Physical Basis for the Use of Long Pulse Electron Beam in Multi-Mirror Trap

Recent high plasma parameters were reached in experiments on plasma heating in the multi-mirror open trap GOL-3. In these experiments deuterium plasma with density 10¹⁴–10¹⁶ cm^-3 in the 12-m trap with corrugated magnetic field of 4.8T/3.2T was heated by a relativistic electron beam of eU 0.8 MeV, I 20 kA, j ~ 1–2 kA/cm², pulse duration ~9 s and angular spread 0.2 rad. The electron temperature T_e ~ 1–4 keV and ion one to T_i ~ 1–2 keV were reached. After the beam pulse the electron temperature of the plasma quickly (~20 s) decreased to -100 eV. In turn, this leads to an increase in the rate of cooling of ions through the ion-electron collisions, which, together with particle losses determines the energy confinement time of plasma as 0.5–1 ms.

To increase the plasma parameters a prolonged heating of the plasma by the electron beam is proposed. The paper considers basic physical phenomena in the beam-plasma interaction and required parameters of the long pulse beam. A choice of long pulse beam parameters is based on the obtained experimental results and scalings. Then estimates of the expected plasma parameters under the influence of the new beam have been done.