94 GHz sixth-harmonic slotted gyrotron

Summary form only given, as follows. High power harmonic gyrotrons utilizing Cusp electron guns are being developed in a new facility at UC Davis. The initial experiment tests a 50 kW, sixth-harmonic slotted pi-mode gyrotron with a predicted efficiency of 20%. The gyrotron is driven by a 70 kV, 3.5 A, vt/vz=1.5, axis-encircling electron beam from a Cusp gun delivered by Northrop Grumman. Since the final velocity ratio of electrons from the Cusp gun depends on the magnetic field only through the product of the magnetic field amplitudes at the cathode and the downstream circuit, the Cusp gun can drive a higher (lower) frequency gyrotron at the same harmonic by increasing (decreasing) the field in the circuit and proportionately decreasing (increasing) the field at the cathode. Using the profile of the adiabatic field reversal of the UC Davis superconducting test-magnet, EGUN simulations predict that an axis-encircling electron beam is generated with an axial velocity spread of 10% axial velocity spread for the desired velocity ratio of vt/vz=1.5. The design is also presented for an 8th-harmonic W-band gyrotron whose magnetic field can be supplied by a lightweight permanent magnet.