Damping of higher-order modes in electron linacs

Future linear e+-e--colliders will operate at frequencies up to ten times higher than existing machines. Therefore beam induced effects like long range and short range wakes cannot be neglected. They are capable of severely deteriorating beam quality. The most dangerous modes existing in an iris structure are evaluated and it is shown to which extent they can be suppressed. Experimental work has been done determining low Q-values using a simple and precise measurement technique. First results are presented