Influence of beam current and cooling water temperature on the frequency characteristics of sub-millimeter wave gyrotron FU-IV

The characteristics of the frequency drift are examined precisely for the SMMW gyrotron FU-IV. The drift of center frequency is reduced to be less than a few MHz during 20 minutes. Then, the frequency, the cooling-water temperature, the beam current and the output power are monitored simultaneously to examine the relationship among these parameters. The results indicate that the frequency drift is caused by thermal expansion and contact-ion of the cavity in a few ∼10 MHz range and is also affected by non thermal frequency pulling effect of beam current when the behaviors within a few MHz range are considered.