1. 1 Radiation Environment at Final Optics of HAPL Mohamed Sawan Fusion Technology Institute University of Wisconsin, Madison, WI HAPL GIMM Conference Call February 15, 2006

2. 2 Design Parameters for Baseline HAPL Design Target yield: 350 MJ Rep Rate: 5 Hz Fusion power: 1750 MW 70% of target yield carried by neutrons with 12.4 MeV average energy Chamber inner radius10.75 m Chamber outer radius12.25 m NWL @ FW 0.9 MW/m 2 GIMM angle of incidence85° GIMM distance from target24 m GIMM dimensions3.4 m x 4.05 m Previous 3-D neutronics calculations performed for final optics SIRIUS-P with KrF laser and Aluminum GIMM [M. Sawan, "Three-Dimensional Neutronics Analysis for the Final Optics of the Laser Fusion Power Reactor SIRIUS-P," Proc. IEEE 16th Symposium on Fusion Engineering, Champaign, IL, Sept. 30- Oct. 5 1995, IEEE Cat. No. 95CH35852, Vol. 1, pp. 29] Modified version of SOMBRERO with DPSSL and fused silica transmissive wedges [S. Reyes, J. Latkowski, and W. Meier, "Radiation Damage and Waste Management Options for the SOMBRERO Final Focus System and Neutron Dumps”, UCRL-JC-134829, August 1999]  A preliminary estimate of nuclear environment at final optics of HAPL will be determined by scaling from results of SIRIUS-P

3. 3 Previous Analysis of SIRIUS-P SIRIUS-P design parameters used in calculation 2444 MW fusion power Chamber radius 6.5 m Blanket/reflector (SiC/Li 2 O/TiO 2 ) 1.5 m Internal concrete wall (1.5 m thick) @ 10 m radius GIMM @ 25 m and FF mirror @ 40 m GIMM diameter 5 m GIMM angle of incidence 85° Containment building @ R = 42 m Trap diameter 1.3 m and depth 4 m Containment building is 1.2 m thick increasing to 3.3 m behind neutron trap GIMM thickness and material in SIRIUS-P Total thickness 24 cm thick with front and rear 2 cm thick zones modeled separately Front and rear zones have 75% Al6061 and 25% water Middle honeycomb structure is 20 cm thick with 0.833 g/cc Al

4. 4 Observations from SIRIUS-P results Fast neutron flux at GIMM is contributed mostly by direct source neutrons (only ~4% from secondary neutrons) Calculating flux @ GIMM is straightforward 50% of flux at FF dielectric mirror contributed by neutron scattering from the GIMM Relative flux values at FF dielectric: With trap and GIMM scattering1 With trap and transparent GIMM0.5 Without trap and transparent GIMM10 In direct line-of-sight of target100 At most a factor of 2 reduction in dielectric mirror flux can be achieved by reducing GIMM scattering Using neutron traps behind the GIMM in the direct line-of-sight of source neutrons significantly reduces the flux at the FF mirror. Largest reduction is obtained when FF mirror is placed as close as possible to the containment wall (factor of 3 less compared to close to trap opening) Inclining sides of neutron trap along the line-of-sight of direct source neutrons such that all source neutrons impinge on bottom of trap reduces chance of secondary neutrons scattering back from the trap Geometric considerations more effective for reducing dielectric mirror flux

5. 5 Scaling from results for SIRIUS-P to HAPL Conditions Fusion power (MW)1750 GIMM radial location (m)24 Fast neutron (E>0.1 MeV) flux @ GIMM (n/cm 2 s)8.9x10 12 (only 4% from secondary neutrons) Fast neutron fluence per year @GIMM assuming 80% availability (n/cm 2 ) 2.3x10 20 Radial location of dielectric FF mirror (m)40 Fast Neutron (E>0.1 MeV) Flux @ FF mirror (n/cm 2 s)4.3x10 10 Fast neutron fluence per year @FF mirror assuming 80% availability (n/cm 2 ) 1.1x10 18 Assumed similar “open” configuration as in SIRIUS-P If beam ducts are used for vacuum and tritium containment, both components of flux @ FF mirror (scattering from trap and GIMM) increase and the % contribution from GIMM scattering increases GIMM scattering contribution depends on material composition, thickness, and size. Effective thickness seen by neutrons is 11.5 times (1/cos85) the actual thickness Flux at lens depends on scattering at the duct inner walls

6. 6 What can we do to reduce flux at dielectric mirror and lens? Use as thin and small size GIMM as possible with minimal support structure Use of low density and less scattering, more absorption GIMM material is preferable (e.g., He cooling instead of water) Place FF dielectric mirror as close as possible to containment wall away from trap opening Increase depth of neutron trap as much as feasible Incline sides of neutron trap along the line-of-sight of direct source neutrons The wall of the beam duct between the chamber and trap can be made of a thin absorber since we do not need to attenuate neutrons leaking from the blanket that are much smaller than those reflected from trap Line the inner surface of trap and beam duct with strong absorber In past studies we showed that lining the ducts by 1/4" (0.635 cm) boral (Al+36% B 4 C) reduced streaming by an order of magnitude Increasing the distance between lens and dielectric mirror helps reducing the flux at the lens 3D calculations with detailed modeling of final optics configuration and GIMM layered structure will be performed once we converge on a design