Equation-of-State Measurement of Dense Plasmas Heated With Fast Protons

We report on the first results of experiments with a new laser-based proton beam line at the GSI accelerator facility in Darmstadt. It delivers high current bunches at proton energies around 9.6 MeV, containing more than 10 9 particles in less than 10 ns and with tunable energy spread down to 2.7% (ΔE=E 0 at FWHM). A target normal sheath acceleration stage serves as a proton source and a pulsed solenoid provides for beam collimation and energy selection. Finally a synchronous radio frequency (rf) field is applied via a rf cavity for energy compression at a synchronous phase of −90 deg. The proton bunch is characterized at the end of the very compact beam line, only 3 m behind the laser matter interaction point, which defines the particle source.

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“…They range from fusion science [1], warm dense matter creation [2][3][4], and diagnostic [5][6][7] up to medical applications [8,9].…”

Section: Introductionmentioning

confidence: 99%

Commissioning of a compact laser-based proton beam line for high intensity bunches around 10 MeV

Busold

Schumacher

Deppert

et al. 2014

Phys. Rev. ST Accel. Beams

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“…However, with the advent of new fourth-generation X-ray light sources, including the free-electron laser in Hamburg 8 (FLASH), soft X-ray intensities that have previously remained the province of high-power optical lasers can now be produced. Experiments at such high intensities using gas jets have already exhibited novel absorption phenomena 9 , and the possibility of irradiating solid samples with intense soft and hard X-rays has aroused interest as a possible means of producing warm dense matter (WDM) at known atomic densities 10,11 .We present the first measurements of the absorption coefficient of solid samples subject to subpicosecond soft X-ray pulses with intensities up to and in excess of 10 16 W cm −2 , two orders of magnitude higher than could previously be obtained. The experiment has two phases: the first occurs during the 15 fs freeelectron laser (FEL) pulse, whereas the second occurs after the pulse.…”

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confidence: 99%

Turning solid aluminium transparent by intense soft X-ray photoionization

Nagler¹,

Zastrau²,

Fäustlin³

et al. 2009

Nature Phys

252

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Saturable absorption is a phenomenon readily seen in the optical and infrared wavelengths. It has never been observed in core-electron transitions owing to the short lifetime of the excited states involved and the high intensities of the soft X-rays needed. We report saturable absorption of an L-shell transition in aluminium using record intensities over 10 16 W cm −2 at a photon energy of 92 eV. From a consideration of the relevant timescales, we infer that immediately after the X-rays have passed, the sample is in an exotic state where all of the aluminium atoms have an L-shell hole, and the valence band has approximately a 9 eV temperature, whereas the atoms are still on their crystallographic positions. Subsequently, Auger decay heats the material to the warm dense matter regime, at around 25 eV temperatures. The method is an ideal candidate to study homogeneous warm dense matter, highly relevant to planetary science, astrophysics and inertial confinement fusion. Saturable absorption, the decrease in the absorption of light with increasing intensity, is a well-known effect in the visible and near-visible region of the electromagnetic spectrum 1 , and is a widely exploited phenomenon in laser technology. Although there are many ways to induce this effect, in the simplest two-level system it will occur when the population of the lower, absorbing level is severely depleted, which requires light intensities sufficiently high to overcome relaxation from the upper level. Here, we report on the production of saturable absorption of a metal in the soft X-ray regime by the creation of highly uniform warm dense conditions, a regime that is of great interest in high-pressure science 2,3 , the geophysics of large planets 4,5 , astrophysics 6 , plasma production and inertial confinement fusion 7 . Furthermore, the process by which the saturation of the absorption occurs will lead, after the X-ray pulse, to the storage of about 100 eV per atom, which in turn evolves to a warm dense state. This manner of creation is unique as it requires intense, subpicosecond, soft X-rays. As such, it has not hitherto been observed in this region of the spectrum, owing both to the lack of high-intensity sources, and the rapid recombination times associated with such high photon energies. However, with the advent of new fourth-generation X-ray light sources, including the free-electron laser in Hamburg 8 (FLASH), soft X-ray intensities that have previously remained the province of high-power optical lasers can now be produced. Experiments at such high intensities using gas jets have already exhibited novel absorption phenomena 9 , and the possibility of irradiating solid samples with intense soft and hard X-rays has aroused interest as a possible means of producing warm dense matter (WDM) at known atomic densities 10,11 .We present the first measurements of the absorption coefficient of solid samples subject to subpicosecond soft X-ray pulses with intensities up to and in excess of 10 16 W cm −2 , two orders of magnitude higher than could ...

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“…We heated solid density copper to temperatures ranging from 5 to 10 eV on a picosecond timescale and measured the resulting dynamic copper plasma similar to recent experiments on warm dense aluminum [8,[14][15][16]. Copper and other transition metals are interesting candidates for EOS study, in part because of the complexities arising from their orbital structure [17].…”

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confidence: 99%

“…We measured the expansion at the back surface of the proton heated Cu sample using Fourier Domain Interferometry (FDI) [15,[23][24][25]. A fraction of the laser energy was picked off at an early stage of amplification and compressed independently to the main pulse, leaving a linear chirp of 2.4 ps/nm, which correlated time to wavelength in a ~50 ps window.…”

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confidence: 99%