The purpose is to measure absolutely the straight field integral of a "BA" 3m long dipole, called the "9th dipole" and located in the "Dipole Shed". It is of the same type as the 8 arc dipoles and is powered in series with them.
The ARC integral setup is basically made of a 3m long plate (the "probe") which is able to move inside the 9th dipole gap along the beam axis and carrying two field measurement devices: a pair of pick-up coils connected in series and a set of NMR probes. The coils are on both ends of the probe and the NMRs close to the center.
-at the "upstream" probe position, the "downstream" coil is close to the dipole center, the "upstream" is outside the dipole and the NMRs at one end of the dipole:
Door
- ....................----DIPOLE---
.............----PROBE---
-at the "central" probe position, each coil is at one end of the 3m long dipole and the NMRs close to the dipole center:
Door- ...................----DIPOLE---
..................................----PROBE---
-at the "downstream" probe position, the "upstream" coil is close to the dipole center, the "downstream" is outside the dipole and the NMRs at one end of the dipole:
Door- ...................----DIPOLE---
....................................................----PROBE---
We call upstream the position where the probe is the closest to the shed access door. Among the 3 above positions, the only one where the NMR can lock on the dipole field is the central one as in the extreme position of the probe, the field homogeneity is not sufficient. The probe position is controlled by a linear encoder. The Z axis refers to the "beam" direction, increasing from upstream to downstream. We use three kinds of "Z":
-Zm to locate a point inside the magnet. The dipole center is at Zm=0 and the yoke ends at +-1500.mm
-Zp to locate a point inside the probe. The probe center is at Zp=0. Each of the 4 NMR probes has a Zp given in the file "magnet.dir". At a temperature of 21C, the coils are at Zp=+-1519.815mm (from magnet.dir)
-Zd to refer to a displacement of the probe w.r.t. the dipole. Zd=0 refers to the upstream (home) position of the probe. The integral measurement is performed from Zd=0.000mm (1st PDI trigger) to Zd=3199.000mm (last PDI trigger), for forward pass. Zd is given by the display (at the top of the rack) or by the master screen ("OUT").
The relationship between Zm, Zp and Zd is:
Zd-Zm+Zp=C
where C is a constant given in magnet.dir (C=1604.000 nomin.). Example of use: to have the probe center at the dipole center, one must set Zd=1604.000mm (set Zm=0 and Zp=0 in the above formula, and solve for Zd)
The integral measurement sequence is the following:
-from the current position (a priori arbitrary) move the probe upstream, up to a limit (optic) switch.
-move downstream by a few mm to cross the encoder index (encoder initialization)
-move to the central position to measure the central field by NMR, the system checks if the NMR locks and if the reading is stable, it will be the "before" field
-move back to upstream position
-move to downstream position while integrating the flux through the coil system,
this measurement will be called the "forward" integral (duration
7s)
-move back to upstream position while integrating the flux through the coil
system, this measurement will be called the "backward" integral
(duration 7s)
-move to the central position to measure the central field by NMR, the system checks if the NMR locks and if the reading is stable, it will be the "after" field.
In addition to the central field, 4 probe temperatures, a local excitation current measurement, the setting of the dipoles P.S, the readback of the dipoles P.S and the probe position at NMR measurement time are recorded "before" and "after".
To perform an integral field measurement:
1-check if the system works (see "details on integral system check" below)
2-run the above integral sequence (see "details on integral run" below)
3-fix the error(s) if any (see "details on integral errors" below)
4-save the data in a file (see "details on integral data save" below)
5-analyze the data (see Arun Saha).