Overview of KrF Laser Development* 18 th High Average Power Laser Program Workshop presented by J. Giuliani from contributed slides Santa Fe, NM April 8-9, 28 *Supported by the Department of Energy/NNSA/DP NRL, : J. Sethian M. Myers S. Obenschain J. Giuliani J. Dubinger M. Wolford Commonwealth Tech: F. Hegeler M. Friedman T. Albert J. Parish R. Jones P. Howard RSI: PLEX: P. Burns M. McGeoch R. Lehmberg S. Searles APP: W. Webster S. Glidden H. Sanders SAIC: R. Jaynes Georgia Tech: A. Mangassarian S. Abdel-Khalik D. Sadowski Delphic Oracle: K. Schoonover A. Robson Voss Sci. 1 D. Rose
Key Components of a Krypton Fluoride (KrF) Laser Laser Input Pulsed Power System B Z Laser Gas Recirculator Cathode Electron Beam Foil Support (Hibachi) Laser Cell Kr + Ar + F 2 Amplifier Window 2
Outline A. Main Amp pulse power oscillator single shot recirculator oscillator rep-rate focal profile B. Cathode Development strip ceramic honeycomb C. Pre-Amp D. Laser System multiplexing rep-rate shots E. Future pre-amp recirculator scalloped hibachi Zirconia cathode foil material 3
Main Amplifier 4
Long duration demonstrated for pulsedpower e-beam diode "Primary" emitter Five times1, continuous shots @ 1 Hz, into cooled anode plate, without breaking diode vacuum. Cathode emission uniformity maintained throughout the whole run. (=> laser pumping uniformity) e-beam Ceramic Honeycomb* 3 mm gap 5
Intrinsic Efficiency 73 J Laser Shot of 9.6% P E-beam (GW) 7 6 5 4 3 2 1 E-Beam Power Efficiency (9.6%)= P Laser (5.75 GW)/ P E-Beam (6.2 GW) 5 1 15 2 Time (ns) 7 6 5 4 3 2 1 P Laser (GW) E-Beam Deposition Power = (Pressure Rise (E)*Radiation Correction (15%)) + Laser Energy (E) Distributed over the pulse width measured in the diode 6
Recirculator removes heat & calms flow. blower A P O N M heat exchanger L B Main AMP C laser head K J throttles D vanes I E 7 F G H
3 J @ 1.6 1 Hz 1.4 (3 W) 1.2 1, shots 1. photodiode amplitude (V) continuous.8 (2.5.6 hrs).4.2. Consistent long duration, monolithic cathode, oscillator, double sided runs shot 1 shot 1 shot 2 shot 3 shot 4 shot 5 shot 6 shot 7 shot 8 shot 9 shot 1 23 J @ 2.5 Hz (575 W) 6,5 shots continuous -.2 5 1 15 2 25 3 time (ns) 4 J @ 5 Hz (2 W) 1.2 5 1shots continuous Intensity (arb.).8.6.4.2 5 1 15 2 Time (ns) Shot 1 Shot 1 Shot 2 Shot 3 Shot 4 Shot 5 other notable results: 25 J @ 5 Hz (1,25 W), 77 shots in four segmented run single sided @ 2.5 Hz 25, shot run. 8
3 7 J, 1 Hz Rep-Rate oscillator with strip cathode Photodiode Signal (V) Intensity (arb.) 2.5 2 1.5 1.5 Shot 1 Shot 5 Shot 1 Shot 15 Shot 2 Shot 25 Shot 3 Shot 35 Shot 4 5 1 15 2 25 Time (ns) 9
High efficiency oscillator maintained with strip cathode independent of rep-rate Energy (J) 8 7 6 5 4 3 2 1 1 Hz (J) 2.5 Hz (J) 5 1 15 2 Shot # 1
3 shots 1 Hz Focal Profile Measurement ( Pseudo ISI ) Probe Beam No E-Beam Probe 1 2 3 Time (s) Probe Beam with E-Beam 1 Hz 39 ms after E-Beam Probe.39 1 1.39 2 2.39 Time(s) 5 microns 11
Hibachi/Cathode Development 12
Strip cathode patterns e-beam to miss ribs, thereby enhancing deposition efficiency. Particle-in-cell simulations Particle e-beam plot anode Radiachromic film image (time-integrated) soft iron slanted strip cathode Position of soft iron rods 13
Ceramic honeycomb Cordierite cathode overlies emitter to provide longevity strip cathode 9 kw/cc gas deposition hibachi e-beam cathode or velvet emitter divided by bars focuses e-beam between hibachi ribs laser cell laser window = aperture vacuum diode hibachi with ribs monolithic cathode 55 kw/cc gas deposition uniform emitter e-beam deposition into laser cell for the two cathodes from Hegeler, et al., POP, vol.11, p.51 (24) ceramic honeycomb 14
Foil is lifetime sometimes limited by debris from Cordierite cathode Evidence of Debris 15
Silica coated reduces debris attack of hibachi foil. Average 27 J @ 2.5 Hz Over Two Hour Time Period 1.2 PDM_1 PDM_1 PDM_2 1 PDM_3 PDM_4 Intensity (arb.) PDM_5 PDM_6.8 PDM_7 PDM_8 PDM_9.6 PDM_1 PDM_11 PDM_12 PDM_13.4 PDM_14 PDM_15 PDM_16 PDM_1668.2-5 5 1 Time(ns) 15 16 2
