New possibilities of collectors with azimuthal magnetic field for multistage energy recovery in gyrotrons

The results of modeling a collector with 4-stage recovery of residual electron energy for the SPbPU gyrotron with a frequency of 74.2 GHz and an output power of 100 kW are presented. For spatial separation of electrons with different energies, an azimuthal magnetic field created by a toroidal solenoid is used. An increase of the recovery efficiency and a decrease of the current of electrons reflected from the collector is achieved by reducing the spread of the radial position of the leading centers of electron trajectories at optimal parameters of the toroidal solenoid, as well as by using a sectioned electron beam. The trajectory analysis of the spent electron beam in the collector region showed the possibility of achieving the total efficiency of the gyrotron, close to 80%.

Numerical investigation of a high-pressure gas medium preionization by runaway electrons

A comparative simulation of the generation and acceleration of runaway electrons in the discharge gap during the initiation of the discharge by nanosecond and subnanosecond pulses is carried out. We used a numerical model based on the PIC-MCC method. Calculations were carried out for N2 6 atm pressure. Numerical simulation of a formation process of the electron avalanche initiated by an electron field-emitted from the top of the cathode microspike was carried out taking into account the motion of each electron in the avalanche. Characteristic runaway electron trajectories, runaway electron energy gained during the motion through the discharge gap, times required for runaway electrons to reach the anode were calculated. We compared our results with calculations using well-known differential equation of electron acceleration using braking force in Bethe approximation. We solved this equation also for braking force based on real (experimental) ionization cross section. The reasons for the discrepancy in the calculation results are discussed.

Траекторный анализ в коллекторе с многоступенчатой рекуперацией энергии для прототипа гиротрона DEMO. Часть II. Тороидальное магнитное поле

The results of modeling of a collector with four-stage recovery of the residual beam energy for the prototype gyrotron designed for the DEMO project are presented. For spatial separation of electrons with different energies, the azimuthal magnetic formed by a toroidal solenoid is used. An increase of the recovery efficiency and a decrease of the flow of electrons reflected from the collector are achieved by reducing the spread of radial position of the leading centers of electron trajectories at the optimal parameters of the toroidal solenoid, as well as by using a sectioned electron beam. Trajectory analysis of the spent beam with electron velocity and coordinate distributions close to those obtained in experiments with high-power gyrotrons showed the possibility of achieving an overall efficiency of the gyrotron higher than 80 %, which is close to the maximum efficiency at ideal separation of electron beam fractions with different energies.

MINIATURE ORBITRON VACUUM GAUGE WITH BINARY ANODE

Miniature (volume~ 6 cm3) ionization vacuum gauge of orbitron type is developed. The anode of orbitron is made as two wolfram wires with 70 μm diameter, located parallel to gauge axis and being at the distance of 0,5 mm from the axis, much smaller than ion collector radii (8 mm). Diameter and length of the collector are 16 mm and 32 mm, accordingly, of the cathode – 70 μm and 9 mm. Potentials of anode and collector are zero, anode potential is 300 V, cathode potential is (5 – 15) V, cathode burning voltage is 1,6 V at the current of 0, 76 A, electron emission current – 5 μA. Binary anode is applied for thermal degasation (gas away) of electrodes. The numerical simulation has shown that electron trajectories have spiral-shuttle form (as at one wire anode). Spiral radius is (1 – 6) mm, step – (4 – 8) mm, rotation and shuttle periods – 6 ns and 30 ns, the number of turns and traveling time – 1500 and 7 μs, path length and energy – 1000 cm and (20 – 200) eV. It was experimentally confirmed that manometer sensitivity is about 1000 Torr– 1, that is 1,5 orders of magnitude more than for PMI-2 ion manometer. The orbitron with binary anode is better than PMI-2 manometer because it has considerably less value of electron current (two orders of magnitude), cathode burning power (5 times) and work volume (3 times).