Development Of Solidified Hydrogen Target System For Laser Ion Source

Laser ion sources are effective devices for the generation of pulsed highly charged ion beams,especially for solid elements.The combination of a laser ion source and RFQ?Radio Frequency Quadrupole?linac based on DPIS?direct Plasma Injection Scheme?can be used as the pre-injectors for heavy ion medical accelerators,which can greatly reduce the size and cost of the whole facility.Carbon ions and protons have their own advantages and complement each other in cancer therapy.Therefore,one of the trends in the development of hadron therapy facilities in the future is to provide both carbon ion and proton beams with the same facility.At present,the C⁶⁺ion beams produced by laser ion sources can satisfy the demands of single-turn injection of the synchrotrons for cancer therapy.In order to meet the needs of the future hadron therapy facilities,the production of proton beams with laser ion sources need to be studied.The emphasis of this thesis is focused on the development of a solidified hydrogen target system utilized on a laser ion source-one of the key technologies for the production of proton beams with a laser ion sources.There are mainly four methods for fabricating solid hydrogen targets:deposition,casting,condensation and extrusion.Taking account of the merits and drawbacks of the methods mentioned above,the characteristics of laser ion sources and the demands for target,it is determined to acquire solid hydrogen with the method of deposition.According to the parameters of the laser ion source at IMP and the planned laser shooting frequency,the calculation of the cooling capacity and the analysis of the heat loads are carried out.The two-stage G-M refrigerator?>1.5 W@4.2 K 35W@50K?is used as the cold source and the corresponding cryostat and its auxiliary system are designed,and the simulation results of ANSYS show that the designed cryostat can achieve the temperature required for the solidification of hydrogen.The experimental results of target fabrication and detection show that the cryostat has good performance.The solidification state of hydrogen can be optimized by adjusting the temperature of the first/second stage cold heads and the inlet hydrogen flow rate.It is estimated that the amount of solidified hydrogen is about26%of the inlet hydrogen,and lower temperature of the first and second stages are propitious to the solidification of hydrogen,moreover the larger amount of inlet gas?up to 60 Nml in the experiments?is beneficial to the survival of the hydrogen ice layer after heat absorption.A preliminary experiment was carried out to produce proton beam by laser shooting with the fabricated solidified hydrogen target.Each laser pulse ablates all solid hydrogen,it is confirmed that the proton beam has been produced,but the intensity of the produced proton beam is weak and the repeatability of the produced proton beam is poor.In the future,we will optimize the target configuration,laser parameters and shooting frequency to improve the intensity and repeatability of produced proton beam.