A calorimetric wire detector for measurement of atomic hydrogen beams

Abstract

The Project 8 collaboration aims to determine the absolute neutrino mass with a sensitivity of 40 meV by measuring the tritium decay spectrum. Project 8 will use atomic tritium confined in a magnetic trap to perform CRES on decay electrons produced directly in the trap and performing cyclotron motion in the same magnetic field.

Reaching the desired sensitivity will require the observation of a large number of tritium decays, since a tiny fraction ($\approx$\qty{e-13}) of all decays produce an electron sufficiently close to the endpoint to be informative for the neutrino mass. Additionally, since molecular tritium sensitivity receives a large statistical penalty to energy resolution caused by the molecular final state distribution, atomic tritium must be used for the desired sensitivity.

Project 8 must develop an atomic tritium beamline capable of injecting $\gtrsim 10^{14} \mathrm{atoms}\,/\mathrm{s}$ into the CRES detection volume. Due to losses in cooling, injection, and trapping, we anticipate that this will require an atomic tritium source that initially produces an atom flux of $\gtrsim 10^{18} \rm{atoms/s}$. The development of such a source is currently underway, and a candidate, the HABS, is used for measurements presented in this thesis.

This thesis focuses on the development of a calorimetric wire detector capable of measuring the intensity and distribution of atomic hydrogen beams as required by Project 8. The detector uses a wire with a micrometer-scale diameter intersecting the beam on which a small fraction of the beam's hydrogen atoms recombine into molecules. The energy released heats the wire and produces a measurable change in its resistance.

We present measurements performed with such a detector to determine the distribution of hydrogen atoms across a beam produced by the test source, and present limits on the total flux of atoms that are produced by this source. We also present a theoretical description of the wire detector, including a simulation.

The results directly contributed to a better understanding of the HABS showing the utility of the calorimetric wire detector in further development of the atomic tritium beamline.