neutron blanket

1. SCHEMATIC neutron dump neutron blanket scattered neutrons GIMM target chamber port M2 (penultimate optic)

2. SCOPE of PROBLEM Aluminum has 6x1022 atoms cm-3 Total scattering cross section of 14.7MeV neutrons is approx. 2 barns This is divided approx. equally into elastic and inelastic Scattering becomes an issue above about 10%, i.e. path in Al > 9mm For incident angle 85 deg., true thickness = 0.8mm of solid density Al at 10% scattered neutrons

3. mb/sr Q. Huiquan et al.,”Fast neutron scattering cross sections at small angles and optical model parameters” Phys. Rev. C 48, 1779-1784 (1993)

4. LIMIT of THIN GIMM neutron dump neutron blanket GIMM “secondary” neutrons target chamber port leakage through blanket M2 (penultimate optic)

5. Case of thin GIMM: IF blanket 100% effective, then M2 only sees leakage from dump Generally, M2 sees blanket leakage too. Case of thick GIMM (e.g. SIRIUS-P): Very few neutrons proceed directly to dump GIMM scattered neutrons fill containment vessel Blanket leakage can be swamped by GIMM scattered neutrons M2 sees GIMM scatter (direct and indirect), blanket leakage and dump scatter only because of proximity (although a small net source).

6. ALL-DIELECTRIC DESIGN M2 neutron dump neutron blanket M1 target chamber port leakage through blanket

7. Dielectrics vs GIMM Dielectrics can be more remote within same neutron containment vessel M1 is nearly normal to neutron flux, so thin case could apply M2 is extremely well protected and may not need to run hot Rest of containment vessel has greatly reduced neutron flux Dielectrics can be mounted directly on massive containment vessel Dielectrics have lower laser fluence for same XDL Dielectrics have much smaller optical area Is there anything good that can be said about GIMMS?