Progress in proton radiography for diagnosis of ICF-relevant plasmas

Proton radiography using laser-driven sources has been developed as a diagnostic since the beginning of the decade, and applied successfully to a range of experimental situations. Multi-MeV protons driven from thin foils via the Target Normal Sheath Acceleration mechanism, offer, under optimal conditions, the possibility of probing laser-plasma interactions, and detecting electric and magnetic fields as well as plasma density gradients with similar to ps temporal resolution and similar to 5-10 mu m spatial resolution. In view of these advantages, the use of proton radiography as a diagnostic in experiments of relevance to Inertial Confinement Fusion is currently considered in the main fusion laboratories. This paper will discuss recent advances in the application of laser-driven radiography to experiments of relevance to Inertial Confinement Fusion. In particular we will discuss radiography of hohlraum and gasbag targets following the interaction of intense ns pulses. These experiments were carried out at the HELEN laser facility at AWE (UK), and proved the suitability of this diagnostic for studying, with unprecedented detail, laser-plasma interaction mechanisms of high relevance to Inertial Confinement Fusion. Non-linear solitary structures of relevance to space physics, namely phase space electron holes, have also been highlighted by the measurements. These measurements are discussed and compared to existing models.

Characterization of a picosecond laser generated 4.5 keV TiK-alpha source for pulsed radiography

K alpha radiation generated by interaction of an ultrashort (1 ps) laser with thin (25 mu m) Ti foils at high intensity (2x10(16) W/cm(2)) is analyzed using data from a spherical Bragg crystal imager and a single hit charge-coupled device spectrometer together with Monte Carlo simulations of K alpha brightness. Laser to K alpha and electron conversion efficiencies have been determined. We have also measured an effective crystal reflectivity of 3.75 +/- 2%. Comparison of imager data with data from the relatively broadband single hit spectrometer has revealed a reduction in crystal collection efficiency for high K alpha yield. This is attributed to a shift in the K-shell spectrum due to Ti ionization. (c) 2005 American Institute of Physics.

TiK alpha radiography of Cu-doped plastic microshell implosions via spherically bent crystal imaging

We show that short pulse laser generated Ti K alpha radiation can be used effectively as a backlighter for radiographic imaging. This method of x-ray radiography features high temporal and spatial resolution, high signal to noise ratio, and monochromatic imaging. We present here the Ti K alpha backlit images of six-beam driven spherical implosions of thin-walled 500-mu m Cu-doped deuterated plastic (CD) shells and of similar implosions with an included hollow gold cone. These radiographic results were used to define conditions for the diagnosis of fast ignition relevant electron transport within imploded Cu-doped coned CD shells. (c) 2005 American Institute of Physics.

Measurement of single mode imprint in laser ablative drive of a thin Al foil by extreme ultraviolet laser radiography

The temporal development of laser driven single mode perturbations in thin A1 foils has been measured using extreme ultraviolet (XUV) laser radiography. 15, 30, 70 and 90 mu m single modes were imprinted on 2 mu m thick A1 foils with an optical driver laser at 527 nm for intensities in the range 5 x 10(12) to 1.5 x 10(13) W cm(-2). The magnitude of the imprinted perturbation at the time of shock break out was determined by fitting to the data estimated curves of growth of the Rayleigh-Taylor instability after shock break out. The efficiency of imprinting is independent of perturbation wavelength in the parameter range of this experiment, suggesting little influence of thermal conduction smoothing. The results are of interest for directly driven inertially confined fusion. (C) 1998 American Institute of Physics.

Characterization of Li-7(p,n)Be-7 neutron yields from laser produced ion beams for fast neutron radiography

Investigations of Li-7(p,n)Be-7 reactions using Cu and CH primary and LiF secondary targets were performed using the VULCAN laser [C.N. Danson , J. Mod. Opt. 45, 1653 (1997)] with intensities up to 3x10(19) W cm(-2). The neutron yield was measured using CR-39 plastic track detector and the yield was up to 3x10(8) sr(-1) for CH primary targets and up to 2x10(8) sr(-1) for Cu primary targets. The angular distribution of neutrons was measured at various angles and revealed a relatively anisotropic neutron distribution over 180degrees that was greater than the error of measurement. It may be possible to exploit such reactions on high repetition, table-top lasers for neutron radiography. (C) 2004 American Institute of Physics.

Characterization of a gamma-ray source based on a laser-plasma accelerator with applications to radiography

The application of high intensity laser-produced gamma rays is discussed with regard to picosecond resolution deep-penetration radiography. The spectrum and angular distribution of these gamma rays is measured using an array of thermoluminescent detectors for both an underdense (gas) target and an overdense (solid) target. It is found that the use of an underdense target in a laser plasma accelerator configuration produces a much more intense and directional source. The peak dose is also increased significantly. Radiography is demonstrated in these experiments and the source size is also estimated. (C) 2002 American Institute of Physics.

Proton radiography as an electromagnetic field and density perturbation diagnostic (invited)

Laser driven proton beams have been used to diagnose transient fields and density perturbations in laser produced plasmas. Grid deflectometry techniques have been applied to proton radiography to obtain precise measurements of proton beam angles caused by electromagnetic fields in laser produced plasmas. Application of proton radiography to laser driven implosions has demonstrated that density conditions in compressed media can be diagnosed with million electron volt protons. This data has shown that proton radiography can provide unique insight into transient electromagnetic fields in super critical density plasmas and provide a density perturbation diagnostics in compressed matter.

Utilisation de la coronarographie en Suisse: une étude de population. [The use of coronary vessel radiography in Switzerland: a population study].

All patients having undergone a coronarography during 1984 have been surveyed in Switzerland. This retrospective study has used existing data in the 13 centers practicing this diagnostic procedure. 4921 coronarographies were carried out in 1984, amongst 4359 patients. In terms of population-based rates, the national figures are 77 procedures/100,000 residents, and 68 patients/100,000 residents. Female rates are one fourth of the male rates (27/100,000 versus 112/100,000). For both sexes, the highest utilization rates are for the age groups 60-64. Swiss figures are relatively low when compared with other developed countries. However, patterns of utilization are very different within the country: according to the Canton of residence of the patient, the utilization rates (standardized for age and sex) vary from 8/100,000 to 160/100,000. There is a distinct gradient from south-west to north-east, which closely corresponds to the distribution of centers practicing the procedure. More intriguing is the fact that cardiovascular mortality shows an inverse geographical gradient, with the highest mortality in Cantons having the lowest rate of coronarography. Various reasons for the observed variations are discussed, in relation with differences in supply of diagnostic and therapeutic equipments, but also in relation with various patterns of demand related to differential morbidity rates and/or differential patterns of clinical decision.