The main use of the integral setup is to measure the integral of the 9th dipole along a straight line, located on the axis of the pole tips. By moving (manually) the dipole in the transverse direction and then performing the integral sequence, one will measure the integral along different axes, and hence extract the gradient of the dipole integral (used to determine the dipole positionning tolerances). By inserting a jumper (short) on one of the pick-up coils and reducing the gain of the PDI, the same sequence as for the integral will provide, after a specific analysis, the field profile of the dipole as seen by the other coil. This profile will cover one half of the magnet, including one of the two fringing fields. Reduce the PDI gain by one step ( example: if the automatic gain is 10, select manually 5) By inserting the jumper on the other coil, one can get the other half profile. These two single coil measurements will provide together the complete profile of the dipole including both fringing fields. For the central part, where the field is uniform, more accurate data can be taken using the NMR probes. Here, there is no change in the hardware, but one must use a specific software: the "mapping" MEDM window. By combining, for a set of transverse positions:
-standard integral measurement
-upstream profile (upstream coil alone)
-downstream profile (downstream coil alone)
-NMR map of the plateau,
one gets a 2D map of the dipole field in its mid-plane with an optimum accuracy and redundancy and a minimum time spent by the operator. This 2D map is used to get the straight-to-curved correction to the integral and a set of tolerances.
Call "medmMew" (and NOT "medm"), then open "arc_map.adl", as this display is written in a new version of MEDM. Due to a bug in this Solaris/MEDM combination, you must enter the name of the display in the open menu, you can't just click on the display file name. You then get the "ARC-MAPPING" screen. You must define the position inside the magnet (Zm) where you want to measure the field, inside the [-1500mm,+1500mm] range. The software will compute the probe position Zd depending on the NMR probe selected (automatic or manual selection). You have to define 3 regions, where the steps may differ. Edit the fields:
-STARTING Zm
-region 1 : NUMBER OF STEPS and STEP SIZE, then the intermediate position Zm is computed automatically by the software as a result of the above input
-region 2 : NUMBER OF STEPS and STEP SIZE, then the intermediate position Zm is computed as above
-region 3 : NUMBER OF STEPS and STEP SIZE, then the final position Zm is computed as above.
Then push "Start". It takes about 20s per point, unless there is a lock problem, where it can take up to 100s (timeout). If the NMR does not lock even far from the ends, push "Stop Map here", use the DAC+-5% lock mode (see "detail on NMR lock"), and start a new map.
Note: after "Stop Map here" the incomplete map can still be saved. Use "Stop" in case of emergency, and then reboot the VME (see detail).
The measured fields are displayed on the screen as a function of Zm. The sequence is:
-a measurement at Zm=0, called "Bref1"
-the list of measurement you entered
-a measurement at Zm=0, called "Bref2".
When done, save the data by pushing "Save". The file is numbered automatically, the name is of the type mapping_nnn.data, where "nnn" stands for the map number. The directory is given by the MEDM screen. An example of file ("mapping_7.data") is given below (EPICS was not responding for the P.S. readback and set, the real current was 90A):
!ARC magnetic measurement mapping data file
!version:1
!date: SAT JUN 12 04:49:40 1999 SAT JUN 12 05:41:32 1999
-1460.00 50 20.00
-460.00 46 20.00
460.00 50 20.00
!temperature x+,z+(deg.C) 29.8 30.2
!temperature x+,z-(deg.C) 31.7 32.0
!temperature x-,z+(deg.C) 28.4 28.2
!temperature x-,z-(deg.C) 28.6 28.2
!tal nbr pts: 146
!initial & final NMR probe: 2 2
Zm (mm), B (T), NMR lckd, NMR flag,local crt(Vadc),crt set(A),crt rdt(A)
0.00 0.1770036 1 1 92.19 0.04 0.00
-1460.00 0.1770068 1 1 92.19 0.04 0.00
-1440.00 0.1770157 1 1 92.19 0.04 0.00
.......
1439.99 0.1770756 1 1 92.19 0.04 0.00
1460.00 0.1770665 1 1 92.19 0.04 0.00
0.00 0.1770044 1 1 92.19 0.04 0.00
!end
Note: "1" is the normal status for NMR lock and NMR (stability) flag. The lines #4,#5 and #6 of the header give the data entred by the operator. The result is a map from -1460 to +1460mm with an uniform 20mm step size. This input is the standard one for the needs of ARC.