Quasi-nonlinear Regime Research Articles

Optical-Period Bunch Trains to Resonantly Excite High Gradient Wakefields in the Quasi-Nonlinear Regime and the E-317 Experiment at FACET-II

Optical-Period Bunch Trains to Resonantly Excite High Gradient Wakefields in the Quasi-Nonlinear Regime and the E-317 Experiment at FACET-II

Resonant excitation of very high gradient plasma wakefield accelerators by optical-period bunch trains

Using a periodic electron beam bunch train to resonantly excite plasma wakefields in the quasi-nonlinear (QNL) regime has distinct advantages over employing a single, higher charge bunch. Resonant excitation in the QNL regime can produce plasma electron blowout using very low emittance beams with a small charge per pulse: the local density perturbation is extremely nonlinear, achieving total rarefaction, yet the resonant response of the plasma electrons at the plasma frequency is preserved. Such a pulse train, with inter-bunch spacing equal to the plasma period, can be produced via inverse free-electron laser bunching. To achieve resonance with a laser wavelength of a few microns, a high plasma density is used, with the attendant possibility of obtaining extremely large wakefield amplitude, near 1 TV/m for FACET-II parameters. In this article, we use particle-in-cell simulations to study the plasma response, the beam modulation evolution, and the instabilities encountered, that arise when using a bunching scheme to resonantly excite waves in a dense plasma.

The two and three-loop matter bispectrum in perturbation theories

We evaluate for the first time the dark matter bispectrum of large-scale structure at two loops in the Standard Perturbation Theory and at three loops in the Renormalised Perturbation Theory (MPTBREEZE formalism), removing in each case the leading divergences in the integrals in order to make them infrared-safe. We show that the Standard Perturbation Theory at two loops can be employed to model the matter bispectrum further into the quasi-nonlinear regime compared to the one loop, up to kmax ∼ 0.1 h/Mpc at z = 0, but without reaching a high level of accuracy. In the case of the MPTBREEZE method, we show that its bispectra decay at smaller and smaller scales with increasing loop order, but with smaller improvements decreases with loop order. At three loops, this model predicts the bispectrum accurately up to scales kmax ∼ 0.17 h/Mpc at z = 0 and kmax ∼ 0.24 h/Mpc at z = 1.

Resonant plasma excitation by single-cycle THz pulses

In this paper, an alternative perspective for the generation of millimetric high-gradient resonant plasma waves is discussed. This method is based on the plasma-wave excitation by energetic single-cycle THz pulses whose temporal length is comparable to the plasma wavelength. The excitation regime discussed in this paper is the quasi-nonlinear regime that can be achieved when the normalized vector potential of the driving THz pulse is on the order of unity. To investigate this regime and determine the strength of the excited electric fields, a Particle-In-Cell (PIC) code has been used. It has been found that by exploiting THz pulses with characteristics currently available in laboratory, longitudinal electron plasma waves with electric gradients up to hundreds MV/m can be obtained. The mm-size nature of the resonant plasma wave can be of great utility for an acceleration scheme in which high-brightness electron bunches are injected into the wave to undergo a strong acceleration. The long-size nature of the acceleration bucket with respect to the short length of the electron bunches can be handled in a more robust manner in comparison with the case when micrometric waves are employed.

Plasma wakefield acceleration at CLARA facility in Daresbury Laboratory

A plasma accelerator research station (PARS) has been proposed to study the key issues in electron driven plasma wakefield acceleration at CLARA facility in Daresbury Laboratory. In this paper, the quasi-nonlinear regime of beam driven plasma wakefield acceleration is analysed. The wakefield excited by various CLARA beam settings are simulated by using a 2D particle-in-cell (PIC) code. For a single drive beam, an accelerating gradient up to 3GV/m can be achieved. For a two bunch acceleration scenario, simulation shows that a witness bunch can achieve a significant energy gain in a 10–50cm long plasma cell.

