Time-of-flight measurements of absolute beam energy in the Fermilab linac

Measurements have been made of the absolute energy of the fourth tank of our linac by measuring the time-of-flight of individual beam bunches passing between strip-line beam monitors at the entrance and exit of each tank of the linac. Accurate time-of-flight measurements are facilitated by the fact that the beam remains well bunched between strip-line monitors in the drift region beyond the fourth tank. Cable lengths were carefully measured using time-domain reflectometry. The data for tank 4 gave the time-of-flight over a 49.17 meter drift as 395.8 (±0.5) nanoseconds. This translates into a measured β of 0.4155. The design β for tank 4 is 0.4141. Further measurements on other linac tanks are planned, if machine time becomes available. In addition to determination of absolute beam energy, the time-of-flight data can be used for absolute energy calibration of the magnetic spectrometer system used for detailed energy analysis of the beam. We plan to implement this technique on the Linac Upgrade to be installed in the summer of 1993