Yuri Kamyshkov/ University of Tennessee Mini-Workshop, WU St. Louis, February 11, 2011 (Playing with various factors)

Fission reactor (TRIGA): ~ 100 MeV per neutron In spallation target (heavy metal): ~ 40 MeV per neutron Spallation is about factor 2.5 more efficient for n-production ~ 1 MW spallation can produce as many neutrons as ~ 3MW reactor

Both fission and spallation neutrons are fast ~ few MeV kinetic energy They need to be moderated down to slowest possible velocities: Thermal neutrons ~ 2.2 km/s (300K) Cold neutrons ~ 700 m/s (30K) Very Cold neutrons ~ 400 m/s (10K) Ultra-Cold neutrons < 6 m/s At low neutron velocities elastic scattering is less effective for cooling. Scattering on phonons (solid D2) or rotons (SF He) – enhances UCN production

Magnetic field shielding should be factor of 10 better or  0.1 nT

At ILL 3  10 6 ucn/s is available now. In best Albert’s scenario with dedicated 1.9K, 200 kW source: 3.3  10 8 ucn/s. Neutrons are produced in 4  but used for ucn conversion only in a small fraction of solid angle. UCN storage NNbar expt.

Reactor beam layout uses typically ~5% of 4  solid angle of all produced cold neutrons With dedicated spallation target almost 100% of produced neutrons potentially can be used. Potential gain factor ~ How we can “use” them?

200 kW

H. Shimizu, KEK/Japan Economically possible in future

Neutron elliptical focusing reflector Sink hole Only fraction of n flux will be intercepted by the focusing reflector. Limitation from Liouville theorem. Suppose  0.1 acceptance

UCN gain factors (in number of neutrons):  10 from production solid angle;  from super-mirror reflections;  0.1 from focusing reflector acceptance + cold neutrons _________________________________ Total possible factor ~ 100 of ucn production enhancement 3  10 8 ucn/s  3  ucn/s HFIRDUSELNANO/UCN P, MW Layouthorizontalvertical Distance, m3001,000 N [n/s] 8.5    t 2 [s 2 ] Nt    In ILL units  400  4000 N-Nbar sensitivity How reliable one can find only with R&D

What can we do with this idea? Need substantial R&D development with MCNP simulations and essential NE component Need the group developing  200 KW cyclotron (in India ?) Discuss with DOE whether we can start an R&D project for UCN spallation target development/optimization (~ March 1 at UT); NSF (?) Include IU (?), NCSU (?), NCSU NE (?), UT NE(?), India (?) Include Tony Gabriel (?) SNS group (Fergusson) (?)