1. Page 1+422003 HEDP Class Inroductory Lecture What is radiation hydrodynamics? The science of systems in which radiation affects the dynamics of the matter There are two radiation-hydrodynamic regimes –Radiative-flux regime, where radiative energy transport is essential (above ~ 30 eV) –Radiative-pressure regime, where thermal radiation pressure is dominant (above ~ 1 keV) Today’s experiments are in the radiative-flux regime Two rad-hydro phenomena: Marshak waves and radiative shocks

2. Page 2+422003 HEDP Class Inroductory Lecture Radiation waves develop when thermal radiation diffuses into a medium They require that the medium be many radiation-mean-free-paths thick (“optically thick”), and so usually involve high-Z materials Marshak waves: the penetration of radiation from a constant temperature boundary into an optically thick medium. Features for simple cases –Depth –Shape constant in time (“self-similar” structure) These features remain approx. true in more complex cases From Drake, High-Energy-Density Physics, Springer (2006)

3. Page 3+422003 HEDP Class Inroductory Lecture Hohlraums rely on Marshak waves to create thermal environments at millions of degrees Put energy inside a high-Z enclosure The vacuum radiation field stays in equilibrium with the resulting hot surface One gets high temperatures because the Marshak wave moves slowly, penetrating few microns Credit LLNL Laser spots seen through thin-walled hohlraum. Hohlraum with experiment attached on bottom From Drake, High-Energy- Density Physics, Springer (2006)

4. Page 4+422003 HEDP Class Inroductory Lecture Shock waves become radiative when Radiative energy flux exceeds incoming material energy flux Where post-shock temperature is Giving a dimensionless threshold MaterialXeXeCH Density 0.01 g/cc10 -5 g/cc0.01 g/cc Threshold velocity60 km/s10 km/s200 km/s downstream Upstream preheated

5. Page 5+422003 HEDP Class Inroductory Lecture The other key dimensionless parameter for steady radiative shocks is “optical depth” Downstream shocked region Upstream preheated region Optically thin Optically thin Optically thick Optically thick “LTE” shocks Some astro Some experiments & astro Larger density ratios Much astro Any experiments? ReighardFleury Blast waves in gasses (photon starved upstream) KeiterHerrmann Z dynamic Recent French work Bouquet, Michaut, & collabs SN blast wave Perhaps some shock- clump interactions

6. Page 6+422003 HEDP Class Inroductory Lecture Geometry of optically thin (upstream) radiative shocks Density Temperature Upstream  o,T o,p o Here we ignore ion-electron decoupling, which occurs on a more-localized scale at the density jump Initial post-shock state  i,T i,p i Downstream final state  f,T f,p f Cooling layer

7. Page 7+422003 HEDP Class Inroductory Lecture The local fluid energy balance provides a solvable system for steady shocks Energy equation Assumptions: 1D, use, the momentum & continuity eqs., Result Where the radiation model is a transport model not a diffusion model, with

8. Page 8+422003 HEDP Class Inroductory Lecture Cooling layers are optically thin  T -4/3  0 (approx. Xe conditions)  = 4/3 here, so  o = 1 mg/cc Our experiments are in this regime but denser and faster From Drake, High-Energy-Density Physics, Springer (2006) Density (ratio to Preshock) downstream An example for the thick-thin case of our experiments

9. Page 9+422003 HEDP Class Inroductory Lecture Amy Reighard is leading experiments to study such shocks for her Ph.D. thesis research Laser drive beams launch Be piston into xenon gas Piston drives a planar shock Radiography detects dense xenon Gold grid provides spatial fiducial Parameters –10 15 W/cm 2 –0.35 µm light –1 ns pulse –600 µm tube dia.

10. Page 10+422003 HEDP Class Inroductory Lecture In 1D simulations with HYADES, the shocked layer grows thicker at nearly constant density 40 µm Be disk At several times ~ 140 km/s Simulation by Amy Reighard

11. Page 11+422003 HEDP Class Inroductory Lecture Data from Omega show a dense and apparently uniform layer of shocked xenon 20 µm Be drive disk Data at 14.6 ns Grid cells are 63 µm squares

12. Page 12+422003 HEDP Class Inroductory Lecture New phenomena become dominant in relativistic HEDP We will discuss –Relativistic electron motion in laser beams –Electron acceleration –Ion acceleration –Some other phenomena “Relativistic” laser beams –Quiver momentum –Lorentz factor –Todd Ditmire will introduce you to this technology –Bill Kruer will explain the interaction physics

