NEW KLYSTRON TEST FIELDS AND IMPROVED VERSION OF 1.2 MW WATER LOAD

Two klystron test fields were built side by side in a KEKB power source building D2 for R&D on high power cw klystrons as well as various rf power components. Each field can be operated separately from KEKB rf transmitters with one-on-one power supply, sharing a vapor condensing system. X-ray shields were reinforced. An improved version of 1.2 MW slanted-tube water load has been developed as a host one for the test field. In an acceptance test on a klystron it must endure rf loading up to 1.2 MW stably for a long time in a frequency range between 508.230 MHz and 509.237 MHz. Tap water is used as an ideal rf power absorber and its flow over 640 l/min passes through a long PFA tubing threaded through a tapered rectangular waveguide. Improvements were made on waterproof quality, water flow conductance, corrosion resistance and rf-leakage by modifying structures and materials of end collars and flange tubings. This type of water load has been continuously operated above 1 MW for 3 h with VSWR about 1.06 without any failure. VSWR over the whole power range could be limited below 1.13.