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Initial results of the TRIUMF ultracold advanced neutron source

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

Abstract

We report the first results on ultracold neutron production from a new spallation-driven superfluid $^4$He (He-II) source at TRIUMF, which is being prepared for a new, precise measurement of the neutron electric dipole moment. A total of $(9.3 \pm 0.8)\times 10^{5}$ ultracold neutrons were observed at a proton beam current of \SI{37}{\uA}, when the target was irradiated for a period of \SI{60}{\s}. The results are in fair agreement with expectations based on a detailed simulation of neutron transport and ultracold neutron source cryogenics. There is some indication that the new source might not be as limited by the conduction of heat through the He-II as originally expected. The results indicate that the source is likely to make its ultimate production goals, once the liquid deuterium cold moderator system is completed, with the expectation that $5.7\times 10^7$~UCNs would be detected in the same experiment with full liquid levels. This would, for example, correspond to delivery of $1.4\times 10^6$~UCNs delivered to each of two nEDM measurement cells, and a statistical uncertainty of $1\times 10^{-27}~e$cm on the neutron EDM in 280 days of running.

Initial results of the TRIUMF ultracold advanced neutron source

Abstract

We report the first results on ultracold neutron production from a new spallation-driven superfluid He (He-II) source at TRIUMF, which is being prepared for a new, precise measurement of the neutron electric dipole moment. A total of ultracold neutrons were observed at a proton beam current of \SI{37}{\uA}, when the target was irradiated for a period of \SI{60}{\s}. The results are in fair agreement with expectations based on a detailed simulation of neutron transport and ultracold neutron source cryogenics. There is some indication that the new source might not be as limited by the conduction of heat through the He-II as originally expected. The results indicate that the source is likely to make its ultimate production goals, once the liquid deuterium cold moderator system is completed, with the expectation that ~UCNs would be detected in the same experiment with full liquid levels. This would, for example, correspond to delivery of ~UCNs delivered to each of two nEDM measurement cells, and a statistical uncertainty of cm on the neutron EDM in 280 days of running.

Paper Structure

This paper contains 5 figures.

Figures (5)

  • Figure 1: The UCN source and detector configuration used in these experiments. The dark blue volume indicates the fill level of the He-II for these experiments, the light blue the D$_2$O level. The proton beam impinges upon the W target horizontally, approximately perpendicular to the tail section orientation (out of the page).
  • Figure 2: Measurement of heat removed by $^3$He pumping as a function of beam current delivered to the spallation target, at a $^3$He temperature of 0.9.
  • Figure 3: UCN counts during a measurement cycle. The source was irradiated at 37 for 60 (blue), after which the UCN gate valve was opened for 120 (orange$\rightarrow$black). After subtracting the background run (grey), the integrated UCN counts during the valve-open period were $(9.3\pm 0.8)\times 10^5$. The inset shows the same data in a semi-log plot.
  • Figure 4: Integrated UCN counts in the 120 counting period as a function of the average beam current during the preceding 60 irradiation period. Most of the error bars are similar to the vertical size of the data points, save the measurements at the highest current with no foil (see text). The data are fitted to a straight line with forced zero intercept. Data are compared with simulations (which all assume the presence of a foil, see text).
  • Figure 5: Measurements of the UCN storage lifetime up to the UCN valve, as a function of the average beam current during the preceding 60 irradiation period. Inset: summary of results for the measured lifetime from the exponential fits shown in the main graph.