EPAC is a new national facility based at Central Laser facility at Rutherford Appleton Laboratory. It will bring together world-leading interdisciplinary expertise to develop and apply novel, laser based, non-conventional accelerators and particle sources which have unique properties. EPAC offers a unique opportunity for accelerator and laser experts from ASTeC to work together with Central Laser Facility staff on an exciting project.
The Accelerator Physics group is designing novel beamlines to effectively capture and transport Laser Wake Field Accelerated (LWFA) electron beams generated at EPAC. The high gradients offered in LWFA can generate high energy beams in a short distance with exceptionally high brightness. But since these beams are highly diverging, it needs a novel design using advanced permanent magnet quadrupoles to capture as close to the source as possible and careful transport to preserve the beam quality. This work involves synergetic collaborations marrying PIC-based LWFA simulation codes with accelerator physics tracking codes to investigate space-charge and coherent synchrotron radiation collective effects, along with novel work on magnet fringe-fields and aberration correction schemes. We will also investigate beam matching in the presence of plasma density down-ramp and similar schemes.
The Magnetics and Radiation Sources (MaRS) group are working closely with the design team at EPAC on the design of magnets for this advanced machine. A high-performance energy spectrometer is in the magnet design stage; this device needs a 1.8 T field to disperse electrons and positrons simultaneously over a very wide energy range (1-6 GeV). The good field region needs to be carefully controlled to ensure a high resolution, giving accurate measurements of the beam's energy. The MaRS group are also producing magnet designs for the triplet of quadrupoles required to focus an accelerated beam immediately after the plasma acceleration stage. These magnets are planned to be a scaled-down version of our ZEPTO quadrupole prototypes.
Femtosecond Laser and Timing and Accelerator Diagnostics and Instrumentation groups at ASTeC are spear-heading development of longitudinal bunch length and profile measurement diagnostics for EPAC using interaction with a THz pulse, which will be very challenging due to ultra-short bunch length and high electron energy from the novel LWFA scheme. Both avenues of THz pulse generation, induced by the bunch itself and external laser driven THz source, will be explored along with different interaction structure designs to enable efficient bunch streaking. Detailed simulations will be carried out using advanced nonlinear optical interaction codes and PIC based particle and electromagnetic field evolution codes. We will also investigate possibility of applying electro-optics (EO) technique for this measurement.
The vacuum solutions group are working to understand and model the challenging vacuum design for high-pressure gas experiments on EPAC. The design of the vacuum system is critical to maintain vacuum pressures in the beamline and handle the high gas loads, our recent experience in designing FEBE give us a unique insight into the challenges this presents.
The project will enhance a long-standing ASTeC collaboration with the SCAPA facility at the University of Strathclyde, and both the SCAPA and EPAC facilities have separate, but complimentary, goals to the FEBE@CLARA project. This work should enhance the capabilities of all three projects. EPAC is synergetic with the development of similar diagnostics for FEBE (and possible FEL) facility on CLARA with less extreme beam parameters of 250 MeV beam energy and FWHM bunch length of 70 fs, and this work will build upon and enhance the existing skills and capabilities of the groups. We are already benefitting from the deep knowledge and experience built up over many years by the CLF in transporting and focusing high power lasers onto a target as we have the ambition to interact a high power laser with the electron beam at FEBE for complementary novel acceleration experiments.