First results of a high‐current electron cyclotron resonance proton source

A 2.45 GHz electron cyclotron resonance (ECR) ion source for producing a 100 mA H+ beam is under study. The microwave power is coupled through a quartz window and a water‐cooled 90° waveguide bend in order to avoid the heating of the electrons backstreaming from the source. The ECR condition is obtained with dc magnetic coils. Preliminary results reported here show that a beam current density of 75 mA/cm2 can be extracted at 10 kV from a 3‐mm‐diam aperture, with 1.2 kW of microwave power at 1×10−3 mbar of hydrogen pressure. The proton fraction is 75% with an alumina‐coated plasma electrode and 85% with a nitride coating.