Thermal Stress Analyses for the NLC Positron Target(LCC-0088)

The power deposition of an incident multislug electron beam in a tungsten-rhenium target and the resultant thermal shock stresses in the material have been modeled with a transient, dynamic, structural response finite element code. The Next Linear Collider electron beam is assumed split into four parts, with each part impinging on a 4 radiation lengths thick target. Four targets are required to avoid excessive thermal stresses in the targets. Energy deposition from each beam pulse occurs over 265 nanoseconds and results in heating of the target and pressure pulses straining the material. The rapid power deposition of the electron beam and the resultant temperature profile in the target generates stress and pressure waves in the material that are considerably larger than those calculated by a static analysis. The 6.22 GeV electron beam has a spot radius size of 1.6 mm and results in a maximum temperature jump of 217 C. Stress pressure pulses are induced in the material from the rapid thermal expansion of the hotter material with peak effective stresses reaching 82 ksi (5.7 x 10{sup 8} Pa) on the back side of the target, which is less than one half of the yield strength of the tungsten/rhenium alloymore » and below the material fatigue limit.« less