A sixth-harmonic magnetron cavity Gyrotron has been built and will be in the testing phase in the near future.  The cavity is excited by a 70 KV, 3.5 A, axis-encircling electron beam produced by a state-of-the-art Northrop Grumman cusp gun.  The 94 GHz, slotted sixth-harmonic Gyrotron is predicted to generate 40 kW with a device efficiency of 16%.  We are hoping to achieve the following objectives.

· Reduce Magnetic field needed by 94 GHz gyrotrons in order to make HPM systems lighter and more practical.
· Develop 25-100 kW W-band high harmonic gyrotron.
· Basis for high-harmonic gyro-amplifiers.

Our approach for achieving the before mentioned objectives is as follows.

· Operation at Sth-harmonic reduces magnetic field by a factor of S.
· Cusp gun produces the needed axis-encircling electron beam.
· Slotted circuit enhances interaction.

So far, we have successfully designed and fabricated a 94 GHz 6th-harmonic gyrotron with an expected output power of 40 kW with a device efficiency of 16%.  We are also awaiting the arrival of a Northrop Grumman Cusp electron gun, and a 94 GHz 8th-harmonic gyrotron that employs a permanent periodic magnet confinement system is currently in the design stage.
 
 

 The axis-encircling beam, provided by the cusp gun, travels down the drift tube.  It then passes into the interaction region where it interacts with the slotted cavity.  Energy is transferred via harmonic gyrotron resonance (cyclotron maser instability) to the electric field in the cavity, thereby amplifying the field.  The bunched electrons then propagate into the output taper region where the magnetic field drops off in intensity; this allows the electrons to diverge into the walls of the collector and the amplified RF field continues out through the output window.