Neutron Guide The Design And Optimization

One of the main purposes of building China Advanced Research Reactor (CARR) is to do neutron scattering experiments, it is one part of CARR project to set up neutron scattering spectrometers and relative equipments. Neutron guide system plays an important role in neutron scattering project. Statistic data show that nearly 2/3 neutron scattering spectrometers are installed in neutron guide halls. The designing work must be done very carefully for followed reasons: Neutron guide tube' s transmission ability directly affects the spectrometer installed after them; Neutron guide system is expensive; it is difficult to replace the guides in pile. After doing much investigations and discussions with foreign experts, we had the original design. I finished writing Monte-Carlo simulation program NGT2002, it can simulate ideal neutron guide system, at the same time it can simulate neutron guide system with width fabricate error and adjustment errors. With the simulation results of this program, we can give the permitted width fabricate range, horizontal adjustment error range. In this article, I used NGT2002 to simulate the neutron guide system CNG1 and CNG2, and optimized parameters of the original design, finished the physics design of the neutron guide system.There are many programs in the world, such as MCSTAS, VITESS, IDEAS, NISP, etc. They have their own characteristics, but they all simulate ideal neutron guide system. When designing our neutron guide system, we found that neutron guide width fabricate error range and horizontal adjustment errors range were very important parameters to designing, purchasing and adjustment of neutron guide system, but programs mentioned above can' t solve those problems. The Japanese program NEUGT can simulate neutron guide system with adjustment errors, but it was set up with oldFORTRAN language, so it isn' t convenient to use this program, and NEUGT' s calculation speed is slow, it can' t simulate super mirror neutron guide either. So I wrote the simulation program NGT2002, it can simulate neutron guide system with width fabricate error and horizontal adjustment errors. I optimized our neutron guide system parameters in two steps: First, I tested programNGT2002 to ensure that its result is single; then had a simulation with parameters used by experiment which was done by Yuji Kawabata, etc. in JAERI, the simulation result accorded well with the experiment result; also I compared results got by NGT2002 and MCSTAS, they gave the same result with same input parameters within error range. Second, I simulated the neutron guide system CNG1 and CNG2 of following parameters: distance between guide in pile and the cold neutron source; neutron guide element width and height; character wavelength of curved neutron guide outside; length of curved neutron guide and direct neutron guide outside; width fabricate error range; adjustment errors ranges. The following parameters are optimized results: length of the guide in pile is 2200mm, distance between guide in pile and cold neutron source is 1965mm, the lifetime of the supper mirror guides used in CNG1 and CNG2 is over 10 years, the character wavelength of CNG1 is 0. 2nm, the curved neutron guide of CNG1 is 21m long, the character wavelength of CNG2 is 0. 4nm, the curved neutron guide of CNG2 is 11m long, the direct neutron guide of CNG1 is llm long, and the direct neutron guide of CNG2 is 9m long. For CNG1 and CNG2, width fabricate error should be less or equal 0. 02mm, width adjustment error range should be less or equal 0.02mm, horizontal adjustment angle error should be less or equal 2 second.