BNCT RFQ高功率耦合器的设计

为满足硼中子俘获治疗试验装置(BNCT_A)RFQ加速器腔耗420 kW、占空比50%的需求。为BNCT_A RFQ加速器设计了一款高功率耦合器。该功率耦合器包含WR2300矩型波导转3-1/8英寸同轴门钮结构、波导窗、功率耦合装置3个部件。波导窗采用同轴扼流结构型式，功率耦合装置采用磁耦合环结构。整个功率耦合器采用分段设计的原则。矩型波导转同轴结构和陶瓷窗分别通过Microwave Studio（MWS）优化仿真，得到陶瓷窗的驻波比（SWR）达到1.000 9@352.2 MHz，带宽大于±58 MHz@SWR≤1.1 MHz。用多端口换算理论确定了耦合环耦合度，并用能量衰减法确定耦合环的尺寸。从热学和结构力学方面校核了该功率耦合器的功率容量，在50%占空比下，单个功率耦合器最高峰值功率可达260 kW，4路功率耦合器最高峰值功率可达1 MW。经过实际高功率测试，目前入腔功率484 kW，占空比达到10%，并具提升峰值功率及占空比的能力。

Design of High Power Coupler for BNCT RFQ

The input power and duty factor of boron neutron capture therapy test equipment_A (BNCT_A) RFQ are respectively 420 kW and 50%. In order to meet the power requirements of the RFQ cavity, a high power RF coupler was designed. This coupler includes WR2300 waveguide-coaxial transformer, ceramic window, and power coupling equipment. The ceramic window employs Choking structure type and power coupling equipment is a magnetic loop. The segmented design method was used in the design of the power coupler. The waveguide-coaxial transformer and ceramic window were respectively optimized by using Microwave Studio (MWS). The standing wave ratio (SWR) of the ceramic window is 1.000 9@352.2 MHz, and the bandwidth is more than ±58 MHz@SWR≤1.1 MHz. The coupling factor of magnetic loop was obtained by multi-port transform theory and by using the energy attenuation method, and the size of the magnetic loop was determined. The thermal and structure analysis result shows that the peak in-put power can achieve 260 kW, with 50% duty factor for a single coupler, and 1 MW power can be achieved under four-channel coupler. After RF power test and conditioning, the RF power feeding to the cavity is reached to 484 kW, with 10% duty factor at present, and the power and duty cycle can be improved in future.