16th International Conference on Muon Spin Rotation, Relaxation and Resonance (μSR2025)

Holding High Bias Reliably

Not scheduled

20m

Poster Presentation Beamlines and instruments Poster session 2

Speakers

Mr River Tranter-Tiffin (Queen's University) Sarah Dunsiger (TRIUMF / Simon Fraser University)

Description

The current beta-NMR/beta-NQR spectrometers in ISAC-1 at TRIUMF constitute a unique research tool, enabling spin polarised ions (typically 8Li+) to be controllably implanted at a depth of between 5 – 200 nm within a material for investigations of thin films and artificial heterostructures. This involves decelerating 8Li+ beams through the generation of a “hill” in the electrostatic potential by raising the entire beta-NMR spectrometer to high voltage (HV) bias. Of necessity, the HV-biased platform must be isolated from ground using a ceramic break in the beamline vacuum envelope, creating an electromagnetic triple point, a junction of metal, insulator and vacuum. Due to the geometry and differences in dielectric properties, the electric field at a triple point can be significantly higher than surrounding areas, potentially leading to the emission of electrons, cascading into a problematic breakdown in high vacuum.

We discuss an OPERA3D simulation of the electric and magnetic fields at the interface of the radioactive ion beamline and high magnetic field beta-NMR spectrometer. Computed field maps are used to address several spectrometer design issues. The geometry of metallic parts may be optimized to suppress electric fields in the vicinity of the triple point. Additionally, field maps are used in ion beam transport simulations; the trajectories of outgoing decay electrons are also subject to strong magnetic fields, impacting the optimal placement of detectors.