GARPUN-MTW: A Combined Subpicosecond/Nanosecond

Transcription

1 GARPUN-MTW: A Combined Subpicosecond/Nanosecond Ti:Sapphire/KrF Laser Facility Presented by: Vladimir D. Zvorykin 1 Participants: S.V. Arlantsev, N.V. Didenko 3, A.A. Ionin 1, A.V. Konyashchenko 1, A.O. Levchenko 1, O.N. Krokhin 1, G.A. Mesyats 1, A.O. Mavritskii 3, A.G. Molchanov 1, M.A. Rogulev 1, L.V. Seleznev 1, D.V. Sinitsyn 1, S.Y. Tenyakov 3, N.N. Ustinovskii 1 1 P.N. Lebedev Physical Institute of Russian Academy of Sciences, Leninsky pr. 53, Moscow, Russia OKB Granat, Volokolamskoe sh. 95, 1344 Moscow, Russia 3 Avesta Project Ltd., Solnechnaya st. 1, Troitsk, Moscow region, Russia 3rd Int. Conf. on the Frontiers of Plasma Physics and Technology FFPT-3, March 5-9, 007. Bangkok, Thailand

2 Contents Historical notes and motivation Ti:Sapphire front-end GARPUN e-beam-pumped facility Numerical simulations and predictions Conclusions

3 Historical notes and motivation Non-linear processes is the main restriction in MOPA schemes with direct amplification of short pulses. In the s KrF lasers had an advantage over solid-state amplifiers. The shortest pulses amplified in KrF laser were 60 fs [S. Szatmári & F.P. Schafer, Opt. Comm., 68, 196 (1988)] and the highest power up to 10 TW was achieved in RAL with KrF large-aperture e-beam-pumped amplifier with expected focused intensities as high as 10 0 W/cm [E.J. Divall, et al., J. Mod. Opt., 43, 105 (1996)]. A rapid progress in CPA technique in combination with OPA in non-linear crystals by today provides most experimental needs. PW laser channels are constructed and projected at the biggest ICF glass facilities NIF (LLNL, USA), Omega (UR LLE, USA), Vulcan (RAL, UK), GekkoXII (ILE, Japan), LMJ (France), ISKRA-6 (Russia) etc. to ignite thermonuclear fuel preliminary compressed by nanosecond pulses. 1000x increased neutron yields and >0% energy coupling to the cone target design was demonstrated. Investigations of both laser physics and laser-plasma interaction during two past decades at kj-class single-shot KrF facilities Aurora (LANL, USA), Nike (NRL, USA), Sprite (RAL, UK), ASHURA (AIS&T, Japan) and GARPUN (LPI, Russia) and especially at rep-rate Electra laser (NRL, USA) have proved that e-beam-pumped KrF laser might be the best challenge for the direct-drive ICF power plant. Only DPSS laser could compete with KrF laser as a future reactor driver. We are going to regenerate an interest to short-pulse amplification in large-aperture e-beam-pumped KrF amplifiers and to verify the fast-ignition ICF concept utilizing KrF drivers that could simultaneously amplify both long laser pulses for pellet compression and short pulses for ignition [V.D. Zvorykin, et al., Bull. of Lebedev Phys. Inst., No. 9-10, 0 (1997)]. The reported work is a first step of Petawatt Excimer Laser Project started at Lebedev Institute.

4 Inertial Fusion Energy power plant with KrF laser driver Requirements for laser: total energy -.4 MJ; rep rate 5 Hz; efficiency- 7.5 % Intrinsic efficiency of energy extraction should be about 1 % Designed by the NRL Driver Amp (000 J) Front End (100 J) 100 m Chamber Target injector Main Amplifier(s) (30-60 kj) each 50 m Multiplexing optics Turning Arrays Long optical paths enclosed in He or vacuum

5 UV laser-target interaction 1 mm Shock wave Crater Laser Beam q=5*10 1 W/cm τ p =100 ns 0.5 mm

6 Properties of KrF molecule Wavelength λ = 48 nm Bandwidth ν 00 cm -1 Radiation lifetime τ r = 6.5 ns Collisional lifetime τ c = ns Gain cross section σ = см Saturation intensity I s = hν/στ 1 MW/cm Saturation energy Q s = hν/σ mj/ cm Intrinsic efficiency η 10% Potential-energy diagram of KrF molecule

