Production of Low Energy Gamma-Ray by Inverse Compton Scattering using a Far Infrared Laser

1.低能γ射线产生技术fir激光通过中空丙烯酸波导输送到存储环形隧道中束线前端的激光入射室，其中有露点温度为-40℃的干燥空气进入。其传输距离约为20m长，传输效率达到80%。开发了使用热电传感器的光束剖面监视器，并将其安装在离腔室上游2米的位置。利用该监测仪，将激光光轴调谐到电子束的相互作用点。通过考虑前端风道多孔径限制衍射效应的计算，估计每2W 118.8μm.2的FIR激光产生γ射线的速率为Nγ=1.1×10^4光子/秒。研制了高功率光抽运FIR激光器，在9P（38）激光线上获得了234.5 w的抽运CO_2激光器输出功率，用于抽运CH_3OH，用于118.8μm激光。FIR激光器的最大输出功率约为1.6W，功率变化为±1%，可实现24小时的长期稳定。为了产生20MeV范围的γ射线，研制了短波长的FIR激光器和用于48μm和57μm激光器的硅光学材料。为了采取探测系统堆积的措施和降低背景，在10mm厚度的铅盒中安装了LYSO闪烁体。在探测器前方安装了吸收器和准直系统。利用^<88>Y的辐射源进行能量校准。结果表明，在逆康普顿散射过程中，存储的电子不会丢失。根据测量结果，我们估计每2W FIR激光产生γ射线的速率为6×10^3光子/秒。为了产生高强度γ射线，一项先进的计划正在进行中，该计划在新的光束线上有一个16米长的相互作用区域。激光束将通过波导传输到近相互作用区域，以恢复由于激光大发散而减少的有效截面。完成了反射镜室的制作和安装，激光洁净室和波导系统的建设。在这个光束线中，γ射线的产生速率预计将超过10^5光子/秒。少

1.Technology of low energy γ-ray productionFIR laser was transported to the laser incident chamber on the beamline front-end in the storage ring tunnel by hollow acrylic waveguides into which dry air of -40℃ dew-point temperature was flow. Its distance is about 20m long, and 80% transmission efficiency was achieved. Beam profile monitor using a pyro-electric sensor was developed and installed at 2m-upstream from the chamber. By using this monitor, laser optical axis was tuned for the interaction point to electron beam. By the calculation considering the diffraction effect by many aperture limits in the duct of front-end, a production rate of γ-ray was estimated to be Nγ=1.1×10^4 photons/sec per 2W FIR laser of 118.8μm.2.Development of high-power optically-pumped FIR laser234.5W-output power of the pumping CO_2 laser was achieved at 9P(38) lasing line, which was used for pumping CH_3OH for 118.8μm lasing. Maximum output power of FIR laser was about 1.6W, and ±1 % of power variation was … More achieved for a long-term stability of 24 hours. To produce 20MeV range γ-ray, a short wavelength FIR laser and optical material of silicon for 48μm- and 57μm-laser were developed.3.Measurement of produced γ-rayTo take measures of pileup of detection system and to reduce a background, LYSO scintillator was installed in 10mm-thickness Pb-box. Absorbers and collimator system were installed in front of the detector. Energy calibration was done by using radioactivity source of ^<88>Y. It was confirmed that stored electrons were not lost during the inverse Compton scattering. From measurement result, we estimated γ-ray production rate at 6×10^3 photons/sec per a 2W FIR laser.4.Future planTo produce high intense γ-ray, an advanced plan is in progress at the new beamline which has a 16m-long interaction region. Laser beam will be transported to near the interaction region by waveguides to recover a reduction of effective cross-section due to a large divergence of laser. Manufacture and installation of the mirror chamber, and construction of the laser clean room and the waveguide system were completed. In this beamline γ-ray production rate will be expected more than 10^5 photons/sec. Less