Analysis of the measurement field of the optical klystron

Vol.11 No.2NUCLEAR SCIENCE AND TECHNIQUESMay 2000Analysis of the measurement field of the optical klystron*DIAO Cao Zheng, XU Hong Liang, JIA QiKa, LI Ge, LI Jing-Yi, LI Wei-Min,ZHOU An-Qi, LIU Gong-Fa, LI Yong-Jun, YAO Cheng-Gui, HE Duo Hui(National Synchrotron Radiation Laboratory,The University of Science and Technology of China, Hefei 230029)AbstractThe measured fields of the optical klystron in NSRL (National Sy-chrotron Radiation Laboratory) are given, including the distribution on the axis, andthe integrated feld distribution. The harmonic magnet field and the spectra of thespontaneous enission are analyzed, and the multiple field is presented by ftting thediagram. The infuence of the integrated field on the close orbit of the bearn and onthe operation paramneters of the storage ring, and the compensation in the cxperimentare also discussed.Keywords Optical klystron, Integrated field, Multiple ficldCLC numbers TL501, TL5941 IntroductionThe NSRL storage ring in Hefei, China has been routinized to run for users since1993. An optical klystron (0K) has been designed and constructed for investigation ofthe storage ring FELL. In the process of manufacturing the optical klystron, because ofthe errors come from the production of the magnet blocks, the fix of the blocks, and thequality of the blocks etc., the magnet field is not ideal and it afects the gain of FEL，the spontaneous emission and the operation of the storage ring. Hence we must analyzethe field of the optical klystron seriously.The measurement fields are presented by Hall probe technical2]. The oritentedprecision of the measurerent device is 0.01 mm/m. The position of measurement pointis located by the dual- frequence laser, and the precision is土5 pm. The size of the hallprobe is 0.5 mmx1 mm. The sampling points is 80 in each period of the magnet field，and the step is 0.9 mm.2 The field distribution on axis and the effect on the spontaneous emis-sionIn order to get the information of the中國煤化工.m SE3D to simulatethe spontaneous emission with the measthe harmonic fieldby using the method of FFT (Fast FouriYHCNMHGThe condition of the 0K is that the gap of the dispersion section is 55 and the gapsof the undulators are 40 mm.Supported by 863 CHG FEL fund and the youth fund of USTCManyssipt preceived date:99-11-23*Email: dex@ustc.edu.cnNo.2 DIAO Cao _Zheng et al: Analysis of the measurement field of the optical klystron137The measured field of Y -axis is approximately a sine function and it is consistentwith the theoretic result. Each peak field of the undulators is different and the RMS ofthe spread of the peak feld is 1.5%.The spatial harmonic distribution of the field will distorted the orbit of the beam,and affect the emission of the optical klystron3l. We analyzed the measured fields byFFT and the result is given in Fig.1. The 7th and 11th harmonics are showed in the figureexpect the 5th, 9th and 13th harmonics. However, the amplitudes are very small (10- 3order of the 1st harmonic), so they are not affect the emission of the optical klystron.We simulated the spontaneous emission of the 0K with the measurement field by theprogram SE3D and the result is shown in Fig.2. The modulated rate is 0.98, approximateto the ideal field. Hence the field distribution on axis is good.。1rm0.0的1001001011Hrmonlc numborsA InmFig.1 Distribution of the OK harmonic fieldFig.2 Spontaneous crmission of the OK3 Integrated fieldWe integrated the field at the direction of Y -axis, and obtained that the 1st integralvalue is 0.005 T.cm and the 2nd integral value is 0.04T.cm2 .The offsets of angle and the position at the exits of OK are x'(z)=9.1x 10-5 rad and△x=- 4.22x10 -3 mm when the energy of the electron is 163 MeV.0.02 |201}-i 0∞0-中國煤化工101-MYHCNMHG-0.02 I@)(b方4”2o24古X /mmFig.3 First integral (a) and 2nd integral (b) over' OK length v8.出138NUCLEAR SCIENCE AND TECHNIQUES ,Vol.11In order to study the multiple field of the OK, We measured the fields of sevenpoints on x-axis, i.e., (0, 0}, (土2, 0}, (士4, 0), (土6, 0), and calculated the 1st and the 2ndintegrated field value, which are given in the Figs.3a and 3b.We fit data in the Fig.3 for analyzing the multiple field and the results are given inFig.4. The ftting formula is:Bds= Ao+ Az+ Azz2 + Ax3where Ao=0.00539T.cm， A1= 0.00483T.cm/mm, A2= -1.06x10-4 T.cm/mm2，03A3= -1.27x10-5 T.cm/mm30.02The integral field of the 6th fieldis，..01given by SIB"ds=一- 1.06T/m, So the0.00intensity is 言」B"ds≈-3.90m-2. Wetook 6th field as a thin-len, tracked theo.011: Measured valueparticles by means of the program NP,.020Cuve : Fting to the 3rd Dower o1X-obtained that: the change of the chro-maticity on X-axis is 0.002 and on the Y-x /mmdirection is 0. The effect on the dynamicFig.4 Fitting curve of OK feld with multipleaperture is very smll4l. .components4 Uniform of the OK fieldWe measured the distribution of the 1% good field range in X- and Y-axis. Inthe direction of X-axis, the undulators section is (-19 mm, 19mm) and the dispersionsection is (-9mm, 9mm). Hence, the good field range is large enough in X-axis. Inthe Y-direction, the modulator section is (-1.7 mm, 1.7 mm), the radiation section is (-1.55 mm, 1.55 mm), and the dispersion section is (-3.7 mm, 3.7 mm). The field is sensitiveto Y-direction, so we must correct the orbit in Y -direction in the experiment.5 Effect on the beamThe non-zero integral field produces the orbit distort:xX,(S)= IB.devV-208CO).cos(πv, - 4(s))2sinπVx中國煤化工where βz(s) and p(s) are the β function and the PTHC N M H Gectively.When the energy of the electron is 200MeV, we obtainea Acmax≤1.1 mm and so theorbit must be corrected.The field of the 0K will change the work point of the storage ring. The changes inX- and Y-direction are diferent: Ovx is zero, but Ovy is not zero. We calculated the萬(wàn)方縝媧ge of the work point by resorting to the measured field,No.2 DIAO Cao Zheng et al: Analysis of the measurement field of the optical klystron139βyAvy= 4(Boy/ B2dzWhere w=3.4m. When the energy of the electron is 200MeV, the dispersion sectiongap is changed from 90mm to 40mm, Ovy = 0.048 ~ 0.074, The change of Uy is cross .the 1/3 line, so the lattice must be compensated.6 ConlusionBy means of the calculation of the program SE3D and the methods of FFT, itis known that the amplitude of the harmonic field is very small and the effect of theerror field on the spontaneous emission is small too. The infuence of the multiple fieldon the dynanic aperture and chromaticity of the electron beam is little. However, theorbit distort by the non- zero integral field is biggish, so we must correct the orbit in theexperiment. The By is distorted and the work point is changed by the effects of the fieldof the OK, so the lattice must be compensated.References1 He D H et al. The status of storage ring FEL project in NSRL, In: Proceedings of 19thFEL.1997Xu H L. The prophase study of coherent harmonic SRFEL, Ph.D Tbesis USTC, 1998NIWANO M, KITAMURA H. Nucl Instr Meth, 1985, 234:388~399Diao C Z, The physical study of coherent harmonic SRFEL, Ph.D Thesis, USTC, 1998中國煤化工MHCNMHG