Magnetic Priming Techniques for Relativistic Magnetrons

Summary form only given. Research is underway to develop a viable technique to implement magnetic priming in the UM/Titan relativistic magnetron (-300 kV, 5-10 kA, 0.3-0.5 mus) for rapid startup and mode control. Magnetic priming involves imposing N/2 azimuthal variations in the axial magnetic field of an N-vane magnetron operating in the pi-mode. This type of magnetic priming has been demonstrated in -4 kV kilowatt magnetrons. Simulations of a highly idealized magnetic priming scheme using the MAGIC PIC code showed rapid growth of the pi-mode and suppression of mode competition in a relativistic magnetron. In the case of the kilowatt oven magnetrons, axial magnetic variations were imposed using external perturbation magnets. Relativistic magnetrons are bulkier and utilize large, pulsed electromagnets, making external priming magnets less practical. Because of this, new magnetic priming techniques are required. A new magnetic priming concept is proposed to alleviate this problem utilizing internal ferromagnetic structures to shape the magnetic field within the magnetron. Physically realizable magnetic field geometry was modeled using the field precision Magnum magnetostatics code. The resulting magnetic field data were then imported into MAGIC PIC and run for the case of a 6-vane relativistic magnetron. Preliminary fully three dimensional (3-D) simulations using MAGIC PIC have shown potential for faster relativistic magnetron startup. Magnetic field measurements will be compared to simulations and experiments on the relativistic magnetron