Colliding pulse injection experiments in non-collinear geometry for controlled laser plasma wakefield acceleration of electrons
An optical injection scheme for a laser-plasma based accelerator which employs a non-collinear counterpropagating laser beam to push background electrons in the focusing and acceleration phase via ponderomotive beat with the trailing part of the wakefield driver pulse is discussed. Preliminary experiments were preformed using a drive beam of a0 sime 2.6 and colliding beam of a1 sime 0.8 both focused on the middle of a 200 mum slit jet backed with 20 bar, which provided sime 250 mum long gas plume. The enhancement in the total charge by the colliding pulse was observed with sharp dependence on the delay time of the colliding beam. Enhancement of the neutron yield was also measured, which suggests a generation of electrons above 10 MeV.

title: Mono-Energetic Beams from Laser Plasma Interactions
abstract: A laser driven wakefield accelerator has been tuned to produce high energy electron bunches with low emittance and energy spread by extending the interaction length using a plasma channel. Wakefield accelerators support gradients thousands of times those achievable in RF accelerators, but short acceleration distance, limited by diffraction, has resulted in low energy beams with 100% electron energy spread. In the present experiments on the L’OASIS laser, the relativistically intense drive pulse was guided over 10 diffraction ranges by a plasma channel. At a drive pulse power of 9 TW, electrons were trapped from the plasma and beams of percent energy spread containing > 200 pC charge above 80 MeV and with normalized emittance estimated at < 2 π-mm-mrad were produced. Data and simulations (VORPAL code) show the high quality bunch was formed when beam loading turned off injection after initial trapping, and when the particles were extracted as they dephased from the wake. Up to 4 TW was guided without trapping, potentially providing a platform for controlled injection. The plasma channel technique forms the basis of a new class of accelerators, with high gradients and high beam quality.

title: High Quality Electron Bunches up to 1 GeV from Laser Wakefield Acceleration at LBNL
abstract: Experiments at the LOASIS laboratory of LBNL have demonstrated production of 100 MeV to 1 GeV electron bunches with low energy spread and low divergence from laser wakefield acceleration. The radiation pressure of a 10 TW laser pulse, guided over 10 diffraction ranges by a few‐mm long plasma density channel, was used to drive an intense plasma wave (wakefield), producing electron bunches with energies on the order of 100 MeV and acceleration gradients on the order of 100 GV/m. Beam energy was increased from 100 MeV to 1 GeV by using a few‐cm long guiding channel at lower density, driven by a 40 TW laser, demonstrating the anticipated scaling to higher beam energies. Particle simulations indicate that the low energy spread beams were produced from self‐trapped electrons through the interplay of trapping, loading, and dephasing. Other experiments and simulations are also underway to control injection of particles into the wake, and hence improve beam quality and stability further.

title: Long-range persistence of femtosecond modulations on laser-plasma-accelerated electron beams.
abstract: Laser plasma accelerators have produced femtosecond electron bunches with a relative energy spread ranging from 100% to a few percent. Simulations indicate that the measured energy spread can be dominated by a correlated spread, with the slice spread significantly lower. Measurements of coherent optical transition radiation are presented for broad-energy-spread beams with laser-induced density and momentum modulations. The long-range (meter-scale) observation of coherent optical transition radiation indicates that the slice energy spread is below the percent level to preserve the modulations.

title: Generation of single pulse particle beams in a plasma channel by laser injection in laser wakefield accelerators
abstract: A laser injection mechanism that generates a single pulse, high quality beam is described. In the past, different all-optical injection schemes for the generation of ultrashort electron bunches were proposed. A very promising scheme proposed by E. Esarey [E. Esarey, R.F. Hubbard, W.P. Leemans A. Ting and P. Sprangle,"  (1997)] uses the collision of two counterpropagation laser pulses to inject particles. However, the results of ours 2D particle-in-cell (PIC) simulations have shown that in addition to the bunch created by pulse collision, a train of pulses is also generated by a different mechanism. In this paper we show that is possible to achieve a single pulse, high quality beam if the generation of the plasma wakefield takes place in a channel and particles are injected by a phase-kick mechanism [J. Cary at this conference]. We have performed 2D PIC simulations of our proposed injection scheme using the code VORPAL [C. Nieter at this conference]. We have obtained a high quality 11 MeV., 6 fs. single electron bunch with energy spread of 4% and emittance of 0.01/spl pi/ - mm - mrad.

title: Design considerations for a laser‐plasma linear collider
abstract: Design considerations for a next‐generation electron‐positron linear collider based on laser‐plasma‐accelerators are discussed. Several of the advantages and challenges of laser‐plasma‐based accelerator technology are addressed. An example of the parameters for a 1 TeV laser‐plasma‐based collider is presented.

