Relativistic Plasmas and Strong B-Fields: New Synergism Between HEA and HEDP Edison Liang Rice University Collaborators: H. Chen, S.Wilks, B. Remington (LLNL); T. Ditmire, (UTX); W. Liu, H. Li, M. Hegelich, (LANL); A. Henderson, P. Yepes, E. Dahlstrom (Rice) Santa Fe, NM, August 4, 2010

LLNL Titan laser New Revolution: Ultra-intense Short Pulse Lasers bring about the creation of Relativistic Plasmas in the Lab Matching high energy astrophysical conditions TPW Trident

Omega laser Omega laser facility, Univ. of Rochester Many kJ-class PW lasers are coming on line in the US, Europe and Asia The National Ignition Facility LLNL Omega-EP ARC FIREX Gekko ILE Osaka RAL Vulcan Laser

 e /  pe log GRB Microquasars Stellar Black Holes LASER PLASMAS Phase space of laser plasmas overlap some relevant high energy astrophysics regimes solid density coronal density PulsarWind Blazar 2x10 22 Wcm -2 2x x10 18 LWFA (magnetization) GRB Afterglow

Relativistic Plasmas and Strong B-Fields 1.Pair Plasma Creation Experiments. 2.Strong-B Creation Experiments. 3.Applications of Pair Plasmas + Strong B Most relativistic plasmas are “collisionless”. Need to use kinetic, e.g. Particle-in-Cell (PIC), simulations to capture essential physics.

e+e- pair plasmas are ubiquitous in the universe Thermal MeV pairs Nonthermal TeV pairs it is highly desirable to create pair plasmas in the laboratory

Internal shocks: Hydrodynamic Poynting flux: Electro- magnetic Gamma-Ray Bursts: High  favors an e+e- plasma outflow? e+e- Woosley & MacFadyen, A&A. Suppl. 138, 499 (1999) What is primary energy source? How are the e+e- accelerated? How do they radiate?

e+e- e Trident Bethe- Heitler MeV e- Ultra-intense Lasers is the most efficient tool to make e+e- pairs In the laboratory

W.cm p s e+e- 125  m Au Early laser experiments by Cowan et al (1999) first demonstrated e+e- production with Au foils. But e+/e- was low (~10 -4 ) due to off-axis measurements and thin target. Cowan et al 1999

Trident process dominates for thin targets. Bethe-Heitler dominates for thick targets. Can the e+ yield keep increasing if we use very thick targets? (Nakashima & Takabe 2002) I=10 20 Wcm -2 ? linear quadratic Liang et al 1998

1 2 Au Set up of Titan Laser Experiments

1 1 2 MeV Monte Carlo simulations Sample Titan data e+/e- ~ few %

Absolute e+ yield (per incident hot electron or laser energy) peaks around 3 mm and increases with hot electron temperature

Only emergent e+/e- ratio can be measured, but discrepancy between theory and data for thick targets remains to be resolved

Omega-EP

Assuming that the conversion of laser energy to hot electrons Is ~ 30 %, and the hot electron temperature is ~ 5 -10MeV, the above results suggest that the maximum positron yield is ~ e+ per kJ of laser energy when the Au target ~ 3-5 mm The in-situ e+ density should exceed /cm 3 The peak e+ current should exceed /sec This would be higher than conventional sources using accumulators and electrostatic traps.

PW laser Double-sided irradiation plus sheath focusing may provide astrophysically relevant pair “fireball” in the center of a thick target cavity: ideal lab for GRB & BH  -flares 3-5mm high density “pure” e+e- due to coulomb repulsion of extra e-’s diagnostics Thermal equilibrium pair plasma and BKZS limit may be replicated if we have multiple ARC beams staged in time sequence.

How are relativistic jets confined and dissipate?

Laser-driven Helmohltz coil can generate MG axial fields (Daido et al 1986). Myatt et al (2007) proposed Omega-EP experiments to confine pair jets. We proposed similar experiments for TPW. TPW long pulse to drive B TPW short pulse to make pairs or proton beam (courtsey J. Myatt 2007)

Helmholtz coil B-field Scaling Estimates 1.Energy Scaling: E B ~ 10% of absorbed laser energy For cylindrical volume of 0.1mm radius x 1 mm length we find B max ~ 15 MG per kJ of incident laser energy assuming 30% absorption into hot electrons. 2.Current Scaling: I scales linearly with foil gap d. For d ~ 1 mm, I max ~ 1.2x10 5 A. Hence we estimate B max ~ 10 MG per kJ of incident laser energy 3.Capacitance Scaling: Assuming 5 x10 13 hot electrons per kJ of laser energy with 50% into capacitor, and d ~1 mm, we find maximum voltage V ~ 2 x10 6 V. Using L (inductance) ~14 nH for copper circuit, we find B max ~ 10 MG per kJ of incident laser energy.

