Development of high power klystron, 2; Development of pulse-mode operation

Hirano, Koichiro  ; Emoto, Takashi; Wang, Y.; Sato, Isamu

A high power klystron has been developed as the RF source of the high power CW electron linac (10MeV, 100mA, 1.249135GHz). CW power of 1.2MW and efficiencies over 65% at a beam voltage 85kV were the design goal. Klystrons have been manufactured untill 1997. The klystron has achieved CW RF output power of 1040kW and beam voltage of 83kV at present. The power required for future applications is about four times the maximum power with CW-mode operation to accelerate electron beam at energy of 30MeV. We have redesigned the klystron, which is able to drive peak power 4.2MW with pulse-mode operation (100sec pulse width, 50 pps) without decreasing efficiency with CW operation. As peak power of 4.2MW at a beam voltage 147kV is required for pulse-mode operation, we have developed the electric gun, the RF window which endures peak power 4.2MW and the way of reducing apparently the output cavity Q optimized for CW-mode operation. The output cavity Q was decreased by two obstacles located on the long window. The klystron has achieved the maximum peak power, witch was 3.55MW with efficiency of 42% at a beam voltage 147kV in present. The unstable phenomenon of the power due to backward electrons hasn't been observed in the design condition. We have succeeded in the development of the klystron so as to be able to drive both CW mode and short pulse mode. The output cavity Q made effective use of two obstacles will be optimized by simulation codes to improve efficiency.