Electron Gun for Powerful Short Pulse Gyrotron with Operating Magnetic Field 8 T

High power short pulse gyrotron with operating frequency 395 GHz operating on the second cyclotron harmonic is now under developing at FIR FU. The gyrotron is planned to use in future experiments for plasma diagnostics. For this purpose the output power about 100 kW and pulse duration 100 ns at least are needed. Preliminary estimations of parameters of some versions of the electron guns with accelerating potential U₀= 70-100 kV were performed. Possibilities of non-adiabatic as well as adiabatic guns were considered. It was shown that non-adiabatic system is not reliable for such rather low value of U₀, the adiabatic magnetron injection gun (MIG) is more preferable for the gyrotron design. Analytical estimations of the suitable MIG dimensions and operating regime to form good quality electron beam were fulfilled. Numerical optimization of the gun shape and position was performed. It was shown that in spite of the extremely big ratio of the operating current (I₀= 18 A) to the Langmuir current of the gun, close to 0.4-0.5, the suggested MIG can form the helical electron beam (HEB) which is suitable for gyrotron operation properties.