Experimental Study Of Intrabeam Scattering Effect In Duke Storage Ring

The light brightness is an essential parameter for synchrotron radiation light sources.For the electron storage ring based light source,the light brightness is critically de-pendent on the electron beam emittance of the storage ring.Therefore,a high brightness light source demands an electron storage ring with a low beam emittance.However,due to the intrabeam scattering(IBS)effect,the electron beam emittance grows with increasing beam current.In general,the intrabeam scattering effect is studied experimentally by measuring the electron beam emittance.The beam emit-tance is typically obtained by measuring the transverse electron beam size using synchrotron radiation.In order to measure the transverse beam size,a new and advanced transverse beam profile measurement system has been developed for the Duke storage ring.This system is optimized to achieve good spatial resolution and characterized for precision measurements.Using this beam profile measurement sys-tem and other diagnostic systems,the intrabeam scattering effect has been studied experimentally on the Duke storage ring.In addition,a project to compensate for the leakage magnetic field due to the Duke FEL wiggler bussbar has been carried out and its results are reported.For a low energy storage ring,the direct imaging method using visible/UV light is a suitable method for beam profile measurements.It has an advantage of being sim-ple,straightforward,and cost-effective.The resolution of such a system can be quite adequate for measuring electron beams with a reasonably large transverse beam size.Using this method,we have developed a new transverse beam profile measurement system for the Duke storage ring.This new system has been fully characterized to al-low absolute measurements of the electron beam size while achieving a better system resolution than previously thought possible for the direct imaging technique.The resolution of the new system is about 30 μm based on the estimation and measure-ment results.The preliminary measurement results show that this system is capable of measuring the horizontal beam size over a wide range of the electron beam ener-gies and beam currents.The system has also been demonstrated as a useful tool to study the intrabeam scattering related emittance increase in the storage ring.While experimental studies of the intrabeam scattering effect have been carried out at several storage rings,including 1.5 GeV electron storage ring at KEK labora-tory and Cornell Electron Storage Ring at Cornell University,these works did not explore the impact of beam coupling,nor for the electron beam over a wide range of energies.The Duke storage ring is an unique accelerator which allows for the study of the intrabeam scattering effect experimentally over a wide range of beam energies and for various beam configurations such as a varying degree of transverse coupling.This dissertation focuses on the experimental study of the intrabeam scattering ef-fect by carrying out these projects:(1)measuring the three-dimensional profiles of the electron beam over a wide range of beam energies(280 MeV to 1 GeV)and beam currents(near zero current to 20 mA);(2)measuring the three-dimensional beam profiles with beam coupling;(3)comparing experimental data with simulation results.Overall,the measurement results are found in agreement with simulation results(based upon Bjorken and Mtingwa model)for the range of parameters that the simulator model is suited for.The Duke storage ring is a dedicated driver for the storage ring based free-electron lasers(FEL)and the High Intensity Gamma-ray Source(HIGS).The monochromatic Gamma-ray beam is produced using Compton scattering between the electron beam and FEL photon beam.The electron beam orbit displacement and its angle at the collision point are two essential factors which can impact the quality of the gamma-ray beam.To maintain consistent e-beam orbits for a range of currents for the FEL wigglers which are electromagnets,and for different electron beam energies,the leak-age magnetic field due to wiggler bussbars needs to be compensated.As a variety of the wiggler configurations are used,a generic compensation scheme is complicated.A specialized compensation scheme for a particular wiggler configuration using two helical OK-5 wigglers has been developed using a beam based technique and a singu-lar value decomposition algorithm.The measured results show that the beam orbit can be efficiently corrected around the storage ring.With the proper implementa-tion of the bussbar field compensation system,the rms orbit distortion is reduced by a factor of 19 and 17 in horizontal and vertical directions respectively.The max-imum residual orbit distortions are small to allow consistent Compton gamma-ray production in the Duke storage ring.