Solid State Laser Triggering System for the HERMES-III Accelerator

The Hermes III accelerator is a 20-MV linear induction accelerator that has been in operation at Sandia National Laboratories since the late 1980’s. Energy is initially stored in the accelerator in ten Marx banks that are discharged into twenty intermediate store capacitors. These intermediate store capacitors are then switched with SF 6 -insulated high voltage Rimfire switches into eighty parallel pulse forming lines that further condition the pulse before finally delivering it to the twenty induction cavities arrayed along the axis of the machine. Currently, a single 0.9-J KrF laser operating at 248 nm, the output of which is divided into twenty separate beamlets, is being used to trigger the Rimfire switches. However, as part of a modernization plan for the accelerator, the gas laser system is being replaced with a new solid-state laser triggering system. The new system is comprised of 10 flash-lamp pumped, Q-switched Nd:YAG lasers (Tempest 300), each having an energy output of 35~40 mJ at a wavelength of 266 nm. Each laser will be responsible for triggering two Rimfire switches. Overall reliability for the accelerator’s operation with these new lasers is expected to increase, and by varying the times at which the individual lasers fire it becomes possible to tailor the shape of the output pulse. The optical layout and other details of this solid-state laser triggering system are presented, along with initial operational data from the HERMES III accelerator using this system.