Killing the Electron Cloud Effect in the LHC ARCS

A getter/electrode assembly has been devised to suppress the regeneration mechanism of the electron cloud effect in the arc dipoles of LHC. The assembly consists of a copper foil electrode, supported through an insulating layer on a stainless steel skid, which would rest upon the flat bottom of the beam screen. The electrode is coated with NEG to provide effective pumping of all non-inert gases from the vacuum. When the electrode is biased ∼+100 V, both electrons from beam ionizations and secondary electrons produced on the beam screen surface would be cleared, killing the regeneration mechanism. The NEG surface can be regenerated by passing a current through the electrode to heat it to ∼~240 C. The heat tran-s fer (radiant + conductive) to the beam screen during regeneration is estimated ∼10 W/m, within limits to maintain the beam screen at nominal 20 K temperature during regeneration.