Optimization of soft x-ray amplifiers by controlling plasma hydrodynamics.

Several coherent soft x-ray lasers are available for applications nowadays. Among them, plasma-based soft x-ray lasers promise to generate high-energy, highly coherent, short pulse beam. Solid target based amplifiers, due to the fact that his density is higher, should store a higher amount of energy. However, to-date output energy from seeded solid amplifiers remains as low as 60 nJ. We demonstrated that the extraction of the energy stored in the plasma is enhanced by carefully tailoring the plasma shape, to inhibit deleterious hydrodynamical effects. With 1 mm wide plasma, energy as high as 22 μJ in sub-ps pulse is achievable. Not only the energy extracted is higher in these tailored plasmas but also gain and pumping efficiency are increased by nearly a factor of ten as compared to the narrowest plasma amplifiers studied previously and here

Laser-driven plasma waves in capillary tubes

The excitation of plasma waves over a length of up to 8 centimeters is, for the first time, demon- strated using laser guiding of intense laser pulses through hydrogen filled glass capillary tubes. The plasma waves are diagnosed by spectral analysis of the transmitted laser radiation. The dependence of the spectral redshift, measured as a function of filling pressure, capillary tube length and incident laser energy, is in excellent agreement with simulation results. The longitudinal accelerating field inferred from the simulations is in the range 1 -10 GV/m

High intensity X/ γ photon beams for nuclear physics and photonics

In this manuscript we review the challenges of Compton back-scattering sources in advancing photon beam performances in the1−20MeVenergy range, underlining the design criteria bringing tomaximum spectral luminosity and briefly describing the main achieve-ments in conceiving and developing new devices (multi-bunch RF cav-ities and Laser recirculators) for the case of ELI-NP Gamma BeamSystem (ELI-NP-GBS)

Study of electron acceleration and X-ray radiation as a function of plasma density in capillary-guided laser wakefield accelerators

Laser wakefield electron acceleration in the blow-out regime and the associated betatron X-rayradiation were investigated experimentally as a function of the plasma density in a configuration where the laser is guided. Dielectric capillary tubes were employed to assist the laser keeping self-focused over a long distance by collecting the laser energy around its central focal spot. With a 40 fs, 16 TW pulsed laser, electron bunches with tens of pC charge were measured to be accelerated to an energy up to 300 MeV, accompanied by X-ray emission with a peak brightness of the order of 10 21 ph/s/mm 2 / mrad 2 /0.1%BW. Electron trapping and acceleration were studied using the emitted X-ray beamdistribution to map the acceleration process; the number of betatron oscillations performed by theelectrons was inferred from the correlation between measured X-ray fluence and beam charge. A studyof the stability of electron and X-ray generation suggests that the fluctuation of X-ray emission can be reduced by stabilizing the beam charge. The experimental results are in good agreement with 3D particle-in-cell (PIC) simulation.Fil: Ju, L.. Universite de Paris Xi; Francia;Fil: Svensson, K.. Lund University; SueciaFil: Ferrari, Hugo Emilio. Comisión Nacional de Energía Atómica. Gerencia del Area de Investigación y Aplicaciones No Nucleares. Gerencia de Física (centro Atómico Bariloche); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Döpp, A.. Universite de Paris Xi; Francia;Fil: Cassou, K.. Universite de Paris Xi; Francia;Fil: Genoud, G.. Lund University; Suecia;Fil: Wojda, F.. Lund University; Suecia;Fil: Burza, M.. Lund University; Suecia;Fil: Persson, A.. Lund University; Suecia;Fil: Lundh, O.. Lund University; Suecia;Fil: Wahlström, C. G.. Lund University; Suecia;Fil: Cros, B.. Universite de Paris Xi; Francia

Charge Fluctuation Forces Between Stiff Polyelectrolytes in Salt Solution: Pairwise Summability Re-examined

