Permanent Magnet-Based Quadrupoles for Plasma Acceleration Sources

Abstract

The laser plasma accelerator has shown a great promise where it uses plasma wakefields achieving gradients as high as GeV/cm. With such properties, one would be able to build much more compact accelerators, compared to the conventional RF ones, that could be used for a wide range of fundamental research and applied applications. However, the electron beam properties are quite different, in particular, the high divergence, leading to a significant growth of the emittance along the transport line. It is, thus, essential to mitigate it via a strong focusing of the electron beam to enable beam transport. High-gradient quadrupoles achieving a gradient greater than 100 T/m are key components for handling laser plasma accelerator beams. Permanent magnet technology can be used to build very compact quadrupoles capable of providing a very large gradient up to 500 T/m. We present different designs, modeled with a 3D magnetostatic code, of fixed and variable systems. We also review different quadrupoles that have already been built and one design is compared to measurements.

Vacuum ultraviolet coherent undulator radiation from attosecond electron bunches

“…The electron beam is quasi-collimated, with a waist located one period (4 cm) upstream from the undulator entrance, and divergence of 0.05 mrad, corresponding to an initial beam size of about 100 for 100 MeV and 40 for 250 MeV. This beam size and divergence is compatible with a laser-driven electron beam collimated using permanent quadrupole magnets 46 . A smaller beam size would be preferable to optimise the transverse form factor, but space-charge effects would be stronger.…”

Ultrafast electron diffraction: Visualizing dynamic states of matter

“…g is the quadrupole gradient and strongly depends on the gap size. For small gaps (mm-scale) quadrupole gradients approaching g ' 1000 Tesla/mm are achievable (Ghaith et al, 2019). In order to get focusing in both directions, the most common configuration is the quadrupole triplet where three quadrupoles with alternating orientations are used.…”

Electron Beam Brightness and Undulator Radiation Brilliance for a Laser Plasma Acceleration Based Free Electron Laser

“…Superconducting magnets come in handy for such applications but they are much more expensive than the conventional electro-magnets due to the cryogenic cost (installation and operation) and the possibility of a quench as a result of heating originating from synchrotron radiation and image charges. Permanent magnet based quadrupoles eliminate the need for power supplies, cables and the large element of infrastructure for the water cooling system and can be reduced in size without losing the magnetic field strength making them suitable for compact applications such as LPA [23].…”

“…The laser beam is focused by an off-axis parabola into a gas mixture composed of 99% He and 1% N 2 . The first magnetic element is a triplet of tunable high gradient permanent magnet-based quadrupoles (QUAPEVA) [23,45,46], placed 5 cm from the electron source. The triplet strongly focuses the LPA electron beam and permits to handle the large divergence at an early stage of the transport and mitigate the emittance growth.…”