ECR heating of laser produced Sn plasma for drift control in B field

A laser produced Sn plasma driven with a pulsed CO2 laser and emitting EUV radiation has been generated in a magnetic field of 0.5T. The multiple-ionized plasma ions are efficiently guided along the B field lines of the double coil magnet. The neutral Sn atoms and Sn clusters, however, expand freely inside the vacuum chamber and contaminate e.g. EUV optics. We therefore evaluated ECR heating of the laser produced Sn plasma with 14GHz microwave frequency to ionize the remaining plasma neutrals. Sn ion signals were measured with micro-channel plates and Faraday cups placed inside the vacuum chamber across and along the B field lines. An increase of the Sn ion signal with ECR heating was observed along the B-field lines. The increase was maximal for the resonant microwave frequency outside the plasma position. Results demonstrate the principle of ECR heating for the cleanliness of a EUV light source.