr
Yury Trunev
(Budker INP SB RAS)
