Study of damage of storage ring vacuum chamber by 8 GeV electron beam abort at SPring-8

The 8 GeV electron beam stored on the SPring-8 storage ring finally hits the vacuum chamber wall, especially stainless steel chamber wall of 0.7 mm thickness in the injection section, when the operation is suddenly stopped by interlock system for safety. At that time the localized heat load is generated in the stainless steel material as a result of the dense electro-magnetic shower. Because of the several times such heat loads, the stainless steel chamber has been broken and vacuum also has. On the cross section of the broken stainless steel wall, one can see the evidence of the degeneration or melting down of the stainless steel which is well described by the cascade calculation for the high energy electro-magnetic events using GEANT3. To avoid such a vacuum break, a thicker stainless steel chamber has been installed and an Al damper, in which density of electro-magnetic shower is low because of its small atomic number, has been developed. (author)