Temperature Control of Irradiated Biological Samples with Pulse Repetition Frequency Modulation of a Gyrotron

The biological effects of terahertz waves have been attracting attention, and high-frequency gyrotrons are being used as a wave source in recent years. In discussing the effects of terahertz waves, it is particularly important to separate them from thermal effects. Therefore, temperature control of the irradiated sample is essential. In this study, a Proportional-Integral-Differential (PID) controller that can adjust the temperature of the irradiated liquid sample by modulating the pulse repetition frequency of the gyrotron has been developed. By optimizing the PID gains, it was found that the temperature could be maintained at the target value of approximately 35 deg. C with an error of less than 0.1 deg. C.