205 kA pulse power supply for neutrino focusing horns

A new underground beamline is being constructed at Fermilab to generate and focus a beam of neutrinos on a detector 450 miles away in Soudan, Minnesota. A compact modulator utilizing capacitive energy storage and SCRs as the switching element has been built and tested at Fermilab. The 0.9 F capacitor bank operates at less than 1 kV. It delivers its output of up to 240 kA directly to the two series connected focusing horns via a multi-layer radiation hard stripline. Dual pulse width capability allows for ready selection of 5.2 ms, for slow beam spills, or 2.6 ms operation for reduced thermal stresses on the focusing horns during fast spill. Intended for installation in an underground equipment room, the design incorporates several novel features to facilitate transport, installation, and maintenance. Various designs were examined to arrive at the most economical approach for providing the high pulse currents to the horns located in the very high radiation field, up to 3×10⁷ kRads/yr absorbed dose of the beamline. These included charge recovery and electronic polarity reversal systems. The direct coupling approach was selected for its overall economy and compactness. The system has been operational for several months and results of those tests are discussed. Controls and safety issues are also discussed.