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Compact cyclotron internal beam measurement technology research

Author: WangZuo
Tutor: ZhangKaiZhi
School: Chinese Academy of Engineering Physics
Course: Nuclear Technology and Applications
Keywords: cyclotron negative hydrogen beam diagnose induced radioactivity thermal analysis PIG ion source arc discharge spectral analysis electrical shielding box
CLC: TL542
Type: Master's thesis
Year: 2011
Downloads: 89
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Abstract

Cyclotrons are widely used in scientific research for national defense, isotopes production, medical diagnosis and therapy. The relevant development at the Institute of Fluid Physics (IFP) of China Academy of Engineering Physical (CAEP) was introduced. At present, a compact cyclotron for PET positron nuclides drug production is being developed in the IFP of CAEP, and a cold-cathode Penning ion gauge (PIG) type ion source is used for generation of negative hydrogen (H-) ions as the internal ion source of this cyclotron. In order to meet the design requirements of the targeting beam of 11MeV energy and 50μA current, the PIG ion source should produce enough beam current at the operational extraction voltage and the beam loss rate should be minimized during the process of beam transportation. Therefore, we should try to increase beam current from ion source and decrease beam loss rate along the beam line. Researches are combined to achieve the above goal, and the experimental research on ion source is the most important among them in the primary phase.The internal beam diagnostic equipment is one of the key devices for cyclotron operation and running, they should be installed to monitor the beam transportation, and provide necessary information for optimization of the cyclotron performance.For the H- ion beam of 11MeV energy and 50μA current, this dissertation focuses on the physical designs of the measuring probe, including the beam range in the probe material, the effect of secondary electron for measurement results, induced radioactivity of the probe material and thermal analysis of the probe. Based on the theoretical analysis and numerical simulation using of the software SRIM, FLUKA and MATLAB, the probe size and material are optimized, and the operating conditions and times limitation are made out.The investigations on the PIG ion source include the arc discharge experiment and the measurement of H- beam current under dc extraction. The effects of gas flow rates, magnetic field strength and arc current are test. And the PIG ion source is also diagnosed by spectroscope. The results indicate that the PIG ion source works normally as negative impedance and the ion source is affected mainly by gas flow and arc current. In the preliminary measurement of the extraction H- beam, the beam current is much higher than the theoretical calculation of space charge limited flow. Thus, a new method called dc beam measurement of electrical shielding box is brought forward. This paper describes the basic principle of dc beam measurement of electrical shielding box, the CST numerical simulation of the beam trajectory and the measurement results of extraction beam. Finally, by employing the "V3/2 law" of space charge limited flow to fit curve, the dc H-beam current of about 4mA from the PIG ion source with the puller voltage of 40 kV and arc current of 1.31 A is extrapolated from the measurement at lower extraction dc voltages.

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