StMagUtilities Class Reference

List of all members.

Public Member Functions

 StMagUtilities (StTpcDb *dbin, TDataSet *dbin2, Int_t mode=0)
 StMagUtilities constructor using the DataBase.
 StMagUtilities (const EBField map, const Float_t factor, Int_t mode=0)
 StMagUtilities constructor not using the DataBase.
virtual void BField (const Float_t x[], Float_t B[])
 B field in Cartesian coordinates - 2D field (ie. Phi symmetric).
virtual void BrBzField (const Float_t r, const Float_t z, Float_t &Br_value, Float_t &Bz_value)
 B field in Radial coordinates - 2D field (ie Phi symmetric).
virtual void B3DField (const Float_t x[], Float_t B[])
 Bfield in Cartesian coordinates - 3D field.
virtual void BrBz3DField (const Float_t r, const Float_t z, const Float_t phi, Float_t &Br_value, Float_t &Bz_value, Float_t &Bphi_value)
 B field in Radial coordinates - 3D field.
virtual void DoDistortion (const Float_t x[], Float_t Xprime[], Int_t Sector=-1)
 Main Entry Point for requests to DO the E and B field distortions (for simulations).
virtual void UndoDistortion (const Float_t x[], Float_t Xprime[], Int_t Sector=-1)
 Main Entry Point for requests to UNDO the E and B field distortions.
virtual void UndoBDistortion (const Float_t x[], Float_t Xprime[], Int_t Sector=-1)
 B field distortions in 3D ( no Table ) - calculate the distortions due to the shape of the B field.
virtual void Undo2DBDistortion (const Float_t x[], Float_t Xprime[], Int_t Sector=-1)
 2D - faster - B field distortions ( no Table ) - calculate the distortions due to the shape of the B field
virtual void FastUndoBDistortion (const Float_t x[], Float_t Xprime[], Int_t Sector=-1)
 3D - B field distortions (Table) - calculate the distortions due to the shape of the B field
virtual void FastUndo2DBDistortion (const Float_t x[], Float_t Xprime[], Int_t Sector=-1)
 2D - faster - B field distortions (Table) - calculate the distortions due to the shape of the B field
virtual void UndoPad13Distortion (const Float_t x[], Float_t Xprime[], Int_t Sector=-1)
 Pad row 13 distortion.
virtual void UndoTwistDistortion (const Float_t x[], Float_t Xprime[], Int_t Sector=-1)
 Twist distortion.
virtual void UndoClockDistortion (const Float_t x[], Float_t Xprime[], Int_t Sector=-1)
 Clock distortion.
virtual void UndoMembraneDistortion (const Float_t x[], Float_t Xprime[], Int_t Sector=-1)
 Membrane distortion.
virtual void UndoEndcapDistortion (const Float_t x[], Float_t Xprime[], Int_t Sector=-1)
 Endcap distortion.
virtual void UndoSpaceChargeDistortion (const Float_t x[], Float_t Xprime[], Int_t Sector=-1)
 Space Charge Correction.
virtual void UndoSpaceChargeR2Distortion (const Float_t x[], Float_t Xprime[], Int_t Sector=-1)
 1/R**2 SpaceCharge Distortion
virtual void UndoGridLeakDistortion (const Float_t x[], Float_t Xprime[], Int_t Sector=-1)
 Grid Leakage Calculation.
virtual void Undo3DGridLeakDistortion (const Float_t x[], Float_t Xprime[], Int_t Sector=-1)
 3D GridLeak Distortion Calculation
virtual void UndoIFCShiftDistortion (const Float_t x[], Float_t Xprime[], Int_t Sector=-1)
 IFC Shift Distortion.
virtual void UndoShortedRingDistortion (const Float_t x[], Float_t Xprime[], Int_t Sector=-1)
 Shorted Ring Distortion.
virtual void UndoGGVoltErrorDistortion (const Float_t x[], Float_t Xprime[], Int_t Sector=-1)
 Gated Grid Voltage Error.
virtual void UndoSectorAlignDistortion (const Float_t x[], Float_t Xprime[], Int_t Sector=-1)
 3D Sector Alignment Distortion Calculation
virtual void FixSpaceChargeDistortion (const Int_t Charge, const Float_t x[3], const Float_t p[3], const Prime PrimaryOrGlobal, Float_t x_new[3], Float_t p_new[3], const unsigned int RowMask1=0xFFFFFF00, const unsigned int RowMask2=0x1FFFFF, const Float_t VertexError=0.0200)
 Convert from the old (Uniform) space charge correction to the new (1/R**2) space charge correction.
virtual void ApplySpaceChargeDistortion (const Double_t sc, const Int_t Charge, const Float_t x[3], const Float_t p[3], const Prime PrimaryOrGlobal, Int_t &new_Charge, Float_t x_new[3], Float_t p_new[3], const unsigned int RowMask1=0xFFFFFF00, const unsigned int RowMask2=0x1FFFFF, const Float_t VertexError=0.0200)
 Apply the (1/R**2) space charge correction to selected data from the microDSTs.
virtual Int_t PredictSpaceChargeDistortion (Int_t Charge, Float_t Pt, Float_t VertexZ, Float_t PseudoRapidity, Float_t DCA, const unsigned int RowMask1, const unsigned int RowMask2, Float_t &pSpace)
 PredictSpaceCharge - Input Physical-Signed DCA and get back spacecharge parameter plus a success or failure flag.
virtual Int_t PredictSpaceChargeDistortion (Int_t Charge, Float_t Pt, Float_t VertexZ, Float_t PseudoRapidity, Float_t DCA, const unsigned int RowMask1, const unsigned int RowMask2, Float_t RowMaskErrorR[64], Float_t RowMaskErrorRPhi[64], Float_t &pSpace)
 PredictSpaceCharge - Input Physical-Signed DCA and get back spacecharge estimate. Includes the SVT and SSD.
virtual void ManualShortedRing (Int_t EastWest, Int_t InnerOuter, Float_t RingNumber, Float_t MissingRValue, Float_t ExtraRValue)
 Manually setup a shorted ring in the TPC.
virtual Int_t GetSpaceChargeMode ()
 Space Charge Correction Mode.
virtual void ManualSpaceCharge (Double_t SpcChg)
virtual void ManualSpaceChargeR2 (Double_t SpcChg, Float_t EWRatio=1.0)
virtual void ManualGridLeakStrength (Double_t inner, Double_t middle, Double_t outer)
virtual void ManualGridLeakRadius (Double_t inner, Double_t middle, Double_t outer)
virtual void ManualGridLeakWidth (Double_t inner, Double_t middle, Double_t outer)
virtual void AutoSpaceCharge ()
virtual void AutoSpaceChargeR2 ()
virtual Double_t CurrentSpaceCharge ()
virtual Double_t CurrentSpaceChargeR2 ()
virtual Float_t CurrentSpaceChargeEWRatio ()
virtual Bool_t UpdateShortedRing ()
virtual void UseManualSCForPredict (Bool_t flag=kTRUE)
virtual void ManualGGVoltError (Double_t east, Double_t west)

