Radio-frequency system of the high energy photon source

Purpose High energy photon source is a 6 GeV diffraction-limited storage ring light source currently under construction in Beijing.A low-frequency fundamental radio-frequency(rf)system of 166.6 MHz was proposed to accommodate the accelerator physics design.Superconducting rf(srf)technologies were chosen for the storage ring rf accompanied by solid-state power amplifiers and digital low-level rf controls.The design of the rf system was completed,and the parameters are frozen.Elucidation of the rf design with key parameters is desired.Methods The requirements from the accelerator physics design will be presented followed by the detailed rf design.The logic behind the choice of key rf parameters is elaborated.The configuration of the entire rf system is presented.Results and conclusions The fundamental srf cavity of 166.6 MHz was designed to accelerate the ultrarelativistic electron beam.Heavy damping of higher-order modes in these cavities is required to avoid the coupled bunch instabilities.An active third harmonic srf of 499.8 MHz was adopted to realize the required rf gymnastics.Normal-conducting 5-cell cavities will be used for the booster rf.Solid-state amplifiers of 2.4 MW in total will be installed at HEPS to drive these cavities in the booster and the storage ring.A digital low-level rf system will be used to regulate rf field inside each cavity with high stabilities.The rf configuration during the commissioning and the operation scenarios are also presented.

Ultrasonication-assisted and gram-scale synthesis of Co-LDH nanosheet aggregates for oxygen evolution reaction

Electrochemical water splitting(EWS)is a highly clean and efficient method for high-purity hydrogen production.Unfortunately,EWS suffers from the sluggish and complex oxygen evolution reaction(OER)kinetics at anode.At present,the efficient,stable,and low-cost non-precious metal based OER electrocatalyst is still a great and long-term challenge for the future industrial application of EWS technology.Herein,we develop a simple and fast approach for gram-scale synthesis of flower-like cobalt-based layered double hydroxides nanosheet aggregates by ultrasonic synthesis,which show outstanding electrocatalytic performance for the oxygen evolution reaction in alkaline media,such as preeminent stability,small overpotential of 300 mV at 10 mA·cm^−2 and small Tafel slope of 110 mV·dec^−1.

Development of a 500-MHz waveguide directional coupler with high directivity for HEPS

Purpose In order to achieve a high-precision measurement of the incident and the reflected power,a WR1800 rectangular waveguide directional coupler with high directivity and high power level has been in-house developed.Multiple couplers will be installed in the 500-MHz high-power radio-frequency transmission lines delivering 200-kW continuous-wave power for the High Energy Photon Source(HEPS).Methods The directional coupler adopts the design scheme of primary and secondary transmission lines and coaxial coupling-head structure.The shape and dimensional parameters of the coupling head were carefully optimized by using microwave simulation codes.An optimum directivity of 64 dB was achieved in simulations.Results and conclusions A prototype coupler was subsequently manufactured,and its directivity was measured to be 48.2 dB following a rigorous calibration procedure,largely exceeding the design goal and the commercial product.The coupler was then connected to an existing 500-MHz klystron system,and a high-power test with short-circuit termination was conducted.The high directivity of the coupler was confirmed up to 200 kW.During the 6 hours of power aging with continuous-wave 200 kW in a standing-wave setup,no performance degradation was observed on the coupler.The coupler temperature was measured to be 20◦C above the ambient environment.The design requirements were comfortably fulfilled.These constitute thefirst in-house development of a large-size waveguide directional coupler with high directivity and high power level for HEPS.The design,fabrication,and performance tests of the directional coupler are presented.

New RF trip diagnostic system of BEPCII

Background The upgrade project of the Beijing Electron Positron Collider(BEPCII)is a high-current electron–positron collider with beam intensity close to 1A.The RF system plays an important role in providing energy for the beam,compressing the beam length and maintaining beam lifetime.Once the RF system shuts down the RF power for various reasons,the accelerator will stop working.Purpose In order to determine which reason causes the RF trip,a new RF trip diagnostic system was built based on the NI PXI system.Method The new RF trip diagnostic system is used to collect the data of the forward power,reflected power,cavity voltage,and beam current in a period of time before and after the RF trip event happens.The system uses LabVIEW as the control software,which conducts I/Q sampling of down-converted RF signals directly,then calculates the amplitude and phase of each RF signal,and plots the change curve.The data and figures are stored in the disk and MySQL database.The change curve can be replotted by the data browser which developed by the Python or PHP language.Results Through the analysis of the RF trip data and figures that produced by the new RF trip system,it can be clear whether the RF trip is caused by the RF system,so as to locate the reason of the RF trip more quickly and improve the reliability and stability of the machine operation.

Improving the RF stabilities of BEPCII by a disturbance observer based controller

Background A digital low level radio frequency(DLLRF)system has been developed to replace the old analog LLRF and operated stably at BEPCII east RF station in the past two years.The RF stabilities required for BEPCII are±1%in magnitude and±1 degree in phase.These are satisfied both by the new DLLRF and the old analog LLRF.Yet,the DLLRF did not improve the RF stabilities so much as expected,especially when the beam current was high in collision mode.Purpose The purpose is to improve the RF stabilities further and meet the requirements by the upgraded BEPCII project(BEPC3).Method A disturbance observer based(DOB)controller to suppress the noise was developed and tested with beam at BEPCII RF system.Results The DOB controller works and the RF stabilities with beam may be improved from±1%to less than±0.5%in magnitude and from±1 degree to less than±0.5 degrees in phase.

RF design of a compact 648 MHz single spoke cavity at CSNS

Purpose In order to increase CSNS beam power from 100 to 500 kW,the linac injection energy needs to be increased from 80 to 300 MeV.The combined layout of superconducting spoke cavities and lliptical cavities will be adopted to accelerate H-beam to 300 MeV.In this paper,a compact single spoke cavity withφ50-mm beam aperture was proposed,with the RF performance of the spoke cavity optimized to E_(p)/E_(acc).<5,E_(p)/E_(acc)<9,as well as the good multipacting behavior.Methods CST Microwave Studio was used to optimize the RF performance(E_(peak)/E_(acc),B_(peak)/E_(acc) R/Q)with cavity geometry parameters.After electromagnetic design was finished,multipacting behavior was studied with CST Particle Studio module,and cavity shape modification was made to get a reasonable<SEY>value.Results The simulation got optimum results of E_(peak)/E_(acc)=4.97 and B_(peak)/E_((acc)=8.42 mT/(MV/m),and the<SEY>max is 1.52at E_(acc)=7.74 MV/m.Conclusion A 648 MHzβ=0.4 single spoke cavity with beam apertureФ50 mm was proposed in the paper.This compact cavity may be a very promising option for CSNS linac upgrading.In addition to the optimization of the RF parameters,the multipacting behavior of the cavity is also studied,and cavity shape is optimized to reduce<SEY>value.