Plasma Metrology
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Plasma, the fourth state of matter, is common in both nature (e.g., lightning,
the earth’s ionosphere, stellar objects) and in modern technology (e.g.,
semiconductor processing, lighting, plasma televisions, medical equipment).
Yet despite this ubiquity, the plasma state is still a wide open frontier,
which we are struggling to understand and control. Plasmas are richly complex,
encompassing an incredible diversity of linear and non-linear phenomena
including atomic collisions, electromagnetic interactions, fluid dynamics,
collective excitations, thermodynamics, chemical reactions, and radiation
transport. The term "meso-scopic" is often used to describe the
intertwining of microscopic and macroscopic phenomena in plasmas that
simultaneously span a wide range of spatial and temporal scales. This
complexity presents a scientific and engineering challenge, but it also opens
opportunities to achieve properties and performance that may not be achieved
with other states of matter. |
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A Familiar Plasma Source
Courtesy NASA/JPL-CalTech
Image of the Sun at a wavelength of 30.4 nm acquired by the Extreme
Ultraviolet Imaging Telescope on September 14, 1999.
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Measurement is fundamental to plasma physics and engineering; measurement to
improve understanding, measurement to guide the development of numerical
models; and measurement for process control. The complexity of the plasma
state increases the challenge of measurement. While progress in other fields
has led to exquisite control of isolated systems and measurement precisions of
1 part in as much as 1016, measurement in plasmas are
frequently considered successful when a precision of 1 part in 10 is
achieved. The purpose of this work is to advance the state-of-the-art in
plasma metrology in support of scientific and commercial applications of
plasmas.
High-Intensity Discharges
High-intensity discharges (HIDs) are generally small, high-pressure plasma
sources with a significantly higher power density (~100 W/cm3)
than low-pressure plasmas. HIDs are commonly used as efficient
general-purpose light sources, and in this application consist of either Hg
or Na gas at pressures in the range of 1 atm to 10 atm. If
metal-halide salts are added to such lamps they are referred to as
metal-halide lamps, and can have a very high luminous efficacy and excellent
color-rendering. Although metal-halide lamps are among the most efficient
sources of high-quality white light, manufacturers continue to seek further
increases in luminous efficacy, as well as longer lamp life and better color
stability. Much of our recent research has been focused on HID/metal-halide
lamps. We have developed two new diagnostic techniques utilizing x-rays to
obtain important information about the discharge parameters that cannot be
obtained with traditional methods.
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