Numerical investigation of beam-driven PWFA in quasi-nonlinear regime

In beam-driven Plasma Based Wakefield Acceleration (PWFA), the quasi-nonlinear model has been designed to combine high efficient ‘blowout’ regimes, where cold and overdense driving electron beams form a totally rarefied plasma channel, with low charge beam distribution assuring the excited wakefield preserves relevant linear properties.This scheme can have applications in experimental facilities, like SPARC 150MeV linac at LNF-INFN laboratories, where low-emittance, low-charge narrow electron beams can be produced to be injected on a preformed plasma channel.Here we present a preliminary numerical investigation of this configuration, using the fully 3D ALaDyn PIC code, as a preparatory work to design optimal conditions for the COMB experimental set-up. Specific numerical tools, having computational and diagnostic advantages in PWFA conditions and checks of the numerical outcomes with analytical results, are also presented and discussed.

Multiscale inference of matter fields and baryon acoustic oscillations from the Lyα forest

We present a novel Bayesian method for the joint reconstruction of cosmological matter density fields, peculiar velocities and power-spectra in the quasi-nonlinear regime. We study its applicability to the Ly-alpha forest based on multiple quasar absorption spectra. Our approach to this problem includes a multiscale, nonlinear, two-step scheme since the statistics describing the matter distribution depends on scale, being strongly non-Gaussian on small scales (< 0.1 h^{-1} Mpc) and closely lognormal on scales >~10 h^{-1} Mpc. The first step consists on performing 1D highly resolved matter density reconstructions along the line-of-sight towards z~2-3 quasars based on an arbitrary non-Gaussian univariate model for matter statistics. The second step consists on Gibbs-sampling based on conditional PDFs. The matter density field is sampled in real space with Hamiltonian-sampling using the Poisson/Gamma-lognormal model, while redshift distortions are corrected with linear Lagrangian perturbation theory. The power-spectrum of the lognormal transformed variable which is Gaussian distributed (and thus close to the linear regime) can consistently be sampled with the inverse Gamma distribution function. We test our method through numerical N-body simulations with a computational volume large enough (> 1 h^{-3} Gpc^3) to show that the linear power-spectra are nicely recovered over scales larger than >~20 h^{-1} Mpc, i.e. the relevant range where features imprinted by the baryon-acoustics oscillations (BAOs) appear.

SIMULATIONS OF BARYON ACOUSTIC OSCILLATIONS. II. COVARIANCE MATRIX OF THE MATTER POWER SPECTRUM

We use 5000 cosmological N-body simulations of 1 h –3 Gpc3 box for the concordance ΛCDM model in order to study the sampling variances of a nonlinear matter power spectrum. We show that the non-Gaussian errors can be important even on large length scales relevant for baryon acoustic oscillations (BAOs). Our findings are the following: (1) the non-Gaussian errors degrade the cumulative signal-to-noise ratios (S/Ns) for the power spectrum amplitude by up to a factor of 2 and 4 for redshifts z = 1 and 0, respectively; (2) there is little information on the power spectrum amplitudes in the quasi-nonlinear regime, confirming the previous results; (3) the distribution of power spectrum estimators at BAO scales, among the realizations, is well approximated by a Gaussian distribution with variance that is given by the diagonal covariance component. (4) For the redshift-space power spectrum, the degradation in S/N by non-Gaussian errors is mitigated due to nonlinear redshift distortions; (5) for an actual galaxy survey, the additional shot noise contamination compromises the cosmological information inherent in the galaxy power spectrum, but also mitigates the impact of non-Gaussian errors. The S/N is degraded by up to 30% for a Wide-Field Fiber-Fed Optical Multi-Object Spectrograph-type survey; (6) the finite survey volume causes additional non-Gaussian errors via the correlations of long-wavelength fluctuations with the fluctuations we want to measure, further degrading the S/N values by about 30% even at high redshift z = 3.

Third-Order Density Perturbation and One-Loop Power Spectrum in Dark-Energy-Dominated Universe

We investigate the third-order density perturbation and the one-loop correction to the linear power spectrum in the dark-energy cosmological model. Our main interest is to understand the dark-energy effect on baryon acoustic oscillations in a quasi-nonlinear regime ($k \approx 0.1h$/Mpc). Analytical solutions and simple fitting formulae are presented for the dark-energy model with the general time-varying equation of state $w(a)$. It turns out that the power spectrum coincides with the approximate result based on the EdS (Einstein de-Sitter) model within 1% for $k<0.4h/$Mpc at $z=0$ in the WMAP (Wilkinson Microwave Anisotropy Probe) 5yr best-fitting cosmological model, which suggests that the cosmological dependence is very small.

