Beam Current Monitor based on a calorimeter
A "true" calorimeter measuring the temperature rise after being exposed
to a beam of a well defined energy for a well defined time can be used
for measuring the beam current. Silver is considered the best material
for such a calorimeter because of its high thermal conductivity
and low radiation length, making the temperature relaxation
time short. The calorimeter size was optimized by shower simulation
using
GEANT3.21.
A silver cylinder was considered. The beam spot was point-like. The energy
dependence of the response in a range of 1-11 GeV was checked.
The results are presented on
these plots.
The conclusions are as follows:
- The energy losses to the sides are as large as
2% for a 10cm diameter cylinder and do not depend on the energy.
- The losses due to back splash are about 0.1% and slightly decrease
with the energy.
- The losses due to forward leakage are about 0.1% at L=24cm and slightly increase
with the energy.
- The full losses at L=24cm are practically independent on the energy.
The recommended diameter is about 15cm, providing a 0.6% leak to the sides,
and 22-24cm length, providing a 0.1% leak to the front and
rear faces, practically independent on the energy. The systematic
error of these calculations should not exceed 30% relative. Assuming
the error of 30%, one can correct the calorimeter result (by 0.7%, on average)
due to the shower leak, with the associated error of 0.2%.
E-Mail :
gen@jlab.org
Last updated: Tue, 11 Aug 2002