The investigation of the rate stability is a huge and
very important topic because the
efficiency of the final experiment relies on stable rates.
The actual HERA operation conditions,
with very high natural proton lifetimes, requires
to aproach the targets close to
the beam, scrape away protons and reduce the lifetime.
The target operates at a very sharp edge of the beam, already 
m steps
alters the rate significantly. Artificial beam excitation to increase the
halo population, e.g. by adding stochastic noise to a quadrupole
and modulate the tune, could help to relax the situation. This is under serious
investigation
and tests are planned for the 1998 operation.
Figure: Power spectrum of the interaction rate showing typical lines
from power supplies at 50 and 100 Hz but also lines from
vibrations of machine elements.
Fig. 15 illustrates that the interaction rate (analyzed with a spectrum analyzer) presently reflects power supply lines and other external impacts.