X-band traveling wave maser (Correspondence)

A traveling wave maser (TWM) has been constructed for use at 8448 MHz. It provides a net gain of 41.5 dB when installed in a closed-cycle helium refrigerator operating at 4.4°K. The maser provides more than 30 dB net gain over a tunable range of 140 MHz. An equivalent input noise temperature of approximately 18°K has been measured. The net gain of the maser (41.5 dB) has a short-term stability such that the radiometer stability (0.08 dB peak to peak) is not degraded when the maser is added to the system. The maser can be tuned over a 140 MHz range with net gain exceeding 30 dB. Cool-down time of the closed-cycle refrigerator with this maser is 4.6 hours (no liquid nitrogen precooking) and 2.4 hours with precooking.