Volume 83, Issue 9, 01 May 1998
Index of content:
- GENERAL PHYSICS: NUCLEAR, ATOMIC, AND MOLECULAR (PACS 01-39)
83(1998); http://dx.doi.org/10.1063/1.367237View Description Hide Description
Finite time thermodynamics is a well established field of applied thermodynamics. The key assumption of this approach is the validity of the concept of endoreversibility. In this article, a hypothesis is formulated, and subsequently formally proved, that this concept rests on a fallacious argument. The concept of endoreversibility is inherently inconsistent with the postulated set of assumptions because the internal reversibility of a thermal system appears to be contradictory to an existence of external finite area heat exchangers that communicate with the endoreversible internal part across the finite temperature gaps. The irreversibilities contributed by the system components are inherently interconnected. As a consequence, the maximum power efficiency between the given temperature levels and as predicted by finite time thermodynamics assuming that the heat input into the system is free to vary, i.e., is incorrect. In addition, the magnitude of this figure of merit may be even smaller compared to the efficiency of a real system.
Narrowband laser produced extreme ultraviolet sources adapted to silicon/molybdenum multilayer optics83(1998); http://dx.doi.org/10.1063/1.367238View Description Hide Description
The extreme ultraviolet radiation emitted from a plasma generated by a pulsed Nd:yttrium aluminum garnet laser is investigated around 13 nm wavelength for several low elements (lithium, nitrogen, oxygen, fluorine). A narrowband EUVsource can be designed by using the narrowband line emission of low elements in combination with the broadband reflection characteristic of silicon/molybdenum (Si/Mo) multilayer mirrors. Experimental results are discussed within a theoretical model, which allows a deduction of an optimization criterion for a maximum conversion efficiency. The Lyman-α line of hydrogenlike lithium ions fulfills the demands for high intense, free-standing narrowband emission at the long wavelength side of the silicon absorption edge.
Numerical calculations of the temperature distribution and the cooling speed in the laser-heated diamond anvil cell83(1998); http://dx.doi.org/10.1063/1.367239View Description Hide Description
Numerical calculations have been done to reveal temperature distributions and cooling speeds of laser-heated samples in a diamond anvil cell. The distributions were calculated for variable experimental parameters including the diameter of the laser beam, anvil gap, and sample. The results show that the radial temperature distribution in all samples is Gaussian. The axial temperature gradient is in samples heated by a broad laser beam of 100 μm diameter, and is when a narrow laser beam of 10 μm diameter is used. The broad beam can generate a less extreme temperature gradient in both radial and axial directions as compared with the narrow beam, whereas the temperature gradient strongly depends on the anvil gap, although this is minimized when a narrow beam is used. When the narrow beam is used to heat samples, the surface temperature of the anvil culet can be kept below 400 K; thus, the narrow beam is suitable for heating samples under high pressure while keeping anvil temperatures low. Cooling speeds of the laser-heated samples were found to be from to The discrepancy between actual sample temperature and measuredtemperature was also evaluated. To measure the peak temperature of a sample heated by a laser with a Gaussian power distribution within 5% accuracy, radiation from a circular area of less than of the Gaussian must be observed.
83(1998); http://dx.doi.org/10.1063/1.367240View Description Hide Description
Phosphor powder of ZnS:Cu,Al,Au has been subjected to electron bombardment (2 keV, ) in residual gas pressures ranging from to Auger electron spectroscopy and cathodoluminescence (CL), both excited by the same electron beam, were used to monitor changes in the surface chemistry and cathodoluminescent brightness versus vacuum conditions during electron bombardment. A direct correlation between the surface reactions and the degradation of CL brightness was observed. The formation of a nonluminescent ZnO layer on the surface of the phosphor was largely responsible for the degradation of the ZnS. The aging of the phosphor was not only a function of the charge per unit area (Coulomb dose) bombarding the surface, but also a function of residual gas pressure and composition. In particular, had the greatest effect on the rate of degradation. The results are interpreted in terms of an electron-beam stimulated surface chemical reaction.