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Ultracold Neutron Guide-Coating Facility at U.Winnipeg

T. Hepworth, A. Zahra, B. Algohi, R. de Vries, S. Pankratz, P. Switzer, T. Reimer, M. McCrea, J. W. Martin, R. Mammei, D. Anthony, L. Barrón-Palos, M. Bossé, M. P. Bradley, A. Brossard, T. Bui, J. Chak, R. Chiba, C. Davis, K. Drury, D. Fujimoto, R. Fujitani, M. Gericke, P. Giampa, C. Gibson, R. Golub, T. Higuchi, G. Ichikawa, I. Ide, S. Imajo, A. Jaison, B. Jamieson, M. Katotoka, S. Kawasaki, M. Kitaguchi, W. Klassen, E. Korkmaz, E. Korobkina, M. Lavvaf, T. Lindner, N. Lo, S. Longo, K. W. Madison, Y. Makida, J. Malcolm, J. Mammei, Z. Mao, C. Marshall, R. Matsumiya, E. Miller, M. Miller, K. Mishima, T. Mohammadi, T. Momose, M. Nalbandian, T. Okamura, R. Patni, R. Picker, K. Qiao, W. D. Ramsay, W. Rathnakela, D. Salazar, J. Sato, W. Schreyer, T. Shima, H. M. Shimizu, S. Sidhu, S. Stargardter, R. Stutters, I. Tanihata, Tushar, W. T. H. van Oers, N. Yazdandoost, Q. Ye, M. Zhao

TL;DR

The paper documents the construction and commissioning of a pulsed-laser-deposition based DLC coating facility at the University of Winnipeg to enhance ultracold neutron (UCN) transport and storage for TRIUMF/TUCAN experiments. It details the 3 m long, 16" chamber, 248 nm excimer laser system, plume-collimation and TOF ion-probe diagnostics, and a graphite target with rastering and biasing capabilities used to deposit DLC on 1 m UCN guides. First coatings on a 1 m aluminum guide achieved DLC densities of 2.2–2.3 g/cm^3, corresponding to real Fermi potentials of ~198–207 neV, with coating thicknesses of ~90–180 nm and no delamination, establishing a functional baseline for the facility. Future work aims to increase the sp$^3$ (diamond) content through plume and substrate optimizations, measure the imaginary Fermi potential via storage tests, and scale coatings to larger substrates and additional components for the TUCAN program.

Abstract

We report the construction and commissioning of a new ultracold neutron (UCN) guide-coating facility at the University of Winnipeg. The facility employs pulsed laser deposition (PLD) to produce diamond-like carbon (DLC) coatings on cylindrical UCN guides up to 1 m in length with a 200 mm outer diameter. DLC is a promising material for UCN transport and storage due to its high Fermi potential, low neutron absorption, and low depolarization probabilities. First coating attempts on a full length aluminum UCN guide were successfully coated with densities of 2.2-2.3 g/cm$^3$, corresponding to Fermi potentials of 198-207 neV as measured by X-ray reflectometry (XRR). Coating thicknesses were measured to be 90-180 nm with no evidence of delamination. These results establish the coating facility. Ongoing and future work focuses on improving the diamond content of films through plasma plume collimation, substrate biasing, and pre/post treatment methods with the goal of providing high quality DLC UCN guides for the TUCAN experiment at TRIUMF.

Ultracold Neutron Guide-Coating Facility at U.Winnipeg

TL;DR

The paper documents the construction and commissioning of a pulsed-laser-deposition based DLC coating facility at the University of Winnipeg to enhance ultracold neutron (UCN) transport and storage for TRIUMF/TUCAN experiments. It details the 3 m long, 16" chamber, 248 nm excimer laser system, plume-collimation and TOF ion-probe diagnostics, and a graphite target with rastering and biasing capabilities used to deposit DLC on 1 m UCN guides. First coatings on a 1 m aluminum guide achieved DLC densities of 2.2–2.3 g/cm^3, corresponding to real Fermi potentials of ~198–207 neV, with coating thicknesses of ~90–180 nm and no delamination, establishing a functional baseline for the facility. Future work aims to increase the sp (diamond) content through plume and substrate optimizations, measure the imaginary Fermi potential via storage tests, and scale coatings to larger substrates and additional components for the TUCAN program.

Abstract

We report the construction and commissioning of a new ultracold neutron (UCN) guide-coating facility at the University of Winnipeg. The facility employs pulsed laser deposition (PLD) to produce diamond-like carbon (DLC) coatings on cylindrical UCN guides up to 1 m in length with a 200 mm outer diameter. DLC is a promising material for UCN transport and storage due to its high Fermi potential, low neutron absorption, and low depolarization probabilities. First coating attempts on a full length aluminum UCN guide were successfully coated with densities of 2.2-2.3 g/cm, corresponding to Fermi potentials of 198-207 neV as measured by X-ray reflectometry (XRR). Coating thicknesses were measured to be 90-180 nm with no evidence of delamination. These results establish the coating facility. Ongoing and future work focuses on improving the diamond content of films through plasma plume collimation, substrate biasing, and pre/post treatment methods with the goal of providing high quality DLC UCN guides for the TUCAN experiment at TRIUMF.

Paper Structure

This paper contains 13 sections, 4 equations, 11 figures.

Table of Contents

  1. Introduction
  2. The Facility
  3. Pulsed Laser Deposition
  4. Laser
  5. Optics
  6. Laser Safety Enclosure
  7. Coating Chamber and Target
  8. Plume Collimator
  9. TOF Ion Probe
  10. First DLC coatings
  11. Future Improvements
  12. Conclusion
  13. Acknowledgements

Figures (11)

  • Figure 1: Fermi potentials in carbon films increase linearly with density. Blue region includes primarily sp$^2$ bonded films, green region includes films with near equal parts of sp$^2$ and sp$^3$ bonding, and the red region shows sp$^3$ dominated films. Higher Fermi potential results in fewer UCN losses due to material interactions.
  • Figure 2: Top: cross-section diagram of the GCF coating chamber and drive system. Bottom: picture of the GCF with major components labeled.
  • Figure 3: Left to Right: Laser (out of frame), collimator, focusing lens, anti-reflective window, coating chamber. Lens is 2" diameter for scale. Laser path shown by red arrow.
  • Figure 4: Side-view of target holder with a target mounted. The target is a 29 mm by 58 mm by 6 mm octagonal piece of pyrolitic graphite, with a 37.5 mm by 6 mm by 19 mm N52 neodymium magnet glued to the back and held by a custom machined aluminum holder. Angle shown to demonstrate how angles are measured in Sec. \ref{['sec:TOF']}.
  • Figure 5: Guide rotation and target motion system. The guides are rotated during film deposition by a stepper motor located (bottom right) to ensure coating uniformity. The graphite target may be moved both horizontally on-axis with the chamber and vertically via the labeled rack and pinon system and a linear actuator.
  • ...and 6 more figures