Novel adiabatic bifilar helical wiggler entrance for free-electron laser applications

Abstract
A new adabatic bifilar helical wiggler entrance is presented. This introduction region is obtained by using a liquid shunt resistance to progressively shunt the current circulating in the wiggler helical windings. We have built a prototype wiggler and measured the field profiles obtained with this new scheme. The results agree very well with computer calculations and show that, indeed, one obtains a high quality adiabatic wiggler with this method.