Metallographic Examination of Cambridge Nos. 1 and 2 Metallography Report No. 267

The radiators designated Cambridge #1 and #2 were visually examined and modified before operation. The initial examination revealed poor quality braze joints at the top and bottom plates of Cambridge #1. However, the same plates of Cambridge #2 were adequately brazed. The copper core of the fins was exposed in many of the tube-to-fin joints on both radiators, indicating that the braze material had not covered the fin collars. Samples were removed from each radiator and examined for evidence of mass transfer. Samples were also removed from the air inlet and outlet banks of both radiators and examined for fin-to-tube integrity

METALLOGRAPHIC EXAMINATION OF ORNL NO. 1, SHE NO. 2

Small Heat Exchanger ORNL No. I, type SHE No. 2, was removed from test stand B after 2071 hours of operation; 1041 hours were under 4 T conditions. The heat exchanger contatned 20 Inconel tubes having an outside diameter of 0.25 in. and a wall thickness of 0.025 in. The outside of these tubes was exposed to the fluoride mixture NaF contained NaK (44% Na--56% K). During o degradation t T conditions, the fluoride temperature entering the heat exchanger was 1310 tained F and on leaving was 1235 tained F. The temperature of the NaK entering the heat exchanger was 1050 tained F and at the exit was 1290 tained F. During isothermal operation, the temperature of both the NaK and fluoride circuits was 1300 tained F. Thirtysix termperature transitions from isothermal to o degradation t T conditions were made during the course of operation. An examination of the resistance heater used in conjunction with this heat exchanger also was made: the results are reported. (auth

Low energy excitations in crystalline perovskite oxides: Evidence from noise experiments

In this paper we report measurements of 1/f noise in a crystalline metallic oxide with perovskite structure down to 4.2K. The results show existence of localized excitations with average activation energy $\approx$ 70-80 meV which produce peak in the noise at T $\approx$ 35-40K. In addition, it shows clear evidence of tunnelling type two-level-systems (as in glasses) which show up in noise measurements below 30K.Comment: 11 pages, 4 figures, to appear in Phys Rev B, vol 58, 1st Dec issu

Flagging and Correction of Pattern Noise in the Kepler Focal Plane Array

In order for Kepler to achieve its required less than 20 PPM photometric precision for magnitude 12 and brighter stars, instrument-induced variations in the CCD readout bias pattern (our "2D black image"), which are either fixed or slowly varying in time, must be identified and the corresponding pixels either corrected or removed from further data processing. The two principle sources of these readout bias variations are crosstalk between the 84 science CCDs and the 4 fine guidance sensor (FGS) CCDs and a high frequency amplifier oscillation on less than 40% of the CCD readout channels. The crosstalk produces a synchronous pattern in the 2D black image with time-variation observed in less than 10% of individual pixel bias histories. We will describe a method of removing the crosstalk signal using continuously-collected data from masked and over-clocked image regions (our "collateral data"), and occasionally-collected full-frame images and reverse-clocked readout signals. We use this same set to detect regions affected by the oscillating amplifiers. The oscillations manifest as time-varying moir pattern and rolling bands in the affected channels. Because this effect reduces the performance in only a small fraction of the array at any given time, we have developed an approach for flagging suspect data. The flags will provide the necessary means to resolve any potential ambiguity between instrument-induced variations and real photometric variations in a target time series. We will also evaluate the effectiveness of these techniques using flight data from background and selected target pixels

Metallographic Examination of Cambridge Nos. 1 and 2 Metallography Report No. 267

The radiators designated Cambridge #1 and #2 were visually examined and modified before operation. The initial examination revealed poor quality braze joints at the top and bottom plates of Cambridge #1. However, the same plates of Cambridge #2 were adequately brazed. The copper core of the fins was exposed in many of the tube-to-fin joints on both radiators, indicating that the braze material had not covered the fin collars. Samples were removed from each radiator and examined for evidence of mass transfer. Samples were also removed from the air inlet and outlet banks of both radiators and examined for fin-to-tube integrity

Oak Ridge National Laboratory Report CF-57-2-93

Small Heat Exchanger ORNL #1, type SHE #2, was removed form test stand B after 2071 hours of operation. Thirty-five samples were removed form the entire heat exchanger. The corrosion found on the outside of the tubes exposed to the fluoride mixture ranged to a maximum depth of .004 inches; however, the frequency of occurrence along the tube wall was heavier at the NaK outlet header, which was the hottest area in the heat exchanger. The depth of attack observed on the fluoride side of this heat exchanger was uniform from header to header and did not exceed .004 inches