  The generation and capture of polarized positrons at a source with a
superconducting helical undulator having 4.3 cm period and 500 GeV electron
drive beam have been simulated. The positron polarization has been calculated
for the different undulator K values (up to K = 2.5). Without applying a photon
collimator, the maximal polarization of positrons is about 25% for 231 meters
active magnet length of undulator with K = 0.7. Using an undulator with K = 2.5
and a collimator with an aperture radius of 0.9 mm results in increase of
positron polarization to 54%. The energy deposition, temperature rise and
stress induced by high intense photon beam in the rotated titanium-alloy target
have been estimated. The maximal thermal stress in the target is about 224 MPa
for the source with photon collimation to achieve a positron polarization of
54%.
