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Structure of the microchannel array: (a)Diagram in cross-section (end-on) of a portion of an array, illustrating the tapered sidewalls of the channel and the 20 μm thick Al electrodes buried in nanoporous Al2O3; (b) SEM in plan view of a portion of a microchannel array comprising six channels, 230 μm in width and having a pitch of 560 μm. The length of the scale at lower right represents 500 μm. Notice in (a) that the thickness of the Al2O3 dielectric between the terminus of each Al electrode and the nearest portion of a microcavity wall is 10 μm. The acronym ITO represents the indium tin oxide film electrode, which has a thickness of ∼100 nm.
Series of images demonstrating the propagation of plasma packets along an array of six microchannels having the structure of Fig. 1(a) . At top is a photograph showing the time-integrated intensity generated when 760 Torr of Ar is excited by a 20 kHz sinusoidal voltage (V = 460 VRMS). Nine false color images, recorded for time delays ( ) between 5.15 μs and 6.35 μs and in increments of 150 ns, are presented. The gate width for the ICCD camera was 10 ns for all of the time-resolved images. A propagation velocity of 20 km-s−1 for the ionization wave is represented by the inclined, dashed white line.
(a) Magnified view of a false color image, acquired at = 5.8 μs, which is similar to those of Fig. 2 ; (b) Transverse intensity lineouts of the image of (a), obtained 17 mm from the ionization wave launch point. The direction for the lineout scan is denoted by the red arrow in (a), and data are also given for = 5.50 μs and 5.60 μs. Each of the open circles indicates the position of a camera pixel. The orange curve associated with the = 5.8 μs profile represents the best fit of a Lorentzian to the data for the third microchannel in the array; its width is 200 ± 5 μm (FWHM).
Sequence of axial intensity profiles (lineouts) recorded in microchannel 3 during the 5.25 μs 6.25 μs interval, illustrating the propagation of the primary wave along the channel. Merging of the initial plasma packet with its left-propagating counterpart is complete at = 6.25 μs.
Temporal decay of the spatially integrated microchannel array emission intensity after the two counter-propagating waves have merged. The experimental data (solid circles) were acquired in the negative half-cycle of Vs(t) and are shown on a semilog scale. Represented by the solid curve, the least-squares fit of (where A and B are constants) yields = 180 ± 25 ns, = 0.6 ± 0.2 μs, and R2 > 0.999. The inset presents the same data in a linear format.
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