IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 29, NO. 1, FEBRUARY 2001 85 The Development of a Diamond Switch for RF Pulse Compression Systems Xiaoxi Xu, Jochen Schein, Niansheng Qi, Rahul R. Prasad, Mahadevan Krishnan, Tamura Fumihiko, and Sami G. Tantawi Abstract—The use of a diamond RF switch for super-high- power microwave/millimeter wave generation has been evalu- ated. An X-band chemical vapor deposition (CVD) diamond window package was theoretically analyzed, designed, and built. Thirty-eight percent of an injected microwave signal with a frequency of 11.424 GHz was reflected from a 100- m thick, 22-mm-diameter CVD diamond window when activated by a 160-mJ, 266-nm Nd:YAG laser. The details of the CVD diamond window design and experimental results are presented. The results have high application potential for building super-high-power microwave systems. Index Terms—Diamond switch, microwave amplifier, RF com- pression, RF switch. I. INTRODUCTION M ANY applications such as advanced accelerators, ma- terial science, and high-range-resolution (clutter rejec- tion) radar systems seek extremely high-power microwave/mil- limeter wave sources. However, no conventional high-power vacuum tube can satisfy these requirements because of electron gun arcing, output cavity breakdown, output window failure, RF pulse shortening, and some high-voltage pulsed power lim- itations. RF pulse compression is a technique that could pro- vide the high powers required. During the past few years, high- power RF pulse compression systems have developed consider- ably [1]–[4]. These systems provide methods for enhancing the peak power capability of high-power RF sources. For example, an active microwave compressor had been studied in the 1970s [3], and power gains of up to 600 were obtained from a resonant energy storage system with a gas discharge switch [4]. In order to get a high compression rate and desired pulse shape at an extremely high power level from an energy storage RF pulse compression system, one of the key elements is the RF switch. Energy storage RF pulse compression systems with gas discharge switches may not be suitable for some applications such as linear accelerators and some radar systems because of reliability and the slow turn-on and -off times of gas discharge switches. The Stanford Linear Accelerator Center (SLAC) has experimented with and more recently implemented several pulse compression systems on the two-mile-long LINAC [5]. A silicon switch, controlled by a Nd : YAG laser (532 nm) was Manuscript received June 29, 2000; revised September 29, 2000. This project was supported by Department of Energy Contract DE-FG03-99ER82736. X. Xu, J. Schein, N. Qi, R. R. Prasad, and M. Krishnan are with Alameda Applied Science Corporation, San Leandro, CA 94577 USA. T. Fumihiko and S. G. Tantawi are with Stanford Linear Accelerator Center, Stanford University, Stanford, CA 94309 USA. Publisher Item Identifier S 0093-3813(01)01612-5. Fig. 1. Principle of three-port RF switch. Reflection coefficient at the end of the Port 3 is . used for such an experiment [6]. 40-kW output power with a compression ratio of 32 and a gain (defined as the ratio of the output power to input power) of 11 was obtained in the experiment. This experiment successfully demonstrated the possibility of the application of fast-controlled, phase-shifting elements in the development of advanced, RF pulse compres- sion systems. However, the voltage hold-off of the high-power microwave switch (Si wafer) used in the experiment at SLAC is around 10 MV/m. This largely limits the output power level of a high-power RF pulse compression system. For a multimegawatt or multigigawatt RF pulse compression system [7], the most promising candidate for a high-power microwave switch is the diamond switch [8], because: • the dielectric strength of a diamond is about 1 GV/m on a microsecond timescale; • the thermal conductivity – W/K m is high; • the loss-tangent tan is low (data for natural type IIa diamond). Diamond has unique properties making it an ideal material for use as a high-power, high-voltage switch. AASC has worked on the development of high-power diamond switches that are op- tically triggered or triggered by e-beam radiation. It has been established that with either way of triggering for natural and CVD diamond conductivities of 40 mho/m can be achieved [9]. The high electrical breakdown strength ( 1 GV/m) allows for high-voltage, monolithic switches in compact packages. Dia- mond is a wide-bandgap (5.5 eV) material. This wide bandgap reduces the leakage current and gives it high dielectric break- down strength. The triggered diamond volume switches from its normal insulating state to a fully conducting state when charges are generated within the diamond. The voltage is held off by the entire diamond thickness. In addition to these advantages, 0093–3813/01$10.00 © 2001 IEEE