A thin film device as a low energy, high flux charged particle spectrometer

We are continuing our investigation of the use of stacks of electrically is olated thin metal foils as spectrometers for lost ions from tokamak fusion plasmas. Devices of this type in which the foil thicknesses were a few micr ometers were installed on the Joint European Torus during the recent first deuterium-tritium experiment in an effort to observe lost energetic alpha p articles. While there was no convincing evidence of lost alpha particles in this experiment, we did observe significant fluxes of low energy (< 500 ke V) charged particles. In an effort to provide an instrument for the investi gation of this phenomenon and of escaping relatively low energy (< 100 keV) ions from other fusion plasma devices, we have developed alternative devic es with very thin (few hundred nanometers) alternating layers of conductor and insulator. Four such devices have been fabricated and tested for proton s with energies between 20 and 160 keV and demonstrated good energy resolut ion (typically about 10%) for proton bombarding energies between about 40 a nd 120 keV. One of the devices, consisting of deposited layers of Al, Ti, a nd SiO2 was operated up to a current density of about 100 m/cm(2) at an ene rgy of 100 keV, corresponding to a power volume density of 100 kW/cm(3) (C) 2001 American Institute of Physics.