On The Origin of Super-Hot Electrons from Intense Laser Interactions with Solid Targets having Moderate Scale Length Preformed Plasmas

We use PIC modeling to identify the acceleration mechanism responsible for the observed generation of super-hot electrons in ultra-intense laser-plasma interactions with solid targets with pre-formed plasma. We identify several features of direct laser acceleration (DLA) that drive the generation of super-hot electrons. We find that, in this regime, electrons that become super-hot are primarily injected by a looping mechanism that we call loop-injected direct acceleration (LIDA)

Enhancing Bremsstrahlung Production From Ultraintense Laser-Solid Interactions With Front Surface Structures

We report the results of a combined study of particle-in-cell and Monte Carlo modeling that investigates the production of Bremsstrahlung radiation produced when an ultraintense laser interacts with a tower-structured target. These targets are found to significantly narrow the electron angular distribution as well as produce significantly higher energies. These features combine to create a significant enhancement in directionality and energy of the Bremstrahlung radiation produced by a high-Z converter target. These studies employ short-pulse, high intensity laser pulses, and indicate that novel target design has potential to greatly enhance the yield and narrow the directionality of high energy electrons and $\gamma$-rays. We find that the peak $\gamma$-ray brightness for this source is 6.0$\times$10$^{19}$ ${\rm s^{-1}mm^{-2}mrad^{-2}}$ at 10MeV and 1.4$\times$10$^{19}$ ${\rm s^{-1}mm^{-2}mrad^{-2}}$ at 100MeV (0.1$\%$ bandwidth).Comment: arXiv admin note: text overlap with arXiv:1310.328

Effects of wind induced soil moisture stress on the germination and early growth of Pinus banksiana Lamb. on three soil texture types

A controlled environment wind tunnel was used to produce three wind speeds and hence three soil drying rates in order to study the effects of soil moisture stress on seeds and germinants of Pinus banksiana Lamb, planted in a sandy loam, loamy sand and sand. Osmotically primed and untreated seed were sown when the soil was saturated and germination was monitored daily. Germinants at five stages of ontogeny, the most advanced stage being the start of epicotyl growth, were placed into the wind tunnel with the soil saturated. When 50% of the germinants were dead and/or wilted, final length and dry weight of the shoots and roots were measured. All experiments were a split plot factorial design with wind speed as the main plots and the soil and seed or ontogeny stage treatments as the subplots. No seed germinated in the wind tunnel for any of the soil type and wind speed treatment combinations. Therefore, seed were transfered from the soil surface to Petri-dishes in a germination cabinet where germination was monitored daily. Compared to controls (primed and unprimed seed taken from cold storage), germination of unprimed seed decreased with each increase in wind speed, the magnitude of the decrease varying with soil type. A similar response was not noted for the primed seed; osmotic priming appeared to negate the effects of the physical environment. The exact cause could not be determined from these studies. The hypothesis that the unprimed seed did not imbibe some critical, minimum amount of water before drying and that something inhibited germination when the seed was rehydrated is presented and discussed. The fewer number of macropores and the more rapid drying rate of the loamy sand and sandy loam soil types was considered to be the cause of poorer establishment with increasing wind speed of the early ontogeny stages (stages up to the point the radicle has penetrated the soil surface and the seed is slightly elevated). The growth and survival of germinants once established was not affected by these factors. The data suggests that the drying rate of the soil and the inability of root growth to keep up with this drying was considered to be a major factor affecting growth and survival of the established germinants. Additionally, the transpiration rate of the germinants probably played a significant role in the survival time. The loamy sand and sandy loam soil types probably could not supply a sufficient quantity of water to the germinant to keep pace with the transpirational demand. The sandy soil was better for growth and survival than the finer soils probably because of the way water is held in the soil profile once the capillaries are broken. Germinants began to die at soil moisture potentials above the permanent wilting point (PWP) at the high wind speed. This supports the view that PWP is not a soil constant The increase in some growth parameters with increasing wind speed supports the view that increasing wind speed is not always detrimental to germinant growth. Application of the results to field conditions is discussed