7 ASE and short-pulse amplification For long pulses τ p τ c and ASE: For short pulses τ p << τ c : g0 = 10 0, α τ Intensity on target: Intensity on target: Contrast ratio (intensity): pump = 100ns, τ ν p ASE S di dx I 1/ g 0 hν NΩ g0 = I Iα +, N = g0 / σ, Iopt = Is 1 1+ I / Is 4πτr α = AGI # 1 τ c ν ASE / f, A =, G = exp 4π τ r ν S ( g L) t ASE s 0 ε = g [ ( ε )] αε ε exp, = Q / Qs, Qopt = Qs ln d dx I = 0.4, t p = CR I = BQ = fs : I s / τ B τ c / τ A Gθ p A = 0.006, t ASE p ~ 10 ( f # θ ), B = 4, 7 Contrast ratio (energy): W / cm, G CR ~ 10 I 4, = 10 9 f # 10 = 1, 10, CR Q = θ = 10 CR Q B τ c / τ A Gθ 4 = 10 rad, 4 pump g α 10 To keep the ASE and CR at a suitable level one should increase a seed pulse and restrict a total gain in KrF amplifier chain. To reduce g 0 it is possible to work at low gas pressure ( 1 atm) or to load amplifiers by a continuous train of ns pulses. 5

8 Layout of short & long pulses amplification in KrF amplifiers

9 GARPUN KrF Laser Facility General view EMG 150 master oscillator: 0.J, 0 ns, 80 Hz, 0. mrad GARPUN e-beam-pumped amplifier: 16*18*100 cm, 100J, 100 ns, ~0.1mrad Berdysh e-beam-pumped preamplifier: 10*10*100 cm, 5J, 100 ns, 0.1 mrad

10 FINAL KrF LASER AMPLIFIER Front view of DM 60-cm diameter and 00-cm cm-long amplified pumped by radially convergent e-beamse

11 High-voltage power supply and synchronization scheme of GARPUN facility PFLs produce 350-kV, 100-ns accelerating pulses applied to cathodes in vacuum diodes Laser pulses of master oscillator synchronize switches of all PFLs

12 7 8 Monte Carlo Algorithm for e-beam e transport through the matter e-beam e-beam ur r d P r ur ur m v = e, e, dt v B P = 1 v / c r ds r = v dt S ' S Q( s'') ds'' 0 ds Q s e = ξ 0 ' ( '), ξ (0,1); Q = Nσ t (1) () Moliere expression dσ in Z 1 1 (T + 1) 1 T = π re dε β T + + ε ε(1 ε) ( T + 1) (1 ε) ( T + 1) Rutherford expression (3) Cross section of GARPUN laser dσ el r = Z dω β + η θ e pe (1 cos ) ( T + 1) TT ( ) 1/ ( Z /137) Z + η = TT ( + ) Bethe-Bloch equation ( + ) /8+ 1 ( + 1)ln = ln[ ] + ds Aβ I ( T + 1) dt Z T T T ρ T (4) (5)

13 Monte Carlo code calculating e-beam e transport

14 Simulation of energy deposition in GARPUN laser chamber Energy deposition vs gas pressure (Garpun, Ar) 500 Energy, J with reflections from diodes (Transp=1) without reflections (Transp=0) with reflections (Transp=0.6) experimental data (Ar) ,5 1 1,5,5 3 Pressure, atm

15 Distribution of specific pumping energy over GARPUN laser chamber filled with Ar at 1.75-atm pressure Распределение энерговклада в сечении камеры (Гарпун) Р1 0,95-1 0,9-0,95 0,85-0,9 0,8-0,85 0,75-0,8 0,7-0,75 0,65-0,7 0,6-0,65 0,55-0,6 0,5-0,55 0,45-0,5 0,4-0,45 0,35-0,4 0,3-0,35 0,5-0,3 0,-0,5 0,15-0, 0,1-0,15 0,05-0,1 0-0,05 Р5 Р9 Р13 Р

16 Quasistationary KrF laser code

17 Non-stationary Monte Carlo code dn N * = P( t) N ( A ρ 1 + B1 ) dt τ τ = N ( A1 + B1 f hν ρ) dt ( ) = k 1 1N Ar + k N Kr N Ar + k3n Kr + k 4 N e + k5 N F + k6 N Kr dρ

18 Comparison of experiments and simulations

19 Calculation of ASE in GARPUN amplifier

20 ASE measurements in GARPUN amplifier Experimental conditions: pumping & configuration Measured values Energy density, mj/cm Intensity MW/cm Values recalculated to the boundary Energy density, mj/cm 8 Intensity, rel. units Intensity MW/cm Time, ns Simulated values Intensity MW/cm Full pumping & single-pass Full pumping & double-pass Half pumping & single-pass Half pumping & double-pass de ASE dω dw ASE dω = J/sr = W/sr

21 Ti:Sapphire front-end Start-48M Facility occupies standard 100*3000 mm lab table. Ti:Sapphire oscillator with pumping laser (λ=53 nm), all-reflected-optics grating stretcher and compressor, regenerative amplifier are all enclosed in a common 600*1100 mm box.

