Design And Test Of The China Material Irradiation Facility RFQ

At the front end of the linac of the China Material Irradiation Facility?CMIF?,a radio frequency quadrupole?RFQ?is designed to accelerate 10 mA deuteron beams from 20 keV/u to1.5 MeV/u,which reaches the energy can be accepted by the superconducting section followed.In the superconducting section,the beams will be accelerated to 50 MeV.In this thesis,the work on radio frequency structure design,radio frequency measurement,RFQ tuning,high power test and beam test will be presented.First part of this thesis is about the RF structure design.Based on the beam dynamics design,some critical parameter will be used in RF design are obtained.The finite element electromagnetic software CST MICROWAVE STUDIO is employed for RF design,optimization and simulation.The cavity structure is four-vane type,which has advantages in stabilization of structure,cooling and power consumption compared to other types.Four-vane type is suitable for RFQ of high frequency,high power loss and high beam intensity.The working frequency is162.5 MHz,vane voltage is 65 kV,and vane length is 5.25 m.The?-mode stabilization loops structure is utilized to compress the azimuthal asymmetry caused by the manufacture error.The frequency separation between the working frequency and its nearest dipole mode is reached to17.66 MHz.Under this design and the tolerance which are within the reach of specialised commercial company,the dipole perturbative component will be suppressed to be smaller than the restriction from the beam dynamics design.After the optimization based on the full length model with the modulated vane tips,the unhomogeneity of the electric field along the longitudinal direction is below 2%.The simulated frequency of ultimate RF model is 162.459MHz,the Q value is 14148 and the RF power loss is 109 kW.Compared to the CW RFQ around the world,the maximum power density is adequate low enough for CW operation.The challenge CW operation of the RFQ is thermal management which is need to be analyzed by multi-physics coupled simulations.The second part of the thesis is the multi-physics study based on quasi 2D simulation.The temperature groups of vane cooling water and wall cooling water under which there is no frequency shift is obtained,the results are linearly related and coincide with the operation records of the ADS-RFQ with the similar structure.Under the temperature group near the circumstance of operation,the frequency shift coefficients of vane cooling water temperature and wall cooling water temperature are obtained.Under the vacuum circumstance,the multipacting phenomenon is a plague of the operation of RF device including resonant cavity.Simulations of multipacting are also performed to verify whether there is a risk of multipacting.The power levels where there is high probability for the occurrence of multipacting is obtained.Manufacture with high accuracy is the key point to realize the high performance of the RFQ.Before and after brazing of single section,the RF measurement is performed to verify whether the cavity is reasonably assembled and to make sure there is no unexpected deformation after brazing.After the full assembly and alignment finished,tuning is performed.Copper tuners are manufacture based on the tuning results.The measured frequency of the cavity with copper tuners and endplate is 162.661 MHz which is high than the nominal frequency due to ignoring the structure modification of the dummy tuners.The measured Q value is 12560.The longitudinal unhomogeneity is below 2%and the azimuthal asymmetry is below 1.5%.The influence on the perturbative components of the other two couplers designed but will be not used during the test is measured to below 0.1%.A tetrode amplifier is used for high power test and beam test.Due to the restriction of the cooling water supply,the cavity will be test under a lower repetitive frequency and lower pulse width,which is lower than 200?s at 1 Hz.After 71 hours conditioning,the RF power in cavity reached 125 kW.In order to lower the cost of shielding,the beam H₂⁺is used instead of deuteron beam.The beam energy measured by using the time of flight method is 3.11±0.01MeV.The transmission efficient measured is 97.6%when the input beam current is 8.04 mA and the output beam current is 7.85 mA.The highlights of this thesis are listed below.?1?A design procedure of design the trapezoidalmodulated RFQ vane tips is developed based on the EM Studio and VBA of CST.?2?Based on transmission line model of RFQ and electrostatic simulation,the frequency separation between the working mode and its nearest dipole mode is specified,which is depend on the mechanical tolerances and dipole perturbative component restriction.?3?The working points of the cooling water temperature groups are obtained,and this is coincidence with the real condition on the ADS-RFQ.?4?Using different methods to calculate the coupling factor during the setup of coupling factor,the results are coincidence with each other with error below 1%.