Static Public Member Functions

static StMagUtilities * Instance ()

Detailed Description

Author:
Jim Thomas 10 October 2000
A package of Bfield routines and distortion corrections for the STAR TPC. Methods included to read the correct Bfield map and scale it according to a scale factor provided during instantiation. All corrections automatically adjust themselves for different B field settings and E field settings. Even reversed fields.

An enumerated argument provided at the time of instantiation selects a constant magnetic field (value=1) or the measured magnetic field (value=2) at a field setting that you select manually. Alternatively, you can use the database to determine the magnetic field setting but you must then provide a a time stamp and use a different instantiation (this is usually done in the chain).

The enumerations for the manual settings are: enum EBField { kUndefined = 0, kConstant = 1, kMapped = 2, kChain = 3 } ; "kConstant = 1" means you wish to work with a constant, uniform, field. "kMapped = 2" means you want to read values from the measured magnet maps. The other enumerations are undefined and reserved for future expansion.

This code works in kGauss, cm - but note that the Bfield maps on disk are in gauss, cm.

A mode switch can be used to select the distortions that will be applied to the data. A choice of mode = 0 will give the default set of distortions. Other modes can be selected by turning on the appropriate bit field, shown below.


Bit counting starts at 1 for the mode switch (...,3,2,1)


enum DistortSelect
{
kBMap = 0x08, // Bit 4
kPadrow13 = 0x10, // Bit 5
kTwist = 0x20, // Bit 6
kClock = 0x40, // Bit 7
kMembrane = 0x80, // Bit 8
kEndcap = 0x100, // Bit 9
kIFCShift = 0x200, // Bit 10
kSpaceCharge = 0x400, // Bit 11
kSpaceChargeR2 = 0x800, // Bit 12
kShortedRing = 0x1000, // Bit 13
kFast2DBMap = 0x2000, // Bit 14
kGridLeak = 0x4000, // Bit 15
k3DGridLeak = 0x8000, // Bit 16
kGGVoltError = 0x10000, // Bit 17
kSectorAlign = 0x20000 // Bit 18
} ;

Note that the option flag used in the chain is 2x larger than shown here in order to allow the first bit to be used as an on/off flag and then it is shifted away before entering StMagUtilities. This can be summarized by saying:


Bit counting starts at 0 for the chain option flag (...,3,2,1,0)

To do:

Definition at line 200 of file StMagUtilities.h.

