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KrF Lasers for IFE J.D. Sethian, Dec 10, 2003

KrF Lasers for IFE J.D. Sethian, Dec 10, 2003. Requirements for IFE, and where they came from How close are we to meeting these requirements? Highlights of recent progress Remaining issues --What is still needed to make KrF a suitable driver for IFE?

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KrF Lasers for IFE J.D. Sethian, Dec 10, 2003

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  1. KrF Lasers for IFEJ.D. Sethian, Dec 10, 2003 Requirements for IFE, and where they came from How close are we to meeting these requirements? Highlights of recent progress Remaining issues --What is still needed to make KrF a suitable driver for IFE? Research Programs to resolve the remaining issues. The Next Step: Full scale Beam Line How development of KrF lasers contributes to HEDP and other areas of science 1

  2. Target physics and power plant economics determine laser requirements Note: all requirements are subject to change, pending current research!

  3. How close are KrF Lasers to meeting the IFE requirements? Why we liked KrF to begin with Determined Electra R&D Program Notes: a. Scale: 1= Requires research and invention, 5= Primarily engineering issue b Length of run varies by component c. Based on advanced switch and system design using pulsed power costing d. Combining Individual components, based on present Electra R&D e. Not operating as a laser

  4. BRIGHTNESS AND FOCUSING:KrF Lasers can meet the requirements for Direct Drive IFE • TARGET BRIGHTNESS Requirement: • Intensity on target: 1015 W/cm2 (maximum under consideration) • Assume 2.5 MJ laser, 5 J/cm2 damage threshold • Then total area of optics is 50 m2 • Optics at 20 m, gives solid angle of .126 sr • or brightness on target = 7.9 x 1015 W/cm2-sr LASER BRIGHTNESS Capability: Brightness = [Ilaser/ (3 XDL)2 ](Daperture//2)2 Example: 40 XDL, Daperture = 2 m, Ilaser = 8 MW/cm2  Laser Brightness = 8.6 x 1015 W/cm2-sr, > Target requirements

  5. BEAM QUALITY:KrF lasers produce the smoothest beams of any high energy UV laser 5 6 7 8 9 y (mm) For 50% of the FWHM diameter: Power tilts < 2% Quadratic curvature: < 3% RMS speckle non- uniformity: 0.3 - 1.3% (all modes)

  6. ZOOMING & PULSE SHAPINGZooming: (Decrease focal spot to follow the compressing target) Straightforward with KrF: optical switchyard controlled by Pockels Cells Same technique used for pulse shaping Amplifier Oscillator target aperture Pockels Cell t1 t2 t3 t1 t2 t3 Laser Pulse Shape S.E. Bodner, D. G. Colombant, A.J. Schmitt, and M. Klapisch, "High Gain Direct Drive Target Design for Laser Fusion," Phys of Plasmas, 7, (2000) 2298.

  7. REPETITION RATE:Components of Electra System have run at 5 Hz Electron Beam: 1 Hz for 50,000 shots (rate limited by anode cooling) Pulsed Power: 5 Hz for 100,000 shots Electron beam though hibachi foil: 1 Hz for 1000 shots, 5 Hz for 150 shots As a laser oscillator 1 Hz and 5 Hz for 10 shots

  8. Diode Laser n++ p n- Silicon Switch n+ p++ Pulse Sciences Division D Laser 100 kJ PULSED POWER MODULE Transit Time Isolator Electron beam Pulse Forming Line Magnetic Switch Fast Solid State Switch Marx PULSED POWER COST:System using Advanced Laser Gated & Pumped Thyristor should be: efficient (> 85%), durable (> 109), and economical (< $8.50/Joule) • CONCEPT: • Flood entire switch with photons • ultra fast switching times (< 100 nsec) • Continuous laser pumping reduces losses • PROGRESS: • Demo 1st (3.2 kV) generation using standard switch • Meets I, dI/dt,Hz and lifetime • Evaluating 2nd gen (16.8 kV using advanced const • Meets V, dI/dt, Hz, needs I and lifetime

  9. EFFICIENCY:Based on our research, an IFE-sized KrF system is projected to have a wall plug efficiency of > 7%.But there are still issues that need basic R&D.

  10. Anode e-beam Cathode “undesirable" parallel plate microwave cavity microwave absorbers in vertical slots Experimental Fast Fourier transform of instability amplitude: Before After After (scale zoomed) .04 .04 amplitude amplitude 0 0 3 3 2 2 0 0 1 1 frequency (GHz) frequency (GHz) E-beam Deposition-Stability:Used experiments and modeling to identify, then eliminate “transit time instability” that compromised electron beam transport 10

  11. BEFORE Laser Gas Kr + F2 + Ar Anode Foil Anode Foil Emitter e-beam E-beam Deposition-Hibachi Transmission:Demonstrated High Transmission Hibachi by eliminating anode and patterning the electron beam AFTER • 35% e-beam energy into gas • 75% e-beam energy into gas • Agrees with LSP models by MRC • Expect >80% @ 800 keV 11

