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Some comments on modeling of ATF magnet strengths and the ATF control system

 

                                                  

 

  Some comments on modeling of ATF magnet strengths and the ATF control system

 

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GENERAL REMARKS

---------------

 

ATF magnetic measurements (MMS) data consist of field measurements (Tesla) for

dipoles and gradient measurements (Tesla/m) for quadrupoles ... no integrated

strength data is available.  The actual effective length of many magnets is,

therefore, a matter for 3D magnet code modeling or conjecture, and fudge

(correction) factors, determined by analysis of observed beam behavior, are

used by the control system in computing magnet setpoints and in determining

magnet strengths from measured currents for the online model.  These fudge

factors reside in an ASCII file which is read by the control system and used

whenever strength -> current or current -> strength computations are performed.

 

(NOTE: as of ~ DEC-1998 only the DR magnets use fudge factors)

 

Note that the control system software computes beam rigidity using 100/3 to

approximate the quantity 1e10/c, where c is the speed of light.  This

introduces a small computational error (~0.07%) in the conversion of magnet

currents to magnet strengths and vice versa.

 

In the following text, all files referred to reside on the ATFAXP computer

unless otherwise noted.  Also, I will use the following acronyms:

 

 MMS = Magnetic Measurements data

 BT  = Beam Transport line

 DR  = Damping Ring

 

 

DATABASE CHANNELS

-----------------

 

Magnet currents are found in the database by referring to the appropriate

channel name.  These names are of the form:

 

 'DB_MAGNET::<magnet name>:CURRENT.DAC.WRITE'

 

where magnet name is something like QM11R.  These values are like "BDES" values

in the SLC control system, in that they are the current that the power supply

is being asked to deliver.  The "readback" or "monitor" current (like BACT) is

considered less reliable by the control system gurus.

 

The energy of the Damping Ring (DR) is found via the following channel name:

 

 'SAD_CONTROL::DR_ENERGY'

 

In my own (Matlab) code which performs the current/strength conversions (see

USER$DISK1:[MDW.DOC]MATLAB.DOC) I use this energy for scaling both DR, BT, and

EXT magnets.

 

 

DR COMBINED FUNCTION BENDS

--------------------------

 

MMS data for the DR combined function bend (field [T] vs current) may be found

in the file:

 

 USER$DISK1:[KURODA.ATF.MAGNET_B_I.DATA]COMBINED_B_MITSUBISHI.DAT.

 

I have been unable to locate MMS data for the gradient of this magnet versus

current, so in my COMFORT models I use the design SAD value ... however, in

order to make my online COMFORT model agree with SAD on what the DR tunes are,

I use a multiplicative factor of 0.932712 for the quadrupole content of the

BH1R family (making the BH1R family weaker in COMFORT than in SAD).

 

(NOTE: see MDW logbook for the full set of availble BH1R MMS data)

 

 

DR QUADS

--------

 

Quadrupole magnet currents (amps) for the DR are converted to gradients (T/m)

by the control system using linear interpolation of MMS data found in files

corresponding to the eight different varieties of DR quads.

 

The conversion from quad current to inverse focal length made by the control

system proceeds as follows:

 

 o B'(quad_type) [T/m] is linearly interpolated from the MMS data

 o |K1| [1/m] = {leff(quad_family) [m] * 10 [kG/T] * B'(quad_type) [T/m]}

              / {(100/3) [kG-m/GeV] * E [GeV]}

 o |K1| [1/m] -> |K1| / (1 + fudge(quad_family))

 

Note that MMS data is associated with quad type, while effective lengths and

fudge factors are assigned on a quad family basis.  When all of the DR quad

trim windings are powered, the fudge factors may even be assigned on a

magnet-by-magnet basis.

 

(NOTE: as of ~ DEC-1998 DR fudge factors are assigned by magnet family)

 

The MMS data files may be found in the following directory:

 

 USER$DISK:[KURODA.ATF.MAGNET_B_I.DATA];

 

the effective length used by the control system for each quad family may be

found embedded in the control system software in the following file:

 

 USER$DISK1:[ATFOPR.SAD]DR_MAG_LIB.FOR subroutine DRMAG_GET_EFFECTIVE_LENGTH;

 

the fudge factors used by the control system for the DR quads, computed by

K. Kubo, may be found in the following file:

 

 USER$DISK1:[ATFOPR.SADDATA]DR_QUAD_CORRECTION.DAT.

 

Note that, because of the way the fudge factors for members of a family are

averaged together and some creative counting, the actual fudge factor for the

DR QF1R and QF2R families used by the control system is (N-1)/N times what is

specified in the file, where N is the number of quads in that family ... this

"adjustment" of the fudge factor for the QF2R family (by the fraction 25/26)

represents an additional 0.07% error in current/strength conversions for that

family.  This all occurs in:

 

 USER$DISK1:[ATFOPR.SAD]SAD_CTRL_DR.FOR subroutine DRQUAD_GET_CORRECTION.

