Research On Device For Online Measuring Of Electron Beam Energy

The paper presents a new method for online measuring the electron beam energy, using the relationship between balance-thickness and electron beam energy. Focusing on this new method, simulation and experimental study were carried on. The Monte Carlo code MCNP which is in common use was used to simulate single energy beams, of which the energy is from 3MeV to10MeV. Situations with different down plate materials were also simulated by MCNP, including aluminum, copper and graphite. The simulation results indicated that: the balance-thickness in this method is sensitive to both electron beam energy and material of under plate; the balance-thickness and the electron beam energy have good linear relationship; the simulation balance-thickness is almost equal to the experiment ones while adopting copper and graphite which has low secondary electron emission coefficient, as the under plate material respectively.An energy-measure-device was designed and processed corresponding to this new method. Experiments using this device were carried on a 4MeV accelerator of Accelerator Laboratory in Tsinghua University. The results have proved that the experimental data, both the normalized voltage vs. up plate thickness curve and balance-thickness, had great coherence with simulation results, and the deviation between actual and simulation balance-thickness didn't surpass 2%. While changing the material of under plate, the experimental results were also in good accordance with simulation ones. After changing the electron beam energy to 3.86MeV, the experimental results also had good coherence with kinetics calculation results, and deviation between actual and simulation balance-thickness was only 0.5%. All these results proved that it is feasible to use MCNP simulation to determine the balance-thickness corresponding to different electron beam energy.The energy ratio under 3.86MeV electron beam and 5.5mm up plate was calculated using 4MeV experimental and simulation data, the calculation result was 0.571, while the actual result was 0.568, the deviation was 0.53%. This result indicates that using simulation energy ratio to predict the experimental energy ratio is also feasible. However, the energy of actual electron beam is not single, which makes the deviation between experimental data point and simulation curve grow larger while the up plate thickness is beyond balance-thickness±2mm. Using simulation result to predict experimental result will become inaccurate in these regions. More experiments need to be carried on other accelerators of different electron beam energy so that the accurate applicable scope can be obtained.The energy-measure-device used in this paper is a passive device, which has many advantages such as simple in structure, ease of manufacturing etc. If taken ceramics as the insulation material, the thermo-stable performance may be greatly enhanced, so that this device can be used online without considering the irradiation time limitation. As simulation energy ratio can be used to predict the experimental energy ratio, the electron beam energy online measurement can be realized by MCNP simulation and certain calibration experiments.