Multiple beam klystron operation

Summary form only given. Results for the operation of a 1.3 GHz, 10 MW multiple beam klystron which is being developed for the TESLA linear accelerator facility are reported. The long operational lifetime required for this application has resulted in the use of off-axis cathodes in the design. The placement of the individual beam axes on a large bolt circle diameter has allowed for larger cathode areas and hence lower cathode current density loadings. The predicted maximum loading of 2.0 A/cm/sup 2/ for the design should lead to cathode lifetimes in excess of 100,000 hours. In such a device, minimization of the off-axis transverse magnetic fields of the focusing solenoid becomes critical for good beam transmission. Extensive three dimensional magnetostatic simulations were used to design the solenoid which has been manufactured and delivered by Stangenes Industries. Measurements of both the axial and transverse magnetic fields on the beam axes agree well with that simulated using the code Maxwell 3D and are also highly symmetric. Further beam transport simulations using the three dimensional code Michelle and these predicted magnetic fields show a maximum displacement of .050 inches of the beam axis relative to the 1.0 inch diameter tunnel geometric axis along the length of the klystron circuit. This indicates that the achieved transverse field level of the solenoid should result in good beam transport with low beam current interception on the circuit. Currently, the klystron has been completely cold tested, assembled and is being baked out to achieve a good internal vacuum level. Electrical testing of the device is scheduled to commence at the end of January. It is predicted that the device will produce 10 MW of peak RF output power and 150 kW of average power using six 114 kV, 22 A electron beams with an efficiency of 65% a -1 dB bandwidth of 4 MHz and 47 dB of large-signal gain.