Experimental results of a high efficiency high power X-band gyroklystron

In order to build a multi-TeV Next Generation Linear Collider with a reasonable length, a high accelerating gradient and high RF frequency are required. A gyroklystron in the frequency range of 30 GHz is considered to be one of the most promising RF sources. Pulsed gyrotron amplifiers have record performance at frequencies significantly above X-Band, e.g., output peak powers exceeding 30 MW were achieved with an efficiency near 30% at the frequency of 19.76 GHz at the University of Maryland. A new first harmonic coaxial three-cavity gyroklystron in X-Band has been built and tested to verify operation of the test bed. This microwave circuit has demonstrated the high power and high efficiency of the system configuration with the ultimate goal of extending the design of coaxial gyroklystrons to 17.1--34.2 GHz. The designed operating frequency is 8.568 GHz with a pulse width of 2 micros and a maximum repetition rate of 2 Hz. The operating beam voltage and beam current for the fundamental circuit are 470 kV and 500 A, respectively. An X-Band mechanically-tunable coaxial magnetron (8.5--9.6 GHz, 2 micros) provides a maximum input signal of 150 kW. The preliminary experimental results showed that an output peak power of 85 MW with an efficiency over 35% can be obtained from this coaxial three-cavity gyroklystron. The details of the design parameters and experimental results of this X-Band gyroklystron will be presented