The results of a study of the interaction of 60 ns pulses from a gain switched TEA CO2 laser with a range of solid targets are described. Measurements using charge collector probes and soft-X-ray detectors and results of the plasma backscatter are reported for laser flux densities up to 1.2*1011 W cm-2.

We are investigating thin foil Faraday collectors as a diagnostic for lost fast ions from tokamak fusion plasmas. Prototype devices have been recently installed in the National Spherical Torus Experiment and DIII-D. Initial results from these devices indicate a loss of energetic ions from a variety of plasma conditions. Results from a device installed immediately outside a thin Be window on ALCATOR C-mod, as a test on the response to moderately intense fluxes of soft x rays indicate an upper limit of about 2ϫ10 Ϫ22 A/photon/cm 2 at a plasma electron temperature of 1.8 keV. An important property of the diagnostic is the expected ability to operate under fairly high neutron/ gamma radiation backgrounds. We have tested this expectation by measuring the current from a thin ͑2.5 m͒ Ni foil placed in the core of a TRIGA fission reactor. At a maximum steady-state power of 950 kW (10 13 n/cm 2 /s), a current of 1.2 nA/cm 2 was measured.

Abstract.-The formation and propagation of laser supported detonation (LSD) waves and thermal coupling for HF laser irradiated solid targets have been investigated as a function of target material, irradiance and ambient pressure. High speed photography has been employed to study the plasma dynamics and the thresholds for plasmotron and LSD wave production obtained. For the 300nsec duration CFWHM) pulses and l-2mm diameter focal spots used, the LSD thresholds for aluminium, stainless steel and platinum targets were measured to be 0,(2-3) x 10 8 W.cm -2 . Above the LSD threshold the initial expansion velocity showed good agreement with the I 1 ' 3 irradiance dependence predicted by theory. Additional data on the interaction for platinum were obtained using thermocouples to measure the thermal coupling to the target as a function of spot size, irradiance and ambient pressure. A maximum thermal coupling coefficient of 14-18% was measured at an irradiance level slightly below the LSD wave ignition threshold.

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A high radiance unstable resonator HF laser (λ=2.8 μm) has been used to produce plasmas from Al and C targets in a vacuum. Measurements of the plasma properties at irradiance levels up to 7×1010 W cm−2 have been made using a range of diagnostic techniques (x-ray detectors, charge probes, streak photography, and plasma reflection).