Simulation And Experimental Study On Dynamic Vacuum Effects On High Intensity Heavy Ion Accelerator

Heavy-ion accelerator is used to study the nuclear structure,the mechanism of nuclear reaction and nuclear process in the evolution of universe.The devel-opment of heavy-ion accelerators is to reach higher beam energy,higher beam intensity and higher beam power.In the heavy-ion accelerator,in order to achieve the required beam lifetime,the vacuum system of accelerator needs to remain ultra-high vacuum environment.When to operate accelerators with high intensity heavy-ion beam,the dynamic vacuum effects induced by beam loss will deteriorate the ultra-high vacuum environment,greatly reducing beam lifetime and affecting the operation of an accelerator.This thesis aims to stabilize the heavy-ion accel-erator vacuum system,and the main content of the thesis is to study the influence of beam loss on the accelerator vacuum system.The specific research contents include the study of beam loss distribution induced by the charge-exchange pro-cess,the study of the dynamic evolution of heavy-ion accelerator vacuum system with gas desorption induced by beam loss,and the study of gas desorption yield measurement with beam bombardment.Firstly,based on the beam optics,the characteristics of the charge-exchanged particles loss are studied.The track of heavy ion beam U³⁵⁺after losing one elec-tron is simulated,and the loss distribution of U³⁶⁺is obtained.The thesis also simulates the situation that the beam collimators are on-line.With calculated beam envelop,the collimation efficiency can be kept above 99%without affecting circulating beam.Secondly,the thesis studies some important beam loss mecha-nisms occurring in heavy-ion accelerators,and builds dynamic beam loss numerical model.Thirdly,a basic vacuum theoretical derivation is carried out,and the vac-uum conductance of BRing vacuum system is calculated.Lastly,based on the loss characteristics of charge-exchanged particles in the synchrotron,a simulation process for calculating the dynamic vacuum evolution is established.Based on the mentioned simulation process for calculating the dynamic vac-uum change over time,the thesis simulates the evolution of BRing vacuum system with high intensity heavy-ion beam U³⁵⁺.On the one hand,the influence of beam intensity on the BRing vacuum system is studied.The present BRing design can make sure that the vacuum system can remain stable with U³⁵⁺beam intensity1×10¹¹ppp.But when the beam intensity exceeds 3.5×10¹¹ppp,the average vac-uum pressure of BRing will increase to about 2×10^-9mbar and therefore the beam lifetime is severely affected.On the other hand,the thesis studies the influence of the beam system loss.The simulation results show that the vacuum pressure fluc-tuations induced by different injection loss percentage can be stabilized in time by the pumps with high pump speed distributed in the injection section.In general,the BRing vacuum system design fully considers the influence of dynamic vacuum effects,and the average vacuum pressure can satisfy the requirement when the vacuum system reach the new dynamic balance.At the end of the thesis,the gas desorption yield measurements with beam bombardment are carried out.The vacuum pipe with different surface treatment has different gas desorption yield.The gas desorption yield is one of the most important input parameters for the dynamic vacuum simulation.The gas des-orption yield of pipe surface is related to the beam type and beam energy.The experiment conducted on the 320 kV High Voltage Platform measures the gas des-orption yield with Xe¹⁰⁺beam and O¹⁺beam under different energy conditions,and experiment conducted on the SSC-Linac also obtains the gas desorption yield with U³⁵⁺bombarding different target materials.The scaling rule between gas desorption yield and the electronic energy loss of particles is also verified.The the-sis provides experience for the further study of gas desorption yield measurements with heavy-ion bombardment in the future,and the obtained gas desorption yield can be reference data for the simulation of BRing dynamic vacuum effects.