POLARIZED HIGH-ENERGY PHOTON BEAM PRODUCTION WITH LASER-COMPTON BACKSCATTERING
POLARIZED HIGH-ENERGY PHOTON BEAM PRODUCTION WITH LASER-COMPTON BACKSCATTERING
复制标题
利用激光康普顿后向散射产生偏振高能光子束
DOI：
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发表时间：
2003
期刊：
影响因子：
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通讯作者：
D. Lic
中科院分区：
文献类型：
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作者：
K. Aokia;K. Hosonoa;T. Hadamea;H. Munenagaa;K. Kinoshitaa;M. Todaa;S. Amanob;S. Miyamotob;T. Mochizukib;M. Aokic;D. Lic
我们利用在NewSUBARU存储环中循环的1 GeV电子对1064 nm激光光子进行康普顿后向散射，产生了一束高能伽马射线。对于20 mmΦ准直器，检测到的光子产率约为3×10光子smAW。准直器的光子能量宽度对应于6.6-17.6 MeV。其基本特征与理论特征完全一致。我们试图用核荧光实验来测量产生的伽马射线的偏振。本文介绍了初步结果。为了对能量范围在几MeV到几十MeV的电磁相互作用进行光核实验，在NewSUBARU[1]存储环上安装了一个激光-康普顿后向散射装置。该系统采用角能相关法。这些伽马射线也可用于存储环上的电子束诊断。激光-康普顿后向散射实验采用了一条11 m长的直线（BL1）。图1显示了激光-康普顿后向散射设施的示意图。所使用的激光源为连续Nd:YVO4激光器（λ =1064 nm， EL=1.168 eV），激光源水平和垂直腰直径均为0.42 mm，全发散度均为3.4 mrad。激光光子通过四个反射镜和一个透镜注入到相互作用区域。我们在电子能量为1 GeV，电流为5 ~ 20 mA，激光功率为0.5 ~ 1.0 W的条件下进行了实验。后向散射光子光束在0.67 mrad（20 mmΦ）、0.335 mrad（10 mmΦ）或0.067 mrad（2 mmΦ）三种10 cm长的引线准直器中进行准直。20、10和2 mmΦcollimators的光子能量宽度分别为6.6 ~ 17.6 MeV、12.4 ~ 17.6 MeV、17.3 ~ 17.6 MeV。准直器放置在距离相互作用区域中心约14 m的伽马射线轴上。我们用180 cm同轴型HPGe或3“×3”NaI探测器监测产生的光子通量。探测器被铅块屏蔽，放置在距离碰撞区域中心约20 m，距铅准直器约1 m的光子束轴上。伽玛射线能量是用来自K和几个标准伽玛射线源的1.461 MeV伽玛射线校准的。图1：激光-康普顿后向散射装置示意图。在电子能量为1 GeV时，测量了后向散射光子的能谱。图2中的实线表示用各种准直器测量的后向散射光子的能谱。轫致辐射光子已从原始光谱中减去。当使用2mmΦcollimator时，可以看到如图2所示的光峰和单逸出峰，但由于探测器的体积，峰非常小。我们使用蒙特卡罗电子-伽马雨模拟代码EGS4[2]将获得的能谱与模拟模型计算结果进行了比较。计算得到的能谱如图2虚线所示。计算得到的能谱形状与实测的能谱形状吻合较好。光子产率可以通过测量光谱和计算光谱之间的归一化来估计。对于20、10和2个mmΦ准直器，探测到的光子分别约为3 ×10、5×10和5×10 smAW。在正面碰撞中，极化激光束经180°康普顿后向散射产生的光子束被完全极化。第1届日本粒子加速器学会年会暨第29届日本直线加速器年会论文集（2004年8月4日至6日，日本船桥）
We have produced a beam of high-energy gamma-rays by Compton backscattering of 1064 nm laser photons from 1 GeV electrons circulating in NewSUBARU storage ring. The detected photon yields were measured at about 3×10 photons smAW for the 20 mmΦ collimator. The photon energy width from the collimator corresponds to 6.6-17.6 MeV. The fundamental characteristics well agree with the theoretical ones. We have tried to measure the polarization of the produced gamma-rays using a nuclear fluorescence experiment. The preliminary results are described in this paper. 1 BACKSCATTERIG FACILITY In order to carry out photonuclear experiments on the electromagnetic interaction in the energy range of several MeV to tens of MeV, a laser-Compton backscattering facility has been installed at NewSUBARU[1] storage ring. The angle-energy correlation method is used in that system. These gamma-rays can be used also for electron beam diagnoses at the storage ring. An 11-m long straight line (BL1), was used for the laser-Compton backscattering experiment. Fig.1 shows a schematic overview of the laser-Compton backscattering facility. The laser source used is a CW Nd:YVO4 laser (λ =1064 nm, EL=1.168 eV) and both the horizontal and the vertical waist diameters of the laser source are 0.42 mm and both the full divergences are 3.4 mrad. The laser photons are injected into the interaction area with four mirrors and a lens. The laser beam waist is located at the center of the interaction area 2 PRODUCTION OF PHOTON BEAM We conducted experiments at an electron energy of 1 GeV, a current of 5-20 mA and laser power of 0.5-1.0 W. The backscattering photon beam was collimated in one of 0.67 mrad(20 mmΦ), 0.335 mrad (10 mmΦ) or 0.067 mrad (2 mmΦ) 10 cm long lead collimators. The photon energy widths correspond to 6.6-17.6 MeV, 12.4-17.6 MeV, 17.3-17.6 MeV for 20, 10 and 2 mmΦcollimators, respectively. The collimator was placed on the gammaray beam axis approximately 14 m from the center of the interaction region. We monitored the produced photon flux with a 180 cm coaxial-type HPGe or 3”×3” NaI detector. The detector shielded by lead blocks was placed on photon beam axis approximately 20 m from the center of the collision area and about 1 m behind the lead collimator. The gamma-ray energies were calibrated with the 1.461 MeV gamma-rays from the K and several standard gamma-ray sources. Figure 1: Schematic overview of laser-Compton backscattering facility The energy spectra of the backscattered photons were measured at an electron energy of 1 GeV. The solid lines in Fig. 2 show the energy spectra of the backscattering photons measured with the various collimators. The Bremsstrahlung photons have been subtracted from the original spectra. When using the 2mmΦcollimator, the photo peak and single escape peak can be seen as shown in Fig. 2, though the peaks are very small due to the volume of the detector. We compared the obtained energy spectra with the simulated model calculations using the Monte-Carlo electron-gamma shower simulation code, EGS4[2]. The calculated energy spectra are shown with the dotted lines in Fig. 2. The shapes of the calculated energy spectra are reproduce the measured ones. The photon yield can be estimated from the normalization between the measured and calculated spectra. The detected photons are about 3 ×10, 5×10 and 5×10 smAW for the 20, 10 and 2 mmΦ collimators, respectively. The details of the production of the photon beam with the Compton backscattering are described in Ref.[3] 3 POLARIZATION OF PHOTON BEAM In the head-on collision, the photon beam generated by 180°Compton backscattering of polarized laser beam is polarized completely. We tried to measure the gammaProceedings of the 1st Annual Meeting of Particle Accelerator Society of Japan and the 29th Linear Accelerator Meeting in Japan (August 4 6, 2004, Funabashi Japan)