1. ICFT/P2006-054 PERSISTENT SURVEILLANCE FOR PIPELINE PROTECTION AND THREAT INTERDICTION 9 th International Fast Ignition Workshop Cambridge, MA 3 November 2006 Designing and Fabricating a Proton Beam Source Suitable for Fast Ignition Targets Richard B. Stephens General Atomics ICFT/P2006-054 P.Patel M. Roth et al

2. ICFT/P2006-054 Contributors from a large collaboration M Mauldin, E Giraldez,C Shearer M Foord, A J MacKinnon, P Patel, R A Snavely, S C Wilks, K Akli, F Beg, S Chen, H-K Chung, D J Clark, K Fournier, R R Freeman, J S Green, C D Gregory, P-M Gu, G Gregori, H Habara, S P Hatchett, D Hey, K Highbarger, J M Hill, J A King, R Kodama, J A Koch, K L Lancaster, C D Murphy,, H Nakamura, M Nakatsutsumi, P A Norreys, N Patel, J Pasley, H-S Park, C Stoeckl, M Storm, M Tabak, M Tampo, W Theobold, K Tanaka, R Town, M S Wei, L van Woerkom, R Weber, T Yabuuchi, B Zhang This work is from a US Fusion Energy Program Concept Exploration collaboration between LLNL, General Atomics, UC Davis, Ohio State and UCSD International collaborations at RAL have enabled the experiments Synergy with an LLNL ‘Short Pulse’ S&T Initiative has helped the work

3. ICFT/P2006-054 Proton ignition concept has evolved Initial concept avoided complexity – External focusing surface – Simple proton transport Velocity spread cause problems – Energy must be delivered in short time Simple solutions … – Reduce energy spread (M. Hegelich, LANL) ä Reduce separation Introduce new problems ä Protection from the imploding shell 25 10 20 30 40 50 60 70 0 05101520 T p (MeV) E ig (kJ) d = 4 mm d = 2 mm d = 1 mm Roth et al., Phys. Rev. Lett. 86, 436 (2001) Atzeni et al., Nucl Fusion 42, L1 (2002)

4. ICFT/P2006-054 Use a reentrant cone for protection Laser  Protects proton source from coronal plasma  Limits accelerating surface  Causes focusing edge effects  Scatters proton beam

5. ICFT/P2006-054 Tested concept by making prototype Cone dimensions same as for electrons –30° full cone opening Focusing surface same as for hemi tests (existing focal length data) –r c = 170  m –d focus ~290  m  Limits accelerating area (125  m dia) Target Cu foil - 32  m thick (29 mg/cm 2 ) –Stops < 4 MeV protons

6. ICFT/P2006-054 Proton source area depends on energy Accelerating electrons cool off as they travel to the edge Hybrid PIC LSP simulation M. Foord - LLNL 100 fs, 50  m FWHM Gaussian beam 45 J beam Patel et al., Phys. Rev. Lett. 91, 125004 (2003)  200  m dia includes most useful protons (flat foil data) Our source will have limited energy output

7. ICFT/P2006-054 Low energy protons are most important to ignition t [ps] Temporal et al., Phys of Plasma 9 3098 (2002) 45 65 85 105 125 100 200 300 10 20 30 40 Proton Energy [MeV] Power [TW] Fusion Emission Proton Deposition Useful for ignition Protons must deliver energy in short time for ignition  limits useful proton energy range Sim parameters: Proton spectrum: Tp = 3 MeV, dn/de  sqrt(  )e -  /Tp Total proton energy = 26 kJ Proton beam radius = 10  m Source distance = 4 mm Target density = 400 g/cc

8. ICFT/P2006-054 Protons are not easily scattered Scattering angle  E -2  3 Mev Protons ~ 5°  15 Mev Protons ~ 1° Broadens spot 5-10  m 15° 5  m Au 1-5° 200  m  The cone tip can be far from the compressed core End wall scattering is insignificant

9. ICFT/P2006-054 Prototype proton focusing cone was constructed Construction is feasible

10. ICFT/P2006-054 K  imager 160  m HOPG Initial tests show moderate proton focusing and heating

11. ICFT/P2006-054 Proton heating is reasonable for conditions Ratio of HOPG intensities gives slope temp 1-4 MeV for protons K  spots have 10 6 counts - to be compared to equivalent shots using full hemi Focal spot is rather large - 160  m –Could be consequence of side walls changing the proton focus.

12. ICFT/P2006-054 Measure focus changes by radiographing grids Send proton beam through grid and detect with RCF stack Magnification determines focus position, fuzziness of grid shows focus size, number of grids show source area These experiments are in preparation Put grids in flat washers for simpler construction

13. ICFT/P2006-054

14. Hi-Z mix? more compact? improve eff’y? Conversion to protons, focusing/ heating? Blob  R ~ 0.44 g cm -2 ~ 120 g cm -3 ~ 0.4 keV Total Energy in blob ~ 0.6 kJ Backlit radiograph (8 keV) at imploded max  R 457 µm 40 µm CD 2 vacuum PW laser 55 * beams, pulse-shape “26” Omega EP hydro simulations (S. Hatchett) What is signature of heating, increased emission? Ka fluorescence? X-ray scattering? neutron production? Abs spectroscopy? Will use data to design integrated experiments for Omega EP

15. ICFT/P2006-054 The proton focal spot radius reduces as laser focal spot increases 50 um spot z=50  m 55  m 60  m 10 um spot z=50  m (long axis) 55  m 60  m Trade-off between fully illuminating surface, and building edge effect Laser spot size influences proton focus

16. ICFT/P2006-054 Tight laser spot gives ‘aberrated’ proton focus X- 20  m heated spot PW laser Laser Proton heating Cu K  image Gekko PW data 320  m Al shell Protons X-ray phc image Cu K  image X-ray phc image Cu K  image RAL PW data