Tagger Hall

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Shielding Basis for Hall D Complex (old note before shielding optimization)

Neutron background estimates in the hall

Radius of the exit electron beam pipe

Do we need a wider beam pipe transporting electrons into the beam dump? By Sept 2014 a 6 inch diameter pipe transports the beam to a place about 2m upstream of the first wall of the beam dump. The pipe ends with a thick flange connected to a 1.5 inch pipe transporting the beam through the wall. There is a girder with a valve between the flange and the wall. The flange became a hot spot during the first beam tune in May 2014. Would it help to install a wider pipe from the flange through the wall?

  • The deflection of the electron beam from the photon beam in that area is about L=400cm
  • The electrons deflected not more than r cm from the trajectory of the non-radiated beam go into the beam dump. The others dump their energy into the hall.
  • The full power of the photons is WB·R, where WB is the power of the electron beam and R is the radiator thickness in R.L.

The energy dumped by the radiated electrons into the hall is

W=WB/Eo·R·∫dk·(Eo−k)/k, where Eo and k are the energies of the incoming electron and of the outcoming photon. The integration limits are Eo·(r/(L+r)), Eo


r, cm    W/(WB·R)
1 5.0
2 4.3
3 3.9
4 3.6
5 3.4
6 3.2
10 2.7

The increase of the exit pipe radius from 2cm to 4cm would reduce the power dumped in the hall by the radiated electrons by about 15%.