Laser-plasma energy transport with high intensity short laser pulses

In order to investigate the production of plasma with simultaneous high density and high degree of ionisation and to study laser-plasma energy transport, experiments have been undertaken to measure the plasma electron densities formed in a thin layer of aluminium buried below an overlay of plastic when the plastic overlay is irradiated by focussed lasers of wavelength (and pulse length) .53μm (20ps); .35μm (20ps) and .27 μm (50ps). For the .53μm and .35μm wavelengths, the shorter pulse length (20ps) results in higher time-averaged electron densities (up to 6 × 1022 cm-3) than for the .27μm wavelength experiments with 50 ps pulse length, but the production of hydrogen-like aluminium relative to helium-like is less with the shorter pulse-length

DIAGNOSTICS OF GOLD LASER PLASMAS

Dans le but d'étudier un schéma de laser X dans les nickeloïdes, on a besoin d'un modèle pour déterminer les paramètres qui décrivent les plasmas d'ions lourds fortement ionisés. Le sujet de ce travail est d'étudier les plasmas d'or créés par laser et de comparer les résultats expérimentaux aux prédictions d'un modele collisionnel-radiatif dans les nickeloïdes. La température et la densité électronique sont mesurées à partir des raies d'emission d'un traceur d'aluminium, et sont comparées aux valeurs obtenues avec le modèle collisionnel-radiatif pour un plasma d'or pur. Les résultats montrent que l'on peut estimer la température et la densité électronique dans un plasma d'or pur.In order to achieve a nickel-like X ray laser scheme we need a tool to determine the parameters which characterise the high-2 plasma. The aim of this work is to study gold laser plasmas and to compare experimental results to a collisional-radiative model which describes nickel-like ions. The electronic temperature and density are measured by the emission of an aluminium tracer. They are compared to the predictions of the nickel-like model for pure gold. The results show that the density and temperature can be estimated in a pure gold plasma

Experiments with 'SPRITE' 12 ps facility

Lateral and axial thermal energy transport in laser-plasma interactions has been studied using a short (12 psec) pre-pulse free KrF pumped Raman laser pulse (λ = 268 nm) of low beam divergence. A new method of producing narrow line foci using random phase plates was employed to study the plasma conditions required to generate high gain, short wavelength recombination X-ray lasers. In addition, the laser energy was focused into a small focal spot (8 μm) for higher intensity (1-2 × 1017 cm-2) interaction studies

KrF pumped Raman lasers as X-ray laser drivers

Recent progress in developing KrF laser pumped Raman lasers has shown their potential as X-ray laser drivers. The combination of short wavelength (268 nm) with low beam divergence and high beam intensity gives the possibility of very high focused intensity in very narrow line foci. An 8 cm × 8 cm beam combining Raman amplifier in the Sprite system has generated 0.4 TW, 12 ps pulses with 20 μrad beam divergence. A 10 μm wide line focus has been produced and plasmas from a NaF target have been studied at irradiances up to 3 × 1014 W cm-2. Numerical simulations suggest that the Sprite system should be able to produce high recombination gain in F IX at 8.1 nm and that larger scale KrF pumped Raman lasers which are being considered for future UK and European facilities would be ideal drivers for Mg XII at 4.5 nm

Strategies among phytoplankton in response to alleviation of nutrient stress in a subtropical gyre

Despite generally low primary productivity and diatom abundances in oligotrophic subtropical gyres, the North Atlantic Subtropical Gyre (NASG) exhibits significant diatom-driven carbon export on an annual basis. Subsurface pulses of nutrients likely fuel brief episodes of diatom growth, but the exact mechanisms utilized by diatoms in response to these nutrient injections remain understudied within near-natural settings. Here we simulated delivery of subsurface nutrients and compare the response among eukaryotic phytoplankton using a combination of physiological techniques and metatranscriptomics. We show that eukaryotic phytoplankton groups exhibit differing levels of transcriptional responsiveness and expression of orthologous genes in response to release from nutrient limitation. In particular, strategies for use of newly delivered nutrients are distinct among phytoplankton groups. Diatoms channel new nitrate to growth-related strategies while physiological measurements and gene expression patterns of other groups suggest alternative strategies. The gene expression patterns displayed here provide insights into the cellular mechanisms that underlie diatom subsistence during chronic nitrogen-depleted conditions and growth upon nutrient delivery that can enhance carbon export from the surface ocean