Adjustable, short focal length permanent-magnet quadrupole based electron beam final focus system

Abstract

Advanced high-brightness beam applications such as inverse-Compton scattering (ICS) depend on achieving of ultrasmall spot sizes in high current beams. Modern injectors and compressors enable the production of high-brightness beams having needed short bunch lengths and small emittances. Along with these beam properties comes the need to produce tighter foci, using stronger, shorter focal length optics. An approach to creating such strong focusing systems using high-field, small-bore permanent-magnet quadrupoles (PMQs) is reported here. A final-focus system employing three PMQs, each composed of 16 neodymium iron boride sectors in a Halbach geometry has been installed in the PLEIADES ICS experiment. The field gradient in these PMQs is 560 T=m, the highest ever reported in a magnetic optics system. As the magnets are of a fixed field strength, the focusing system is tuned by adjusting the position of the three magnets along the beam line axis, in analogy to familiar camera optics. This paper discusses the details of the focusing system, simulation, design, fabrication, and experimental procedure in creating ultrasmall beams at PLEIADES.

Miniature magnetic devices for laser-based, table-top free-electron lasers

“…9. Three-dimensional field simulations (CST EM Studio) as well as electron tracking simulations revealed a sufficient optical quality of this simple design, comparable to the more complex one recently realized by the PLEIADES group [12].…”

“…On the one hand, the absolute field on the magnet poles B r i has to be maximized while, on the other, the bore radius r i has to be minimized. A reasonable compromise can be achieved for r i 3 mm and B r i 1:5 T leading to a gradient of the order of 500 T=m [12]. Here, a simple and economical design has been chosen, where the quadrupole field is defined by four radially magnetized wedges of Nd 2 Fe 14 B magnets [15].…”

“…High gradient and thus short focal-length magnetic lenses have the potential for generating focal spots in the sub-micron range. These could be used as pointlike sources of hard radiation for phase contrast imaging with unprecedented transverse coherence [11], for compact Thomson scattering sources [12], or for the localized deposition of high radiation doses. Short focal-length lenses are further mandatory for the compact relay imaging of electron bunches between consecutive acceleration stages in cascaded laser-plasma acceleration schemes.…”

Award Final Technical Report

“…The initial work written up in an article that has been published in PRSTAB. 43 The development of this unique scientific tool has caused considerable notice in the field; a similar system has been adopted at the Neptune ICS experiment, and is under study for adoption at SLAC and LBNL experiments. The technology itself has also been licensed by UCLA to RadiaBeam Technologies for commercial development.…”

Metamaterial anisotropic flux concentrators and magnetic arrays

“…Permanent magnet constructions that produce a powerful magnetic flux density, either uniformly or with a prescribed spatial variation, in a specified volume are used in a number of applications, such as nuclear magnetic resonance (NMR) equipment, 5,6 accelerator magnets 7,8 and magnetic refrigeration devices. 9,10 A widely used permanent magnet configuration is the so-called Halbach cylinder which can generate either a uniform flux density or a multipole field.…”