Sheet beam for W-band extended interaction klystron (EIK)

Both the generation and the stable transport of high-perveance, relatively low-voltage sheet beams suitable for millimeter wave and submillimeter wave amplifiers are quite challenging. We have designed and fabricated a beam stick to validate our design of a 19.5 kV, 3.5 A sheet beam having a cross section of 0.3 × 4 mm, whose parameters were selected to drive a W-band extended interaction klystron (EIK). The electron gun uses a shielded cathode at an average loading of 8 A/cm², with single-plane focusing to achieve a final beam density of ~275 A/cm². The beam is transported through a 0.4 × 5 mm beam tunnel by a permanent magnet solenoid that produces a field of ~8.5 kG over a distance of 1.8 cm, which is sufficient for a 3-cavity EIK interaction structure having a gain of ~30 dB. A single-stage depressed collector collects the exiting beam.