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Based on 20 years of solar investigations, the extreme-ultraviolet (EUV) spectrum in the range 50-500 Â has proved to be extraordinarily rich in providing information on the density, temperature, and element abundances of the plasma in the Sun's chromosphere and corona, especially when observed with high spectral resolution. With the advent of new instruments using multilayer optics and CCD detectors, similar measurements with a spectral resolution of about 10,000 become possible on large numbers of nearby stars, in contrast with lower resolution instruments now scheduled for space flight. In this paper we provide a description of the lines from the most abundant ions in this spectral region that have special diagnostic significance. These lines are from plasmas in the temperature range from 10 5 to 10 7 K. We demonstrate their utility for determining temperature, density, and abundances. We also describe an objective grating spectrometer, based on the Naval Research Laboratory Skylab slitless spectrograph, for making celestial observations in the EUV spectral region with high spectral resolution.

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Tungsten was injected by means of laser ablation in both ohmic and additionally heated plasmas of the ASDEX Upgrade tokamak experiment. Spectroscopic investigations were performed in the extreme ultraviolet (EUV) wavelength region, 4 to 140 nm. Besides the quasi-continuum structure at ≈ 5 nm emitted by tungsten ions around W27+, isolated lines of tungsten were observed in the same spectral region and also in the range from 12 to 14 nm. By comparison with calculations from the HULLAC and RELAC codes, these lines could be identified as transitions of bromine to nickel-like tungsten ions. The concentration cW of tungsten after laser ablation was determined from comparisons between the total tungsten radiation PW and the calculated radiation losses. Calibration of the quasi-continuum intensity with the help of the PW measurements allows the tungsten concentration to be determined from spectroscopic observations, which are more sensitive. Both concentration measurements (quasi-continuum, PW) agree well in discharges with laser ablation. From a comparison of the intensity of the isolated lines with code results, cW could be estimated in the central region of hot, additionally heated plasmas. The lower detection limit of the spectroscopic method allows the extraction of cW during the tungsten divertor experiment of ASDEX Upgrade.

The laboratory end-to-end testing of the Extreme-Ultraviolet Imaging Spectrometer (EIS) for the Solar-B satellite is reported. A short overview of the EIS, which observes in two bands in the extreme-ultraviolet wavelength range, is given. The calibration apparatus is described, including details of the light sources used. The data reduction and analysis procedure are outlined. The wavelength calibration using a Penning source to illuminate the aperture fully is presented. We discuss the aperture determination using a radiometrically calibrated hollow-cathode-based source. We then give an account of the predicted and measured efficiencies from consideration of the efficiencies of individual optical elements in first order, an account of efficiencies out of band when radiation incident in one band is detected in the other, and efficiencies in multiple orders. The efficiencies measured in first order for in band and out of band are compared with the predictions and the sensitivity, and its uncertainties are derived. Application of the radiometric calibration is discussed.

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Glauber. But, from a practical point of view, we must take into account the fact that g, (t) is measurable only for / of the order of a few units or at best of a few tens, and for a non-negligible intensity of radiation. With these restrictions we have found that large fluctuations will be reached only for mo of order smaller than E . This result means that the atomic system must be prepared in a state very near the excited state. For example, if the excitation can be described by an angle 8, mo is given by the relation m, = , ' N (-co so+ 1) .Obviously, in the limit of large N, mz wil]. be a great number even if 8 is very near m. For 8= me, then mo=N~E . Therefore, unless the system is almost completely excited, it will exhibit in the present conditions of technology a classical behavior. 'R. Bonifacio, P. Schwendimann, and Fritz Haake, Phys. Rev. A 4, 302 (1971). G. S. Agarwal, Phys. Rev. A 2, 2038 (1970); R. H. Lemberg, Phys. Rev. 181, 32 (1969). 'Fritz Haake and Roy J. Glauber, Phys. Rev. A 5, 1457 (1972). 4A. M. Ponte-Goncalves and A. Tallet, Phys. Rev. A 4, 1319 (1971). 'R, Bonifacio, P. Schwendimann, and Fritz Haake, Phys. Rev. A 4, 854 (1971).

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