X-ray or gamma ray systems or devices – Specific application – Diffraction – reflection – or scattering analysis
Reexamination Certificate
1999-05-21
2001-07-10
Kim, Robert H. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Diffraction, reflection, or scattering analysis
C378S084000
Reexamination Certificate
active
06259763
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to diagnostic apparatus for use with an extended X-ray source and is particularly directed to a doubly focusing crystal spectrometer for providing spatially and temporally resolved diagnostic data on hot plasmas. In addition to these diagnostic applications for the investigation of extended plasma sources, the doubly focusing crystal spectrometer can also be used to generate radiation fields with a large cross-section of parallel, or near parallel, monochromatic X-rays. Such radiation fields are of interest for the spectral analysis of the composition of an object or body under study—for example, for the detection of forgery in a painting—and may find applications in other areas such as medicine and lithography.
BACKGROUND OF THE INVENTION
X-ray crystal spectroscopy has played an important role in the diagnostics of tokamak fusion plasma, in particular, by Doppler measurements of the central ion temperature, which was, in general, determined from the Doppler width of the resonance lines of the helium-like ions of medium-Z elements, like Ar, Ti, Cr, Fe and Ni. The observed satellite spectra of these heliumlike ions also provided information on various other plasma parameters, e.g., central electron temperature, ionization balance and ion impurity transport.
X-ray crystal spectroscopy is expected to become even more important for the diagnostics of future large hot plasmas, such as will be produced in the International Thermonuclear Experimental Reactor (ITER), because other diagnostic methods will encounter technical difficulties and not be able to measure the central plasma parameters of this fusion device. X-ray lines from high-Z elements such as krypton in the He-like charge state will be well-suited for measurement of the central ion temperature and other central plasma parameters at ITER.
However, the requirements for X-ray crystal spectrometers will change as experimental fusion plasmas increase in size and approach break-even conditions. Under these conditions, the plasma will emit neutrons and gamma radiation. It will therefore be necessary to restrict the size of diagnostic windows and to place diagnostic instruments at large distances from the plasma. Moreover, the concentration of high-Z impurities in the hot core of the plasma will have to be as small as possible, in order to avoid an unacceptable dilution of the burning hydrogen plasma. This latter requirement, especially the intensity of the X-ray line radiation which is needed for plasma diagnostics, will be severely reduced. For the X-ray diagnostics of the core plasmas in future large fusion devices, such as ITER, it is therefore necessary to develop new types of crystal spectrometers having improved focusing properties and which employ very large crystals to enhance the spectrometer throughput or the X-ray flux to the detector.
Crystal spectrometers with improved focusing properties are also needed for the diagnostics of present-day tokamak and stellarator plasmas to satisfy the demands for advanced diagnostics having good spatial resolution and which are capable of providing an image of an extended plasma. The requirements that apply to an imaging X-ray crystal spectrometer for the present-day plasma devices are, however, distinctly different from the requirements for future large devices, such as ITER, which are discussed above. The experimental constraints at present devices are less restrictive because the background of neutron and gamma radiation is orders of magnitude smaller than expected in ITER. The diagnostic windows are larger and the diagnostic instruments are closer to the plasma than they will be in ITER. It is therefore possible to view a large part of present plasmas and to obtain information on the spatial distribution of plasma parameters.
The presently used instruments are Johann spectrometers with cylindrically bent crystals. These instruments only provide focusing for the meridional rays, which are parallel to the main diffraction plane, whereas the sagittal rays, which are oblique to the plasma, are not focused. With exception of the experimental arrangement by Bartiromo et al. (see discussion below), information on the spatial distribution of plasma parameters was previously obtained by arrays of such Johann spectrometers, where each spectrometers records spectra from a single line of sight through the plasma. The number of spectrometers and thus the number of lines of sight, which can be installed at a tokamak is limited and usually not larger than five, because of experimental and budget constraints. The experimental arrangement by Bartiromo et al. also uses a Johann spectrometer with a cylindrically bent crystal. However, in Bartiromo's arrangement, there is a horizontal slit between the crystal and the plasma, so that rays, which emanate from different parts of the plasma above or below the main diffraction plain pass through the slit and are reflected from different parts of the crystal below or above the main diffraction plain onto the detector. Although this arrangement provides spatial resolution in the plasma, the throughput of the instrument is significantly reduced by the slit.
The present invention addresses the limitations of the prior art in terms of future more demanding applications by providing a doubly focusing crystal spectrometer capable of providing simultaneous measurements of spectra from an essentially unlimited number of lines of sight (or chords) through the plasma and thus produce an image of the plasma in a direction perpendicular to the main diffraction plane.
OBJECTS AND SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an X-ray spectrometer employing a single crystal for the spatial and temporal resolution of the parameters of an extended hot plasma.
It is another object of the present invention to permit the observation and study of an extended hot plasma simultaneously from many different lines of sight through the plasma.
Yet another object of the present invention is to provide an X-ray spectrometer employing a very large, single, spherically or toroidially curved crystal for improved spectral analysis of the composition of an object under study.
A still further object of the present invention is to provide the monochromatic radial imaging of the X-ray emission of an extended hot plasma for studying the transport and confinement characteristics of the plasma.
This invention contemplates a doubly focusing crystal spectrometer for providing spatially and temporally resolved data on various parameters of an extended hot plasma such as the plasma's ion temperature, plasma rotation, electron temperature, ionization equilibrium, and impurity ion transport. The inventive spectrometer employs a spherically or toroidally curved crystal and takes advantage of the imaging properties of the curved crystal for Bragg angles near 45°. The spherically curved crystal when used at Bragg angles near 45° focuses parallel bundles of X-rays (the cross section of which is determined by the cross section of the crystal) from the plasma to a point on the detector. Parallel rays that are inclined to the main plane of diffraction are focused to different points on the detector. Thus, a spectrally and spatially resolved X-ray image of the plasma is provided on a two-dimensional detector using a single crystal. Obtaining data from all of the different chords through the plasma from the same diffracting element, i.e., the spherically curved crystal, eliminates the necessity for cross-calibration of the data from the different radial chords, thus substantially simplifying the diagnostics system and increasing data throughput. The inventive spectrometer permits radial imaging of the plasma X-ray emission at different wavelengths simultaneously using only a single crystal. Thus, a spectrally and spatially resolved X-ray image of the plasma is provided on a two-dimensional detector using a single crystal.
The inventive X-ray Imaging Crystal Spectrometers can be installed at present
Bitter Manfred L.
Fraenkel Ben
Gorman James L.
Hill Kenneth W.
Roquemore A. Lane
Alwan Joy
Anderson Thomas G.
Caress Virginia B.
Kiknadze Irakli
Kim Robert H.
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