Cold Test on Coupling of Photonic Crystal Cavity for High-order-mode Gyrotron

Summary form only given. Photonic crystal (PC) cavity is employed in high-order-mode gyrotron using the concept of photonic band gap (PBG), to overcome mode competition and the limited beam propagation in harmonic operation devices. It has been an important issue to couple the cavity mode out to the external structure effectively. In this study, the coupling of the photnic crystal cavity with high order mode, TM₁₃₀ mode, is studied both numerically and experimentally. The diameter and period of alumina rod, which has dielectric constant of 9.85 and loss tangent of 0.0001, are 1.15mm and 3.75mm, respectively. Twenty seven rods (3x9) are removed for rectangular PC cavity to support TM₁₃₀ mode at about 32GHz, which has smooth variation of field strength through lateral direction. By removing one line of rods and connecting to WR-28, the coupled wave is measured. Sensitive coupling depending on the coupling position is obtained both numerically and experimentally. Using MAGIC2D code, TM₁₃₀ photonic crystal cavity gyrotron is simulated. Effective coupling of high order mode photonic crystal cavity (TM₁₃₀ mode) is achieved. The measured coupling is in a good agreement with simulated one. The details of design and experiment of high order mode gyrotron using photonic crystal cavity will be presented along with coupling of high order mode photonic crystal cavity.