 

The DR quad types and their associated MMS data files names are:

 

 type        name                 file

 ----   ----------------   --------------------

   1    Hitachi type 1     Q_HITACHI_TYPE1.DAT

   2    Hitachi type 2     Q_HITACHI_TYPE2.DAT

   3    Hitachi type 3     Q_HITACHI_TYPE3.DAT

   4    Hitachi type 4     Q_HITACHI_TYPE4.DAT

   5    Tokin 18 cm        Q_TOKIN_18CM.DAT

   6    Tokin 18 cm (42p)  Q_TOKIN_18CM_42P.DAT

   7    Tokin 6 cm         Q_TOKIN_6CM.DAT

   8    Tokin 6 cm (42p)   Q_TOKIN_6CM_42P.DAT

 

The family names, types, control system effective lengths, and fudge factors

(as of 7-DEC-1998 18:32) for the DR quads are summarized here:

 

  family  type   N   leff      fudge

  ------  ----  --  ------   ----------

  QF1R      1   28  0.0788    0.0126096

  QF2R      5   26  0.1986    0.0011024

  QM1R      3    2  0.1985   -0.0089336

  QM2R      2    2  0.079     0.0226221

  QM3R      2    2  0.079     0.0226284

  QM4R      3    2  0.1985   -0.0089336

  QM5R      4    2  0.1987   -0.0103301

  QM6R      4    2  0.1987   -0.0103299

  QM7R      7    2  0.0789   -0.0193019

  QM8R      7    2  0.0789   -0.0193022

  QM9R      4    2  0.1987   -0.0103299

  QM10R     4    2  0.1987   -0.0103301

  QM11R     6    2  0.1987    0.0055920

  QM12R     8    2  0.0855    0.0099402

  QM13R     8    2  0.0855    0.0099401

  QM14R     8    2  0.0855    0.0099402

  QM15R     6    2  0.1987    0.0055920

  QM16R     4    2  0.1987   -0.0103301

  QM17R     4    2  0.1987   -0.0103299

  QM18R     4    2  0.1987   -0.0103301

  QM19R     4    2  0.1987   -0.0103299

  QM20R     3    2  0.1985   -0.0089336

  QM21R     2    2  0.079     0.0226285

  QM22R     2    2  0.079     0.0226285

  QM23R     3    2  0.1985   -0.0089336

 

Finally, in order to make my online COMFORT model agree with SAD on what the DR

tunes are, I use yet another multiplicative factor of 0.9984212 for the QF2R

family (making the QF2R family weaker in COMFORT than in SAD).

 

All of this information is contained in the Matlab function file:

 

 USER$DISK1:[MDW.MATLAB]GET_DR_QUADS.M

 

(see USER$DISK1:[MDW.DOC]MATLAB.DOC for more on Matlab functions for ATF).

 

 

BT QUADS

--------

 

Quadrupole magnet currents (amps) for the BT are converted to gradients (T/m)

by the control system using linear interpolation of MMS data found in a SAD

script file corresponding to the three different varieties of BT quads.

 

The conversion of quad current to inverse focal length is done in SAD itself

using this script, and, as of ~ DEC-1998, no fudge factors are used.

 

The SAD script file is located on the acsad3 unix machine as:

 

 acsad3:/users/atfopr/sad/atflib.n

 

The effective lengths of the BT quads have been taken from the (design?) SAD

input file:

 

 acsad3:/users/atfopr/sad/btdaihon.sad

 

The BT quad types are:

 

 type   name

 ----   ----

   1    QICA

   2    QICB

   3    QICC

 

The names, types, and effective lengths for the BT quads are summarized here:

 

  name   type   leff   comments

  -----  ----  ------  ------------------------------------------

  QD10T    1   0.1980  powered in series with QD32T <-----------+

  QF10T    1   0.1976  powered in series with QF31T <---------+ |

  QD11T    2   0.1978  powered in series with QD31T <-------+ | |

  QF11T    1   0.1976  powered in series with QF30T <-----+ | | |

  QD12T    2   0.1978  powered in series with QD30T <---+ | | | |

  QF20T    3   0.1970  powered in series with QF21T <-+ | | | | |

  QF21T    3   0.1970  powered in series with QF20T <-+ | | | | |

  QD30T    2   0.1978  powered in series with QD12T <---+ | | | |

  QF30T    1   0.1976  powered in series with QF11T <-----+ | | |

  QD31T    2   0.1978  powered in series with QD11T <-------+ | |

  QF31T    1   0.1976  powered in series with QF10T <---------+ |

  QD32T    1   0.1976  powered in series with QD10T <-----------+

  QF40T    1   0.1976

  QD40T    1   0.1976

  QF41T    1   0.1976

  QD41T    2   0.1978

  QF42T    2   0.1978  powered in series with QF43T <-+

  QD42T    2   0.1978                                 |

  QF43T    2   0.1978  powered in series with QF42T <-+

  QD50T    1   0.1976

  QF50T    1   0.1976

  QD51T    1   0.1976

  QF51T    2   0.1978

  QF52T    3   0.1970

  QD52T    2   0.1978

  QF53T    2   0.1978

 

All of this information is contained in the Matlab function file:

 

 USER$DISK1:[MDW.MATLAB]GET_BT_QUADS.M

 

(see USER$DISK1:[MDW.DOC]MATLAB.DOC for more on Matlab functions for ATF).

 

 

STEERING CORRECTORS

-------------------

 

Corrector (ZH,ZV) magnet currents in both the BT and the DR are converted to

field (Tesla) using a single-point magnetic measurement relating field (T) to

current (amp):

 

 B(ZH,ZV) [T] = Cmms(ZH,ZV) * I [amp]

 

where Cmms(ZH) = 0.0108  [T/amp] and Cmms(ZV) = 0.0112 [T/amp].

 

The conversion to radians of kick

 

 theta(ZH,ZV) [rad] = {leff(ZH,ZV) [m] * 10 [kG/T] * B(ZH,ZV) [T]}

                    / {(100/3) [kG-m/GeV] * E [GeV]}

 

involves a value for the effective length that may be found embedded in the

control system software in the file:

 

 USER$DISK1:[ATFOPR.SAD]DR_MAG_LIB.FOR subroutine DRMAG_GET_EFFECTIVE_LENGTH.

 

The value for the effective lengths of ZH and ZV correctors from this file

(0.1232 m) is sufficiently different from their SAD deck effective length

values (0.06 m) that this must be represent another type of fudge factor.

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