Development And Experimental Research Of A Magnetic Proton Recoil Spectrometer

Neutron energy spectrum from fusion reactions provides importantinformation about the plasma core region, such as ion temperature and fusionpower. The magnetic proton recoil (MPR) spectrometer is a novel diagnosticinstrument with high performance for measurements of the neutron spectra fromhigh power fusion devices. A compact MPR-type spectrometer for close quartersmeasurements of both steady-state and pulsed neutron spectra in complicatedenvironments has been designed and built. The spectrometer employs largerecoil angle, small size permanent analysis magnet, short beam transport lineand dual-purpose detector array for both steady-state and pulsed measurements,in order to achieve high energy resolution, reasonable efficiency (or sensitivity)and good signal-to-noise ratio (SNR).The associated spectrometer design and simulation code, which includesmultifunction of2-D beam transport,3-D electromagnetic emulator,3-Dcharged particle transport and Monte Carlo simulation, is developed for accuratespectrometer design and modeling as well as performance simulation andoptimization. Simulation results of the spectrometer illustrate that the energyresolution and efficiency of the compact MPR spectrometer are mainlydetermined by the recoil proton method itself, and the n-p recoil foil and protonapertures are chief factors which influence the spectrometer's performance. ForDT (deuterium-tritium) neutrons, energy resolution of the compact MPRspectrometer is between3%-7%, where the corresponding efficiency is between(0.2-3.5)×10-8cm2and the sensitivity of neutron detection is between(0.1-1.2)×10-20C·cm2. The aforementioned performance can be easily adjustedby changing the thickness and area of the recoil foil, as well as the protonaperture geometry. The measured noise of the spectrometer comes mainly fromthe outer straight irradiation and inner scattered background. The steady-statemeasuring SNR can reach10:1level by applying complete shielding, when thepulsed neutron measuring SNR can reach5:1at the same time.The spectrometer's technical principle is validated by neutron experimentsusing an accelerated DT neutron source. Since the neutron source strength is comparatively low, efficiency of the spectrometer is increased to10-6cm2levelby adjusting the geometry parameters of the recoil foil and proton aperture, andthe precision of the experiments is increased to better than10%. The neutronexperiments employ PIN detectors with small sensitive volumes, and simpleshielding. As a result, the steady-state measuring SNR is about1:2and thecorresponding SNR of pulsed neutron measurements is only1:4, which areconsistent with the MCNP simulation results. However, the SNR capability canbe increased by10more times by applying large area strip detector arrays andcomplete shielding. Moreover, neutron experiments of the compact MPRspectrometer on a DT neutron accelerator have been simulated by the associateddesign and simulation code. The results illustrate that the simulation andexperimental results have good consistency with maximal difference less than10%, which corresponds with the experimental precision. Thus the spectrometerassociated design and simulation code possesses good accuracy and reliability.