We formulate low-frequency charge-fluctuation forces between charged cylinders - parallel or skewed - in salt solution: forces from dipolar van der Waals fluctuations and those from the correlated monopolar fluctuations of mobile ions. At high salt concentrations forces are exponentially screened. In low-salt solutions dipolar energies go as $R^{-5}$ or $R^{-4}$; monopolar energies vary as $R^{-1}$ or $\ln{R}$, where $R$ is the minimal separation between cylinders. However, pairwise summability of rod-rod forces is easily violated in low-salt conditions. Perhaps the most important result is not the derivation of pair potentials but rather the demonstration that some of these expressions may not be used for the very problems that originally motivated their derivation.Comment: 8 pages and 1 fig in ps forma

Laser frequency stabilization using folded cavity and mirror reflectivity tuning

International audienceA new method of laser frequency stabilization using polarization property of an optical cavity is proposed. In a standard Fabry–Perot cavity, the coating layers thickness of cavity mirrors is calculated to obtain the same phase shift for sand p-wave but a slight detuning from the nominal thickness can produce sand p-wave phase detuning. As a result, each wave accumulates a different round-trip phase shift and resonates at a different frequency. Using this polarization property, an error signal is generated by a simple setup consisting of a quarter wave-plate rotated at 45°, a polarizing beam splitter and two photodiodes. This method exhibits similar error signal as the Pound–Drever–Hall technique but without need for any frequency modulation. Lock theory and experimental results are presented in this paper.

Modification of the Sandia National Laboratories/California advanced coordinate measuring machine for high speed scanning

The Moore M48V high accuracy coordinate measuring machine (CMM), while mechanically capable of exact measurement of physical artifacts, is not, in its original configuration, well suited for rapid gathering of high density dimensional information. This report describes hardware and software modifications to the original control and data acquisition system that allow relatively high speed scanning of cylindrical features. We also estimate the accuracy of the individual point data on artifacts measured with this system and provide detailed descriptions of the hardware and software apparatus as an aid to others who may wish to apply the system to cylindrical or other simple geometries. 6 refs., 18 figs., 1 tab

Numerical evidence toward a 2-adic equivariant ''Main Conjecture''

International audienceWe test a conjectural non abelian refinement of the classical 2-adic Main Conjecture of Iwasawa theory. In the first part, we show how, in the special case that we study, the validity of this refinement is equivalent to a congruence condition on the coefficients of some power series. Then, in the second part, we explain how to compute the first coefficients of this power series and thus numerically check the conjecture in that setting

Study of rapid ionisation for simulation of soft X-ray lasers with the 2D hydro-radiative code ARWEN

We present our fast ionisation routine used to study transient softX-raylasers with ARWEN, a two-dimensional hydrodynamic code incorporating adaptative mesh refinement (AMR) and radiative transport. We compute global rates between ion stages assuming an effective temperature between singly-excited levels of each ion. A two-step method is used to obtain in a straightforward manner the variation of ion populations over long hydrodynamic time steps. We compare our model with existing theoretical results both stationary and transient, finding that the discrepancies are moderate except for large densities. We simulate an existing Molybdenum Ni-like transient softX-raylaser with ARWEN. Use of the fast ionisation routine leads to a larger increase in temperature and a larger gain zone than when LTE datatables are used

Spectral analysis and zeta determinant on the deformed spheres

We consider a class of singular Riemannian manifolds, the deformed spheres $S^N_k$, defined as the classical spheres with a one parameter family $g[k]$ of singular Riemannian structures, that reduces for $k=1$ to the classical metric. After giving explicit formulas for the eigenvalues and eigenfunctions of the metric Laplacian $\Delta_{S^N_k}$, we study the associated zeta functions $\zeta(s,\Delta_{S^N_k})$. We introduce a general method to deal with some classes of simple and double abstract zeta functions, generalizing the ones appearing in $\zeta(s,\Delta_{S^N_k})$. An application of this method allows to obtain the main zeta invariants for these zeta functions in all dimensions, and in particular $\zeta(0,\Delta_{S^N_k})$ and $\zeta'(0,\Delta_{S^N_k})$. We give explicit formulas for the zeta regularized determinant in the low dimensional cases, $N=2,3$, thus generalizing a result of Dowker \cite{Dow1}, and we compute the first coefficients in the expansion of these determinants in powers of the deformation parameter $k$.Comment: 1 figur