Off-line Commissioning of the St. Benedict Radio Frequency Quadrupole Ion Guide

Abstract

The Superallowed Transition Beta-Neutrino Decay Ion Coincidence Trap (St. Benedict) is currently under construction at the Nuclear Science Laboratory (NSL) of the University of Notre Dame. It aims to measure the beta-neutrino angular correlation parameter for superallowed mixed mirror beta decay transitions. Measurements of this kind offer unique insight into the electroweak part of the Standard Model through tests of unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) matrix. St. Benedict is comprised of several beam-manipulating components including a radio frequency quadrupole (RFQ) ion guide. This ion guide features an off-line source at $90^\circ$ to the beam path for testing and calibration of downstream components once St. Benedict is online. Off-line commissioning of the ion guide demonstrated a transport efficiency greater than 95% for ions coming from the upstream RF carpet chamber. When taking ions from the $90^\circ$ off-line source a lower efficiency of 60% was obtained.

Figures (13)

• Figure 1: A diagram displaying each of the four main components of St. Benedict
• Figure 2: A diagram of the St. Benedict radio frequency quadrupole ion guide off-line commissioning setup. (a) Head on view displaying the quadrupole structure of the rods. (b) Side view of the RFQ ion guide displaying the segmentation of the rods, the 90° ion source, both apertures as well as the lens and Faraday cup electrodes. The supporting frame has been removed for clarity.
• Figure 3: (A) The 90° source as shown in reference to (B) the ion guide rods and (C) the supporting framework.
• Figure 4: The ion guide RF circuit displaying A) an open air transformer leading into three separate circuits for each section of the ion guide. Each section contains B) two secondary inductors and C) a variable capacitor. D) A switch is used to add or remove RF from the lower two rods of the center section. E) Also shown is the ion guide mounted to the ceiling of its chamber.
• Figure 5: The off-line set up for the commissioning of the Ion Guide showing A) the flange containing the $^{39}$K source and the feed-through for the He gas. B) the nipple containing the RF carpet and C) the circuitry for the RF carpet. Also shown is D) the ion guide circuitry mounted in its final location and E) the location of the ion guide. Finally F) the nipple containing the two lens electrodes and G) the cross with a turbomolecular pump attached allowing for the evacuation of the chamber containing the Faraday cup. H) A copy of the RF carpet installed in the vacuum chamber.