A Novel Application of Relativistic Pairs + Strong B: Laser Cooling of “Landau Atom” to make dense Ps Key advantages of laser produced positrons are short pulse (~ps), high density (>10 17 /cc) and high yield efficiency (~10 -3 ). To convert these >> MeV positrons to slow positrons using conventional techniques, such as moderation with solid noble gas, loses the above inherent advantages. We are exploring intense laser cooling, using photons as “optical molasses” similar to atomic laser cooling, to rapidly slow/cool MeV pairs down to keV or eV energies.  e+/e- o  2 o

In a strong B field, resonant scattering cross-section can become much larger than Thomson cross-section, allowing for efficient laser cooling: analogy to atomic laser cooling To Compton cool an unmagnetized >>MeV electron, needs laser fluence  ~mc 2 /  T ~ J.cm -2 = 8MJ for ____~ 100  m diameter laser But resonant scattering cross section peaks at f  T, f>10 3,  is reduced to 8MJ/f < kJ. As in atomic laser cooling, we need to “tune” the laser frequency as the electron cools to stay in ________resonance. How?_________. For B=10 8 G, h  cyc =1eV cyc =1  m TT f>10 3  T

B~100MG  e+/e- t3t3 t2t2 t1t1 toto cyc = laser  (1-vcos  ) Idea: we can tune the effective laser frequency as seen by the e+/e- beams by changing the laser incident angle to match the resonant frequency as the positron slows.

B~100MG  e+/e- toto t1t1 t2t2 t3t3 cyc = laser  (1-vcos  ) Idea: change the incident angle by using a mirror and multiple beams phased in time We are developing a Monte Carlo code to model this in full 3-D. Initial results seem promising (Liang et al 2010 in preparation)

High density slow positron source can be used To make BEC of Ps at cryogenic temperatures (from Liang and Dermer 1988).

Ground state of ortho-Ps has long live, but it can be spin-flipped into para-Ps using 204 GHz microwaves. Since para-Ps annihilates into 2-  ’s, there is no recoil shift. The 511 keV line has only natural broadening if the Ps is in the condensed phase.

A Ps column density of cm -2 could in principle achieve a gain-length of 10 for gamma-ray amplification via stimulated annihilation radiation (GRASAR). (from Liang and Dermer 1988). Such a column would require ~10 13 Ps for a cross-section of (1 micron) e+ is achievable with 10kJ ARC beams of NIF. Ps annihilation cross-section with only natural broadening

1 micron diameter cavity 10 ps pulse of e cm -2 Ps column density Porous silica matrix at 10 o K sweep with 204 GHz microwave pulse Artist conception of a GRASAR (gL=10) experimental set-up

Solid target B- field laser radiation high energy protons B- field absorption ablation energy transport ionization fast particle generation & trajectories (Courtesy of Tony Bell) Short pulse laser plasma interactions naturally generate superstrong B in laser plasmas

X-Wave cutoffs Region of harmonic generation ncnc ncnc 22 33 44 55 66 77 88 99    µm (courtesy of Krushelnick et al)

Experimental results are in agreement with “ponderomotive” source for fields “ponderomotive” source for fields

can create reconnection layer

shows thin current sheet

Summary: New Synergism between HEA and HEDP 1. Titan laser experiments and numerical simulations point towards copious production of e+e- pairs using lasers with I > Wcm Maximum e+ yield can exceed per kJ of laser energy (emergent e+/hot e- ~ few %). 3.The in-situ e+ density can exceed cm Laser-driven Helmholtz coil can create B > 10 7 G 4.Dense pair plasmas and jets, coupled with > 10 7 G magnetic fields, can simulate many astrophysics phenomena, from black hole flares, pulsar winds, blazar jets to  -ray bursts. 5.Collisionless shocks, reconnection, and shear layers may also be studied in the laboratory with HEA applications.