title: The Chiral Phase Transition from Lattice QCD with Physical Pion Masses and Domain Wall Fermions
abstract: The HotQCD collaboration has extended its study of the finite temperature transition in 2+1 flavor QCD using domain wall fermions (DWF) to the physical point. With chiral fermions and truly physical pion masses, these calculations are arguably the most realistic of their kind to date, and not possible without a combination of algorithmic advances (chiefly the dislocation suppressing determinant ratio, DSDR), highly optimized BAGEL/CPS software, and access to the LLNL/IBM 20 Petaflops Sequoia Blue Gene/Q. All results are for a fixed temporal lattice size of 8, yet discretization effects, at least for the spectrum at zero temperature, are expected to be at the 5% level. Presented here are early results – in particular, the critical temperature and pion mass dependence of the light quark chiral susceptibility.

title: Equation of state in ( 2+1 )-flavor QCD
abstract: We present results for the equation of state in (2 + 1)-flavor QCD using the highly improved staggered quark action and lattices with temporal extent N tau = 6, 8, 10, and 12. We show that these data can be reliably extrapolated to the continuum limit and obtain a number of thermodynamic quantities and the speed of sound in the temperature range 130-400 MeV. We compare our results with previous calculations and provide an analytic parameterization of the pressure, from which other thermodynamic quantities can be calculated, for use in phenomenology. We show that the energy density in the crossover region, 145 MeV <= T <= 163 MeV, defined by the chiral transition, is epsilon(c) = (0.18-0.5) GeV/fm(3), i.e., (1.2-3.1) epsilon(nuclear). At high temperatures, we compare our results with resummed and dimensionally reduced perturbation theory calculations. As a byproduct of our analyses, we obtain the values of the scale parameters r(0) from the static quark potential and w(0) from the gradient flow.

title: Chiral symmetry breaking in nearly conformal gauge theories
abstract: We present new results on chiral symmetry breaking in nearly conformal gauge theories with fermions in the fundamental representation of the SU(3) color gauge group. The number of fermion flavors is varied in an extended range below the conformal window with chiral symmetry breaking ($\chi{\rm SB}$) for all flavors between $N_f=4$ and $N_f=12$. To identify $\chi{\rm SB}$ we apply several methods which include, within the framework of chiral perturbation theory, the analysis of the Goldstone spectrum in the p-regime and the spectrum of the fermion Dirac operator with eigenvalue distributions of random matrix theory in the $\eps$-regime. Chiral condensate enhancement is observed with increasing $N_f$ when the electroweak symmetry breaking scale $F$ is held fixed in technicolor language. Important finite-volume consistency checks from the theoretical understanding of the $SU(N_f)$ rotator spectrum of the $\delta$-regime are discussed. We also consider these gauge theories at $N_f=16$ inside the conformal window. The importance of understanding finite volume, zero momentum gauge field dynamics inside the conformal window is pointed out. Staggered lattice fermions with supressed taste breaking are used throughout the simulations.

title: Lattice simulations with eight flavors of domain wall fermions in SU(3) gauge theory
abstract: We study an SU(3) gauge theory with Nf=8 degenerate flavors of light fermions in the fundamental representation. Using the domain wall fermion formulation, we investigate the light hadron spectrum, chiral condensate and electroweak S parameter. We consider a range of light fermion masses on two lattice volumes at a single gauge coupling chosen so that IR scales approximately match those from our previous studies of the two- and six-flavor systems. Our results for the Nf=8 spectrum suggest spontaneous chiral symmetry breaking, though fits to the fermion mass dependence of spectral quantities do not strongly disfavor the hypothesis of mass-deformed infrared conformality. Compared to Nf=2 we observe a significant enhancement of the chiral condensate relative to the symmetry breaking scale F, similar to the situation for Nf=6. The reduction of the S parameter, related to parity doubling in the vector and axial-vector channels, is also comparable to our six-flavor results.

title: Probing technicolor theories with staggered fermions
abstract: One exciting possibility of new physics beyond the Standard Model is that the fundamental Higgs sector is replaced by a strongly-interacting gauge theory, known as technicolor. A viable theory must break chiral symmetry dynamically, like in QCD, to generate Goldstone bosons which become the longitudinal components of the W ± and Z. By measuring the eigenvalues of the Dirac operator, one can determine if chiral symmetry is in fact spontaneously broken. We simulate SU(3) gauge theory with ns = 2 and 3 staggered flavors in the fundamental representation, corresponding to Nf = 8 and 12 flavors in the continuum limit. Although our first findi ngs show that both theories are consistent with dynamically broken chiral symmetry and QCD-like behavior, flavor breaking effects in the spectrum may require further c larifications before final conclusions can be drawn. We also compare various improved staggered actions, to suppress this potentially large flavor breaking.