Mechanical features of the ATS ramped-gradient DTL

At Los Alamos, a short, lightweight drift-tube linac (DTL) has been designed. This accomplishment is possible by varying the accelerating gradient from 2 MV/m at the RFQ end to 4.4 MV/m at the output end, with the gradient rising as a cubic polynomial. The object of raising the gradient to such a high level is to reduce the length of the proposed 50-MeV machine that ultimately will attach to the ramped-gradient drift-tube linac (RGDTL) tank. This is the first proton linac structure to propose such a ramping scheme and the first to attempt reliable long-term operation at such elevated accelerating gradients. It is also the first to attempt to accomplish this with a lightweight aluminum structure designed to operate at 5% duty factor.