UCN

The Ultracold Neutron group, now the TRIUMF Ultracold Advanced Neutron (TUCAN) collaboration was created to measure the neutron electric dipole moment (nEDM). This fundamental property, if non-zero, has serious ramifications for resolving the Baryogenesis problem.

Overview

The project has two main components: (a) the UCN source and (b) the nEDM experiment.

The source was largely completed and shown to be functional in 2026. It is operated primarily though EPICS, with monitoring though MIDAS histories with a MySQL database. It operates on beamline 1U (BL1U), splitting off of 1V (which later becomes BL1A). With a fast kicker magnet, the TUCAN collaboration can kick individual beam buckets to BL1U to take a fraction of beam, while enabling beam to BL1A. Design operating current is 40 uA. The UCN source has two end stations for experiments: one for the nEDM experiment, and the other is planned for PENeLOPE.

The nEDM experiment is the primary experiment for the UCN source and is composed of many subsystems, each with their own controls and DAQ setup. Experiments are generally conducted as follows:

1. produce UCNs in the source,
2. open a valve to let the UCNs diffuse to the experimental chamber
3. store the UCNs in the chamber for some time, while applying high voltage, and RF pulses
4. open the chamber valve to let the UCNs diffuse to the detectors

The subsystems with DAQ interfaces are as follows:

• Comagnetometer
  • An atomic gas (¹⁹⁹Hg) inhabits the cell the UCNs are stored in. The gas is polarized with a free laser, and that polarization state is also measured with a laser. Measures magnetic field.
  • DAQ not yet implemented

• Cs Magnetometers
  • An array of glass cells containing Cs gas are distributed inside the magnetically shielded room. The polarization state is also pumped and probed with lasers, this time through fibre optics. Measures magnetic field gradients.
  • DAQ exists as a set of student python scripts, yet to be integrated into MIDAS

• B0 Coil
  • A coil which produces a highly stable and uniform static magnetic field
  • DAQ not yet implemented

• B1 Coil
  • A coil which produces the oscillating RF fields for spin flips
  • DAQ not yet implemented

• Shim Coils
  • An array of coils inside the MSR to homogenize the field
  • DAQ exists as a python script which controls an arduino, yet to be integrated into MIDAS

• Guiding coils
  • An array of coils to maintain UCN polarization in their journey to and from the magnetically shielded room
  • DAQ not yet implemented

• Ambient Magnetic Coil (AMC)
  • A large Helmholtz coil to counteract the cyclotron magnetic field
  • DAQ not yet implemented

• High voltage
  • A large electric field to tease out the electric dipole moment
  • DAQ not yet implemented

• Ambient monitoring
  • Monitoring of ambient temperature and magnetic field
  • Temperatures are measured through "canaries": battery-powered arduinos with a temperature sensor on the TRIUMF IOT network. Integrated into MIDAS.
  • Magnetic fields are measured through fluxgates and a custom DAQ produced by the TRIUMF electronics group

Useful Links

• UCN Plone
• UCN DAQ (old - daq01)