Difference between revisions of "Magnetic Field Maps for Solenoid"

Latest revision as of 14:11, 1 June 2018

Several field maps exists for the GlueX superconducting solenoidal magnet. This page lists them along with some notes for each and how to specify one in the simulation/reconstruction software.

Location of the Field Maps

The map files themselves are stored as JANA resources, accessible via the web on a JLab server. The exact location is contained in an entry in the CCDB. Generally, retrieval and storage of the appropriate map files to the local computer is done automatically when a sim-recon program is run so users don't need to do anything special to get these. A typical situation would have one or more files in the local directory $JANA_RESOURCE_DIR/Magnets/Solenoid.

How sim-recon determines the which map to use

When a sim-recon program is run (e.g. hd_root) it will look in the CCDB for an entry in the Magnets/Solenoid/solenoid_map item. This will contain a single string specifying the specific map to look for in the CCDB. To see a list of maps by run number, do the following:

 > ccdb vers Magnets/Solenoid/solenoid_map
(ID)   (Created)              (Modified)              (variation)     (run range)      (comments)
94913  2018-01-14 15-11-51    2018-01-14 15-11-51     default         40843-40848     
94909  2018-01-14 02-06-03    2018-01-14 02-06-03     default         40853-inf       
94884  2018-01-13 05-12-05    2018-01-13 05-12-05     default         40844-inf       
22955  2017-02-06 08-16-37    2017-02-06 08-16-37     default         30000-inf       
22954  2017-02-06 08-14-18    2017-02-06 08-14-18     default         30000-inf       
17522  2016-12-14 21-53-26    2016-12-14 21-53-26     default         21913-inf       
17451  2016-12-01 17-52-17    2016-12-01 17-52-17     mc_generic      0-inf           
...

To see the map that would be used for a specific run, (e.g. run 41234) do the following:

 > ccdb -r 41234 cat Magnets/Solenoid/solenoid_map
Working run is 41234
+------------+
| map_name   |
| string     |
+------------+
| Magnets/Solenoid/solenoid_1350A_poisson_20160222 |
+------------+

To see the actual URL where the map file can be obtained, again use the ccdb 'cat' command, but for the specific item obtained from the command above:

> ccdb cat Magnets/Solenoid/solenoid_1350A_poisson_20160222
+--------------------------------------+
| URL_base   | path       | md5        |
| string     | string     | string     |
+--------------------------------------+
| https://halldweb.jlab.org/resources | Magnets/Solenoid/solenoid_1350A_poisson_20160222 | a96263c5e2f3936241b3eadb85e6559f |
+--------------------------------------+ 

The URL is obtained by combining the "URL_base" and "path" strings. In this case:

https://halldweb.jlab.org/resources/Magnets/Solenoid/solenoid_1350A_poisson_20160222

n.b. No run was specified when running ccdb cat Magnets/Solenoid/solenoid_1350A_poisson_20160222 because the specific map file items are only meant to specify a permanent location of the file on the web. They do not change with run number. The solenoid_map item however, does change with run number since the field current may be changed between runs.

Source used to generate a field map

The source for generating the field maps can be found here:

https://halldsvn.jlab.org/repos/trunk/home/davidl/PoissonConfigFiles

See the README file there for more info. on specific maps.

Specifying a different field map

Numerous field maps exist for the solenoid and a system is in place where one can specify the map of choice when running the simulation/reconstruction software. To specify a different field map for hdgeant to use, use

Technical details require that a recompile of hdgeant be done when specifying a different map for the simulation, but any existing reconstruction program can be reconfigured to use a different map without recompiling. Here I'm referring only to full maps, not the special field types of "Const" and "Spoiled" described below.

It should be noted that the *easiest* way to switch fields is really just to replace the default file in the calib directory tree with the desired map. Just be careful if you go that route since it will be easy to get confused since the file name will no longer be indicative of the content of the file.

Simulation

To change the map used in the simulation, edit the control.in file to indicate the alternate field map. This is in a section that looks like this:

c The magnetic field map is accessed through the HDGEOMETRY library
c so that the same map can be used for both simulation and reconstruction.
c There are multiple map types and for each type, more than one map may
c exist. The map types consist of the default type of "CalibDB", the 
c constant type of "Const" and the spoiled field type of "Spoiled".
c The type is set using the BFIELDTYPE card. If no BFIELDTYPE card is
c present, then no the default type "CalibDB" is used.
c The specific parameters used for the field can be specified using the
c BFIELDMAP card. If undefined, then the default that is hardcoded into
c the HDGEOMETRY library is used. Note that these correspond to the
c similarly named configuration parameters used in the econstruction.
c The difference being that underscores are not allowed here. To
c specify the values to the reconstruction code used here, use the
c -PBFIELD_TYPE=CalibDB and -PBFIELD_MAP=Magents/Solenoid/solenoid_1500
c BFIELDMAP 'Magnets/Solenoid/solenoid_0750_poisson_20091123_03'
c BFIELDTYPE 'Const'

The "c" in the first character indicates a comment. The default control.in file has this commented out and so used the default map.