Pre- Amp 17
Preamp: measured laser energy output is consistent with Orestes simulations. Laser Output (J) 3. 25. 2. 15. 1. 5. Orestes.5 J Input Measured Input ~.5 J Orestes.7 J Input Measured Input.6 J. 8 12 16 2 Pressure (psi) 8% Ar,.3% F 2 18
25 J Output of Two Beam Angularly Multiplex Preamplifier Beam 1 Dimensions Beam 2 9. cm 9.7 cm 8.1 cm 7.6 cm Calorimeter Data Volts.4.35.3.25.2.15.1.5 7 6 5 3 mj Laser Input Laser Beam separation ~26 ns 2 4 6 8 1 Time (ns) Intensity 4 3 2 1-1 25 5 75 1 Time (ns) 25 J Laser Output 19
Angularly multiplex 3 J preamplifier yield with strip cathodes Preamplifier Strip Cathodes Zircar to Suppress Electron Emission Deposition 3% Larger than Monolithic Gas Composition Pressure 82.2% Ar, 18 psi 17.5% Kr,.3% F 2 81.2% Ar, 17 psi 18.5% Kr,.3% F 2 8% Ar, 19.7% 16 psi Kr,.3% F 2 59.7% Ar, 4% 15 psi Kr,.3% F 2 Laser Yield 29.5 J 3.3 J 28.4 J 29.8 J Least stress on foils 2
Full Laser System 21
Electra KrF Laser Layout main amp 3 cm x 3 cm pre-amp 1 cm x 1 cm seed osc 1cm x 3 cm 22
Schematic of the laser beam multiplexing in full Electra system Beamlet # s correspond to temporal sequencing E mirror 1 2 3 4 5 6 6 5 4 3 2 D 1 C main amp B 2 1 preamp 2 1 A beam splitters Note: This simplified sketch neglects two mirror arrays, including the main amp input array. Labeled positions refer to following slides. 1 oscillator 23
Photodiode signals of the multiplexed laser beam through the Electra system 5 A.4 Beam 1 (PIA) Beam 2 (PIA).3.2.1 2 4 6 8 1 Intensity (Uncalibrated arb.) Intensity (Uncalibrated arb.).5 B 4 Beam 1 (POA) Beam 2 (POA) 3 2 1-1 -.1 2 4 Time (ns) 3 15 8 1 1.4 E 1.2 Photodiode Center of Rear Mirror 1 Intensity (arb.) Intensity (Uncalibrated arb.) 2 6 Time (ns) Beam 1 (MIA) Beam 2 (MIA) Beam 3 (MIA) Beam 4 (MIA) Beam 5 (MIA) Beam 6 (MIA) C 25 1 5.8.6.4.2 5 1-5 Time (ns) 15 2 24 -.2 1 2 Time (ns) 3 4
Final signals at the output array 2.5 Intensity (arb.) 2 D Beam 1 (MOA) 81 J Beam 2 (MOA) 42 J Beam 3 (MOA) 7 J 1.5 Beam 4 (MOA) 8 J 1 Beam 5 (MOA) 81 J Beam 6 (MOA) 16 J.5 2 -.5 25 3 35 4 45 5 Time (ns) Photodiode Signal Sum is 46 J, Calorimeter on same shot measured 462 J 25
Split Beam OSC 1 2 Energy (J) 452 J single shot yield PRE AMP 5 4 3 2 1 Split Each Beam into 3 2 6 Main Amp 3 x 3 cm 2-1 1 2 3 4 5 6 Time (s) 1 2 3 4 5 6 Output Beams Calorimeter 15 x 15 cm 2 Array Big 33 x 33 cm 2 Small 18 x 18 cm 2 26
Full laser system yield 1.585 kj in one second 5 Hz burst PDM Main Amp 1 2 3 4 5 6 Intensity (arb.) 1.2 1.8.6.4 Shot 1 (46 J) Shot 2 (365 J) Shot 3 (412 J) Shot 4 (268 J) Shot 5 (134 J) PDTarget.2 5 1 15 2 25 3 Time (ns) 27
Pre-amp requires a recirculator for efficient rep-rate system operation 1.4 1.2 5 shots @ 5 Hz amplitude (arb. units) 1..8.6.4.2. 1st shot 5th shot Pre-amp without gas recirculator photodiode amplitude (V) 1.4 1.2 1.8.6.4.2 -.2-2 2 4 6 8 1 time (ns) 5 shots @ 5 Hz 5 1 15 2 25 time (ns) shot 1 shot 1 shot 2 shot 3 shot 4 shot 5 Main-amp with gas recirculator 28
Orestes predicts laser system output from ~35 J to ~8 J depending on cathode Efficiency includes rise and fall of e-beam. laser output (J) 1 9 8 7 6 5 4 3 2 1 2% 2 psia Kr/Ar/F=39.7/6/.3 T window =93% E in = input laser energy from preamp!t= t input laser -t e-beam filling factor = 9% 1% intrinsic laser efficiency gas deposition efficiency from diode 3% 4% 5% 6% 25 J, 4 ns 15 J, 4 ns monolithic ceramic cathode 15 J, ns velvet strip cathode E in =25 J,!t= ns 2 4 6 8 1 e-beam energy deposition into main amp (kj) 29
Future 1) Zirconia has similar electrical properties to ceramic cordierite, but 5X mechanical strength. (July 8) 3) Pre-amp recirculator for full system rep-rate runs. 1 m 2) Scalloped hibachi significantly lowers mechanical stress on foil, even at elevated temperatures. 4) Monel or Inconel foils: more resistance to F 2, less grain structure which initiate mechanical failure modes. 3