DRAFT:
We had discussion of the recent UK results on the shock wave phenomena
in the beam dump. Here is a brief summary of our conclusions.
Analyzing the increase of pressure of ~120bar, in a volume where
the beam is deposited, we need to take into account:
-- the beam is deliberately off-center in the cylindrical vessel, so the
focusing of reflected waves back to the beam location is not possible;
-- asymmetry of elasticity of the vessel, due to details of its construction
or support, in reality is important, and helps to disperse the waves;
-- waves are generated primarily in radial direction, due to small radius
of shower and sharp gradient of temperature, however in the longitudinal
direction the shower profile is very smooth (adiabatic in space), and generation of
longitudinal waves is suppressed, so that the intensity of direct waves
reaching the window would be much less;
-- when the waves reach the walls, the pressure is reduced as 1/r and would
be attenuated by a factor of several hundreds, with remaining spike of the
order of a bar;
-- in terms of Joules/g, which is one of the relevant criteria, the ILC dump is more difficult
than the SLC dump only by a factor of four (taking beam rastering into account);
(See Lew's slide on the web site)
-- the internal walls of the vessel may be covered with some "ribs" which could be
done in a way not to produce impedance to the flow, but would help to scatter the
waves.
So, it shows from the first principles that the shock waves should not be a problem.
