Table 2: Phase advance, beta functions and dispersion
at collimators and targets.
The following convention for the type notation is used:
p -primary collimator, t - target, s1, s2 - two stages of secondary
collimators for the primary collimator, t1, t2 - secondary collimators
for the target.
The redesign of the proton collimator system [3, 5] required an optimized compromise between the limited available space, the capability to shield the other HERA experiments effectively against natural proton background and to catch protons, which are scattered under large angle in the target, before they hit the other HERA experiments [6]. The main design criteria is given by the optimum phase advance of secondary collimators with respect to the primary collimator or the target:
where m is an integer number and 
are the amplitudes of the
main collimator or target and the secondary collimator in units of beam sigma
respectively.
The system was built as a three stage collimator setup. The phase advances
and the 
functions are given in Tab. 2.
A simulation code with particle tracking was developed to study
the target induced background and the capability of the collimator
system [7].
In the 1996 run it was proven that the collimator system
has a high capability to catch scattered particles from the target
and to shield the other experiments very efficient.
This was a very important milestone in the cooperation with HERA
and the HERA experiments; allowing
long term high rate operation of the target.
