The papers in this session were concerned with either L-Band or X-Band klystrons, all intended for relatively high average power operation in different kinds of applications, with an emphasis on particle accelerators. A trend into multi-beam klystron (MBK) operation became obvious.

The session was opened with a paper by Al Mizuhara, CPI, describing the development of a 100 kW CW L-Band klystron intended for FEL application at Jefferson Lab, VA. Since the 1497 MHz cryogenic cavities of the FEL require very accurate and fast feedback, the klystron has relatively high bandwidth (14 MHz at – 1 dB points) and exceptionally high gain (60 dB). Three klystrons have been built and delivered.

Part of the effort to develop a suitable 75 MW short-pulse, PPM focused 11.4 GHz klystron for SLAC’s Next Linear Collider (NLC) was described in a joint CPI/SLAC paper, presented by Edward Eisen, CPI. The main issue in this development section was the improvement of the mechanical design of the klystron body via a Design for Assembly/Design for Manufacturing (DFA/DFM) effort. This resulted in improved thermal stability and reduced part count.

Adam Balkcum, CPI, presented the current status of the development of a 1.3 GHz long-pulse, multi-beam klystron for the TESLA linear collider project of DESY, Germany. The device, which is intended to produce 10 MW peak power pulses of 1.5 ms duration at a duty cycle of 1.5 %, employing a beam voltage of only 114 kV, has finished its simulation phase. Most effort was spent on the issue of focusing its six off-axis beams. The prototype is expected to be in test by end of the year.

The next paper, a joint effort of KEK and Toshiba, Japan, and presented by Yong Ho Chin, KEK, led back to X-Band and 11.4 GHz linear colliders. The PPM-2 version of the KEK/Toshiba klystron for the Japan Linear Collider (JLC) has reached its goal of 75 MW at 1.5µs pulse length with the remarkable efficiency of 56 %. The next goal is the increase of the repetition rate from 25 to 150 pps.

The closing paper of the session was the account of Ding Yaogen, Chinese Academy of Science (IECAS), on another L-Band MBK. I this case the emphasis was on broadband application. The described 18-beam device, operating at a voltage of 18 kV, has achieved a bandwidth of 9.2 % around a center frequency of 1.3 GHz, with peak output power levels around 200 to 250 kW and efficiencies between 35 and 47 %. Problems have been encountered with spurious noise through returning electrons, and with the evaporation of cathode material.