120‐kV testing of a 10×40‐cm prototype of the U. S. common long pulse neutral beam source

The 10×40‐cm long pulse neutral beam source developed at Lawrence Berkeley Laboratory has been selected as the prototype for the design of the U. S. common long pulse source to be used on tokamak fusion test reactor (TFTR), Doublet‐III, and mirror fusion test facility (MFTF‐B). The long pulse source consists of a magnetic line cusp bucket with an actively cooled backplate electron dump and a four‐grid accelerator using slot apertures and water‐cooled molybdenum rails. Deuterium testing of the long pulse source at 120 kV and 53 A and with a 2‐s pulse length has been completed on the neutral beam engineering test facility, including an 8‐h 100‐shot test to demonstrate the durability and reliability of the source. Maximum 2‐s beam parameters obtained (not simultaneously) are 125 kV, 58 A (deuterium), and 7.1 MW. Beam pulse length has been extended to 5 s at 120 kV. Atomic species fractions in excess of 80% have been obtained, with a beam divergence (full energy, 1/e half‐angle) of approximately 0.8×0.4°. Cal...