Browsing by Author "Aliaga-Rossel, R"

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    Development of a short pulsed corona discharge ionization source for ion mobility spectrometry
    (2005) An, YA; Aliaga-Rossel, R; Choi, P; Gilles, JP
    The development of a pulsed corona discharge ionization source and its use in ion mobility spectrometry (IMS) is presented. In a point-plane electrode geometry, an electrical pulse up to 12 kV, 150 ns rise time and 500 ns pulse width was used to generate a corona discharge in air. A single positive high voltage pulse was able to generate about 1.6x10(10) ions at energy consumption of 22 mu J. Since the temporal distribution of ions is in a pulsed form, the possibility of removal the ion gate has been investigated. By purposely arranging the interface between discharge field and drift field, nearly 10(7) positive ions were drawn into the drift region with absence of the ion gate after every single discharge. The positive spectrum of acetone dimer (working at room temperature) was obtained with a resolving power of 20 by using this configuration. The advantages of this new scheme are the low power consumption compared with the dc method as well as the simplicity of the IMS cell structure. (c) 2005 American Institute of Physics.
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    Optical measurements of plasma dynamics in carbon fiber Z-pinches
    (1998) Aliaga-Rossel, R; Lebedev, SV; Chittenden, JP; Mitchell, IH; Saavedra, R; Dangor, AE; Haines, MG
    A series of experiments has been carried out on the Mega Ampere Generator for plasma Implosion Experiments (MAGPIE) generator in order to study the dynamics of carbon fiber Z-pinches. The generator was operated at 1.4 MV, with a peak current of 1 MA, and a rise time of 150 ns. In some shots, a current prepulse of about 30 kA was provided to Study its influence on the dynamics of the fiber pinch. Carbon fibers of 7, 33, and 300 mu m diameter were used during these experiments. The diagnostics employed were a self-referencing interferometer, a two-frame Schlieren system, an optical streak camera, and a four-frame X-ray framing camera. A novel feature of these measurements is the employment of an optical streak camera with a set of four slits arranged along the fiber axis and displaced in the radial direction. This permitted the study of the temporal evolution (axial and radial) of the plasma regions emitting in the visible part of the spectra. Correlation between these regions of the plasma and the location of X-ray hot spots is discussed. In carbon fibers of 33 mu m diameter, the radial expansion velocity measured from Schlieren images was 3.6 x 10(6) cm/s and 5.5 x 10(6) cm/s for shots with and without prepulse, respectively. The dominant axial wavelengths of instabilities in the coronal plasma were between 0.05 and 0.2 cm, which correspond to ka values between 10 and 20, where k is the wavenumber of the instability and a is its amplitude. The dynamics of carbon fibers of different diameters are compared.