13725223
Plasma gradient controlled injection and postacceleration of high quality electron bunches
Plasma density gradient control of wake phase velocity and trapping threshold in a laser wakefield accelerator produced electron bunches with absolute longitudinal and transverse momentum spreads more than ten times lower than in previous experiments (0.17 and 0.02 MeV/c FWHM, respectively) and with central momenta of 0.76±0.02 MeV/c, stable over a week of operation. Simulations validated against diagnostics show that use of such bunches as a wakefield accelerator injector can produce stable beams with 0.2 MeV/c‐class momentum spread at high energies. Preservation of bunch momentum spread requires high simulation momentum accuracy, and related self‐trapped simulations showed that high order particle weight effectively suppresses simulation momentum errors allowing design of low emittance stages.
9545680
Long-range persistence of femtosecond modulations on laser-plasma-accelerated electron beams.
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.
118442980
Optimized laser pulse profile for efficient radiation pressure acceleration of ions
The radiation pressure acceleration regime of laser ion acceleration requires high intensity laser pulses to function efficiently. Moreover, the foil should be opaque for incident radiation during the interaction to ensure maximum momentum transfer from the pulse to the foil, which requires proper matching of the target to the laser pulse. However, in the ultrarelativistic regime, this leads to large acceleration distances, over which the high laser intensity for a Gaussian laser pulse must be maintained. It is shown that proper tailoring of the laser pulse profile can significantly reduce the acceleration distance, leading to a compact laser ion accelerator, requiring less energy to operate.
21248438
Mono-Energetic Beams from Laser Plasma Interactions
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.
55045125
Design considerations for a laser‐plasma linear collider
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.
118397655
High Quality Electron Bunches up to 1 GeV from Laser Wakefield Acceleration at LBNL
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.
116984453
Equation of state in ( 2+1 )-flavor QCD
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.
118294378
Calculating the running coupling in strong electroweak models
One possibility for Beyond Standard Model physics is a new strongly-interacting gauge theory. One way to determine if a non-abelian gauge theory is QCD-like or conformal is to measure the running of the renormalized gauge coupling. We define the renormalized coupling from Wilson loop ratios, and measure these ratios via lattice simulations. We test this method in SU(3) pure gauge theory and show some first results for simulations with dynamical fermions in the fundamental representation.
16605823
New Higgs physics from the lattice
We report the first results from our comprehensive lattice to ol set to explore non-perturbative aspects of Higgs physics in the Standard Model. We demonstrate in Higgs-Yukawa models that Higgs mass lower bounds and upper bounds can be determined in lattice simulations when triviality requires the necessity of a finite cutoff to maintain n on-zero interactions. The vacuum instability problem is investigated and the lattice approa ch is compared with the traditional renormalization group procedure which sets similar goals to corr elate lower and upper Higgs mass bounds with the scale of new physics. A novel feature of our lattice simulations is the use of Ginsparg-Wilson fermions to represent the effects of Top quark loops in Higgs dynamics. The need for chiral lattice fermions is discussed and the approa ch is extended to full Top-Higgs-QCD dynamics. We also report results from our large NF analysis of Top-Higgs Yukawa models to gain analytic insight and to verify our new lattice tool set which is deployed in the simulations. The role of non-perturbative lattice studies to investigate he avy Higgs particle scenarios is illustrated in extensions of the Standard Model.
118519706
Chiral symmetry breaking in nearly conformal gauge theories
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.
118400281
Maximum-likelihood approach to topological charge fluctuations in lattice gauge theory
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.