Page 1 Collisionless and relativistic plasma astrophysics 2007 CRPA The quest for questions: a reflective summary of the discussion Monday: edited during Tues. discussion R. Paul Drake University of Michigan Rice Workshop May 2007

Page 2 Collisionless and relativistic plasma astrophysics 2007 CRPA The approach we developed Find compelling astrophysical questions Identify underlying issues that can be addressed in laboratory experiments Discuss the potential contribution of experiments in this context

Page 3 Collisionless and relativistic plasma astrophysics 2007 CRPA 1. What is the role of antimatter in the most energetic events of the universe? –Gamma ray bursts –Pulsar dynamics –AGN jets Underlying issue –What happens when electron-positron pair plasmas interact? –How do shocks in colliding pair plasmas behave? Potential experiments –Jason Myatt described a design for Omega Comment by RPD –This topic seems promising to me for formation of a collaborative team (with Rochester people) aimed long term at NIF

Page 4 Collisionless and relativistic plasma astrophysics 2007 CRPA 2. Why are jets spectacularly collimated over enormous distances? –Young Stellar Objects (perhaps not relevant) –Galactic jets Underlying issues –Stability behavior of large currents carried by MHD plasmas over distances of many skin depths –Unique behavior of Poynting dominated jets Potential experiments –Evolution of jet experiments with plasma guns and Z pinches (?)

Page 5 Collisionless and relativistic plasma astrophysics 2007 CRPA 3. How does tenuous plasma stop super-relativistic particles? –Pulsar winds –Gamma Ray Bursts Underlying issues –Development and saturation of Weibel and particle acceleration in plasma –Radiation from Weibel-produced structures Potential experiments –Weibel has been seen in relativistic lasers but not diagnosed in detail –Could do an experiment with beam in gas –n b ~ cm -3, n gas ~ cm -3, beam length ~ 300 µm to 3 mm, background skin depth ~ few µm, beam charge ~ 1 to 10 nC, use probe beam, Faraday rotation, emission – Potential facilities -- EP, Vulcan, ZR

Page 6 Collisionless and relativistic plasma astrophysics 2007 CRPA 4. How do shock waves produce cosmic rays? –Supernova remnant shocks Modeling of SNR 1006 has failed –Termination shocks Underlying issues –What is the electromagnetic structure of collisionless shocks? –How are particles heated from the thermal distribution so they can be “injected” into long-term acceleration? –How do such shocks amplify magnetic fields? Potential experiments –Need facility that can do high beta and high Alfven Mach number with small collisions and strong magnetization of the ions –This is feasible

Page 7 Collisionless and relativistic plasma astrophysics 2007 CRPA 5. This question needs work or to drop How does turbulence dissipate energy in astrophysical plasmas? –An issue from the solar wind to intergalactic space –Accretion disks Underlying issues –What is the nature of MHD turbulence in space and astrophysical plasmas? –How is energy in magnetic fields delivered to particles? –Away from stars, where does the magnetic energy come from? –The nature of the heating/acceleration produced by magnetic reconnection? Potential experiments –Need facility that can do high beta and high Alfven Mach number with small collisions and strong magnetization of the ions –This is feasible –Next-generation (less collisional, I think) reconnection experiment

Page 8 Collisionless and relativistic plasma astrophysics 2007 CRPA 6. Poynting dominated flows somehow Maxim?

Page 9 Collisionless and relativistic plasma astrophysics 2007 CRPA There seems to be a trend here Need facility that can do high beta and high Alfven Mach number with small collisions and strong magnetization of the ions A “thinking big” wish list –Vacuum chamber of 50 to 100 cubic meters –Flexibly configurable internal coil set –Substantial auxiliary heating –Two 5 kJ ns laser beams (to launch shocks and photoionize) –A ( ps) petawatt laser (to provide relativistic particles) This could be a community user facility –It would revolutionize the study of high-beta plasma dynamics –Much of its research would have astrophysical relevance UCLA Proposal parameters D/r Li ~ 100 b ~ 5 M A ~ 2 (v A = 63 km/s) v Shock ~ 120 km/s T He > 100 eV postshock B ~ 100 G in shock region With the addition of internal coils, LAPD might evolve in this direction

Page 10 Collisionless and relativistic plasma astrophysics 2007 CRPA Things that did not fit and notes from discussion It is interesting for many astrophysical systems to get –B 2 /  e c 2 > 1 and R  pe /c >> 1 –Large “  ” and skin depths –Dusty plasmas –Unifying idea: nonlocality in collisionless systems –Possible question: what’s the difference between collisional and collisionless systems? – Results depend strongly on boundary conditions Lab experiments could explore Example: voltage source vs current source vs resistive power dissipation

Page 11 Collisionless and relativistic plasma astrophysics 2007 CRPA Notes from discussion White paper needs to specify definite system applications An example from HED lab astro should be in white paper … Magnetically dominated plasmas -- not clear to me what can be done. Edison: assign discussion leaders.