1 / 33

Simulation and Optimisation of the JLab/AES DC Photo-injector

Simulation and Optimisation of the JLab/AES DC Photo-injector. Fay Hannon. Overview. Background specification Simulation 135pC scenario By hand Multivariate optimisation Simulation 1nC Conclusions. Background. Designed by Advanced Energy Systems

brian-cabrera
Download Presentation

Simulation and Optimisation of the JLab/AES DC Photo-injector

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Simulation and Optimisation of the JLab/AES DC Photo-injector Fay Hannon

  2. Overview • Background • specification • Simulation 135pC scenario • By hand • Multivariate optimisation • Simulation 1nC • Conclusions

  3. Background • Designed by Advanced Energy Systems • Many iterations (7 cell +/- 3rd harmonic) • Now a demo of 1nC/135pC • Not completely modelled at AES in present form • Possible upgrade route

  4. Injector Layout Minimise the drift between gun and accelerating cavities. Single cell cavities. 750MHz

  5. Specification For 7 cell design

  6. Simulation: ASTRA model • A Space-charge TRacking Algorithm • For rotationally symmetric components on-axis field maps give good approximation. Radial E and B fields generated from derivative. • Can be fully 3D • Field maps created using SUPERFISH/ POISSON

  7. Layout & Field Maps

  8. Simulation technique • By hand: aim for spec. • Piecewise methodology, starting with gun and solenoid • Parameter scans • Start with 135pC (easier) case & FEL laser properties for initial distribution • Thermal emittance excluded – rough modelling • Difficult to meet the target energy

  9. 135pC Simulation

  10. Results 135pC JLab laser parameters assumed for initial distribution

  11. Multivariate Optimisation Ivan Bazarov @ Cornell 100mA injector with DC gun – showed improved design. Evolutionary algorithm Can optimise a number of beam parameters simultaneously • Start with 2 objectives: minimise longitudinal and transverse emittance • After a number of generations solutions converge on an optimisation front • Pick solution that is best suited to the application

  12. PISA Platform and programming language independent Interface for Search Algorithms Institute of Technology, Zurich Evaluate candidate solutions -> select promising candidates -> generate new candidates by variation - Text based interface for search algorithms - Consists of 2 parts: variator and selector

  13. Selector: algorithm specific operations. Assigning fitness functions. Creating new mating pools from the better solutions. Various selector modules can be chosen eg. Simulated annealing, genetic algorithms. Variator: Problem specific. Objectives, decision variables and constraints. Crossing and mutation operators that act on the candidates chosen by selector. Variator includes a parallel implementation of ASTRA. Variator and Selector talk to each other via a state machine and common text files

  14. Initial Population Decision variables Field strengths – phases etc Evaluate: ASTRA & parallel processing J-Lab HPC 5*128 node cluster (24hr limit) Constraints (spec) Objectives ‘fitness’ evaluated Solutions Mating pool created from best solutions. Crossing & mutation New Population ++ Generation

  15. 100mA Optimisation Problem Decision variables (10) Laser spot size Solenoid B 4 cavities: max gradient and phase Constraints (7) Bunch length < 3mm KE >7 MeV Longitudinal emittance < 55 keV mm Transverse size > 1.0 mm Energy spread < 70keV <x.x’>,<z dE> < 0 Objectives (2) Minimise transverse emittance Minimise longitudinal emittance Selector Module: Strength pareto evolutionary algorithm 2 (SPEA2)

  16. Problems noted… Tail overtakes the head.

  17. Decision Variables

  18. 128 population 200 Generations 1k Macro-particles Tracked to 5m Evolution

  19. Results 135pC – 100 generations Population size 128, 200 generations, 1k macro-particles for ASTRA.

  20. Results 135pC – 200 generations Doesn’t meet longitudinal emittance spec of 15keV mm Other constraints met

  21. Results 135pC – XYrms 1 – 2.5mm Improvement – spec not met. Thermal emittance/halo increases.

  22. Try to re-arrange Conventionally 3rd harmonic cavities are placed last in an injector purely to make the longitudinal phase space linear

  23. Best Solution Comparison

  24. Best Solution Comparison Absence of a dedicated buncher cavity makes longitudinal spec. difficult to meet. First cell and 3rd harmonic doing the bunching.

  25. Energy trade off 7MeV was goal of 7 cell design. Energy can be reduced for demo. Lower energy – can get close to longitudinal spec

  26. Energy Trade Off

  27. What if bunch length a variable? 128 population 200 Generations 1k Macro-particles Tracked to 5m Trms < 10ps, Meet specification at 7MeV

  28. 1nC Simulation

  29. 1nC (7MeV constraint) Unsuccessful in achieving both goals (<45keV mm, <10um)

  30. 1nC Case All possible solutions (meeting spec) are below 5.5MeV

  31. Solution (4.6MeV)

  32. Shorter laser pulse Not typical optimal front because not enough generations

  33. Conclusions & Future plans • Specification can be met in both cases when the target energy is lowered to ~5MeV • Spec and 7MeV can be met if laser pulse is 10ps duration • Multivariate optimisation is an excellent tool for injector design (operating points and dependencies) • More cells – greater flexibility • Currently under construction at JLab • Gun & laser ready. Diagnostic beamline in design • More detailed simulation (thermal emittance, realistic distributions, macro particles)

More Related