A superheated Na cell for X-ray photoionization experiments

The performance of a superheated alkali vapor cell, with a geometry suitable for x-ray photoionization experiments, is described. An internal heater was used to superheat sodium vapor in a split-wick heat pipe. At a Na pressure of 20 Torr, the transmission through the cell in the region of theC–X molecular band of Na₂ increased to 50% from the 5% observed when the cell was operated in a conventional heat-pipe mode. In the presence of a Na atom density of 2×10¹⁷ cm^–3, the average molecule density over the length of the cell was measured to be 2.5×10¹⁵ cm^–3. In the hot central region of the superheated cell, the molecule density was predicted to have been reduced by a factor of 50 to 3×10¹⁴ cm^–3.