13. Page 13+422003 HEDP Class Inroductory Lecture Electrons in a light wave oscillate and drift The force equation is For an electron in a light wave one can show For small laser irradiance the motion is a drifting figure 8 with At very high laser irradiance the oscillations become extremely anharmonic and the motion is mainly along z with pxpx pzpz Enam Chowdhury, Ph.D. Thesis

14. Page 14+422003 HEDP Class Inroductory Lecture To experience acceleration on a wake, go wakeboarding or surfing A wakeboarder can surf the wake on a boat… gaining momentum http://www.nickandjulz.com/pro/photos/wake/

15. Page 15+422003 HEDP Class Inroductory Lecture To accelerate lots of electrons, take them surfing too Electrons can surf the wake on a pressure pulse in a plasma The pressure pulse can be produced by one or more laser beams or by an electron bunch. This is wakefield acceleration. –Eric Esarey will introduce you to the alphabet soup of detailed approaches Credit: LBL OASIS Group Laser pulse Electrons Plasma Wake Hogan et al., PRL 2005 SLAC beam Acceleratedelectrons

16. Page 16+422003 HEDP Class Inroductory Lecture To accelerate ions, repel them If you remove the electrons somehow, the remaining ions will push each other apart How to remove the electrons: Thermally –Hot electrons leave a surface plasma much faster than the ions do –This produces “sheath acceleration” –The electron “temperature” and the sheath potential increase with a o –The maximum ion energy is ~ 20 Z a o MeV – Ponderomotively, which means from the laser light pressure –“Coulomb explosions” occur when a group of ions blows apart –For a sphere

17. Page 17+422003 HEDP Class Inroductory Lecture One can create lots of new phenomena with relativistic lasers Transmit light through high-density plasma Drill holes in dense plasma Make lots of electron-positron pairs Cause nuclear reactions Create GigaGauss magnetic fields And many more You will see some of these this week

18. Page 18+422003 HEDP Class Inroductory Lecture Part Two: The Toys Hardware –J X B guns –Z pinch –High-energy lasers –Ultrafast lasers –Beams Codes –Eulerian –Lagrangian –PIC –Hybrids

19. Page 19+422003 HEDP Class Inroductory Lecture Marcus Knudson is a gunslinger with ICE in his veins He will show you what one can learn by shooting “bullets” at targets to create shocks and learn from what they do –These bullets are called “flyer plates” –One gun is the electric pulse generator of the “Z machine” at Sandia J B J X B The trick is to drive a current on one surface of a thin conducting material These bullets are called “flyer plates” One can launch flyer plates this way with velocities above 20 km/s By arranging the currents to create gentle compression, one can do Isentropic Compression Experiments (ICE)

20. Page 20+422003 HEDP Class Inroductory Lecture Chris Deeney is a chef Much of his career has been cooking samples using “Z pinches” Today’s biggest x-ray barbecue is the Z machine at Sandia, when run as a Z pinch (> 2 MJ of x-rays) Z pinches exploit the attraction between parallel currents Cylindrical wire array Implosion Stagnation Inward J X B force Inward acceleration Shock heating & Radiative cooling

21. Page 21+422003 HEDP Class Inroductory Lecture The action is at the center of a large though compact structure

22. Page 22+422003 HEDP Class Inroductory Lecture Bill Kruer and Todd Ditmire are space rangers They spend their time zapping things with lasers and analyzing what happens when you do High energy lasers amplify the light energy across a large area then compress the beam(s) in space to create high energy density amplify protect Smooth (spatial filter) amplify vacuum irradiate

23. Page 23+422003 HEDP Class Inroductory Lecture High-Energy lasers: big facilities; small targets

24. Page 24+422003 HEDP Class Inroductory Lecture Today’s workhorse in the US is Omega Target chamber at Omega laser

25. Page 25+422003 HEDP Class Inroductory Lecture The National Ignition Facility will provide much more energy > 1 MJ on target 192 beams LMJ in France will be on the same scale 18-wheeler cab and trailer

26. Page 26+422003 HEDP Class Inroductory Lecture Ultrafast lasers compress pulses in time as well as space Amplify a long pulse over a large area Compress it to a small volume in time and space A “lambda-cubed” laser has a spot one wavelength in diameter and a pulse one cycle long Grating pairs to stretch and compress the laser pulses in time

