利用線型加速器中高重覆率相對論性短脈衝電子束產生兆瓦級高功率微波之研究

Extraction of High Power Microwave from GHz-Repetition Rate Relativistic Short Electron Pulses

黃正瑋(Cheng-Wei Huang)

指導教授 ： 柳克強 ； 劉偉強

國立清華大學/原子科學院/先進光源科技學位學程/碩士(2011年)

https://doi.org/10.6843/NTHU.2011.00302

摘要

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。

關鍵字

微波 ； 高功率微波 ； 尾場 ； 小型化X光自由電子雷射 ； 電子束 ； 微波擺盪器

並列摘要

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.

並列關鍵字

Microwave ； High power microwave ； Wake fields ； Compact X-ray free electron laser ； electron beam ； Microwave undulator

參考文獻

[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.

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[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.