  In the future, International Linear Collider (ILC), a helical undulator based
polarized positron source is expected to be chosen. A high energy electron beam
passes through a superconducting helical undulator in order to create
circularly polarized photons which will be directed to a conversion target, the
result of which, will be electron-positron pairs. The resulting positron beam
is longitudinally polarized. In order to produce the required number of
positrons in ILC250 the full undulator length is needed. Since the photons are
created with an opening angle and traveling through a 320 m long undulator, it
is expected that the superconducting undulator vacuum will be hit by the
photons. Photon masks are needed to be inserted in the undulator line to keep
the power deposition in the vacuum below the acceptable limit which is 1W/m. A
detailed study of the power deposition in the vacuum and masks is needed in
order to design the photon masks. This paper describes the power deposition in
the undulator vacuum due to secondary particles assuming an ideal undulator. In
addition, the mask model is proposed.
