Beamline

The CLAS12 Detector Beamline includes several interdependent systems that guide and perform diagnostics on the electron flow from the accelerator through the fixed target into the Faraday cup at the beam dump.

All measurements from the beamline are relayed to the operators in the counting room during data measurement, and also provide inputs for orbit lock feedback and rapid shutdown of the accelerator if needed.

Parts
Dipole and quadrupole magnets deflect and focus the beam of electrons in the way that optical lenses focus light. Antenna cavity beam position monitors run at continuous currents at 1 nA (nanoamp) with accuracies of 20 μm (micrometers) at 100 Hz.

Wire scanners with 20 μm thick tungsten measure the profile of the beam by passing through at two stereo angles. This helps make sure that the beam is not poor quality.

Scintillating fibers surround the target to keep track of the offset of the beam.

An insertable YAG screen also allows for checking of beam position and profile downstream at the dump. Finally, the beam current is monitored by the charge deposited in a Faraday cup.

Links/Sources
CLAS12 beamline: http://www.jlab.org/Hall-B/clas12-web/subsystems/beamline-intro.html