Kew Yong Sung

A diode design study of the virtual cathode oscillator with a ring-type reflector

A numerical simulation study of the high-power microwave generation from the vircator (virtual cathode oscillator) is carried out for coaxial diode structure by using a three-dimensional particle-in-cell (PIC) code called MAGIC. The coaxial vircator has a centered annular cathode body, cathode ring and cylindrical meshed-anode in order to enlarge the active interaction region in the virtual cathode space. In order to enhance a conversion efficiency of the output microwave power, ring-type reflector was installed to coaxial-type diode structure. The simulation results show that the output microwave frequency has a narrow bandwidth and its output microwave power sensitively depends upon the position and width of ring-type reflector. The maximum output microwave power is obtained by adopting a ring-type reflector 10 mm in width and 40 mm in the distance from the intense relativistic electron beam to the ring-type reflector. The output microwave mode without a ring-type reflector is a mixture of TM and TE mode. However, the TM/sub 01/ mode with its resonance frequency of 2.2 GHz is dominant for the ring-type reflector.

A diode design study of the virtual cathode oscillator with ring-type reflector

Summary form only given, as follows. A numerical simulation study of the high power microwave generation from the virtual cathode oscillator (vircator) is carried out for various diode configurations by a 3 dimensional particle-in-cell (PIC) code called MAGIC. The coaxial vircator has a cylindrical cathode, cylindrical anode-mesh, and reflector, in order to enlarge the active interaction region in the virtual cathode space. The simulation results show that the output microwave frequency has a narrow bandwidth and its output microwave power depends sensitively on the position and width of ring-type reflector. The maximum microwave output power is obtained with a reflector 10mm in width and 40mm in distance from the intense relativistic electron beam. Output microwave mode without the ring-type reflector was mixture of the TM mode, however, it is found to be dominantly TM/sub 01/ mode with a resonance frequency of 22 GHz with the ring-type reflector.

Numerical simulation of the reflex triode virtual cathode with an intense relativistic electron beam

A virtual cathode reflex triode is investigated by numerical simulation with a 3 dimensional particle-in-cell (PIC) code called MAGIC. The reflex triode virtual cathode oscillator has a disk cathode and a disk anode-mesh. Here anode-cathode (A-K) gap distance has been varied from 10 mm to 30 mm. Simulation results show that the output microwave frequency has a narrow bandwidth and its output microwave power depends sensitively AK gap distance. Output microwave mode is mixture of TE mode at A-K gap distance 10 mm, however, TE is to be dominant mode at A-K gap distance 30 mm.

Radiation pattern of high power microwave from axially extracted virtual cathode oscillator

Summary form only given, as follows. We have investigated a radiation pattern of high power microwave from an axially extracted virtual cathode oscillator (vircator) by adoption a horn-type transmitting antenna at the downstream end of waveguide in this experiment. This high power microwave generator is powered by the Chundoong intense relativistic electron beam pulser (Max 600 W, 88 kA and 60 ns duration). The 3 kinds of receiving horn antenna, WR 187, WR 137, and WR 90 have been alternatively used in this experiment to determine the high power microwave frequency. The receiving antenna has been located at 1 meter distance away from the transmitter antenna surface, where the angle of their respective receiving antenna has been varied to be 10/spl deg/ up to 90/spl deg/ in both horizontal and vertical directions along their respective arcs to measure a directivity of axially extracted high power microwave in free space propagating from transmitter antenna. It is found for high power microwave from axially extracted vircator that both horizontal and vertical radiation pattern have good directivity with plateau characteristics within 20/spl deg/ with respect to their 0/spl deg/ reference planes. It, is also noted that the maximum microwave power and its frequency are measured to be 200 MW and 67 GHz, respectively, under diode voltage of 300 kV and diode current of 25 kA.

Perveance and sheath plasma expansion characteristics in high power cylindrical diode

Perveance and sheath plasma expansion characteristics for high power electron beams have been experimentally investigated in a cylindrical diode. An experimental scaling law for perveance in high power cylindrical diodes have been obtained in terms of anode-cathode (A-K) gap distance, d. It is found that the diode perveance in a high power cylindrical diode has a scaling law of /spl sim/d/sup -1.83/ in terms of the A-K gap distance, d, which is in close agreement with that of /spl sim/d/sup -2/ for infinite planar diode. It is also noted in high power cylindrical diode that the sheath plasma expansion speed is about 7 cm//spl mu/s at A-K gap distance of 4 mm, which is about two times faster than that in high power axial diode, in this experiment.