混合型波荡器的研制

RESEARCH OF A HYBRID UNDULATOR

介绍一台１．５ｍ的混合型波荡器（ＵＮＤＵＬＡＴＯＲ）的研制，包括设计、磁块的优化组合、磁场测量系统和磁场调整技术。这台波荡器主要用于中红外自由电子激光的研究，其磁场峰值均方根误差０．５％，磁场导向误差１ｍＴ·ｃｍ，电子轨迹偏离０．０３ｍｍ。

AbstractOur REC一steel hybrid undulator is 1.5m long and sketched by Fig.1.The length of onemagnetic period is 30mm. The permanent magnets is SmCo_5(2: 1 7).The peak magnetic fieldrequired at 14mm magnetic gap iS 0.3T,which can be easily achieved.Designing works areconcentrating on how to satisfy the requirement of magnetic field quality一the rms field errorshould be less than 1.0% and the deviation of electron beam less than 0.1mm. Using PANDIRA,effects of errors on magnetic field have been analyzed and shown in Table 1.The most sensitiveerror is the magnetic gap △g_2. This has been paid attention during designing and constructionof undulator.Using Simulated Annealing(SA)method,200 megnets has been chosen from 400 mangnets toreduce the magnetic field errors resulted from the inhomogeneous of residue magnetization M_x,M_y,M_z of permanent magnets.To minimize the electron trajectory deviation,the cost functionused in SA has been carefully chosen,Fig. 2 shows the electron trajectory calculated before andafter sorting of magnets. In our magnetic field measurement system,a GaAs hall probe is adopted as the sensor(sensitivity 5～20mV/mA·0.1T,effective area 0.1mm × 0.1mm).A photon一electric encoder de-tects the displacement of the probe with the precision 0.005mm. The field acquisition channel con-sist of hall probe, digital volt meter (DVM),GPIB interface bus, the DS一GPIB interface cardand AST一386 micro一computer.The control system form a closed loop. The precision ofthe system is(△B/B_0)_(rms)≤(0,3～1.5) × 10￣(-4)(when △B/△z<0.01T/mm)or(△B/B_0)_(rms)≤(1.5～5) × 10￣(-4)(when 0.01T/mm<△B/△z<0.06T/mm)。Two methods are used in the adiustment of undulator.At first,the total 100 magneticperiod units are measured.Their positions in undulator are re一arranged using Simulated An-nealing method according to their magnetic field distribution. This has reduced the rms magneticfield errors of undulator to 1.3%。Then iron shimming is adopted to reduee error to a disirablevalue 0.5%,and the electron trajectory deviation is 0.03mm,which are shown on Fig.5.