Bandpass Dependence of X-ray Temperatures in Galaxy Clusters

We explore the band dependence of the inferred X-ray temperature of the intracluster medium (ICM) for 192 well-observed galaxy clusters selected from the Chandra Data Archive. If the hot ICM is nearly isothermal in the projected region of interest, the X-ray temperature inferred from a broad-band (0.7-7.0 keV) spectrum should be identical to the X-ray temperature inferred from a hard-band (2.0-7.0 keV) spectrum. However, if unresolved cool lumps of gas are contributing soft X-ray emission, the temperature of a best-fit single-component thermal model will be cooler for the broad-band spectrum than for the hard-band spectrum. Using this difference as a diagnostic, the ratio of best-fitting hard-band and broad-band temperatures may indicate the presence of cooler gas even when the X-ray spectrum itself may not have sufficient signal-to-noise to resolve multiple temperature components. To test this possible diagnostic, we extract X-ray spectra from core-excised annular regions for each cluster in our archival sample. We compare the X-ray temperatures inferred from single-temperature fits when the energy range of the fit is 0.7-7.0 keV (broad) and when the energy range is 2.0/(1+z)-7.0 keV (hard). We find that the hard-band temperature is significantly higher, on average, than the broad-band temperature. Upon further exploration, we find this temperature ratio is enhanced preferentially for clusters which are known merging systems. In addition, cool-core clusters tend to have best-fit hard-band temperatures that are in closer agreement with their best-fit broad-band temperatures. We show, using simulated spectra, that this diagnostic is sensitive to secondary cool components (TX = 0.5-3.0 keV) with emission measures >10-30% of the primary hot component.Comment: Accepted for publication in Ap

The Rule of Law and Technocratisation

Contribution to a festschrfit for Martin Krygier; argues that the technocratisation of the rule of law has been a problem for the establishment of the global rule of law, but that taking a pluralist view of the norm & settng it in its proper historical context allows for a more postive view of the potenital for suport to local social actors to work in the domestic politics of of 'recipient' states to slowly build a thicker rule of la

Selective Deuterium Ion Acceleration Using the Vulcan PW Laser

We report on the successful demonstration of selective acceleration of deuterium ions by target-normal sheath acceleration (TNSA) with a high-energy petawatt laser. TNSA typically produces a multi-species ion beam that originates from the intrinsic hydrocarbon and water vapor contaminants on the target surface. Using the method first developed by Morrison, et al.,$^{1}$ an ion beam with $>$99$\%$ deuterium ions and peak energy 14 MeV/nucleon is produced with a 200 J, 700 fs, $>10^{20} W/cm^{2}$ laser pulse by cryogenically freezing heavy water (D$_{2}$O) vapor onto the rear surface of the target prior to the shot. Within the range of our detectors (0-8.5$^{\circ}$), we find laser-to-deuterium-ion energy conversion efficiency of 4.3$\%$ above 0.7 MeV/nucleon while a conservative estimate of the total beam gives a conversion efficiency of 9.4$\%$.Comment: 5 pages, 5 figure

Characterisation of deuterium spectra from laser driven multi-species sources by employing differentially filtered image plate detectors in Thomson spectrometers

A novel method for characterising the full spectrum of deuteron ions emitted by laser driven multi-species ion sources is discussed. The procedure is based on using differential filtering over the detector of a Thompson parabola ion spectrometer, which enables discrimination of deuterium ions from heavier ion species with the same charge-to-mass ratio (such as C6+, O8+, etc.). Commonly used Fuji Image plates were used as detectors in the spectrometer, whose absolute response to deuterium ions over a wide range of energies was calibrated by using slotted CR-39 nuclear track detectors. A typical deuterium ion spectrum diagnosed in a recent experimental campaign is presented.Comment: 7 pages, 7 figure

The f_LT Response Function of D(e,e'p)n at Q^2=0.33(GeV/c)^2

The interference response function f_LT (R_LT) of the D(e,e'p)n reaction has been determined at squared four-momentum transfer Q^2 = 0.33 (GeV/c)^2 and for missing momenta up to p_miss= 0.29 (GeV/c). The results have been compared to calculations that reproduce f_LT quite well but overestimate the cross sections by 10 - 20% for missing momenta between 0.1 (GeV/c) and 0.2 (GeV/c) .Comment: 12 Pages, 10 figure