Caught In A Trap: Monte Carlo Methods For A Travelling-Wave
Zeeman Decelerator

Abstract

Our group has previously designed and constructed a modular travelling-wave Zeeman decelerator, incorporating a pulsed-valve supersonic expansion source with dielectric barrier discharge. The decelerator comprises a set of custom-made flattened helical coils driven by a bespoke programmable power electronics control system. The decelerator produces very strong longitudinal magnetic forces that generate an effectively three-dimensional moving trapping potential, compared to a `conventional' Zeeman decelerator. An additional transverse focussing field was originally added by a wire quadrupole circuit, with a possible replacement being constructed from permanent magnets. The decelerator is intended as a loading stage for a novel hybrid magnetic trap / magneto-optical trap, designed for the sympathetic cooling of atomic or molecular species for which conventional laser cooling is not an option.

This thesis describes some proposed adjustments and enhancements to the experimental apparatus. A suite of software tools has been developed in order to simulate the various components of the experiment. By its nature the travelling-wave decelerator produces a complex signal at a detector and Monte Carlo analysis has been necessary to understand it. For each part of our simulation process the theoretical underpinning and physical implementation is detailed. Models for fitting and characterising supersonic beam data are developed and demonstrated, and applied to the generation of simulated expansions. Key to the operation of the dynamical simulations is a novel interpolation library which is used to solve particle motion in time-dependent magnetic fields. Computer codes for calculating Stern-Gerlach type forces in different species are described. The phase-space acceptance of the decelerator and proposed trap are estimated.

Metastable argon has been guided and decelerated for the purposes of characterising the decelerator; data is presented and analysed, showing a demonstrable reduction by 6~ of the kinetic energy of a portion of the beam. Predictions show that this could be increased to ~ 14% for the decelerator in its current state, and up to ~ 30% should be achievable for the case of argon with a proposed extension of the deceleration stage.

Further predictions are made regarding the deceleration of other species of scientific interest, including a dual-species beam of hydrogen and lithium. Some preliminary results regarding the suggested hybrid trap design are given.