1. December 17, 2014 StarDriver: An Update (a) EIMEX, 107 Siebe Drive, Fairfield, CA 94534, (925)-413-0777 (b) Sandia Natl Lab, (c) WFK Lasers, (d) Logos, (e) LLNL (ret), (f) LLE David Eimerl (a), E. Michael Campbell (b), W.F.Krupke (c), Jason Zweiback (d), W.L.Kruer (e), John Marozas (f), J. Zuegel (f), J. Myatt (f), J. Kelly (f), D. Froula (f), R.L.McCrory (f) Fusion Power Associates, December 2014 WFK Lasers

2. December 17, 2014 StarDriver is motivated by considerations of both target physics and laser science and engineering Laser experiments in both Indirect Drive and Direct Drive ICF have exposed several types of instabilities that present significant challenges to achieving ignition and burn. (A) Hydrodynamic Imprint, target manufacturing and ablation drive symmetry (B) Laser-Plasma Spatial interference pattern, spatial coherence (phase matching), laser coherence time

3. December 17, 2014 Hydrodynamic and Laser-Plasma Instabilities occur in different forms in both types of target Indirect Drive Hohlraum Thermal X-rays? Direct Drive corona UV/visible light Control and perhaps elimination of instabilities may possibly be achieved using UV/visible radiation with (enough of) the highly incoherent features of thermal X-rays. 2  pe, CBET RT SRS/SBS 2  pe /CBET Wall motion Time-dependent asymmetry RT

4. December 17, 2014 Comparison of Thermal Radiation with Laser Radiation Mean Wavelength ~ 1nm Bandwidth ~ 10 6 THz Spatial coherence length ~ 2nm Coherence time ~ 10 -18 s Glass Lasers: Wavelength ~ 350nm Bandwidth ~ 0.001 - 1THz KrF Laser : Wavelength ~ 248nm Bandwidth ~ 5THz Spatial coherence length ~ 1000nm Coherence time ~ 10 -9 - 10 -13 s Thermal/X-ray:Legacy Laser Systems:

5. December 17, 2014 Broad or ultra-broad bandwidth is key to controlling instabilities Imprint and ablative drive pressure non-uniformities are significantly reduced by increasing the bandwidth of the laser drive. Asymptotic smoothing levels can be reached in 100fs rather than 100ps, with adequate bandwidth. One method to reduce or suppress the most significant laser-plasma instabilities is high laser bandwidth and/or a high density of modes in k-space. StarDriver delivers this control by configuring the laser drive as many near monochromatic beamlets spanning a wide range in frequency,

6. December 17, 2014 A representative StarDriver-class laser fusion concept In total, there are 10,000 to 200,000 beamlets, each one 10-200 Joules, 2- 10cm in aperture, delivering ~2MJ on target Effectively ~4  illumination Grouped to allow collection of released energy Target Each beamlet is near monochromatic Each beamlet has a different wavelength from the others The effective bandwidth of the laser drive is the bandwidth spanned by overlapping beamlets at the target. Different focusing/timing strategies will enable Zooming

7. December 17, 2014 NIF: 192 beams with 10 kJ of 0.35 µm light (>20 kJ of 1 µm light ) LMJ (France) : 220 beams Omega(LLE): 60 beams Nike(NRL,KrF): 56 beams IFE concepts (e.g. LIFE) ~400 beams The StarDriver concept is to replicate many beamlets: a “building block” approach. Each beamlet is ~100 joules, so that a fusion laser driver would require thousands of beams, each optimized and independent: analog of massively parallel processing in super-computers StarDriver laser innovation: legacy laser drivers are large systems with large optics, with the intent of minimizing cost.

