Evaluation of Wavelength Detuning to Mitigate Cross-Beam Energy Transfer Using the Nike Laser

Backlighter beams dm: !3 Å KrF 10 J in 400 ps (FWHM*) Drive beams dm: !3 Å (KrF) Target 1.8 kJ in 4 ns 200-nm outer diameter

Nike target chamber

57th Annual Meeting of the American Physical Society P. W. McKenty Division of Plasma Physics University of Rochester Savannah, GA Laboratory for Laser Energetics 16–20 November 2015

1 Summary The Nike laser can be employed to examine the effects of laser wavelength detuning to mitigate cross-beam energy transfer (CBET)

• Wavelength detuning is predicted to shift the CBET interaction region within the corona, affecting the gains/losses because of CBET

• The Nike platform is well suited for these studies, providing a well- diagnosed system over a range of detunings (Dm ~6 Å KrF)

• Initial experiments have commenced on Nike, measuring energy dependence of wavelength detuning

TC12419

2 Collaborators

J. A. Marozas University of Rochester Laboratory for Laser Energetics

J. Weaver, S. P. Obenschain, and A. J. Schmitt Naval Research Laboratory

3 Successful wavelength detuning shifts the resonance location sufficiently to mitigate CBET

When probe rays are blue-shifted, the resonance shifts to a higher Mach Pump beam number where intersecting probe rays are negligible

When probe rays are red-shifted, the resonance shifts to a lower Mach number where probe rays are blocked CBET causes probe rays and/or have negligible intensity Target to extract energy from rc high-intensity pump rays Parabolic locus of turning points

Probe beam

TC11766e

4 The NIKE experiments will evaluate the disposition of the scattered light at two specific locations

OMEGA Nike

CBET

Target Target

Scattered-light disposition

TC12420 D. H. Edgell et al., JO5.00004, this conference.

5 The predicted scattered light from the single probe beam failed to produce discernible signals

1.4 1.4 No CBET dm = +6 Å (KrF) Scattered light (mJ/cm2) 1.2 1.2 z 0.00 1.18 1.0 1.0

0.8 1.0 1.2 1.4 1.4 dm = 0 2 r 1.2 z

1 1.0

1.4 z dm = –6 Å (KrF) 0 1.2

–1 1.0

–2 –1 0 1 2 0.8 1.0 1.2 1.4 r r TC11503a

6 Enhancement of CBET requires using all backlighter beams and retiming them to come on earlier in the implosion

CBET temporal diagnostic CBET temporal diagnostic 0.5 1.0 270 No Dm 200 240 = +6 Å 0.4 Dm 0.8 210 Dm = –6 Å 150 180 0.3 0.6 150 100 120 0.2 0.4 90 Dm = –6 Å

Laser power ( TW ) Laser power 0.1 50 ( TW ) Laser power 0.2 Dm = +6 Å 60 Dm = 0 30 CBET energy transfer ( mJ ) transfer CBET energy No BL ( mJ ) transfer CBET energy 0.0 0 0.0 0 0.0 0.5 1.0 1.5 0.2 0.60.4 0.8 1.0 1.2 Time (ns) Time (ns)

TC12421

7 The Nike experiment will be able to evaluate spatial and spectral mitigation of CBET

XBT temporal dignostic XBT temporal dignostic 0.25 0.25 Target offset Wavelength detuning 0.20 0 nm 0.20 Dm = 0 50 nm Dm = +6Å 100 nm Dm = –6Å 0.15 150 nm 0.15 200 nm 0.10 0.10

0.05 0.05 CBET energy transfer ( J ) transfer CBET energy ( J ) transfer CBET energy

0.00 0.00 0.0 0.2 0.4 0.6 0.8 0.0 0.2 0.4 0.6 0.8 Time (ns) Time (ns)

TC12615

8 Analysis of the scattered light (SL) looks at the temporal behavior of the spatial average behind the target

Scattered-light diagnostic surface Scattered-light diagnostic surface x x

z y z y SL SL (mJ/cm2) (mJ/cm2) 28.58 9.53 22.58 7.64 17.19 5.76 11.49 3.87 5.80 1.99 0.10 0.10

Average SL at 700 ps 6.40 mJ/cm2 total 4.95 J

TC12422

9 The averaged scattered light tracks that predicted by the CBET gain term

20 Dm = –6 Å Dm = +6 Å Dm = 0 No BL 15

Scattered light ( J ) Scattered 5

0 0.6 0.8 1.0 Time (ns)

TC12423

10 Evaluation of the temporal histories of the scattered-light spectra yields unique signatures

Rear of target Probe exit (i = 180°) (i = 35°)

No probe SL (W) (×109) 7. 6 Dm = 0 6.2 4.7 3.3 Dm = +6 Å 1.9

Wavelength ( nm ) Wavelength 0.5

Dm = 2 Å Dm = –6 Å

500 600 700 800 900 1000 500 600 700 800 900 1000 Time (ps) Time (ps) TC12505

11 Initial experiments have commenced on Nike, examining energy dependence of spectral shifts

Nike energy output at various imposed wavelength shifts 50

20 Energy ( J ) Energy

0 –3.0 –2.0 –1.0 0.0 1.0 2.0 3.0 Wavelength shift (angle)

TC12616

12 Summary/Conclusions The Nike laser can be employed to examine the effects of laser wavelength detuning to mitigate cross-beam energy transfer (CBET)

• Wavelength detuning is predicted to shift the CBET interaction region within the corona, affecting the gains/losses because of CBET

• The Nike platform is well suited for these studies, providing a well- diagnosed system over a range of detunings (Dm ~6 Å KrF)

• Initial experiments have commenced on Nike, measuring energy dependence of wavelength detuning

TC12419