Production Of High-quality Beams Research Articles

Design principles for high quality electron beams via colliding pulses in laser plasma accelerators

Laser plasma based accelerators have the potential to reduce dramatically the size and cost of future particle colliders and light sources. Production of high quality beams along with reproducibility, tunability, and efficiency are required for many applications. We present design principles for two-pulse colliding laser pulse injection mechanisms, which can meet these requirements. Simulations are used to determine the best conditions for the production of high quality beams: high charge, low energy spread, and low emittance. Simulations also allow access to the internal dynamics of the interaction, providing insight regarding further improvement of the beam quality. We find that a 20 pC beam can be accelerated to 300 MeV in 4 mm with only a few percent energy spread and transverse normalized emittance close to 1 mm mrad, using a 10 TW laser. We demonstrate that this design scales according to linear theory. Control of the laser pulse mode content and subsequent evolution in the plasma channel are shown to be critical for achieving the highest beam quality.

The C-Band accelerating structures for SPARC photoinjector energy upgrade

The use of C-Band structures for electron acceleration and production of high quality beams has been proposed and adopted in several linac projects all over the world. The two main projects that adopted such type of structures are the Japanese Free Electron Laser (FEL) project in Spring-8 and the SwissFEL project at Paul Scherrer Institute (PSI). Also the energy upgrade of the SPARC photo-injector at LNF-INFN (Italy) from 150 to more than 240 MeV will be done by replacing a low gradient S-Band accelerating structure with two C-band structures. The structures are Traveling Wave (TW) and Constant Impedance (CI), have symmetric axial input couplers and have been optimized to work with a SLED RF input pulse. The paper presents the design criteria of the structures, the realization procedure and the low and high power RF test results on a prototype. The high power tests have been carried out by the Frascati INFN Laboratories in close collaboration with the Japanese Laboratory KEK. Experimental results confirmed the feasibility of the operation of the prototype at 50 MV/m with about 10−6 breakdowns per pulse per meter. Such high gradients have not been reached before in C-Band systems and demonstrated the possibility to use C-band accelerators, if needed, at such high field level. The results of the internal inspection of the structure after the high power test are also presented.

Conception and performance of the new Lagrippa facility

A new Lagrippa facility has been constructed for the production of high quality beams of multicharged ions with energies of 1–25 q keV. The machine is based on the new 10 GHz, Caprice ECR-ion source which operates partially on the second harmonic. A new extraction optics for ECR sources with variable electrode distance has been employed which allows high currents at an emittance of less than 40 π mm mrad (corresponding to a beam spot of a diameter less than 4 mm with a divergence ≤±20 mrad). Together with an acceleration–separation–deceleration scheme this machine furnishes beam currents of 11 μA O7+ at 15 q keV, 80 pA Ar17+ at 20 q keV, 6 pA Ar17+ at 20 q keV, and a significant current of Kr31+. Further details of the conception of the machine, its performance, and the first experiments up to June 1989 will be presented.