New Type of sub-THz Oscillator and Amplifier Systems Based on Helical-Type Gyro-TWTs

This work presents the development and systematic investigation of a new sub-THz source for the generation of trains of coherent high-power ultra-short pulses at 263 GHz via passive mode-locking of two coupled helical gyrotron traveling wave tubes (helical gyro-TWT). The frequency of 263 GHz is an established figure for continuous wave (CW) DNP-NMR application and, therefore, the investigated source will allow the development of novel spectroscopy methods such as time-domain DNP-NMR for which powerful sub-THz pulses with highest coherency are required.
For the first time, it is shown that the operation of the passive mode-locked helical gyro-TWTs in the hard excitation regime is of particular importance to reach the optimal coherency of the generated pulses. To enable the operation in the hard excitation regime, a new extended passive mode-locked oscillator is proposed. The extended passive mode-locked oscillator will furthermore enable the generation of specific pulse sequences in addition to the generation of pulses with constant repetition frequency. This could be of particular interest for some time-domain DNP-NMR methods where well-defined pulse sequences are required.