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A new polymorph of carbon, hexagonal diamond, has been discovered in the Canyon Diablo and Goalpara meteorites. This phase had been synthesized recently under specific high-pressure conditions in the laboratory. Our results provide strong evidence that diamonds found in these meteorites were produced by intense shock pressures acting on crystalline graphite inclusions present within the meteorite before impact, rather than by disintegration of larger, statically grown diamonds, as some theories propose.

The Spallation Neutron Source (SNS) linear accelerator (LINAC) consists of 81 superconducting radio frequency (SRF) cavities cooled to 2.1 K by a cryogenic refrigeration system. The 2-K cold box consists of four stages of cold compressors with liquid nitrogen cooled variable speed motors. Transitioning from 4.5-K operation to 2.1-K operation in the cryomodules involves pumping the cryomodules down from approximately 1 bar to 0.040 bar. This effort is conducted through the use of several sequences developed as a collaborative effort between Thomas Jefferson National Accelerator Facility (TJNAF) and SNS personnel during the original commissioning of the SNS cryogenic system. Over the last ten years, multiple lessons have been learned about VFD behavior, thermal stability, procedural development and refining the sequences. From 2012 to 2014, there were multiple pump down iterations that were not successful. Studies have been conducted to determine the cause of these unsuccessful iterations. The results of these studies including components replaced and aspects that have not yet been solved are presented in this paper. Future plans to refine the sequence and determine the cause of unsuccessful pump downs will also be presented.

The helium cryogenic system at Spallation Neutron Source (SNS) provides cooling to 81 superconducting radio frequency cavities. During the first ten years of operation, much operational experience and lessons learned have been gained. The lessons learned include integrated system issues as well as component failures in the areas of mechanical, electrical and controls. Past issues that have been corrected as well as current issues in the system will be detailed in this paper. In 2009, a Process Failure Modes and Effects Analysis (PFMEA) was completed as a way to identify high risk items and prioritize efforts. Since 2009, the progress on mitigating the identified high risk items has been tracked. The results of the PFMEA and the progress made in reducing risk to the cryogenic system operation will be detailed in this paper.