Superconducting Solenoid Lens for a High Energy Part of a Proton Linac Front End

Development of a high-current proton linac at FNAL went through many stages, starting from a pulsed 8 GeV linac, then to the HINS linac front end R&D, and now toward the ProjectX CW linac. For different parts of the accelerator front end in each of these linacs, the design requires solenoid-based focusing lenses that can provide the needed transverse focusing on a very tight real estate environment. The multiple, often contradictory, design requirements of focusing lenses include the need for high focusing strength, small footprint, very low fringe field, and embedded steering coils. To meet these requirements, a series of prototype lenses were built and tested. Performances of the lenses designed for low energy parts of the linac front end have been reported earlier. This report presents lens design and test data for the high energy part of a proton linac front end, up to an energy of ~ 100 MeV. For these lenses, reliable protection from high voltages or temperatures during a quench becomes important, and a new protection scheme was developed, which allows more flexibility and reliability. Details of the magnetic axis position have also been investigated.