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Two vertical cosmic ray telescopes for atmospheric cosmic ray ionization event detection are compared. Counter A, designed for low power remote use, was deployed in the Welsh mountains; its event rate increased with altitude as expected from atmospheric cosmic ray absorption. Independently, Counter B's event rate was found to vary with incoming particle acceptance angle. Simultaneous co-located comparison of both telescopes exposed to atmospheric ionization showed a linear relationship between their event rates. [ABSTRACT FROM AUTHOR]

A silicon field emitter neutralizer is under development at the Rutherford Appleton Laboratory for the LISA Pathfinder mission [B.J. Kent et al., Class Quantum Grav. 22, S483 (2005)]. A summary of this project from the fabrication point of view is presented in this article. An investigation of the effect of fabrication uniformity on emission characteristics showed that the geometrical nonuniformity, including tip height and gate diameter, across a 4-in. wafer is below 15%. This variation had only a small effect (∼10%) on the field-emission characteristics. In order to improve the reliability of the silicon field emitters for the space environment operation, a thin aluminum nitride (AlN) film is coated on the silicon emitters, and the chromium gate electrode is oxidized in furnace. The effects of adding the layer of AlN and thermal oxidation of the chromium gate electrode on field emission and lifetime were investigated in this article. A fabrication yield analysis estimated that 50% of arrays on the original wafer functioned correctly in the final device, but that this can be substantially improved by a more rigorous device handling control. [ABSTRACT FROM AUTHOR]

Development of reliable field emission devices requires detailed characterization of variability over the device lifetime. Silicon tip manufacturing processes and test equipment limitations are theoretically predicted to cause ∼5% variability in field emission currents. Long-duration emission current measurements at both constant voltage and constant current, controlled with a software feedback loop, were made. Power spectra from the two operational modes were significantly different. The software feedback loop response was determined; it is expected to contribute ∼1% of the standard deviation in emission current when used to control emission by modulating the gate voltage. Convolution of constant voltage time series with the software feedback loop response reproduced the spectral characteristics of constant current time series, indicating that many of the differences between the two operating modes were caused by the operating mode itself rather than the field emitters tested. This has implications for the operating mode of the application for which the device is intended. [ABSTRACT FROM AUTHOR]

Measurements of ions in atmospheric air are used to investigate atmospheric electricity and particulate pollution. Commonly studied ion parameters are (1) air conductivity, related to the total ion number concentration, and (2) the ion mobility spectrum, which varies with atmospheric composition. The physical principles of air ion instrumentation are long established. A recent development is the computerized aspirated capacitor, which measures ions from (a) the current of charged particles at a sensing electrode, and (b) the rate of charge exchange with an electrode at a known initial potential, relaxing to a lower potential. As the voltage decays, only ions of higher and higher mobility are collected by the central electrode and contribute to the further decay of the voltage. This enables extension of the classical theory to calculate ion mobility spectra by inverting voltage decay time series. In indoor air, ion mobility spectra determined from both the voltage decay inversion, and an established voltage switching technique, were compared and shown to be of similar shape. Air conductivities calculated by integration were: 5.3±2.5 and 2.7±1.1 fSm-1, respectively, with conductivity determined to be 3 fSm-1 by direct measurement at a constant voltage. Applications of the relaxation potential inversion method include air ion mobility spectrum retrieval from historical data, and computation of ion mobility spectra in planetary atmospheres. [ABSTRACT FROM AUTHOR]

Motivated by the detection of infrared absorption bands from atmospheric cluster ions in laboratory experiments, a narrowband filter radiometer has been constructed for ion detection in the atmosphere. It uses a filter centered at 9.15 μm wavelength with 5% bandwidth, protected by a diamond-like-carbon coated germanium auxiliary filter, and fitted to a standard pyrradiometer. A sensitivity of (29.3±0.1) μV/(W m-2) has been determined in a laboratory calibration using a blackbody source. Atmospheric experiments show that the filter radiometer, when used with a stable, low-noise amplifier, can respond to cluster-ion fluctuations. The filter radiometer’s sensitivity to atmospheric ion changes is (0.47±0.05) (mW m-2)/(ions cm-3). [ABSTRACT FROM AUTHOR]

The authors' comments on B.E. Sauer and his colleagues' research paper "A Robust Floating Nanoammeter" published in the online version of the journal on May 7, 2009. They say it is surprising the paper authors do not focus more on the novel aspects of nanoammeter. According to them, the paper also does not offer any information on the time response of the nanoammeter. This information could have been used by other scientists and engineers to determine the applicability of the device.

Ion measurements in atmospheric air allow atmospheric ion-aerosol charge exchange to be investigated, which is thought to be important in cloud processes. Classical aspiration ion measurement techniques have been significantly improved by the use of electronic switching systems to permit the selection of different mobilities, with adjacent instruments using the combination of Voltage Decay and ion current techniques used for calibration. An integrated programable ion mobility spectrometer using the same collection electrodes in both modes is described here, with which high-resolution measurements (1 s sampling) of ion concentration fluctuations have been made. Mobility spectrum information has also been extracted by varying the bias voltage under full computer control. The integrated system can determine small ion concentrations to ±1%, to a minimum mobility μ∼0.1 cm2 V-1 s-1 (corresponding to a particle radius of ∼2 nm). © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Accurate measurements of atmospheric ions are desirable in order to investigate atmospheric aerosol processes. A cylindrical capacitor ion counter is described which has a flexible computerized control system, to allow selection of ion mobility by changing the bias voltage across the capacitor. Ion measurements obtained correlate well with the ionization rate measured with an adjacent Geiger counter in clean air. Measurements of air ions using the device in current and voltage decay modes show consistent results. The collecting electrode is exposed directly in the air stream to be sampled, eliminating diffusive losses in intake tubes. The system can measure ion concentrations from 20 ions cm[sup -3] (including typical atmospheric concentrations) and can sample ions rapidly. These characteristics enable comprehensive air conductivity measurements to be made. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]