Initial Emittance Measurements of the Fermilab Linac Beam Using the MTA Beamline

Abstract

The MTA beam line has been specifically designed to facilitate measurements of the Fermilab Linac beam emittance and properties utilizing a long, 10m, element-free straight. Linac beam is extracted downstream of the 400-MeV electrostatic chopper located in the Booster injection line. This chopper cannot be utilized for MTA beam, and therefore the entire Linac beam pulse is directed into the MTA beamline. Pulse length manipulation is provided by the 750-keV electrostatic chopper at the upstream end of the Linac and, using this device, beam can be delivered from 8 {\mu}sec up to the full 50 {\mu}sec Linac pulse length. The 10 m emittance measurement straight exploits and begins at the 12' shield wall that separates the MTA Experimental Hall and beamline stub from the Linac enclosure. A quadrupole triplet has been installed upstream of the shield wall in order to focus a large, 1.5-2" (~95% width) beam through the shield wall and onto a profile monitor located at the exit of the shielding. Another profile monitor has been installed upstream of the shield wall, ~5 m upstream of the central, or focal-point monitor. With the triplet, a small, 0.2-0.5" spot size was produced for the initial measurement reported here. As will be shown in this report, a small, approximate beam waist located near a center profile monitor reduces the number of unknown linear optical parameters to two Courant-Snyder parameters, {\beta} and {\epsilon}, since, {\alpha}, or the rotation of the phase ellipse can be determined by propagating the beam envelope from this waist (using the simple linear transfer matrix that describes a drift).