UCN Source at the NCSU PULSTAR Reactor Bernard Wehring and Albert Young North Carolina State University International Workshop on Neutron-Antineutron Transition Search with Ultra Cold Neutrons September 2002 Bloomington, Indiana Outline NCSU PULSTAR Reactor Desirable Attributes NCSU UCN Source Conceptual Designs Conclusion NCSU PULSTAR Reactor NCSU PULSTAR Core 5 x 5 array of fuel assemblies 5 x 5 array of pins Sintered UO 2 pellets 4% enriched 1-MW power Graphite, Be reflected Light water moderated and cooled Desirable Attributes Properties Heavy loading of U kg Low ratio of H to U-235 atoms High ratio of fast to thermal flux in the core Benefits High fast-flux leakage High sensitivity to reflector material Long core lifetime PULSTAR Flux 1-MW TRIGA Mark II U-ZrH fuel 19.7% enrichment 3.5 kg U-235 mass ~ 64 liter core volume n/cm 2 s core avg thermal flux 6.4 x n/cm 2 s core avg. fast flux Thermal flux UCN Source at PULSTAR Parametric design calculations CN fluxes in the UCN converter and heating rates by MCNP simulations of the PULSTAR reactor, CN source, and UCN converter. UCN production rates by integrating the converter CN energy spectrum with the UCN production cross sections. UCN intensity at end of an open UCN guide using lumped-parameter and UCN-transport calculations. NCSU UCN Source Details UCN Converter Solid ortho D 2 4-cm thick 18-cm diameter CN Source Solid methane 1-cm thick Cup shape around UCN converter Conceptual Design I (top view) CN Flux (MCNP) Averaged over UCN converter Integrated, 0 to 10 meV CN energies = 1.0 x CN/cm 2 -s Neutron and Gamma Heating Rates (MCNP) UCN converter, 86 g0.7 W UCN converter chamber, 484 g2.1 W CN source, 408 g4.0 W CN source chamber, 1164 g4.4 W UCN Production Rate P = N V = + = 5 x b/D = 1 x b/D V = 1000 cc P = 3.6 x 10 7 UCN/s UCN Intensity at End of Open Ni-58 Guide I o = f P f = absorption leak / ( absorption + leak ) absorption = 50 ms leak = 4 V / (S ) = 4 t / = 32 ms f = 0.6 I o = 2.2 x 10 7 UCN/s Conceptual Design II (side view) CN flux averaged over UCN converter 4-cm thick x 18-cm diameter = 1.0 x CN/cm 2 -s UCN intensity at end of open Ni-58 guide 50-cm rise, 2-m level I o = 1.2 x 10 7 UCN/s Conceptual Design III (side view) CN flux averaged over UCN converter 4-cm thick x 18-cm diameter = 1.2 x CN/cm 2 -s UCN intensity at end of open Ni-58 guide 50-cm rise, 2-m level I o = 1.5 x 10 7 UCN/s N-N Bar Experiment Conclusion UCN intensity at bottle entrance (2 MW) I o = 3 x 10 7 UCN/s Bottle equivalent radius, R = 150 cm Avg. chord length, L = 4/3 x R = 200 cm L / (avg. UCN speed), t = 0.5 s Bottle lifetime, = 300 s Discovery potential, coherent free path > 2L > I o x ( /2t) x (2t) 2 = 9 x 10 9 s (> 6 ILL)