Abstract
We have conducted a multiobjective computational optimization of a high brightness, high average current photoinjector under development at Cornell University. This injector employs a dc photoemission electron gun. Using evolutionary algorithms combined with parallel computing resources, the multivariate parameter space of the photoinjector was explored for optimal values. This powerful computational tool allows an extensive study of complex and nonlinear systems such as the space-charge dominated regions of an accelerator, and has broad areas of potential application to accelerator physics and engineering problems. In the present case, the optimized injector is simulated to deliver beam of very high quality (e.g., a rms normalized emittance of 0.1 mm mrad for 0.1 nC, and 0.7 mm mrad for 1 nC bunches). The field strengths of the active elements of the injector are moderate and technically practical. The relevance of these results to various novel linac-based accelerator proposals is pointed out.
Highlights
The successful operation of a cw energy recovery linac (ERL) with moderate beam current for the Jefferson Laboratory free electron laser [1], combined with the demonstration of reliable high gradient operation of cw superconducting accelerator cavities at several laboratories [2,3], has led to great current interest in developing ERLs for a number of applications
Prior to the development of ERLs, the need for high average current electron injectors was limited by the practical problems in accelerating such currents to even moderate beam energies
We show how the use of multiobjective evolutionary algorithms helped us address the following questions: What is the optimal transverse and longitudinal shape of the laser pulse? How high should the gun voltage be for good injector performance? How does the thermal emittance of the photocathode affect the final emittance? What are the trade-offs between bunch length, emittance, and bunch charge? We conclude with a brief discussion of our results, and the prospects for future developments using this powerful computational technique
Summary
The successful operation of a cw energy recovery linac (ERL) with moderate beam current for the Jefferson Laboratory free electron laser [1], combined with the demonstration of reliable high gradient operation of cw superconducting accelerator cavities at several laboratories [2,3], has led to great current interest in developing ERLs for a number of applications These applications include electron cooling [4], very high power free electron lasers, linac-ring versions of an electron-ion collider [5], and the production of high brightness, short pulse synchrotron radiation x-ray beams [6]. Most high average current electron injectors have employed dc electron guns delivering cw or long pulse beams from gridded thermionic emission cathodes The beam from these guns is drift bunched, sometimes following rf chopping, subharmonic bunching, or prebunching systems, to produce a bunched beam for subsequent acceleration. The emittance is limited by the relatively high thermal emittance of the cathode, effects due to the grid, and emittance growth during the bunching process
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