arXiv subjects
Publications and source records attributed to James MacLachlan.
An experimental procedure for measuring gamma-T has been developed and tested in two different measurements, with the gamma-T quads on and off. The results were compared to MAD calculations. The discrepancy between the measured gamma-T and the calculated gamma-T is less than 5%.
Twelve pulsed gamma-T quads have been installed in the Booster to provide fast transition crossing. The less time the beam stays in the non-adiabatic period near transition, the less the longitudinal emittance grows. From the past experience, the gamma-T quads are not well aligned relative to the usual closed orbit. Quad steering can cause beam loss and a dispersion wave after transition. To make the gamma-T quads routinely operational, procedures for finding the center of the beam relative to the quads and centering the beam through all of them are very important. A program, which uses the difference in the closed orbits when gamma-T quads are on and off and calculates the offsets of the beam relative to gamma-T quads, has been developed and tested. A radial orbit offset (ROF) of about 3 mm has been experimentally determined to be nearly the optimal radial position for centering the beam through all the gamma-T quads, thereby eliminating the immediate need for repositioning the quads.
The match between the Linac beam energy and the energy determined by the bending field of the Booster magnets is crucial for rf capture, beam quality, and the transmission efficiency in a Booster cycle. The observation of the injection energy match is important for injection tuning. Several signals, such as phase shift drive (PSD), radial position error (RPOS), synchrotron phase (SPD), and fast phase error (FPERR), provide consistent information on the energy match and can be used for a injection match tuning.
The dipole mode synchrotron frequency is a basic beam parameter; it and a few similarly basic quantities measured at small time intervals serve to characterize the longitudinal beam dynamics throughout the acceleration cycle. The effective accelerating voltage, in conjunction with the amount of rf voltage required for the acceleration, is important for the estimate of the beam energy loss per turn. The dipole mode frequency can be used to obtain the effective accelerating rf voltage, providing that it can be measured precisely. The synchrotron frequency measured from the synchrotron phase detector signal (SPD) generally agrees well with calculation, and it can be applied for such purposes as inferring the effective rf voltage.
Understanding the transition-crossing process is crucial for improving Booster performance at high intensity. The synchronous phase appears to drop toward 90 degrees right after transition regardless of beam intensity, more so at higher beam intensity. The implication is that the effective rf voltage (RFSUM) will run into a limit right after transition when the synchronous phase reaches 90 degrees for high intensity beam. A reduction in RFSUM is also observed at the same time. Solutions, such as raising the rf voltage during the transition period or controlling the RFSUM reduction by increasing longitudinal emittance before transition, are potentially important for high intensity operation.
It is important to have experimental methods to estimate the maximum beam intensity for the Fermilab Booster as objective input into long term program commitments. An important existing limit is set by the available rf power. This limit is difficult to set a priori because the real longitudinal impedance is not well known. The synchrotron phase at transition crossing was measured using both the mountain range plot and the direct phase measurement of the RF accelerating voltage relative to the beam, and results were consistent. They were applied to predict 6E12 maximum Booster beam intensity with present running conditions.