  12. E-beam Deposition-Hibachi Trans Code work by MRC:Use 3-D LSP modeling to specify required cathode rotation, strip width, and predict observed transmission 2.) Simulation gives initial cathode strip angle to allow e-beam to "miss" the ribs 1.) 3D simulation with floating field-shapers & gas transport (including backscattering), and actual experimental current returns 3.) Code predicts observed e-beam deposition Calculations courtesy D. Rose, MRC ABQ

  13. Pe-beam/Plaser = 5.3/63 = 8.4% 6 5 4 3 2 1 0 Plaser (GW) Electra achieved  8% intrinsic efficiency as an oscillator...based on this we expect 12% as an amplifier(no output coupler, amplify from large signal, clean windows) 70 60 50 40 30 20 10 0 Pe-beam (GW) 0 50 100 150 200 t (nsec)

  14. mirror ASE e-beam e-beam laser output KrF PhysicsWe are developing the Orestes code to design large, efficient, KrF systems with the proper pulse shaping for IFE Philosophy Combines relevant physics into a single “First Principles” KrF Physics code Electron deposition (1-3D) Non-Maxwellian distribution Plasma Chemistry 23 species 25 Vibrational levels > 123 Reactions Laser Transport (3D) (includes gas heating) Amplified Spontaneous Emission (3D)

  15. Neutral Channel Ion Channel e- pump Ar+ Ar* ArF* F- F2 2Ar 2Ar 2Ar F F- F2 Ar2* Ar2F* Ar2+ Kr Kr Kr Kr Kr Kr KrF* F2 Kr* Kr+ F- 2Ar 2Ar 2Ar 2 Kr F2 F- F- ArFr* ArKrF* ArKr+ F F- Kr Kr+Ar Kr Kr+Ar Kr Kr+Ar F2 Kr2* Kr2F* Kr2+ Adopted from Johnson & Hunter, J. Appl. Phys,. 31 p 2046 (1980) KrF Kinetics is a complex process

  16. Orestes predicts the output of a wide range of KrF lasers But misses some others....(Electra Oscillator data) Expt shows operation at lower F2... better than code!

  17. KrF Research Program # 1:Fully Develop Orestes KrF Physics Code Benchmark Code with experiments on Electra and Nike (each has two e-beam pumped amplifiers) Develop code sufficiently so that it can: Be used a tool to design future KrF lasers Evaluate effects of pulse shaping, angular multiplexing, segmentation Explore ideas to increase KrF efficiency

  18. Durability: The last big challenge in KrF Development.This requires advanced R&D...It is not yet just an engineering problem! (I wish it was!) • Pulsed Power • Solved with LGPT switch • Amplifier Windows • Solution using thin film optical coating getting close • Resistant to Laser, HF, F2, x-rays, and electrons • Hibachi Foils • Materials • Cathode physics (minimize e-beam rise and fall) • E-beam transport • Thermal management

  19. KrF Research Program # 2:Develop long-lived Hibachi foils 2. E-BEAM TRANSPORT ex: 1. tailor gas to minimize backscattering 2. magnetic materials to guide beam 1. MATERIALS ex: 1. Composites 2. Diamond film (small systems) 3. Advanced alloys/sandwiches 3. CATHODE PHYSICS (faster rise and fall) ex: New honeycomb ceramic 4. THERMAL MANAGEMENT: ex: deflect laser gas to cool foils 19

  20. The next step is a Full Scale Power Plant Beam line(60 kJ) NEXT GENERATION SYSTEM…. WHERE WE ARE NOW….  60 kJ output (Representation) Nike 60cm Amplifier - 3 kJ output 2 electron beams 200 x 60 cm2 40 kJ each Laser 60 kJ Laser 5 kJ Optical Aperture 60 x 60 cm2 16 electron beams, 50 x 80 cm2 40 kJ each Two Optical Apertures 80 x 80 cm2

  21. Science WITH KrF lasers: The virtues of "Shot on Demand" Allows: Many shots (statistics reduces uncertainties) "On the fly" tuning of experimental conditions Scoping studies Complement to large single shot systems Applications: HEDP Physics Laser/Target code validation Precise determination of material properties Small signal gain study on Electra… 23 shots in 4 hours

  22. Science OF KrF lasersmulti-discipline, cross-cutting research Electron beam physics Generation Transport Stability Deposition (details of distribution) Excimer Laser Science (Underlying physics and chemistry is universal) E-beam deposition Kinetics Laser transport through media Code development PIC codes Integrated multi-discipline codes Solid State Pulsed Power Optical Thin Films

  23. Summary • For Inertial Fusion Energy, KrF lasers meet the requirements for: • Brightness, Beam quality, Zooming (Pulse shaping) • As a result of the HAPL work, significant advances made in • Efficiency, Rep-rate, Cost, Durability • Biggest remaining challenge is durability of hibachi foils • Resolved with coordinated R&D program to look at: • Cathodes • Foil materials • E-beam transport • Thermal management • 2nd challenge, some “residual” efficiency issues • Resolved with development of Orestes Code benchmarked on Nike/Electra • We believe these issues will be resolved within 2-3 years • ASSUMING continued HAPL funding at present levels • The Next step is a Full Scale Power Plant Beam Line (60 kJ)

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