• vacuum
• gas
• velo
• fixed-target
• luminosity
• density
• smog2
• molflow
• lhcb
• storage cell

The luminosity is a useful value to characterize the performance of a particle
accelerator. In particular, all collider experiments aim to maximize their
integrated luminosities, as the higher the integrated luminosity, the more data
is available to analyze.
For beam-target collisions the luminosity, in addition to the beam parameters,
depends on the fixed target density. Here comes SMOG2.
The core of SMOG2 is the use of a Storage Cell (designed as two halves that
will be opened and closed) for the injected gas to be installed upstream of the
VELO detector. The main advantage is to increase by up to two orders of
magnitude the effective target areal density, thus resulting in a significant
increase of the luminosity for the fixed-target collisions.
Other important advantages are the possibility to inject additional gas species,
including H2 and D2, a better defined interaction region, displaced with respect
to the nominal interaction point, and thus possibly compatible with running in
parallel to the collider mode, resulting in a substantial increase in integrated
luminosity.
The goal of this thesis is the development of a code with Molflow+ for the
storage cell to compute the contribute of the target density, and its uncertainty,
to the luminosity measurement.
Several gas species are injected in the storage cell with different value on
injection velocity and cell temperature. This running will tell us the contribute
of the areal density to the luminosity uncertainty, smaller than 1%.
After that is analyzed the case of unexpected gas loss due to the fact that
the two halves are not completely closed. In this case the gas density will
be reduced vanishing the configuration of SMOG2. After the mechanic
measurements of the gap and the installation we can conclude that there are
no losses along the all length of the cell. This must not be confused with the
gas loss at the ends of the cylinder, that is predicted.
In the end the impact of the gas on VELO surface is analyzed. Since this
surface is made by a Non-Evaporable Getter (NEG) coating, it’s reasonable to
assume that it has a sticking factor (probability of the particle to be absorbed
after the collision) higher than zero, obtaining that almost the 99% of the gas
is absorbed before reaching the end of the VELO.