Graphite Sublimation Tests for the Muon Collider/Neutrino Factory Target Development Program
A passively cooled graphite target was proposed for a 1.5 MW neutrino production research facility because of its simplicity and favorable performance as a target material for neutrino production. The conceptual design for the target in the Reference 1 study was a graphite rod 15 mm in diameter by 800 mm long. Figure 1 shows the graphite target rod supported by graphite spokes, which are mounted to a water-cooled stainless steel support tube. The target is radiatively cooled to the water-cooled surface of the support tube. Based on nuclear analysis results, the time-averaged power deposition in the target is 35 kW. If this power is deposited uniformly along the axial length of the target, the volumetric power deposition in the target is about 250 MW/m{sup 3}. The target surface temperature required to radiate the deposited power to a water-cooled tube is estimated to be about 1850 C, and the temperature at the center of the target is about 75 C hotter. The sublimation erosion rate (e), estimated assuming that the graphite is submersed in a perfect vacuum environment, can be derived from kinetic theory and is given by: e = p{sub sat}(m/2{pi} kT){sup 1/2} where p{sub sat} is the saturation pressure, m is the molecular weight, k is the Boltzmann constant, and T is the surface temperature. The saturation pressure given in Ref. 3 can be approximated by: p{sub sat} =exp(-A/T + B) where A = 9.47 x 10{sup 3}, B = 24.2, and the units of p{sub sat} and T are atmospheres and K, respectively. Using these equations, the saturation pressure and sublimation erosion rate are plotted in Fig. 2 as a function of temperature. The surface recession rate shown with units of mm/s in Fig. 2 assumes one-sided erosion. At the average power deposition value of 250 MW/m{sup 3}, the surface temperature is 1850 C resulting in a sublimation erosion rate of only 2.2 {micro}m/day. However, if the actual power deposition were peaked by a factor of two in the axial direction, then the surface temperature would be 2260 C and the surface recession rate would be 2.8 mm/day, which is clearly unacceptable.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- AC05-00OR22725
- OSTI ID:
- 814540
- Report Number(s):
- ORNL/TM-2002/27; TRN: US200317%%282
- Resource Relation:
- Other Information: PBD: 25 Mar 2002
- Country of Publication:
- United States
- Language:
- English
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