Armor Surface Research Articles

Mechanical behavior of graphite first wall during disruptions

The mechanical behavior of graphite first wall armor during plasma disruptions was examined by applying fracture mechanics concepts. A fracture mechanics approch is suitable for lifetime evaluation, because the armor surface is expected to be damaged by intense heat load. Two stages are supposed for the lifetime of the armor: crack initiation and crack propagation, which are related to the fatigue life and the energy release rate, respectively. The terms are calculated for the disruption conditions of the Fusion Experimental Reactor (FER), which is referred to as a post JT-60 machine. The analytical results indicate that even though some damage is expected on the armor surface after a few disruptions, unstable failure does not necessarily occur for all disruption conditions.

Nonuniform Sediment Transport Model

ABSTRACT Anonuniform sediment transport model was evaluated by applying it to all the Little and Mayer's laboratory data. The model called STREAM was developed earlier by Borah, Alonso, and Prasad for simulating graded sediment transport in alluvial streams. Minor model modifications were made in this study. The model performed extremely well in predicting sediment discharges for the experimental runs producing complete armor surfaces and the run without producing any armoring but showed considerable discrepancies with the runs producing partial armoring. Predicted size distributions of eroded materials and materials at the armor surface were reasonable for most of the runs.

Neutral beam interlock system on TFTR using infrared pyrometry

Although the region of the Tokamak Fusion Test Reactor (TFTR) vacuum vessel wall which is susceptible to damage by neutral beam strike is armored with a mosaic of TiC-clad POCO graphite tiles, at power deposition levels above 2.5 kW/cm2 the armor surface temperature exceeds 1200 °C within 250 ms, and itself becomes susceptible to damage. In order to protect the wall armor, a neutral beam interlock system based on infrared pyrometry measurement of the armor surface temperature was installed on TFTR. For each beamline, a three-fiber-optic telescope views three areas of ∼30 cm diameter centered on the armor hot spots for the three ion sources. Each signal is fiber-optic coupled to a remote 900-nm pyrometer which feeds analog signals to the neutral beam interrupt circuits. The pyrometer interlock system is designed to interrupt each of the 12 ion sources independently within 10 ms of the temperature exceeding a threshold which can be set in the range of 500–2300 °C. A description of the pyrometer interlock system and its performance will be presented.