The beam dumps for ELBE must be capable of absorbing an average beam power of 50 kW at an electron beam energy of 50 MeV. After passing a 500 mm thick beryllium foil the incident electron beam enters a purified graphite absorber (r = 1.7 g/cm³). The power dissipation for a first design of the beam dump was calculated using the particle transport code GEANT [1,2]. Further calculations have been performed with the transport code FLUKA [3], which makes possible to consider nuclear reactions like the (g,n) process. Two geometrical shapes of the graphite core (V1, V2) have been compared with respect to the power dissipation and the temperature distribution. Version V1 corresponds to the first layout [1] with a radius of  15 cm and a cone-shaped hole of 35 cm depth. The power dissipation for V1 is shown in Fig. 1. After reducing of the radius to 10 cm, the implementation of a second cone-shaped hole at the entrance (10 cm deep) and the elongation of the first cone-shaped hole up to 45 cm, the power dissipation in this version V2 is more homogeneously distributed as shown in Fig. 2.

Fig. 1: Power released in graphite core V1.	Fig. 2: Power released in graphite core V2.

On the base of the power dissipations the thermal loads were calculated for the two graphite cores using the Finite-Element-Code ANSYS [4]. The model comprises the heat transfer in the graphite and the radiation effect according to the Stefan Boltzman equation between the surface and the water cooling which surrounds the graphite core. The resulting temperature curves along the outer lines of the halfmodel for the two graphite cores are shown in Fig. 3. The maximum surface temperature at the centerline in V1 amounts to 2834 K and is near to the graphite sublimation temperature of 3300 K at a pressure of 5 mbar [1]. The improved geometry in V2 results in a smaller maximum surface temperature of 2256 K.
		Fig. 3: Profiles of the surface temperatures for two graphite core versions at an electron beam energy of 50 MeV.

¹ Institut für Kern- und Teilchenphysik, TU Dresden
² Institut für Sicherheitsforschung, FZ Rossendorf

References

[1]	B. Naumann et al., Strahlfänger für maximale Energien an ELBE, FZR Report FZR-267 (1999);
	Annual Report 1998/1999, FZR-271 (1999) 36.
[2]	GEANT-Detector Description and Simulation Tool, CERN Program Library W5013 (1994).
[3]	A. Fasso et al., Proc. of the III Spec. Meeting on Shielding Aspects, Sendai (1997) 61-74.
[4]	ANSYS User's Manual for Rev. 5.6., Swansons Analysis Systems, Inc. (1999).

 IKH 05/21/01 © B. Naumann