Trident Laser Facility Introduction to Laser-Plasma Interaction (LPI) Physics David S. Montgomery LPI Principal Investigator Plasma Physics Group (P-24) Physics Division Los Alamos National Laboratory Onset behavior of SRS Langmuir Decay Instability cascades 4040 4080 4120 4160 ls (Å) 10Å Los Alamos Trident Laser Facility Very exciting results obtained on the Trident laser that are: - Good Science - Can have a large impact on ICF program

Laser Plasma Interaction: extreme physics target Laser Intensity: 1012 - 1020 W/cm2 (30,000 GV/m) Pulse Widths: 10-8 - 10-14 sec Temperatures: 106 - 109 °C Plasma flows: 107 - 108 cm/sec (100’s mile/sec) Plasma size: 1 µm - 1 mm laser • Inverse Bremsstrahlung Absorption (e-i collisions) • Parametric Instabilities ncr laser scattered light Heat transport fast particles X-rays

Major U.S. high-power laser facilities Omega Laser (Univ. of Rochester) 30 kJ, 30 TW Z Backlighter (Sandia, Albuquerque) under construction, 40 kJ, 20 TW Trident (Los Alamos) 500 J NIF - National Ignition Facility (Livermore) under construction, 2 MJ, 500 TW Nova Laser (Livermore) Defunct 30 kJ, 30 TW Nova Target chamber (defunct)

Cool Laser Fusion Pictures X-ray micrograph of Hohlraum experiment on Omega Inside Omega chamber during a fusion experiment NIF target chamber (under construction) Fusion Yield (DT) ≈ 1014 (14.1 MeV) neutrons ~ 300 J of fusion energy ~ 30 kJ of laser energy ~ 1% fusion yield 30 ft. dia. 1 million lbs.

Several important laser-plasma applications have been developed over the years Heat outside • Inertial Confinement Fusion (laser fusion) • X-ray lasers • Plasma-based accelerators • VUV and X-ray lithography • Plasma processing • Remote sensing (laser-induced breakdown spectroscopy) • Ion, proton beam production • Basic and applied physics research - direct nuclear excitation - high energy-density physics (high Te, pressure, density) - laboratory astrophysics - laboratory general relativity simulations? - others... DT Implosion Fusion Energy!!!

Plasma oscillations have a simple analogy to a mass on a spring mass M suspended on a spring of constant k (spring provides restoring force F = kx) k Eq. of motion M x x(t) = A sinwt + B coswt mass oscillates with frequency w

Electron Plasma Oscillations: a simple derivation Electric field is restoring force No magnetic Field (B=0) plasma uniform density ne x test electron wp is the plasma frequency

Electron Plasma Wave Derivation: advanced Continuity Eq. Force Eq. Goal: develop wave equation for density fluctuations. Assumptions: B=0, small amplitude ∂n, fixed ions, adiabatic

Background on Waves in Plasmas • Waves in unmagnetized plasmas Electron Plasma Wave (EPW) or Langmuir wave Ion Acoustic Wave (IAW) Electromagnetic Wave (EMW) or Light wave BACKUP (c = ln)

Parametric instability of coupled oscillators: a mechanical analogy Resonance occurs when the “driving frequency” w0 equals the sum of the two “daughter” oscillation frequencies: w0 = w1 + w2, oscillation amplitude exponentiates!! k1 k2 w0 w1 w2 w12 = k1/M1 w22 = k2/M2 M1 M2

Parametric coupling between intense laser wave, plasma wave and scattered light wave dn Parametric Instability Feedback loop Self-focusing (filamentation) high ne low ne intensity increases laser hotspot JT ~ dnE0 Force ~ (ES E0) Instability occurs when growth rate exceeds damping of wave energy in interaction volume Interplay and competition can occur between these instabilities Instabilities Remain a Threat to ICF Nova large plasma experiments Up to 50% SRS Up to 30% SBS scattered wave ES SRS and SBS: • energy loss • scattered light in undesired locations • preheat due to hot electrons (SRS) (killed Helios and Shiva) • potential damage to NIF optics (SBS) Self-focusing • beam breakup, spraying, steering • enhance SRS, SBS

Some of the important parametric decay mechanisms for laser plasmas stimulated Brillouin scattering (SBS) stimulated Raman scattering (SRS) EMW EPW IAW laser EMW Parametric Decay Instability (PDI) Two-plasmon Decay (TPD) EPW IAW EPW laser laser EPW IAW Langmuir Decay Instability (LDI) EPW

Typical setup for a laser-plasma interaction experiment beam-splitter diagnostic lens focusing lens target or plasma incident laser Wavelength (nm) Scattered light diagnostics • Energy, Power • Spectra • Images X-rays (energy, spectra, images) particles

Typical day of shots at Omega (7am - 11pm) Experiments team & Junk food Hmm… what’s for lunch?? I want to go home now... David, almost the end of the day... Experiments Team Deciding who’s going to pick up dinner... I’m running the shot... I’m really in charge... It’s not my turn... I went last time...

Summary and Conclusions • Laser-Plasma Interaction Physics - extreme physics in a small lab environment - complex, challenging - interesting applications • Laser Fusion - Laser-plasma instabilities a potential threat - need for understanding in order to control instabilities Laser-plasma interaction physics is a challenging and exciting area of research