Velocity-selected magnetic guiding of Zeeman-decelerated hydrogen atoms

Abstract

Abstract. An original design of magnetic guide is presented, suitable for use with Zeeman-decelerated supersonic beams of ground-state hydrogen atoms and other light paramagnetic species. Three-dimensional particle trajectory simulations show that, by combining a series of permanent-magnet Halbach arrays with pulsed high-current wire electromagnets, this guide can be used to efficiently transmit the slow, decelerated atoms and discard the faster, undecelerated atoms and other species in the gas beam. The curved guide would be suitable for guiding hydrogen atoms into an ion trap to investigate low temperature ion-molecule collisions. It is also shown that the device could be used for the guiding or velocity selection from an undecelerated supersonic or effusive beam.

Preparation of individual magnetic sub-levels of $^4$He($2^3$S$_1$) in a supersonic beam using laser optical pumping and magnetic hexapole focusing

“…For the magnetic focusing of He(2 3 S 1 , M J = +1), we use a set of two Halbach arrays [44,45] in hexapole configuration, sketched in Fig. 1 (c), whose design has already been described previously [46,47]. Each hexapole array consists of 12 magnetized segments (Arnold Magnetic Technologies, NdFeB, N42SH, remanence of B 0 = 1.3 T) which are glued into an aluminium housing and placed on a position-adjustable rail at a center-to-center distance of 14.6 mm.…”

“…The magnetic field by the two Halbach arrays is implemented using the analytical expressions given in Ref. [47]. Particles are removed from the simulation if their transverse position inside a Halbach array exceeds the 3.0 mm inner radius of the assembly (cf.…”

“…If we assume the same He beam diameter as in the optical pumping experiments described above (i.e., 2.9 mm), the maximum efficiency η +1,max at the focal point is reduced to 84 %. To further improve the sub-level selectivity, we suggest the use of a bent magnetic guide [47,[51][52][53][54] or by the use of a central stop behind the Halbach arrays [35][36][37][38].…”

Manipulating hydrogen atoms using permanent magnets: Characterisation of a velocity-filtering guide

“…Secondly, a shutter would also transmit all species travelling at the same speed as the decelerated radicals of interest (such as slow-moving seed gas or precursor molecules). A filter such as a bent magnetic guide using hexapole magnets in a Halbach array (HA) configuration has been proposed, 12 but in such an approach, the target velocity range is determined by the radius of the bend and thus not easily varied.…”

A stand-alone magnetic guide for producing tuneable radical beams

“…A number of alternative designs have been proposed for bent magnetic guides, including overlapping pairs of quadrupole coils and combining current carrying wires with a series of Halbach arrays. [12][13][14] The curvature of a bent magnetic guide is fixed, chosen to suit a particular system of interest. As such, there is limited flexibility in the range of radical species that can be guided, and no ability to adjust the velocity range of the transmitted species; a bent guide can only act as a low-pass velocity filter, and therefore cannot provide continuous tunability in the radical beam velocity.…”