Summary of a Meeting on Pressure Calculations
for the LHC Straight Sections
06.02.2003 

present: Chris Benvenuti, Adriana Rossi,
Paolo Chiggiato, Frank Zimmermann
----------------------------------------------------

The calculated pressure is a concern for the experiments,
which has been noticed b Daniel Treille.

Assumed outgassing rates were too high in some of
the earlier calculations. The outgassing of methane
should be 10000 times less than for stainless steel.

Beam pumping was ignored, but it is significant for 
the getter. Every ionized molecule will stick to 
the wall. In addition, the electrons will also ionize 
the gas with a 100 times higher cross section,
and this could be the dominant effect, when an
electron cloud builds up. In this case, the pressure
might even go down due to the electrons.
Ionization cross sections for molecules as a function
of electron energy can be found in book by Lafferty.

There is no limit to what the getter can absorb
(10000 years estimate). 

Several measurements will be conducted in the
next month: methane outgassing (3e-17 Torr/l/s
is upper bound at prsent), methane outgassing
due to electron bombardement as a function of
electron energy, pumping speed for CO after 
10 activation cycles, desorption yield after
10 cycles as a function of dose, secondary emission
yield.

The effect of surface roughness may also be 
studied later on.

The secondary emission yield at low incident
energies has not been measured, but suspicion
is that the getter repells electrons.