We are continuing our investigation of the use of stacks of electrically isolated thin metal foils as spectrometers for lost ions from tokamak fusion plasmas. Devices of this type in which the foil thicknesses were a few micrometers were installed on the Joint European Torus during the recent first deuterium–tritium experiment in an effort to observe lost energetic alpha particles. While there was no convincing evidence of lost alpha particles in this experiment, we did observe significant fluxes of low energy (<500 keV) charged particles. In an effort to provide an instrument for the investigation of this phenomenon and of escaping relatively low energy (<100 keV) ions from other fusion plasma devices, we have developed alternative devices with very thin (few hundred nanometers) alternating layers of conductor and insulator. Four such devices have been fabricated and tested for protons with energies between 20 and 160 keV and demonstrated good energy resolution (typically about 10%) for proton bombarding energies between about 40 and 120 keV. One of the devices, consisting of deposited layers of Al, Ti, and SiO2 was operated up to a current density of about 100 m/cm2 at an energy of 100 keV, corresponding to a power volume density of 100 kW/cm3

We are continuing our development of a radiation-hard, charged-particle detector consisting of a series of thin parallel conducting foils as a lost ion diagnostic for high yield d-t tokamak fusion plasmas. Advantages of this detector concept include economy, ability to operate in relatively intense neutron/gamma ray radiation backgrounds and at moderately high temperatures, and a modest degree of energy resolution. A detector consisting of four parallel foils of Ni, each of thickness 2.5 μm, was operated in the Joint European Torus during the recent DTE-1 experiment. During the highest yield pulses of this campaign, (16 MW), the flux of energetic alpha particles at the detector was measured to be less than about 2 nA/cm2. This upper limit is significantly greater than the expected flux assuming classical losses and given the geometry of the detector. During most of the nearly 2500 pulses of the DTE-1 experiment for which the detector response has been inspected, a relatively intense (up to 200 nA/cm2) flux of low energy positively charged particles was observed which appears related to the D-α photon flux at the plasma edge. Similar detector designs have been recently evaluated using monoenergetic helium ion beams from the tandem accelerator at Sandia National Laboratories. One such detector, consisting of six foils of 6 μm thick Al demonstrated an energy resolution of about 7% for 7 MeV alpha particles. Possible improvements to this detector concept include the fabrication of an “integrated circuit” like design consisting of alternately deposited layers of insulator and conductor. Future applications of the detector concept include first wall lost ion diagnostics for the ignition device to test engineering concepts and NSTX.

A premixed methane-air flame was produced on a flat flame burner and exposed to electric fields between the burner and a flat grid electrode. Equivalence ratios of 0.8 and 1.0 were tested at electrode supply voltages up to 10 kV. A Langmuir probe was used to record ion current within the flame. The current increased at low potentials but decreased at higher potentials. Maximum ion current was greater for an equivalence ratio of 1.0. The change in ion concentrations was attributed to the ionic wind at low potentials and dissociative recombination at high potentials. NomenclatureI = Current lp = Langmuir probe length ni = Number density of ions q = Elementary charge r = Distance from edge of the burner rp = Langmuir probe radius SLM = Standard Liters per Minute U = Flow velocity Vb = Langmuir probe bias Vss = Electrode supply voltage y = Distance above burner grid ϵ0 = Permittivity of freespace µi = Ion mobility ϕ = Equivalence ratio