Simulation Studies of the Lampf Proton Linac

The LAMPF accelerator consists of two 0.75-MeV injectors, one for H + and the other for H − , a separate low-energy beam transport (LEBT) line for each beam species, a 0.75 to 100-MeV drift-tube linac (DTL) operating at 201.25 MHz, a 100-MeV transition region (TR), and a 100 to 800-MeV side-coupled linac (SCL) operating at 805 MHz. Each LEBT line consists of a series of quadrupoles to transport and transversely match the beam. Each LEBT also contains a prebuncher and an electrostatic deflector, but share a common main buncher. The deflector is used to gate beam into the linac. The DTL consists of four rf tanks (modules 1-4), each driven by a separate rf amplifier, and uses singlet FODO transverse focusing. The focusing period is doubled in the last two tanks by placing a quadrupole only in every other drift-tube. Doublet FDO transverse focusing is used in the SCL. The SCL tanks are bridge-coupled together into rf modules with a single klystron powering each module. Modules 5-12 consist of four coupled-cavity tanks bridgecoupled together with 32-36 cells/tank. Modules 13-48 consist of two bridge-coupled tanks with 49-61 cells/tank. The TR consists of separate transport lines for the H + and H − beams. The path lengths for the two beams differ, by introducing bends, so the arrival of both beams is properly phased relative to the rf field. Peak H + beam currents typically range from 12 to 18 mA for varying duty factor, which give an average beam current of 1 mA. The number of particles per bunch is of the order 10 . The work presented here is an extension of our previous work [1]. We have attempted to do a more complete simulation by including modeling of the LEBT. No measurements of the longitudinal structure of the beam, except phase-scans, are performed at LAMPF. Transverse measurements include slit and collector emittance measurements, and wire scans to determine beam size and centroids. Comparison of simulations to beam loss data suggest that the primary causes of beam spill are incomplete longitudinal capture and the lack of longitudinal matching. Measurements to support these claims are not presently made at LAMPF. However, agreement between measurement and simulation for the transverse beam properties and transmissions serve to benchmark the simulations. ____________________________ *Work supported by Los Alamos National Laboratory Directed Research and Development, under the auspices of the United States Department of Energy. II. SIMULATION TECHNIQUES