Study Of A Compact And High-performance Pulse Modulator

With the development of compact high gradient x-band accelerating structure,more requirements are put forward for high power x-band klystron modulator.High power pulse modulator is a key component of high-power microwave system of linear accelerator.The performance of pulse modulator directly determines the performance of klystron output high power microwave,then further affects the beam performance of linear accelerator.For pulse modulator,pulse to pulse stability is one of the most important specification.The stability of pulse modulator influences the microwave amplitude and phase of klystron output.This paper describes the relationship between the stability of the pulse modulator and the amplitude and phase fluctuation of the klystron output microwave quantitatively.In this paper we give the test result of 10 sets of pulse modulator used in Shanghai Soft X-ray Free Electron Laser.From the analysis of measured results,we put forward the following hypothesis: for a certain constant current inverter charging power supply,PFN(pulse forming network)charging step is fixed,higher charging setting voltage will get better stability measuring results;The conduction characteristics of thyratron also affect the stability of pulse modulator.Based on the above assumptions,the principle of the charging power supply is analyzed,and the relationship between LC resonance parameters and charging step is clarified.Furthermore,the feasibility and necessity of double loop LC resonant converter used to charge PFN to improve the stability are given.The conduction characteristics of thyratron can be improved by adopting DC heating power supply and trigger signal synchronizing with AC line.This paper develops a new generation of oil-immersed high performance pulse modulator suitable for X-band 50 MW klystron.This modulator is the first compact oilimmersed pulse modulator suitable for x-band 50 MW klystron in the world,which fills the gap in domestic research and development of oil-immersed pulse modulator.Pulse forming is based on lumped parameter pulse forming network under the condition of the load impedance matching the PFN characteristic impedance.The switch device adopts oil-cooled thyratron CX1836.Pulse transformer,as a key part of pulse modulator,has great influence on pulse waveform.Detailed design of X-band high-power pulse transformer is given,and the influence of relevant parameters of pulse transformer on pulse waveform,especially on pulse leading edge,pulse flat-top drop,and flat-top ringing,is further analyzed.The design parameters of the pulse modulator is pulse voltage 427 kV,pulse current 304 A,top width no less than 1.5?s,full width at half maximum no more than 3.5?s,flat-top flatness less than 2%,repetition frequency 50 Hz.Due to the limitation of the condition,the developed oil-immersed pulse modulator cannot be tested under X-band klystron load.Experiment were carried out in the laboratory with a water load.The test results show that the oil-immersed pulse modulator meet the design requirement.The measurement of stability and timing jitter cannot be measured with a water load,because the impedance of water load is astable.