A Possible Beam Dump Design for Intense Electron Beams

B. Naumann, W. Neubert, H. Prade and D.Pröhl1

Experiments at the radiation source ELBE require beam dumps fulfilling the safety conditions up to the maximum electron beam current of @ 1 mA. The construction materials have to meet requirements as low specific energy deposition, heat resistance combined with sufficient thermal conductivity, modest neutron production rate and a low level of produced long-living nuclides. Here, we present a possible layout for a power dissipation of 50 kW. The core is proposed to be built from purified graphite covered by a water cooled copper coating.
The construction shown in Fig. 1 was imaged by a corresponding GEANT geometry including the material parameters [1]. The origin of the electron beam characterized by a spatial distribution of sx,y =2 mm and a divergence of sx,y=12 mrad was assumed to be at a distance of 2 m in front of the entrance of the graphite core. Under these conditions, the incident beam strikes completely the cone-shaped hole of the beam dump.

section DE/Ekin
[%]
DP
[kW]
beam line 0.072 0.036
Al separation foil (50mm) 0.049 0.024
graphite core 92.175 46.087
copper coating (20 mm) 3.271 1.635
Fe shielding plate (15 cm) 3.973 1.987
concrete wall 0.459 0.230
air gap 8.0·10-4 4.0·10-4

Table 1 Energy deposition in the dump materials

The slowing-down of the electrons and the production of bremsstrahlung as well as the associated energy release were simulated with the GEANT 3.21 package. In this way, we calculated the energy deposition in all construction materials involved (see Table 1). The power dissipation in the graphite core is plotted in Fig. 2. Dose calculations were performed with a cubic water phantom ( l = 20 cm ) which was positioned at the downstream position 2.20 m, i.e. 20 cm backward the simulated beam origin. The expected dose from the photons and electrons backscattered by the graphite core amounts to 9 Gy/h provided that the incident beam current is 1 mA. A complete representation of the Monte Carlo simulations is published in [2].

naumann11.gif
Fig. 1 Construction of the beam dump (the vacuum separation foil (Al) mentioned in Table 1 is placed in front of the concrete wall).

naumann12.gif
Fig.2  Power released in the graphite core.

1 Department of Research and Information Technology

References

[1] GEANT - CERN Program Library W5013, March 1994

[2] B. Naumann. W. Neubert, D. Pröhl, FZR Report FZR-267, Juli 1999.

FZR
 IKH 10/25/99 © B. Naumann