CLIC Meeting Minutes of 24 November 2000
T. Kamitani: CLIC positron source.
Takuya presented his study of the unpolarised and polarised positron
source. He investigated the target and the capture section to evaluate
the positron yield.
Reducing the target thicknes from 4.5 radiation lengths to 4 reduces the
power deposition by 20% and the positron yield by only 2%.
Increasing the beam size at the target from 1.6 to 2 mm reduces the
peak power to about 50% of its limit value. The loss in positron yield is
only 10%.
A wider longitudinal acceptance of the predamping ring could increase the
total positron yield from 0.31/GeV to 0.39/GeV.
The dependence of the yield on the accelerating field is weak, which should
allow to reduce the field from a very high 25 MV/m to some more resonable
value.
The overall yield is about 0.3/GeV.
Takuya also looked into the the possiblity to use a TESLA-like scheme for the
production of polarised positrons at Ecm=500GeV.
The transverse emittances are small enough to be able to achieve very
high polarisation. A tradeoff has to be made bewteen degree of polarisation
and number of positrons produced. Sample simulations showed that the electron
beam will loose 33GeV and a 1.4 GeV energy spread will be introduced
in this beam. This would lead to 0.77 positrons per electron with a
polarisation of 0.57.