Effective energy coupling for 200-Mhz pulsed radiofrequency spectroscopic discharges
✍ Scribed by David M Coleman; Mario A Sainz
- Publisher
- Elsevier Science
- Year
- 1986
- Tongue
- English
- Weight
- 414 KB
- Volume
- 184
- Category
- Article
- ISSN
- 0003-2670
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✦ Synopsis
The introduction of various new radiofrequency electrical discharges has placed increased emphasis on circuit design which provides optimal energy transfer between a generator and its corresponding spectroscopic "load" . This technology is well developed for high-frequency (ca. 27 MHz) inductively-coupled plasma discharges and for cavity discharges which operate in the microwave region (e .g., 2450 MHz) . The 200-MHz very high frequency (VHF) region has received less attention . New circuitry is described which allows effective transfer of high power (5-kW), pulsed (2 .5-µs), VHF (200-MHz) energy into a plasma suitable for analytical purposes . A triple-stub tuner is used in this circuitry . Comparison with other approaches and applicability to a variety of discharge systems are discussed .
Recent experiments which segregate the "sampling" step from the "excitation" step in a spark discharge have resulted in spectral simplification, minimization of background continuum, and narrow line emission [1] . This system involved a unidirectional spark which ablated a metal surface followed by inductively-coupled re-excitation of the resultant toroidal port-discharge environment [2] . A 2 .5-µs burst of 200-MHz radiofrequency energy was used. Although emission intensities corresponding to re-excitation of the post-discharge torus are weak, compared to direct spark emission, signal-tobackground ratios are often improved by several orders of magnitude . Photographic integrations exceeding 1-h duration were typical . [The time/space/ wavelength-resolved spectrometer system used to collect such data operates with an optical time resolution of ca. 80 ns at a discharge repetition rate of 360 Hz . Thus, a "1-h exposure" corresponds to an integrated exposure of events totaling approximately 100 ms . The system will be described at a later date .] This research indicated the need for more efficient transfer of power for re-excitation purposes . Discharge luminosity was used to indicate optimum performance .
Instrumentation reported here dramatically improves such energy transfer .