Summary of ARC operations:

Six scanners of the same type, called "ARC scanner" and labelled from scanner #1 to #6, are installed on the Hall-A beamline. Scanners #1 to #4 are used for the ARC energy measurement and they are located on the Hall-A arc: #1 and #2 just upstream of the arc, in the BSY, and #3 and #4 in the Hall-A tunnel, just upstream the Compton polarimeter. Scanners #5 and #6 are located between the Moller and the target to control the beam geometry on the target and their use will not be discussed here.

Each scanner has a motor/ball-screw/shaft-encoder/vacuum-penetrator system moving accurately a set of 3 tungsten wires through the beam. Each time a wire crosses the beam a PMT located a few meters downstream records a signal due to the electromagnetic shower induced by the beam in the wire. Both forward and backward passes are recorded. The motion is a horizontal translation and, for a forward pass:

-the translation is from beam left to beam right,

-the two first wire crossing the beam are at 45deg from the vertical,

-the third wire, which is the only important for the ARC energy measurement, is vertical.

Recording, during the scan, the scanner position and the PMT output voltage allows us to determine the beam position at each scanner location. Then, using calibration data not detailed here, we deduce the net beam bend angle through the arc. This result measured in dispersive arc tuning, along with the field integral of the arc dipoles, provides an accurate determination of the beam energy.

The list of the operations for an ARC energy measurement is given here and will be detailed after:

1/check the pulser (scanners)

2/check the HV (scanners)

3/check EPICS (scanners)

4/check space on disk(scanners)

5/check the integral (see "Details on integral system check" below)

6/ask for chicane off, put target in a safe position, ask 5$\mu$A (achromatic)

7/perform a scan test in achromatic at 5$\mu$A $-->$ solve the trips $-->$ final adjustment of gains of scanners #1 and #2 $-->$ save the last (non saturated) scan

8/if everything is OK, ask for dispersive beam 5$\mu$A

9/check dispersive beam:

-CW 5$\mu$A

-Fast Feedback ON

-Energy Feedback ON $\leftarrow$ important

-Kresting ON

-arc's quads and steerers OFF

-beam stable at entrance and exit (Bscope) (see the test plane of the dispersive mode in MCC)

10/perform a scan in dispersive at 5uA (see details below)

-solve the trips

-finish the 4 gains adjustment

-perform and save 3 good scans

11/perform a field integral (see details below)

12/restore beam for the experiment, unmask the diagnostics, restore achromatic mode and chicane, quit MEDM and turn both HV channels OFF.

13/analyze scan data (dispersive only) and integral data.