A concept of the photon collider beam dump
  Photon beams at photon colliders are very narrow, powerful (10--15 MW) and cannot be spread by fast magnets (because photons are neutral). No material can withstand such energy density. For the ILC-based photon collider, we suggest using a 150 m long, pressurized (P ~ 4 atm) argon gas target in front of a water absorber which solves the overheating and mechanical stress problems. The neutron background at the interaction point is estimated and additionally suppressed using a 20 m long hydrogen gas target in front of the argon. 
L. I. Shekhtman and V. I. Telnov (Institute of Nuclear Physics and   Novosibirsk State Univ., Novosibirsk, Russia)
physics.acc-ph hep-ex physics.ins-det