International Journal of Advanced Engineering Research and Science (IJAERS) [Vol-2, Issue-12, Dec- 2015] ISSN: 2349-6495 www.ijaers.com Page | 63 Output window for high power Gyrotron MK Alaria , AK Sinha Microwave Tubes Area, CSIR-Central Electronics Engineering Research Institute, Pilani, India Abstract—In this paper, the design and development of output window for high frequency and high power Gyrotron have been carried out. The design and development of edge cooled single disc RF window for 170 GHz Gyrotron has been carried out. A diameter and thickness of the ceramic window are 90 mm and 3.2 mm, respectively, whose edge is directly cooled by water. The return loss (S 11 ) and insertion loss (S 21 ) of the window have been obtained as -47.5 dB and -0.02 dB respectively. In this paper thermal analysis of RF window has also been carried out using ANSYS software. The disc center and disc edge temperature has been found as 385 K and 288 K, respectively. The cold characterizations have also been carried out using Vector Network Analyzer (VNA). It is also found that simulated results are close to the experimental results. Keywords— Gyrotron, Alumina ceramic, Gaussian mode, RF window, S-parameters. I. INTRODUCTION Gyrotron oscillators are high power microwave sources mainly used for electron cyclotron resonance heating (ECRH) and plasma stabilization through the localized current drive in the magnetically confined plasmas for the controlled thermonuclear fusion experiments [1]. Gyrotrons have wide applications in the field of plasma diagnostics, material processing, radar systems, communications, medical research, etc. Interest in Gyrotron has grown tremendously due to its potential application in energy generation from fusion energy under global International Thermonuclear Experimental Reactor (ITER) program. The Gyrotron output system consists of an output taper which connects the cavity with the quasi- optical mode converter and the RF window. Fig.1 shows the schematic view of Gyrotron output system [2]. Gyrotron window is required for transmitting significant amount of microwave energy without exhibiting thermal runway. The design requirement of the window is that it should withstand high power handling, mechanical and thermal stresses, vacuum leak tight joining, etc. Therefore care must be taken in selecting a proper window material with low loss tangent, high thermal conductivity, suitable mechanical strength and perfect design to minimize power reflection and absorption for better transmission. The desired features of an ideal window are minimum return loss, minimum insertion loss, high power handling capability and wide bandwidth. The material selection is very important for a Gyrotron window operating at high power and high frequencies [3]. For high power Gyrotrons the advanced materials such as alumina, sapphire, chemical vapor deposited (CVD) diamond, born nitride (BN), etc. have to be used. Gyrotrons operating at 24-70 GHz with moderate power capabilities, generally use double discs RF window which allow surface cooling to keep the disc temperature below a safe limit. But it is always preferable to use single disc edge cooled window because of its simplicity of fabrication and reliability. Fig. 1: Schematic view of high power Gyrotron II. DESIGN OF RF WINDOW The electrical design of edge cooled single disc alumina window for 170 GHz, 1MW Gyrotron has been carried out using CST microwave studio. A diameter and thickness of the ceramic window are 90 mm and 3.2 mm, respectively, whose edge is directly cooled by water. The