8. December 17, 2014 Rectangular Beam Square Beam Bi-cylindrical lenses Two out-of-plane mirrors Square segments. The phase plate is rotated to align its segments with the rotated beam profile Laser system Beam reshaper Beam Rotator Phase plate Final Focusing lens Debris Shield Rotated Square Beam To Target Beam positioning and pointing optics StarDriver beamlets are small aperture: each beamline can be configured for maximum effectiveness using optical elements available today. Frequency convertor

9. December 17, 2014 Wavelength (nm) Δλ ~ 17 nm (1.6% BW) APG1 is a well- established average power material that enables a StarDriver with coherence time ~ 100fs Small aperture enables ~full bandwidth to be exploited The StarDriver system bandwidth is effectively that of the (complete set of) gain media. For example, APG-1 Nd:glass by itself has a 1.6% effective bandwidth as a StarDriver Gain Material

10. December 17, 2014 104510501055106010651070 Fluoroberyllates Fluorophosphates Phosphates Silicates Δλ eff ~ 30 nm (2.8% bandwidth) 1075108010851090 Silica Δλ eff ~ 45 nm (4.2% bandwidth) A StarDriver bandwidth of ~ 3-4% can potentially be realized using several Nd:glass types* *Data source: LLNL Report M095 Rev 2, V1 (1981) (StarDriver TM Potential Operating Bandwidth) Wavelength (nm)

11. December 17, 2014 104010501060107010801090 Nd:glasses Δλ eff ~ 75 nm (7% bandwidth) 110011101120 With StarDriver an ultra-broad bandwidth ~ 7% can possibly be realized using Nd* and Yb:glass types *Data source: LLNL Report M095 Rev 2, V1 (1981) (StarDriver TM Potential Operating Bandwidth) Yb:glasses? Wavelength (nm) The Drive bandwidth can be further expanded by developing new laser host materials, and perhaps using other ions, as well as nonlinear optical methods (e.g. SRRS in D 2 ). Bandwidth greater than 10% appears to be potentially achievable by a combination of these approaches.

12. December 17, 2014 With beamlets of 100J and 10Hz rep rate, and 1-10 ns pulsewidth, StarDriver enables participation from small companies in the ICF mission The legacy glass laser drivers have a large aperture because that was believed to minimize the cost. With new laser technology and advanced control systems, the cost for 100J beamlets at 5cm aperture is no longer prohibitive. Development of the beamlets is within the scope of smaller companies and Universities

13. December 17, 2014 The high bandwidth and large number of beams in StarDriver enables much faster smoothing than any other smoothing scheme, thereby enabling reduction of hydro-instabilities

14. December 17, 2014 ProcessN e /N crit T e (keV)γ 15 (sec -1 )γ 13 (sec - 1 ) γ 15 /Δω 2ω pe 0.252-410 13 10 12 0.1 SBS0.12-43 x10 12 3 x10 11 0.03 StarDriver bandwidth using APG-1 as the laser medium should significantly reduce/eliminate LPI (2ω pe, SBS,CBET) ProcessN e /N crit T e (keV) (1 + 4(Δω/  ) 2 ) -1 CBET0.12-4.0003 Experiments/simulations will be required to demonstrate this potential

15. December 17, 2014 Threshold laser bandwidth for LPI control: 2  pe :~2–5% SRS:~1–3% SBS:≤0.1% StarDriver TM vs Large Aperture Laser Systems: LIFE bandwidth 0.02% KrF bandwidth 0.25% StarDriver TM bandwidth 1%-10% The high ultra-broad bandwidth of StarDriver enables the suppression of Laser-Plasma instabilities The bandwidth of StarDriver can be as large as that of the range of available (and suitable) laser gain media. Bandwidth adequate to suppress LPI completely(i.e. ultra-broad bandwidth) appears feasible. The bandwidth of StarDriver can be as large as that of the range of available (and suitable) laser gain media. Bandwidth adequate to suppress LPI completely (i.e. ultra-broad bandwidth) appears feasible.

16. December 17, 2014 Summary Incoherent addition (beam smoothing): laser coupling improves Control of the most significant LPI Increased overall laser efficiency (optimized beam manipulations) Greater flexibility in tuning the drive features Industry / small company participation in ICF mission Advanced manufacturing and material options Less expensive development costs and time Technology spin-off applications for “unit cell”

17. December 17, 2014 Reference: David Eimerl. E.Michael Campbell, William F. Krupke, Jason Zweiback, W.L.Kruer, John Marozas, J. Zuegel, J. Myatt, J. Kelly, D. Froula, R.L.MCCrory, “ StarDriver, A Flexible Laser Driver for Inertial Confinement Fusion and High Energy Density Physics”, J. Fusion Energy (2014) 33:476-488