Study On Beam Losses And Radiation Fields In High Intensity Cyclotrons

High-energy and high-intensity accelerators are widely used in many diferent scien-tific disciplines, ranging from nuclear physics to medicine and beyond. When increasingthe beam intensity, demanded by many present and future projects, beam loss and result-ing radiation fields are of primary concern.In order to avoid conservative designs in which the source of the radiation field isgiven based on experience, a detailed analysis of beam losses are mandatory to allow pre-cise prediction of radiation field. In this thesis, mechanisms and computational methods ofbeam losses in high-intensity H cyclotrons are analyzed in detail. The distribution func-tion of beam loss in the6D phase space is obtained and is used to calculate the radiationfield. The maximum intensity is given according to the limit of the radiation field.Main points of this thesis are:1) Beam losses in high-intensity H cyclotrons are described and analyzed by meansof, Lorentz stripping losses, residual gas stripping losses, extraction region losses and thelosses caused by space charge efects. Particle tracking, including these physics processes,enables the calculation of beam loss in the6D phase space in the accelerator. This allowsthe precise determination of radiation fields.2) The efect of space charge on beam losses is studied combing theory, experimentand simulation. a) The necessary physics and post processing tools are incorporated intothe general particle tracking program OPAL. The3D space charge and efects from parti-cle matter interactions can be computed together, with enough statistics to make realisticpredictions on beam losses in present and next generation high intensity particle accel-erators. b) An analytical model based on the negative mass instability is introduced toexplain the formation of the breakup of a coasting beam into small clusters in isochronousmachines such as the small isochronous ring (SIR) of Michigan State University (MSU).The relationship between the fastest-growing instability mode and the beam parameters,such as energy, bunch length, intensity, and emittance, is obtained analytically. The theoryis applied to the100MeV H cyclotron (CYCIAE-100) under design and construction atChina Institute of Atomic Energy. c) Several experiments combing theory analysis andsimulations are performed at the590MeV Ring cyclotron at the Paul Scherrer Institut (PSI), predicting limiting tails of the beam distribution at the extraction septum on levelsof3σ～4σ. The results can be seamless extrapolated to future high power cyclotrons, toenable the precise prediction of crucial parameters, such as losses, based on an existingcw megawatt facility experiences.3) The prompt and residual radiation fields in the vault of CYCIAE-100are calcu-lated based on the beam loss distribution. The radiation field limits in CYCIAE-100areobtained in accordance to operating experiences of accelerators worldwide. An intensitylimit for CYCIAE-100is obtained and several methods are proposed to increase the limit,without compromising the loss and radiation budget.