[en] A brief review is given of the development of hydropower in the UK. Most of the untapped potential has head heights below 10 metres and recent developments in turbines to exploit such installations are reported. (UK)

[en] The simultaneous achievement of thermonuclear temperatures and densities of 1000 X solid by directly driven laser compression makes very high demands on the performance of the laser and on the fabrication of the targets. The degree of pressure multiplication in the implosion is limited by the symmetry and hydrodynamic stability of the imploding shell, which means that the laser is required to produce an ablation pressure of 50-100 Mbar, with low preheat and high hydrodynamic efficiency. These constraints have forced laser implosion experiments to shorter wavelengths, and the paper reports a series of experiments performed with the second harmonic output (green) of the Rutherford Appleton Laboratory six-beam Nd-glass laser, and on some preliminary results with the new twelve-beam system. The six-beam implosion experiments were performed with a laser energy of 250 J and an irradiance on target of about 2x10¹⁴W.cm^-2. Two different types of target were imploded: a thick-walled, low aspect ratio target designed for good hydrodynamic stability, and a thinner wall target designed to reach thermonuclear temperatures. The low aspect ratio targets were diagnosed by pulsed X-ray backlighting, giving time-resolved two-dimensional images of the imploding shell. The symmetry of illumination of the target could be varied by changing the focusing conditions. The non-uniform illumination was observed in optical harmonic emissions, in X-ray emission from layered targets and in the symmetry of the implosion shadowgrams. The peak compression observed was to less than 10% of the initial target radius, with measured core densities in excess of 10 g.cm^-3. (author)

[en] Experimental observations and numerical simulations covering several important physics aspects of inertial confinement fusion are discussed. The work has been carried out in connection with the high power laser programme of the SERC Central Laser Facility at the Rutherford Appleton Laboratory. The non-linear interaction of an intense laser beam with large millimetre sized preformed plasmas has been studied. A long cylindrical plasma was produced with the multibeam VULCAN laser in line focus configuration. Observations of Stimulated Raman and Brillouin Scattering and laser beam filamentation of an intense green laser beam interacting axially with the preformed plasma have been made. The coalescence of laser induced shocks has been studied by observing the shock breakout on the rear of multiple step aluminium targets using optical streak photography. Coalescence of two shocks has been clearly observed when a shaped laser pulse was used. The observations were modelled with hydrodynamic simulations. The transport process of soft X-ray radiation through thin foil targets were investigated by time resolved XUV spectroscopy. Targets consisting of thin foils overcoated with 100 nm of gold were irradiated with a green laser pulse 800 ps in duration. The soft X-ray radiation from the gold plasma which was transported through the target was time resolved in the 15 to 80 A spectral wavelength region. The experimental observations were modelled with a radiation transport code which was coupled to a 1-dimensional hydrocode. The neutron yield and implosion behaviour were studied on microballoon targets with very large aspect ratios of about 400 which were filled with deuterium. Neutron yields of 2.5x10⁷ were observed. Finally, thermal transport processes occurring both into and along the surface of laser irradiated targets were simulated with a 2-dimensional Fokker-Planck code. Short pulse experiments have been modelled showing that a substantial departure from Spitzer heat flux occurs. 5 refs, 6 figs

[en] Eight experimental and theoretical projects are presented, covering important physics aspects of inertial confinement. An experiment on energy transport employed green laser light on massive plastic spheres with buried diagnostic substrates that emit X-rays at different temperatures. Consistent with theory there was no evidence of a foot in the non-linear heat flow. Time and space resolved density profiles were obtained from the Stark spectroscopy of aluminium tracer dots in plastic targets. When tightly focussed laser beams are employed, megagauss magnetic fields are generated by ∇Tx∇n effects and measured by Faraday rotation. Theoretically, the convection and amplification of magnetic fields by inward heat flow has been extended to non-linear transport by solving the Fokker-Planck equation. Implosion studies employing X-ray back-lighting and spectral emission techniques have shown the influence of variation of the aspect ratio r₀/Δr of polymer shell targets in the range 10-60 driven ablatively by twelve beams (0.53 μm, 0.8 ns) at an absorbed irradiance of 10¹⁴W·cm^-2. Rayleigh-Taylor instabilities in accelerated plane foils have been studied by a novel technique of alpha particle transmission. Non-linear simulations of this instability in spherical geometry show the phenomenon of coalescence of bubbles, while no Kelvin-Helmholtz mushrooming of the spike tips is observed. Fine-scale jets have been diagnosed by a Schlieren technique on spherical targets, showing that the jets occur towards the end of the laser pulse. A non-local treatment of the heat flow driven collisional Weibel instability has shown that inclusion of the Nernst convection of magnetic fields leads to stabilisation. (author). 6 refs, 8 figs

[en] Recent experiments carried out at the Central Laser Facility clearly show amplification of spontaneous emission at 182A with a gl -- 4 in a recombining carbon plasma. Thin 7μm diam. carbon fibres were irradiated with the VULCAN Nd. glass laser system. This scheme was extended to shorter wavelengths by using LiF-coated carbon fibre targets. Initial analysis of the experimental data indicates gain of the Balmer α transition of fluorine at 81A

[en] In, Pb, Zn, and Cu are used to prepare metal-semiconductor contacts on p-type PbTe thin films. They are analysed by I-V and C-V techniques to determine barrier heights, depletion widths, and carrier profiles. The effective barrier energies for In, Pb, and Zn are in the order of the band gap. For Cu on PbTe the effective barrier height is found to be smaller than the band gap. The carrier dependence of the barrier heights is studied and found to be consistent with the inversion model of Walpole and Nill for the In, Pb, and Zn devices. Cu barrier devices on the other hand do not show inversion. (author)

[en] High resolution (better than 20 nm) contact micrographs have been produced with exposure times of about a nanosecond. The illuminating source was a short-lived carbon plasma produced by focusing a single short (approx. 1 ns) 100 J pulse from the Vulcan laser at the Rutherford Appleton Laboratory (RAL) to a 300 μm spot on a graphite target. This plasma emits strongly in the soft X-ray region, particularly at the CVI (3.37 nm) and CV (4.03 nm) lines. The specimens were behind a 100 nm thick Si₃N₄ window, at atmospheric pressure in an environmental cell. The images of diatoms recorded on X-ray resist showed features down to the limit of resolution of the SEM used to view the developed resist, which was about 20 nm. (author)