Abstract
This paper presents the simulation results of a multistage depressed collector for a MW-class gyrotron. The energy distribution of spent electrons is obtained by a beam–wave interaction code. By increasing the number of depressed electrodes, the maximum collection efficiency can be increased to 81% with a low percentage of backstreaming 0.04% with regard to a four-stage depressed collector. By considering the secondary electron emission, the effects of different kinds of secondary electrons are simulated in the CST software, which is developed by Computer Simulation Technology Company in Germany. In order to reduce bad effects of secondary electrons, the structure of the fourth depressed electrode has been adjusted to form a slope. The axial length and slant angle of the slope have been optimized. The results indicate that the collection efficiency can exceed 70% and the percentage of backstreaming is less than 1%. Besides, in view of the limited power capacity of the collector wall, a magnetic field sweeping system has been introduced. The maximum power density is reduced to 392 W/cm2, and the deposited length of the electron beam trajectory is 470 mm.
Highlights
Gyrotrons as a high power microwave source can generate MW-class continuous wave (CW) output power at millimeter and sub-millimeter frequency bands
Taking the influences of true, rediffused, and backscattered secondary electrons into consideration, the collection efficiency of 71.3% and percentage of backstreaming of 0.71% are obtained with a four-stage depressed collector
Compared with the axial length, the slant angle of the slope has a stronger impact on the electron trajectory
Summary
Gyrotrons as a high power microwave source can generate MW-class continuous wave (CW) output power at millimeter and sub-millimeter frequency bands. Spent electrons still carry MW-class energy with regard to the MW-class power output. For a gyrotron with 1 MW power output, the collection efficiency can reach 58% by using a simple single-stage depressed collector.. By means of the classified recovering energy of spent electrons, namely, employing multistage depressed collectors, the collection efficiency can be enhanced further. As the number of depressed electrodes increases, the increase in collection efficiency becomes weaker and weaker and the design of power supply is more complex. Taking design complexity and collection efficiency into account, a four-stage depressed collector is adopted in this paper. With the consideration of confined power density on the collector wall, a magnetic field sweeping system is introduced.
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