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Ion velocity distribution (IVD) and ion charge state distribution of silver ions in a plasma beam emitted by two compact, serially connected, and simultaneously operating vacuum arcs were measured using a dynamic time-of-flight diagnostics. The anode and cathode of each arc were made of two strips of silver layers pasted on an alumina wafer and separated by a narrow 100-[micro]m gap. The two arcs were laterally separated by 0.015 m and located on the same horizontal plane, emitting two plasma plums, which merged into a single one and is few centimeters away from the arcs. Each arc was ignited by high-voltage breakdown on the alumina surface gap by 3-[micro]s 100-A current. The IVD of the merged plasma beam was analyzed 0.7 m away from the arcs and compared with that of the ions emitted by a single arc. When only a single arc was active, the plasma beam consisted of more than 90% of Ag ions with an average velocity of = (0.7 - 0.8) * [10.sub.4] m/s and charge state z = 1. About 10% of the beam ion population consisted of oxygen and carbon. When the two arcs operated simultaneously, the form of the IVD was significantly different, containing a second peak with a velocity of = (1.15 - 1.25) * [10.sub.4] m/s, which is significantly higher than that observed with a single arc. However, the integrated ion charge in the merged beam was lower by 30% from the sum of the ion charge obtained from the plasma of each arc. It was found that the observed phenomena were correlated with a formation of conducting channel between the cathode of the first serially connected arc and the anode of the second arc, which is occurring when the plasma plums are expanding from the two arcs merged. When a physical barrier was inserted between the two arcs to prevent a contact between the two expanding plums, the observed plasma shunting did not occur, although the two beams merged in space beyond the barrier, as before. The effect on the IVD due to arc transfer from the first cathode to the second arc anode is currently being investigated. Index Terms--Ion charge state distribution (ICSD), ion energy distribution (IED), silver, time-of-flight (TOF) measurements, vacuum arcs.

Accurate timing alignment and stability are important to maximize the true counts and minimize the random counts in positron emission tomography. Its importance increases in time-of-flight (TOF) scanners. We propose using a central positron emitting source enclosed in a detector which detects the excess energy of the positron before it annihilates as a timing reference. All crystals can be time-aligned with respect to this central source. We evaluated 10 [micro]Ci [sup.22]Na and [sup.68]Ge sources embedded in cylinders of plastic scintillator coupled to a fast PMT. Light flashes produced after the parent isotope emits positrons are detected, and the anode signals from the PMT are the reference time for each positron decay. The time delay before the gamma ray is detected by the scanner's conventional gamma ray detectors is the time offset to be applied to that crystal. Since all detectors are almost the same distance from the central source, TOF errors are minimized. Preliminary results show a mean signal amplitude of >0.5 V from [sup.22]Na at 1000-V PMT bias, a timing FWHM of 850 ps with respect to a small LSO crystal. This suggests it could be useful to align both conventional and TOF PET scanners. Index Terms--Calibration, central source, positron emission tomography, time of flight, timing alliance.

The performance of the superconducting-tunnel-junction (STJ) detectors for time-of-flight mass spectroscopy (TOF-MS) is examined by using the Ta cluster ion source, which produces the peaks with a mass interval of 180.95 Da in the mass spectra. Two kinds of single-element STJ detectors with different spatial profiles are compared in TOF-MS experiments with a Ta cluster ion source.

Based on time of flight method, influence of short time vacuum arc current jump on arc plasma parameters were investigated. Superposition of the current pulse of a vacuum arc with a high operating voltage results in the appearance of ions of higher charge state in the discharge plasma and in an increase in the mean ion charge state for most of the cathode materials used in the experiment. The method of a 'short-time current jump' can be also used to investigate the parameters of a vacuum arc, in particular to estimate the ion direct velocities in vacuum arc plasmas. Our estimates show that in the presence of a current step the ion velocities are almost identical for all differently charged ions and depend only on the peak current and the ion mass. Index Terms - Charge state distribution, current jump, ion direct velocities, time-of-flight mass-spectrometer, vacuum arc.

The problem of estimating the envelope of a narrowband signal within additive noise simultaneously with its time delay, where a priori information about the signal shape is minimal, is investigated. A class of baseband correlation receivers was developed and a series expansion of the signal envelope was performed by a set of Laguerre basis functions. Possible applications include object identification and surface profiling in robotics.

The article describes the pre and post desiccation sound speeds through ex vivo porcine skull specimens by using time-of-flight measurements.