Experimental Results from the NRL 8-Beam, 4-Cavity S-Band Multiple-Beam Klystron

Summary form only given. We present recent experimental progress with the NRL 8-beam, 4-cavity multiple-beam klystron. The electron gun and circuit were designed by an NRL/ATK MRC/beam-wave research team with mechanical design and fabrication support from CPI. The MBK is designed to operate at a frequency of ~3.25 GHz, producing >600 kW of peak RF power with a saturated gain of ~33 dB and an instantaneous 3-dB bandwidth of ~2%. The gun is Brillouin focused and is operated at a cathode-anode potential of -45 kV, producing a total beam current of 32 A (8times4 A); individual emitter loading is ~10 A/cm². The beam current measured during low-voltage gun tests (-1250lesV_ak les-200 volts) was in excellent agreement with particle simulations using the 3-D gun code, MICHELLE, confirming that (i) the electron emission is space-charge limited; and (ii) fabricated dimensions and component alignment are within specified values (zero or minimal interception in the gun region). High-power beam transport tests conducted at the full beam voltage and current and a solenoidal axial magnetic field of 1.8 kG are in excellent agreement with the design values, with a measured beam transmission of ges99% for the duration of the pulse flat-top and a total beam perveance very close to the predicted value of 3.35times10^-6 A/V^3/2. RF amplification testing is currently in progress