Numerical study of efficiency for a 670 GHz gyrotron

Abstract

In this paper, the results of the efficiency study of a 670 GHz gyrotron operating at TE31,8-mode are presented. Calculations are performed by using the self-consistent nonstationary code MAGY. Three cavity configurations were examined. The effects of ohmic losses and electron velocity spread were included in the simulation. The results show that the output efficiency can reach 35% and the velocity spread in the electron beam does not degrade the operation significantly. Furthermore, we verified that the smoothing of the sharp corners for a small tapering angle would reduce mode conversion; the parasitic excitation of neighboring radial modes is less than 1% of the amplitude of the operating mode and the effect on efficiency is small. Lastly, the simulation results show that the after-cavity interaction causes only slight variations in the efficiency.

Experimental investigation of powerful 0.67 THz gyrotron with a pulsed solenoid for remote detection of concealed radioactive materials

“…The maximum output efficiency 20% was realized at lower currents, in a 57 kV, 16 A operating regime. Taking into account microwave losses in a 3 mm thick teflon window (17-20%) and about 9-10% of ohmic losses of the power radiated in the TE 31,8 -mode one can conclude that the interaction efficiency in this experiment was at about 30% level that agrees with the simulation data [7,8]. The radiated power was converted with the use of standard quasi-optical methods (see, e.g., [9]) into a Gaussian-like wave beam and focused by a teflon lens on the metallic plate with some sharp metallic needle-like breakdown initiators.…”

Terahertz gyrotrons

“…As shown in Ref. 37, when such a gyrotron operates at a high-order mode (such as TE 31,8 ), ohmic losses of radiated power in the circuit walls are relatively small; therefore the output efficiency can exceed 30% at the power level about 300 kW. Among other issues there are a study of production of free electrons by gamma rays, propagation and attenuation of gamma rays, free electrons and THz radiation in air (specifically, in maritime environment), the role of electron diffusion and other processes in air, THz-wave scattering from a small plasma object.…”

A 670 GHz gyrotron with record power and efficiency

“…Taking into account microwave losses in a 2 mm thick teflon window (17%-20%) and about 9%-10% of ohmic losses of the power radiated in the TE 31,8 -mode, one can conclude that the interaction efficiency in this experiment was at about 30% level that agrees reasonably well with the simulation data. 19 The radiated power was converted with the use of standard quasi-optical methods (see, e.g., Ref. 9) into a Gaussianlike wave beam and focused by a focusing mirror on the metallic plate with some sharp metallic needle-like breakdown initiators.…”

“…7 Design of a 670 THz gyrotron operating in this mode 19 showed that the ohmic Q factor of a copper cavity can be as high as 30 000, while the cavity diffractive Q responsible for the outgoing sub-THz radiation does not exceed 3000. So the ohmic losses should be less than 10% of the radiated power, while in devices such as, for example, extended interaction klystron even in the W-band (95 GHz) ohmic losses are at a 1/3 level of the power radiated by an electron beam.…”

“…The cavity profile was found to yield 35% interaction efficiency even in the presence of electron velocity spread. 19 The cavity profile and the efficiency as the function of the external magnetic field are shown in Figures 1(a) and 1(b), respectively. (The length of a constant radius straight section is equal to 10 wavelengths.…”