Offline Commissioning of the St. Benedict Gas Catcher

Abstract

Precision measurements of $β$ decay transitions offer a promising channel through which the Standard Model (SM) can be probed. There is currently an ongoing effort to increase the precision on measurements of $\mathcal{F}t$-values for superallowed $β$ decay transitions between mirror nuclides. These allow for a determination of $V_{ud}$ which is complementary to that obtained from pure Fermi $0^+ \rightarrow 0^+$ transitions. The Superallowed Transition BEta-NEutrino Decay Ion Coincidence Trap (St. Benedict), under construction at the Nuclear Science Laboratory (NSL) at the University of Notre Dame, seeks to measure the Fermi-to-Gamow-Teller mixing ratio for transitions between mirror nuclei in order to expand the list of nuclides from which $V_{ud}$ can be extracted. Production and selection of the species of interest will be done in-flight, using the \textit{TwinSol} magnetic separator system. The first element of St. Benedict will be a large volume gas catcher which will thermalize radioactive ion beams for low energy delivery to the rest of the system. Offline commissioning of this gas catcher has been completed using an internal potassium source, and the device demonstrated a transport efficiency upwards of 95\% for pressures of 66 mbar and lower.

Figures (12)

• Figure 1: Cross sectional diagram of the gas catcher during offline commissioning with all of the independently tunable electrodes labeled. (A) is FC2, (B) is the location of the "cone low" electrode, (C) marks the end of the body electrodes and beginning of the cone, where "body low" and "cone high" sit next to each other, (D) marks the location of the "body high" electrode, (E) is FC1, shown in its retracted position, (F) is the ion source and square anode plate, and (G) is the window. The thicker electrodes in section 2 and 3 are the spokes on those electrodes. The "nozzle" electrode is represented here as the vertical line between the cone and FC2. This image was generated with the SIMION program.
• Figure 2: Photo of the gas catcher during offline commissioning. Beam direction is from right to left. (A) is an MKS type 121A Absolute Baratron Manometer mounted to measure the pressure in the main volume of the chamber. (B) is a Piezogauge mounted on the exit side of the nozzle. (C-E) are the transformers which supply RF power to the cone (C), section 1 (D), and sections 2/3(E) of the electrodes. (F) is the linear drive used to move FC1 in and out of the path of the ions. (G) is the insulated VCR-O gas line used to supply helium.
• Figure 3: Relationship between applied power and corresponding peak-to-peak voltage for each of the RF sections. Voltage amplitudes were measured at both ends of the secondary pickup coil in order to measure RF phase difference. Uncertainties denote the difference between signals of opposite phase.
• Figure 4: Head-on view of the ion source. The plate and the source were electrically isolated from each other and could be independently biased.
• Figure 5: View of the entrance-side collection plate. The plate was attached to a linear drive fed through the top of the chamber. A thin, Kapton insulated copper wire carried current readings from the plate to a BNC feedthrough.