Amplitude-frequency characteristic of a nonlinear spin wave interferometer operating in a quasi-nonlinear regime

A thin-film nonlinear spin wave interferometer has been experimentally studied. The concept of a quasi-nonlinear operation regime is introduced for the first time and the boundaries of the quasi-nonlinear dynamic range of the interferometer are experimentally determined. It is shown that the nonlinear spin wave interferometer operating in the quasi-nonlinear regime can be characterized, like linear devices, by the amplitude-frequency characteristic (AFC). However, an increase in the signal power level within the quasi-nonlinear dynamic range at the input of the nonlinear interferometer leads, in contrast to the case of a linear device, to a frequency shift of the AFC. An analysis of the AFC shift indicates that a 180° change in the phase difference between the interfering signals at each separate frequency is achieved for the input power varied within the limits of the quasi-nonlinear dynamic range. This behavior shows the possibility of using the nonlinear interferometer for the processing of microwave signals without undesired distortion of the signal waveform.

Correspondence between the adhesion model and the velocity dispersion for the cosmological fluid

Basing our discussion on the Lagrangian description of hydrodynamics, we studied the evolution of density fluctuation for nonlinear cosmological dynamics. Adhesion approximation (AA) is known as a phenomenological model that describes the nonlinear evolution of density fluctuation rather well and that does not form a caustic. In addition to this model, we have benefited from discussion of the relation between artificial viscosity in AA and velocity dispersion. Moreover, we found it useful to regard whether the velocity dispersion is isotropic produces effective pressure or viscosity terms. In this paper, we analyze plane- and spherical-symmetric cases and compare AA with Lagrangian models where pressure is given by a polytropic equation of state. From our analyses, the pressure model undergoes evolution similar to that of AA until reaching a quasinonlinear regime. Compared with the results of a numerical calculation, the linear approximation of the pressure model seems rather good until a quasinonlinear regime develops. However, because of oscillation arising from the Jeans instability, we could not produce a stable nonlinear structure.

Density field in extended Lagrangian perturbation theory

We analyze the performance of a perturbation theory for nonlinear cosmological dynamics, based on the Lagrangian description of hydrodynamics. In our previous paper, we solved the hydrodynamic equations for a self-gravitating fluid with pressure, given by a polytropic equation of state, using a perturbation method. Then we obtained the first-order solutions in generic background universes and the second-order solutions for a wider range of polytrope exponents. Using these results, we describe density fields with a scale-free spectrum, SCDM, and LCDM models. Then we analyze the cross-correlation coefficient of the density field between N-body simulation and Lagrangian linear perturbation theory, and the probability distribution of the density fluctuations. From our analyses, for scale-free spectrum models, the case of the polytrope exponent 5/3 shows better performance than the Zel'dovich approximation and the truncated Zel'dovich approximation in the quasinonlinear regime. On the other hand, for SCDM and LCDM models, the improvement by including the effect of the velocity dispersion was small.

The Signatures of Voids and the CMBR

Annals of the New York Academy of SciencesVolume 759, Issue 1 p. 710-713 The Signatures of Voids and the CMBR Sharon L. Vadas, Sharon L. Vadas Center for Particle Astrophysics, 301 Le Conte Hall University of California; Berkeley, CA 94720-7304Search for more papers by this author Sharon L. Vadas, Sharon L. Vadas Center for Particle Astrophysics, 301 Le Conte Hall University of California; Berkeley, CA 94720-7304Search for more papers by this author First published: September 1995 https://doi.org/10.1111/j.1749-6632.1995.tb17641.xCitations: 1AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume759, Issue1Seventeenth Texas Symposium on Relativistic Astrophysics and CosmologySeptember 1995Pages 710-713 RelatedInformation