Laser Triggered Injection of Electrons in a Laser Wakefield Accelerator with the Colliding Pulse Method
An injection scheme for a laser wakefield accelerator that employs a counterpropagating laser (colliding with the drive laser pulse, used to generate a plasma wake) is discussed. The threshold laser intensity for electron injection into the wakefield was analyzed using a heuristic model based on phase‐space island overlap. Analysis shows that the injection can be performed using modest counterpropagating laser intensity a1 ⩽ 0.5 for a drive laser intensity of a0 ≃ 1.0. Preliminary experiments were preformed using a drive beam and colliding beam. Charge enhancement by the colliding pulse was observed. Increasing the signal‐to‐noise ratio by means of a preformed plasma channel is discussed.

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: 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: 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: 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: 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: Lattice QCD thermodynamics in the presence of the charm quark
abstract: We present an update on the 2 + 1 flavor QCD equation of state of the Wuppertal–Budapest Collaboration, extending our previous studies to finer lattice spacings and providing a continuum extrapolation of the trace anomaly. A Symanzik improved gauge and a stout-link improved staggered fermion action is utilized. We also present preliminary results for the fully dynamical charmed equation of state.

title: Conformal finite size scaling of twelve fermion flavors
abstract: Extended simulation results and their analysis are reported in a strongly coupled gauge theory with twelve fermion flavors in the fundamental SU(3) color representation. The conformality of the model is probed using mass deformed conformal finite size scaling (FSS) theory driven by the fermion mass anomalous dimension. Two independent conformal FSS fitting procedures are used in the analysis. The first one deploys physics motivated scaling functions, complemented by a second fitting procedure with spline based general B-forms for the scaling functions. The results at fixed gauge coupling show unresolved problems with the conformal hypothesis.

title: Two-color gauge theory with novel infrared behavior.
abstract: Using lattice simulations, we study the infrared behavior of a particularly interesting SU(2) gauge theory, with six massless Dirac fermions in the fundamental representation. We compute the running gauge coupling derived nonperturbatively from the Schrödinger functional of the theory, finding no evidence for an infrared fixed point up through gauge couplings g(2) of order 20. This implies that the theory either is governed in the infrared by a fixed point of considerable strength, unseen so far in nonsupersymmetric gauge theories, or breaks its global chiral symmetries producing a large number of composite Nambu-Goldstone bosons relative to the number of underlying degrees of freedom. Thus either of these phases exhibits novel behavior.

title: Maximum-likelihood approach to topological charge fluctuations in lattice gauge theory
abstract: We present a novel technique for the determination of the topological susceptibility (related to the variance of the distribution of global topological charge) from lattice gauge theory simulations, based on maximum-likelihood analysis of the Markov-chain Monte Carlo time series. This technique is expected to be particularly useful in situations where relatively few tunneling events are observed. Restriction to a lattice subvolume on which topological charge is not quantized is explored, and may lead to further improvement when the global topology is poorly sampled. We test our proposed method on a set of lattice data, and compare it to traditional methods.

title: Neutron-antineutron oscillations on the lattice
abstract: One possible low energy process due to beyond the Standard Model (BSM) physics is the neutron-antineutron transition, where baryon number changes by two units. In addition to providing a source of baryon number violation in the early universe, interactions of this kind are natural in grand unified theories (GUTs) with Majorana neutrinos that violate lepton number. Bounds on these oscillations can greatly restrict a variety of GUTs, while a non-zero signal would be a "smoking gun" for new physics; however, to make a reliable prediction, the six-quark nucleon-antinucleon matrix elements must first be calculated non-perturbatively via lattice QCD. We review the current understanding of this quantity, describe the lattice formalism, and present preliminary results from $32^3\times256$ clover-Wilson lattices with a pion mass of 390 MeV.