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Plasma/Ionized Gas Impurity Sensor The Impurity Filterscope for measuring visible light emission from plasmas and ionized gases The filterscope is a diagnostic for monitoring visible light emission from plasmas and other ionized gases. Light from a plasma is conducted to the filterscope via optical fibers. This light is split into multiple paths, and optical bandpass filters in each path pass the light from visible wavelengths, including H, He, N, C, Ar or any other impurity ion that emits visible light. The filtered light is then detected by compact photomultipliers and the resulting data digitized and stored. Because of the large number of data channels that can be employed for spatial profile information, the filters and electronics are designed to be compact. Measured light intensities are absolutely calibrated such that absolute impurity densities can be deduced. Filterscopes are presently employed on the DIII-D, NSTX and CDX-U tokamak plasma devices, but are equally well suited to many other plasma and ionized gas applications. Key to this compact design is the use of phototubes with built-in high voltage power supplies. The phototubes and associated electronics are built into modules, with each module capable of handling up to five phototubes. Light from the plasma is imaged on an optical fiber, which may extend several hundred feet between the plasma device or ionized gas and the data acquisition room. The light is then split into 3-5 paths, each of which is terminated by an optical bandpass filter and a photomultiplier tube. Spectral lines from the ionized impurities are recorded. Signals are digitized at rates up to 100 kHz, allowing the study of fast fluctuating turbulence.

Reference: R.J. Colchin, D.L. Hillis, and R. Maingi (ORNL),"The Filterscope", Review of Sci.

Instrum. (March 2003) (accepted for publication) Features: Absolute impurity densities determined Simple and compact design Multiple photodiodes for high rate signal analysis Can handle fast fluctuating turbulence Point of Contact: D. L. Hillis Senior Research Staff Fusion Energy Division Oak Ridge National Laboratory P.O. Box 2008 Oak Ridge, TN 37831-8071 Phone: 865-576-3739, Fax: 865-576-7926 FUSION ENERGY DIVISION

Fusion Energy
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