27. Page 27+422003 HEDP Class Inroductory Lecture Accelerators produce high-energy-density beams Table from NAS report

28. Page 28+422003 HEDP Class Inroductory Lecture All the toys are worthless without good diagnostics David Meyerhofer will discuss diagnostics

29. Page 29+422003 HEDP Class Inroductory Lecture Now we turn to computer codes These toys are essential to Evaluating long-term applications Designing present-day experiments Interpreting aspects of experiments that can’t be measured Connecting HEDP experiments with other systems, for example in astrophysics There are many approaches; all have strengths and weaknesses

30. Page 30+422003 HEDP Class Inroductory Lecture Eulerian codes calculate in a fixed geometric space The computational zones are defined in an Eulerian space Strengths –Adaptive grids are straightforward –Can follow swirling motions Weaknesses –Trouble following material boundaries –Large diffusion –Must start with very large box –Resolving shock waves can be hard Credit Kifonidis et al.

31. Page 31+422003 HEDP Class Inroductory Lecture Lagrangian codes track the motion of mass Features –Fixed mass in each zone –Zone boundaries can move Strengths –Keeps materials separate –Follows shocks well –Complex physics models straightforward Weaknesses –Material cannot swirl –Not readily adaptive Simulation by Laurent Boireau

32. Page 32+422003 HEDP Class Inroductory Lecture Various modern codes combine both Lagrangian and Eulerian features CALE (LLNL, Omar Hurricane) RAGE (LANL, Bernie Wilde) Diverging Instability ExperimentSupersonic Jet Experiment

33. Page 33+422003 HEDP Class Inroductory Lecture Particle In Cell (PIC) codes track particles or superparticles Simulate motion of actual or representative particles with correct mechanical equations Evolve electromagnetic fields based on Maxwell’s equations using particle properties Strengths –Exact simulation Weaknesses –Limited space and time –Collisions are approximate Chuang Ren will discuss PIC codes Friday Collisionless shock driven by ultrafast laser Credit: Louis Silva

34. Page 34+422003 HEDP Class Inroductory Lecture Part 3: The applications Inertial fusion Experimental Astrophysics Accelerators

35. Page 35+422003 HEDP Class Inroductory Lecture These cool toys were developed for inertial confinement fusion (ICF) research

36. Page 36+422003 HEDP Class Inroductory Lecture ICF is exciting but also a tough challenge Take a mm-scale cryogenic capsule filled with DT Implode it –At 300 km/s using giant lasers or Z pinches –So gently that the fuel stays frozen –Without letting instabilities rip it apart –Possible ignite it with a relativistic laser Get an energy gain of > 100 from the fusion burn Applications –Defense –Power generation

37. Page 37+422003 HEDP Class Inroductory Lecture In ICF one first compresses the fuel using an ablatively driven implosion This is necessary to avoid blowing up the lab Fuel layer is first compressed by shocks. Then the shell is accelerated inward by high-pressure, low-density corona. Stagnation creates a central hot spot surrounded by cold dense fuel An ablatively driven implosion ICF fusion Capsule

38. Page 38+422003 HEDP Class Inroductory Lecture After compression, one has to make the ICF fuel burn by fusion Two approaches This is the traditional approach Riccardo Betti will tell you about it Design the central hot spot so it ignites the fuel Let the central hot spot be much smaller and rapidly ignite the compressed fuel Options: lasers, particles, slugs This is called fast ignition Max Tabak will tell you about it. Rick Freeman will discuss particle transport, also essential.

39. Page 39+422003 HEDP Class Inroductory Lecture Some of us are using these new tools to create experimental astrophysics New tools enable new science, and create new sciences e.g., Hubble diagram Spectroscopy enabled and created astrophysics Astronomy: the human eye and brain High Energy Density facilities are new tools ….. Dmitri Ryutov will describe some of the astrophysical applications

40. Page 40+422003 HEDP Class Inroductory Lecture Others are using these tools to create the next generation of particle accelerators Eric Esarey will discuss this Credit:

41. Page 41+422003 HEDP Class Inroductory Lecture In you want a better foundation in HEDP Come next summer to the second offering of Foundations of High Energy Density Physics A thorough introduction to the foundations of this subject Taught by one lecturer (me) to provide a continuous discussion with common notation based on a book A two week course The 28 students last year were strongly enthused –Otherwise I would not be doing this again! –Contact rpdrake@umich.edu

42. Page 42+422003 HEDP Class Inroductory Lecture High-energy-density physics is exciting!