A tokamak edge phenomenon, dubbed the 'marfe' (for multifaceted asymmetric radiation from the edge), is described. This phenomenon, observed in medium-to high-density Alcator C discharges, is characterized by greatly increased radiation, density and density fluctuations, and decreased temperature in a relatively small volume at the inner major radius edge of the plasma. The marfe appears to be confined to minor radii greater than or of the order of that of the limiter. The affected region is typically above the midplane, extending poloidally for about 30° and toroidally for 360°. The temperature and density of the core plasma are unaffected by the marfe. A simple transport model is used to show that the marfe is the manifestation of a thermal instability, with impurity radiation being the main energy loss mechanism out of the marfe volume. A density threshold n m for marfe onset is observed; n m is found to be an increasing function of plasma current and a decreasing function of intrinsic low-Z impurity levels. Detailed observations from spectroscopy, bolometry, Langmuir probe measurements, interferometry and CO 2 scattering are presented.

DISCLAIMERPortions of this document may be illegible electronic image products. Images are produced from the best available original document. LA-1 3422-M Manual UC-700Issued: November 1998 Application Guide to Neutron Multiplicity Counting AbstractThis document is intended to serve as a comprehensive applications guide to passive neutron multiplicity counting, a new nondestructive assay (NDA) technique developed over the past ten years. The document describes the principles of multiplicity counter design, electronics, and mathematics. Existing counters in Department of Energy (DOE) facilities are surveyed, and their operating requirements and procedures and defined. Current applications to plutonium material types found in DOE facilities are described, and estimates of the expected assay precision and bias are given. Lastly, guidelines for multiplicity counter selection and procurement are summarized. The document also includes a detailed collection of references on passive neutron coincidence and multiplicity publications over the last ten to fifteen years. 1 I . Introduction A . Purpose of the Application GuideDuring the past ten years, a new nondestructive assay (NDA) technique for plutonium, called passive neutron multiplicity counting, has been developed as an extension of neutron coincidence counting. The new technique has led to the design and fabrication of a new generation of instruments, neutron multiplicity counters, one of which is pictured in Fig. 1 -1. The development of new neutron counters has been accompanied by advances in data-processing electronics, analysis algorithms, and data-collection software. Development activities have been funded primarily by the Department of Energy (DOE) Office of Safeguards and Security, Technology Development Branch. Altogether, the new technology has led to significantly better measurement accuracy for plutonium metal, oxide, scrap, and residues. There is extensive and growing literature on neutron multiplicity detector design, electronics, data analysis algorithms, performance, and applications as documented in the Reference Section at the end of this guide. Also, Krick (94) has prepared an Application Note on the Passive Neutron Multiplicity Counter that provides a brief summary of the new technology.However, NDA specialists at a number of DOE facilities have requested a comprehensive 2 document that pulls together the most important information describing the technique, how it works, and how it can be applied. This application guide, sponsored by the DOE Office of Safeguards and Security, is intended to meet this need. B . Definition of Neutron Multiplicity CountingMultiplicity is a word that has, well, a multiplicity of meanings! Recently this word even served as the title for a Hollywood movie, in which multiple copies of the leading actor were cloned. Our use of the word begins in a similar way, with the fact that the important NDA signature for plutonium is the process of spontaneous fission, leading to the nearly simultaneous emission of multiple, ind...