Halo Detectors
Halo counters are pairs of movable scintillators installed on opposite sides of the beam. During the shutdown of 2016-2018 two pairs of halo detectors were moved from beamline nearby Cave M to TH2 sector. The new location was chosen such, that the phase advance with respect to the pion production target is pi or 2pi (using standard new optics), so the beam shape should be the same in both locations.
The counters are called:
- GTH2DVZHR and GTH2DVZHL - horizontal ones
- GTH2DVYVO and GTH2DVYVU - vertical ones
They are driven by stepper motors with the following names: GTH2DDYOS, GTH2DDYUS, GTH2DDZLS, GTH2DDZRS. The variable names in Lassie-spill are: GTH2DDYO, GTH2DDYU, GTH2DDZL, GTH2DDZR.