1. Voltage Standing Wave Ratio Protection System for RF Power Source at CSNS LINAC Zhexin Xie,Jian Li,Zhenchen Mu, Linyan Rong,Wenzhong Zhou, Meifei Liu, Bo Wang, Maliang Wan, Yuan Yao Xinan Xu,Zonghua Zhang, Jimin Qiao Institute of High Energy Physics; Dongguan Neutron Science Center,Dongguan, China SCHEME OF THE VSWR PROTECTION SYSTEM All the analog units including the analog moudle (AM) and clock distribution module (CDM) are put into a temperature stabilizing chamber. The high power protection module (HPM) is mainly in charge of the precise power measurement and VSWR protection along the power transfer system. r. Detector takes an RF signal from the directional coupler at the input, and outputs a DC voltage proportional to the RF peak voltage, eight channel of ADCs sample DC voltage with a clock of 72MHz and translate the smaple data to FPAG. FPGA calculate the power and VSWR, if large reflect power detects, FPGA spread a signal to cut off power source.The VSWR and power data were sent to the IPC in real time through DSP. INTRODUCTION China spallation neutron source(CSNS) is located in Dongguan city in Guangdong province. The accelerators of CSNS mainly consist of an H- linac which accelerates the H- beam energy to 81 MeV. The infrastructure and equipment manufacture are now in progress. The RF system for the 81 MeV Linac requires 9 units of RF power sources: two 4616 tubes power RFQ, 4 klystrons power DTLs, and 3 solid state amplifiers power two bunchers and one debuncher. A VSWR protecion system is introduce to avoid high power reflect to power source. This system will cut off excitation source within 1 us if VSWR is high than the setting value. Abstract When electrical breakdown in the form of arcing in the accelerator cavity, high-power RF signal reflect to the RF power source,which brings severe damage to the RF power source and wave-guide output window. In this paper,we introduce a Voltage Standing Wave Ratio(VSWR) Protection System to avoid this damage. Once the system detect VSWR greater than the threshold value, the system spread out a signal quickly to cut off excitation source of RF power source within 1 us. In this System, VSWR and protection number can be displayed in screen, protection time in every pluses can be set manually. This system is now used in CSNS RF-linac RFQ, Buncher,DTL RF power source systems. PERFORMANCE The assemble of the prototype was finished in May, 2015, the commissioning was done with the available 324MHz RFQ accelerator and two Buncher accelerators. The test results satisfied the design requirements, The delay of the system within 1us. Real time recorder of arcing was saved as log in IPC. Figure: waveguide directional coupler(WGDC) Figure: Ferrite circulator Figure: Response time of cut off excitation source Figure: Real time record of VSWR protection. CONCLUTION The design of VSWR Prection system is complete, the initial commissioning results indicate that the performance met our requirements of within 1us, well protecting the power source in CSNS LINAC. The Low-Level Radio Frequency Workshop 2015. Arcing phenomenon brings great damage to equitment <1us Excitation signal Reflect signal 打火 次数 时间 Figure: Detectors and Response time of detcter(88ns) The active detector is chosen to provide enough power to drive ADC which is 50 Ohm inputs Figure: Linear of Detector The high power protection module(HPM) hardware consists of a motherboard and one daughterboards, the daughterboards owns eight 14bit, 72MHz ADCs,. The core devices in the motherboard are one Altera straix II FPGA and two TI C6000 DSPs, the primary control logic is implemented in the high-speed and high-density FPGA, the DSPs is mainly responsible for the communication with IPC through Ethernet and some coefficient calculations. This structure can reduce the logic elements usage and simplify the floating point arithmetic, also make the Ethernet communication easy to realize. Delay time Protection Number in one second AD Sample data input power(dBm)