SD 2 UCN Source Performance at LANSCE

1. SD2 UCN Source Performance at LANSCE A. Saunders, T. Bowles, R. Hill, G. Hogan, K. Kirch, S. Lamoreaux, C. L. Morris, A. Pichlmaier, S. Seestrom (Los Alamos National Laboratory) S. Hoedl, C.-Y. Liu, D. A. Smith, A. R. Young (Princeton University) B. Filippone, T. M. Ito, J. Martin, B. Tipton, J. Yuan (California Institute of Technology) P. Geltenbort (Institut Laue-Langevin) M. Hino, T. Kawai (University of Kyoto) A. Serebrov (Petersburg Institute for Nuclear Physics)

2. Solid D2 Spallation UCN Source Concept • SD2 source † • SD2 has a large downscattering rate R • Cold SD2 is predicted to have small absorption and upscattering cross sections-> long UCN lifetime t • UCN density, Rt, is predicted to be large. • Spallation driver‡ • High cold neutron density • Shutter source • †R. Golub and K Boning, Z. Phys. B 51, 187 (1993). • ‡A.Serebrov, “First UCN Factory Workshop’” Jan 18-22, 1988, Puskin, Russia.

3. Estimated density

4. UCN Source Layout SS UCN Bottle 58Ni coated stainless guide Liquid N2 Flapper valve Be reflector LHe Solid D2 UCN Detector 77 K poly Tungsten Target

5. Line C Measurements UCN Detector Cold Neutron Detector Proton Beam • Line C results show reduced ( 100) UCN production. • D2 frost on guide windows and walls. • Gravity+Aluminum detector window

6. Solid D2 in a “windowless” container Grown from a gas phase at 50 mbar Cooled through the triple point

7. First Blue Room Run • Improved cryogenics • Good signal from solid D2. • Low backgrounds, especially at long times of flight. • UCN production still very low!

8. July 1999 Blue Room Runs Mr flapper 58Ni coated stainless guide Liquid N2 Be reflector LHe Solid D2 77 K poly UCN Detector Predicted lifetime from D2:  = V D2/VD2 = ~18 s Tungsten Target

9. Life time summary • Significant UCN fluxes are produced from 50 cm2 SD2. • SD2 lifetime looks shorter than expected even for 10 K up-scatter cross section. • Temperature? • Other up-scatter mechanisms?

10. UCN Lifetime in Solid Deuterium • Nuclear absorption in SD2 cannot be avoided • Lifetime is 150 ms • Other sources of UCN loss can be controlled • Lattice phonon absorption (150 ms at 5 K) • Nuclear absorption on hydrogen (150 ms at 0.2% H) • Conversion of para-deuterium (150 ms at 1% para-D2) • Lifetimes add as resistance: 1/=(1/1+1/2) • Total lifetime is then about 40 ms.

11. UCN bottle UCN guide Cryostat Beam detector UCN setup in line B at LANSCE

12. SD2 Lifetime Measurements • UCN trapped in “bottle” with SD2 • Valve opened to release UCN at different times

13. Temperature dependence (20 cc .02 para-deuterium)  

14. Ortho-para dependence (4.5-6 K) Monte Carlo Data   Data 

15. UCN bottle Input valve Output valve Bottle measurements

16. Volume Dependence 1600 calculations x 0.75 no aperture 0.2 % HD 1400 5 K 1 % para 1200 2 % para 1000 800 UCN/10^12 protons 600 400 Measured Runs 1847-1941 200 MT run = 1847 0 0 50 100 150 200 250 300 350 SD2 volume (cc)  REH 4/12/00 Transport Model does not include flapper valve, details of bottle.

17. High current runs (heating) Volume=100 cm3 =200 cm3 Para-deuterium fraction=.02 T = 5.29 K 24 mCoul

18. Open valve Background Valve leakage World Record UCN Density6/29/00 

19. Beam Heating Effect Temperature (K) Time

20. Future Uses for Prototype • Confirm lifetime and other physics measurements • Test bottles, UCN guides • First experiments with new source • Beta spectrum • Neutron lifetime in magnetic bottle • Test run at AGS?

21. SD2 Source • 800 MeV protons • from fast kicker Source plans: commission the LD2 pit and Area B at LANSCE • Already in place: • Shielding • Power • Water cooling • Cryogenics • Proton beamline

22. Conclusions • We have successfully tested the new source at LANSCE. • We have observed stored UCN densities of over 100/cc, the highest in the world. • UCN production and lifetime depend on para contamination and temperature as expected. • Work continues to optimize full scale source design and experiments!