兆瓦級的高功率微波源，在高梯度線型加速器與微波擺盪器方面都有重要之應用。由於線型加速器所產生的相對論性電子束，品質優異且束流穩定。利用相對論性電子束團通過電磁波結構來產生尾場，藉由尾場的效應來產生高功率的微波是有別於傳統高功率微波源的一種可行的方案。到目前為止，文獻上已經有提到利用微波結構或者微波材料特性的不同，來產生高頻高功率的微波源。本研究中，我們參考CLIC（Compact Linear Collider）雙電子束的計劃（Two Beam Accelerator Scheme）中的微波功率轉換器的設計（PETS），依國家同步輻射研究中心高亮度注射器研究計劃中所提出的小型化Ｘ光自由電子雷射之構架，希望能夠產生峯值在100 MW以上之12 GHz高功率微波，設計符合我們需求的功率轉換器。本設計以一般常見的線型加速器（Disk-Loaded Waveguide Structure）作為參考模型，微波功率轉換器（Microwave Power Extraction）的結構包含圓柱型波導管，以開孔圓盤固定間隔隔開，形成週期性的結構，以及頭尾兩端各有輸出微波的耦合結構。根據模擬的結果，在時域的尾場位能（Wake Potential）以及尾場阻抗（Wake Impedance）計算上都明顯可以觀察到產生的電磁波頻率都落在12 GHz。也可以在頻域上，看出耦合結構對於12 GHz的微波接近於臨界耦合（Critical Coupled）。為了要印證電腦模擬所得之參數的正確性，我們製作了一低功率的微波功率轉換器原型（Prototype），測量相關設計參數。

RF linacs are able to provide stable ultra-relativistic electron beams with excellent beam quality. Such beams can be used to produce high power microwaves by extracting the wave power from a specially designed rf structure in which wake-fields are excited by the electron beam and are stored in the structure. The power level of this type of high power microwave source can be as high as a few hundred megawatts and can be used to drive high gradient linear accelerator as well as microwave undulator for free electron lasers. A compact design of X-ray free electron laser using short-period microwave undulator is under discussion at National Synchrotron Radiation Research Center (NSRRC) in the high brightness injector research team. In this study, we tentatively designed a 12 GHz, 2□/3 mode disk-loaded periodic waveguide structure such that 100 MW of microwave power can be extracted from a 3 GHz repetition-rate electron beam of 5 nC bunch charge. The geometry of this structure (including upstream and downstream output couplers) has been set by extensive electromagnetic wave and wake-field calculations by HFSS and CST particle studio. We also built a prototype structure for characterization of microwave properties at low power level. We have identified that a 2□/3 mode has be excited in the structure with resonant frequency and group velocity close to their design values. R/Q has been obtained by means of bead-pull measurement that agrees very well with the designed value.

[1] R.J. Barker and E. Schamiloglu, Eds., High Power Microwave Sources and Technologies, New York: IEEE Press/J. Wiley& Sons, 2001.
[2] T. Shintake, et al., Development of Microwave Undulator, Japanese Journal of Applied Physics, Vol. 22, No. 5, 1983.
[3] T. Garvey et al., RF Measurement on a possible Transfer Structure. CERN-LEP-RF/86-35, 1986.
[4] T. Garvey et al., Studies of a frequency scaled model transfer structure for a two-stage linear collider, Proc. New Developments in Particle Acceleration Techniques, CERN 87-11, 1987
[5] T. Garvey, et al., A radio-frequency transfer structure for CERN Linear Collider, CERN-LEP-RF/89-25, 1989.
[6] E. Jensen, Design Calculations of the CLIC Transfer Structure, in IEEE Particle Accel. Conf., 1991.
[7] L. Thorndahl, Model Work on a Transfer Structure for CLIC, in IEEE Particle Accel. Conf., 1991.
[8] W. Schnell, The Study of a CERN Linear Collider, CLIC, CERN-LEP-RF/88-48, presented at the Linear Accelerator Conference, 1988.
[9] A. Millich, Simulation of the CLIC Transfer Structure by Means of MAFIA, CAP93, 1993.
[10] W. Schnell, The CLIC Study of an Electron-Positron Collider, Contribution to LC92 ECFA Workshop on e+e- Linear Colliders, 1992.
[11] L. Thorndahl, G. Carron, Impedance and Loss Factor Measurements on a CLIC Transfer Structure (CTS), Proceedings of the Third European Particle Accelerator Conference, 1992.
[12] G. Guignard, et al., A 3 TeV e+e- Linear Collider Based on CLIC Technology, CERN 2000-008, 2000.
[13] H. H. Braun, et al., The CLIC RF Power Source, CERN 99-06, 1999.
[14] I. Syratchev, 30 GHz High Power Production for CLIC, 7th Workshop on High Energy Density and High Power RF, 2005.
[15] I. Syratchev, Mode Launcher as an Alternative Approach to the Cavity-Based RF Coupler of Periodic Structures, CLIC-Note-503, 2002.
[16] P.B. Wilson, Introduction to Wake fields and Wake Potentials, SLAC-PUB-4547, 1989.
[17]　 G. Carron, A. Millich and L. Thorndahl, The 30 GHz transfer structure for the CLIC study, International Computational Accelerator Physics Conference, 1998.
[18] A. Chao, Physics of Collective Beam Instabilities in High Energy Accelerators, John Wiley & Sons, Inc., 1993
[19] B. W. Zotter and S. A. Kheifets, “Impedances and Wakes in High-Energy Particle Accelerators, Word Scientific, 1998.
[20] Thomas P. Wangler, RF Linear Accelerators, (WILEY-VCH, Weinheim, 2008)
[21] Gao Feng, HIGH-POWER RADIO FREQUENCY PULSE GENERATION AND EXTRACTION BASED ON WAKEFIELD EXCITED BY AN INTENSE CHARGED PARTICLE BEAM IN DIELECTRIC-LOADED WAVEGUIDES, ANL-HEP-TR-09-49, 2009.
[22] I. Syratchev, et al., PETS power extraction coupler evolution.ppt, EDMS#981650, 2008.
[23] I. Syratchev, et al., TIME DOMAIN SIMULATION OF THE CLIC PETS (POWER EXTRACTOIN AND TRANSFER STRUCTURE) WITH GdfidL, Proceedings of the 2001 Particle Accelerator Conference, 2001.
[24] I. Syratchev, et al., HIGH POWER PRODUCTION FOR CLIC, Proceeding of PAC07, 2007.
[25] I. Syratchev, et al., CLIC RF HIGH POWER PRODUCTION TESTING PROGRAM, CERN-Note-741, 2008.
[26] 　Ansoft HFSS 輔助說明.
[27] CST Particle Studio 輔助說明
[28] David M. Pozar, Microwave Engineering, 3rd edition, Wiley, 2005.
[29] Paul J. Petersan and Steven M. Anlage, Measurement of resonance frequency and quality factor of microwave resonators: comparison methods, J. appl. Phys. 84, 1998.
[29] Karantzoulis, E., An Overview on Impedances and Impedance Measuring Methods for Accelerators, Sincrotrone Trieste note ST/M-91/1, 1991.
[30] E. L. Ginzton, Microwave Measurement, New York: McGraw-Hill, 1957.