22 Block diagram of Ti:Sapphire laser system Start-48M consists of Ti:Sapphire oscillator TiS-0 with 4-W CW Finesse 53 DPSS pumping laser (λ=53 nm), grating stretcher and compressor, regenerative amplifier and multi-pass amplifiers pumped by pulsed Nd:YAG LS-134 laser (*100 nm), 3-ω frequency converter, 1-ω and 3-ω spectrometers ASP.

23 Optical Scheme of Start-48 M

24 TIS-0 master oscillator f =80 MHz, W = W, λ~30 nm, τ p =30 fs P A1 M4 PR M7 S A OC M5 L M6 M3 Pm1 P1 M1 TiS M A3

25 Regenerative amplifier Compressor

26 Optical scheme of 5-pass 5 amplifier Output energy 15 mj

27 Ti:Sapphire front-end Start-48 M M was installed and characterized SYSTEM PARAMETERS Repetition rate 0-10 Hz Pulse width at λ=744 nm < 50 fs Pulse width at λ=48 nm < 60 fs Pulse energy (@ 10 Hz) at λ=744 nm > 8 mj Pulse energy (@ 10 Hz) at λ=48 nm > 0.5 mj Beam diameter at λ=744 nm 10 mm Beam diameter at λ=48 nm 8 mm Stability of energy at λ=744 nm < 3% Stability of energy at λ=48 nm < 5%

28 Fs pulse of Ti:Sapphire front-end was synchronized and amplified in the discharge-pumped KrF amplifier In pilot experiments fs pulse was amplified in double-pass dischargepumped KrF amplifier with a gain factor of 5 with output energy of ~1.5 mj and Q= 6.5 J/cm, which is 3.5 times more than saturation energy density Q s.

29 Long & short pulses amplification in Berdysh df f 0( )(1 ) 0( ), 0 dx = < < g x e a x f x L

30 Long & short pulses amplification in GARPUN df 0( )(1 f ) 0( ), 0 dx = < < g x e a x f x L

31 Long & short pulses amplification in DM With the projected 60-cm-aperture, 00-cm-long DM amplifier 18 J energy in a single short pulse is expected on a par with 4 kj in 50-ns train of long pulses amplified with a stage gain M 0 and intrinsic efficiency η eff 10%. The contrast ratio of short-pulse intensity on a target to the ASE is expected in the range

32 Parameters of excimer molecules Transition XeF(C A) Kr F(4 Γ 1, Γ) KrF (B X) λ max, nm λ, nm τ lim, fs τ r, ns σ, cm Q sat, J/cm

33 Layout of fluorescence and absorption measurements at Berdysh laser module

34 Capillary-discharge light source for absorption measurements and calibration of wavelength response Spectral brightness of light source: B λ = c 5 λ exp T b = 39± kk h ( hc / kλ ) 1 T b

35 Fluorescence spectra of Ar/Kr/F mixtures Gas mixture Ar/Kr/F = 0.3/8.9/91.8% at p = 1.8 atm under e-beam excitation presents fluorescence bands of KrF (B X), KrF (C A), and Kr F(4 Γ 1, Γ). Using these spectra small-signal gain coefficient g 0KrF ~0,00 cm -1 was found.

36 Transient absorption spectra of Ar/Kr/F mixtures Absorption spectrum of Ar/Kr/F = 0.3/8.9/91.8% gas mixture at p = 1.8 atm demonstrates bond-bond transitions by transient species and broad continues band of photodissociation of Kr F (4 Γ) molecule. Dashed line is the spectrum measured by Schloss et al, J. Chem. Phys., 106 (13), 543, (1997).

37 SUMMARY The first step of Petawatt Excimer Laser Program was started at P.N. Lebedev Physical Institute. Multi-terawatt hybrid Ti:Sapphire/KrF laser system is currently under development for combined laser-plasma interaction studies and verification of the fast-ignition KrF laser scheme utilizing simultaneous amplification of both short (ps) and long (ns) laser pulses in the same e-beam-pumped modules. ACKNOWLEDGMENTS This research was implemented within the Programs of the Russian Academy of Sciences Fundamental problems of relativistic pulsed and stationary high-power electronics and Femtosecond optics and new optical materials. It was supported also by Russian Ministry of Science and Education, and US Naval Research Laboratory.