Design and analysis of metallic photonic band gap cavity for a Gyrotron

Abstract

Design and analysis of a 35 GHz metal photonic band gap (PBG) resonant cavity operating in the TE 041 -like mode has been presented. The dispersion characteristics of a 2D metal PBG structure comprising of triangular array of rods has been obtained using FDTD method. Global band gap regions have been obtained to be used for the PBG cavity design. A mode map has been also generated to examine the occurrence of the possible modes in the PBG cavity. Electromagnetic simulation of the designed PBG cavity has been performed to study the operating modes and quality factors. Role of the number of metal rods layers around the defect in PBG structure has also been illustrated for confining the desired mode and deciding the diffractive quality factor. PBG cavity results have been compared with the analogous cylindrical cavity for the designed mode along with the possible nearby modes to examine the mode competition. It has been found that the mode competition has been successfully reduced in designed PBG cavity and nearly a single mode operation is achieved. It is hoped that present study would be useful for the application of the metal PBG structures in the Gyrotron devices to alleviate the mode competition problem while operating in the higher order modes.Index Terms-FDTD, Gyrotron, PBG structure. I. INTRODUCTIONGyrotrons have emerged as the potential device for the generation of high power millimeter and sub-millimeter waves with good efficiency among various devices of its class. In the recent past, significant improvements in performance of the gyrotrons are achieved for both pulse as well as CW operation [1]. Gyrotrons find variety of technological, scientific and industrial applications, including electron cyclotron resonance heating (ECRH), electron cyclotron current drives (ECCD), material processing, stability control and diagnostics of magnetically confined plasmas for generation of energy by controlled thermonuclear fusion, dynamic nuclear polarization enhanced nuclear magnetic resonance (DNP/NMR) spectroscopy, etc. [1]-[3].High frequency operations of gyrotrons have made it possible to use them for newer applications but still many challenges remain in terms of achieving stable single mode operation of the overmoded cavities. At such higher frequency operation, significant reduction in transverse dimension of the RF interaction cavities lead to increase in heat load on the cavity walls, fabrication difficulties as well as increased problem of the beam interception [4]. High magnetic field requirement for the fundamental

Design and simulation of 94 GHz metal PBG waveguide

“…4. It is demonstrated by the study that the PBG waveguide can be equivalent to a traditional cylindrical waveguide with radius 'R e ' approximately equal to the radius of the inscribed circle of the defect region [9], as illustrated in Fig. 4.…”

“…The design operating point represented in Fig. 6 by a red mark is in the pass band of the global band gap diagram [9], and which has the coordinates of fa/c=0.452 and r/a=0.359. The equivalent radius equation of an MPBG waveguide is given by…”

Beam-wave interaction behavior of a 35 GHz metal PBG cavity gyrotron

“…Detailed design methodology of the present metal PBG cavity has been reported earlier and the design parameters are listed in Table I. 12 Start oscillation current is calculated for the TE 04 -like and TE 24 -like modes as shown in Fig. 1, where plus (þ) and minus (À) signs represent the counter and co-rotating modes, respectively.…”