To specify a different map, you will want to uncomment the BFIELDMAP line and set the desired map. For example, to use the standard 1500A map, add this line to control.in

BFIELDMAP 'Magnets/Solenoid/solenoid_1500_poisson_20090814_01'

Note that this will only have access to maps the current CCDB has available. To see a list of available maps do the following:

ccdb ls Magnets/Solenoid

You will see a lot of maps listed. Ignore any with names that include "_parms_". Look to the table below for details on individual maps.

Reconstruction

For reconstruction, one simply needs to specify the BFIELD_MAP configuration parameter either on the command line or through a configuration file. For example, using the command line one passes a "-PBFIELD_MAP=Magnets/Solenoid/solenoid_1500_poisson_20090814_01" argument as follows:

hdview2 -PBFIELD_MAP=Magnets/Solenoid/solenoid_1500_poisson_20090814_01 hdgeant.hddm

Special Field Types

There are 2 special field types available also. They are the "Const" and "Spoiled" fields.

The "Const" field type is a uniform-everywhere-in-the-universe field. The parameters are set in the Magnets/Solenoid/solenoid_const calibration parameters. One can specify the 3 components of the field in cylindrical coordinates so the field is necessarily radially symmetric. The default values are just a 2T field in the -z direction. To specify this field in simulation, one needs to set the "BFIELD" parameter in the control.in file to "'Const'". This already exists, but is commented out, in the default control.in file one gets from the repository with the HDGeant package. To specify the "Const" map in a reconstruction program, one just needs to se the BFIELD_TYPE configuration parameter. This can be done by adding the "-PBFIELD_TYPE=Const" argument to the command line when the reconstruction program is started.

The "Spoiled" field type uses a full field map, but spoils it by scaling the amplitude with some combination of r, phi, and z dependences. Each of the dependences has both an amplitude and an angular frequency that are set using configuration parameters. The relevant configuration parameters are:

BFIELD:PHI_AMP
BFIELD:PHI_OMEGA
BFIELD:R_AMP
BFIELD:R_OMEGA
BFIELD:Z_AMP
BFIELD:Z_OMEGA

The underlying unspoiled map that is determined using the BFIELD_MAP configuration parameter as is normally done when using an unspoiled field.

Known field maps

The following are in chronological order. Look to the bottom of the table for the most recent maps.

"David and Elton,
The results are in the folder below.
1. Note that because of the FEA calcultion doesn't do well on the sharp corner of a wedge, we don't have a field value on the Magnet Axis
2. We have changed the Z axis to the standard Z axis origin for the experiment, the inner surface of the Upstream Front Yoke.
3. We have solutions at 1500 to 1800 A.  So far, the nominal current is 1500A.  I don't know how we want to characterize beyond that.
4. ANSYS output is in comma delimited EXCEL files.  I didn't want to cram more huge, translated  files in our folders, so I will let you do the translations to what you need.
5. We will title the files by date and run on that date.  The translation file to what the run consisted of is in the main folder.
6. We don't have the FCAL steel plate in these runs.
7. As more runs accumulate, we will have to maintain configuration control with a designation of what is the OFFICIAL RUN and notify everyone if the run changes. "

The differences I can see are:

On the initial 20081209-1 tabulation (pg 9):
1) The small upstream yoke bore liner was 1.5"
2) Coil locations and sizes were at room temperature.

On the latest 20090312-2 tabulation (pg 14):
1) The small upstream yoke bore liner is 1.25"
2) Coil locations & sizes are at a liquid Helium state.

I think that's the only differences between the two dates.

Creating a ROOT file of the magnetic field

The bfield2root program can be used to create a ROOT file of the magnetic field map as is used by the simulation/reconstruction code. The ROOT file will contain a TTree with entries from several points in the map. It is important to note that the values going into the TTree come from interpolating the map whose grid is determined by the ASCII file. The bfield2root program has default settings to match the default grid of the ASCII files. If a map with different grid spacing is generated then the bfield2root program will still work but one should be aware that the resulting ROOT file will contain interpolated values.

Another "gotcha" is that the origin of the lab coordinate system used by the original field maps is not in the same location as is currently used. The TOSCA generated maps have the origin close to the center of the target, 26 inches (=66.04 cm) offset from the modern coordinate system. As of svn revision 5316 on June 22, 2009, the reconstruction code no longer assumes this offset is there and so one must correct for it when using a TOSCA map. In the mean time, the bfield2root program must be told about this offset via a command line parameter (see below).

The following instructions are for doing this on the JLab CUE system (e.g. ifarml3). However, one can of course do this on another system where the Hall-D software is compiled and the desired map is located in the directory indicated by the JANA_CALIB_URL environment variable (note: this is set in step 1 below for the CUE).

1. Make sure bfield2root is in your path. If it's not, then source a setup script for a pre-built Hall-D software release.

   e.g. source /group/halld/Software/builds/release-2009-05-27/setenv.csh

2. Run bfield2root specifying the specific map

   e.g. bfield2root -PBFIELD_MAP=Magnets/Solenoid/solenoid_1500_20090312-2

3. Run bfield2root using an older, TOSCA generated map

   e.g. bfield2root -PBFIELD_MAP=Magnets/Solenoid/solenoid_1500 -Z0 -66.04