Member Function Documentation

void StMagUtilities::ApplySpaceChargeDistortion ( const Double_t  sc,
const Int_t  Charge,
const Float_t  x[3],
const Float_t  p[3],
const Prime  PrimaryOrGlobal,
Int_t &  new_Charge,
Float_t  x_new[3],
Float_t  p_new[3],
const unsigned int  RowMask1 = 0xFFFFFF00,
const unsigned int  RowMask2 = 0x1FFFFF,
const Float_t  VertexError = 0.0200 
) [virtual]

Apply the (1/R**2) space charge correction to selected data from the microDSTs.

Given the charge and momentum of a particle and a point on the circular path described by the particle , this function returns the new position of the point (cm) and the new momentum of the particle (GeV). The momentum p[] must be the momentum at the point x[].

Input x[], p[] and return x_new[], p_new[]. x[] in cm and p[] in GeV.

The program works by calculating the hits on the TPC rows for the input track, removes the distortion from the hits according to the 1/R**2 spacecharge presciption, and then refits the new hits to find the new track parameters. If the track is a primary track (PrimaryOrGlobal == 0) then x[] is assumed to be the vertex and it is included in the refit. If the track is a global track (PrimaryOrGlobal == 1) then x[] is assumed to lie somewhere (anywhere) on the track but it is not included in the fit. For a global track, x[] must lie on the track because it is used to determine where the track flies (ie. angle phi).

PrimaryOrGlobal = 0 for a primary track. PrimaryOrGlobal = 1 for a global track. You can also use the "Prime" enumeration in the .h file.

The code attempts to be as realistic as possible when it does the refit. Therefore, it asks you for the hit masks from the microDSTs. These masks tell you which TPC rows were used in the original track fit. For future reference, the masks come in two words. The first word covers TPC rows 1-24 and the second word covers rows 25-45. The first 8 bits of the first word are reserved for the FTPC and therefore 0xFFFFFF00, 0x1FFFFF represent all 45 rows of the TPC.

VertexError is quoted in cm (RMS). It is for experts. If you are working with primary tracks, the vertex is included in the fit. The true error bar is multiplcity dependent. (sigma**2 increase linearly with mult). So you can calculate this, external to the function, and then work with a realistic vertex error bar if you wish to do it. 200 microns error is a good average value for central Au-Au events.

Definition at line 3484 of file StMagUtilities.cxx.

References BField(), and UndoSpaceChargeR2Distortion().

void StMagUtilities::FastUndo2DBDistortion ( const Float_t  x[],
Float_t  Xprime[],
Int_t  Sector = -1 
) [virtual]

2D - faster - B field distortions (Table) - calculate the distortions due to the shape of the B field

Distortions are calculated and then stored in a table. This calculation uses a 2D magnetic field which is phi symmetric. The real 3D field has a slight twist that may be important for high precision work. I recommend using this faster version (JT) if you don't care about distortions smaller than 200 microns. This method requires about 10 seconds of CPU time to generate the table but it is very fast after the table has been created. Use it when you have a large number of points ( > 10,000 ).

Definition at line 1248 of file StMagUtilities.cxx.

References Undo2DBDistortion().

Referenced by UndoDistortion().

void StMagUtilities::FastUndoBDistortion ( const Float_t  x[],
Float_t  Xprime[],
Int_t  Sector = -1 
) [virtual]

3D - B field distortions (Table) - calculate the distortions due to the shape of the B field

Distortions are calculated in 3D and then stored in a table. This method requires about 1 minute of CPU time to generate the table but it is very fast after the table has been created. Use it when you have a large number of points ( > 10,000 ).

Definition at line 1169 of file StMagUtilities.cxx.

References UndoBDistortion().

Referenced by UndoDistortion().

void StMagUtilities::FixSpaceChargeDistortion ( const Int_t  Charge,
const Float_t  x[3],
const Float_t  p[3],
const Prime  PrimaryOrGlobal,
Float_t  x_new[3],
Float_t  p_new[3],
const unsigned int  RowMask1 = 0xFFFFFF00,
const unsigned int  RowMask2 = 0x1FFFFF,
const Float_t  VertexError = 0.0200 
) [virtual]

Convert from the old (Uniform) space charge correction to the new (1/R**2) space charge correction.

Applicable to 200 GeV Au+Au data that is on the P02ge (and other) microDSTs. Given the charge and momentum of a particle and a point on the circular path described by the particle , this function returns the new position of the point (cm) and the new momentum of the particle (GeV). This is done by undoing the old space charge corrections and then applying the new space charge corrections.

Input x[3], p[3] and return x_new[3], p_new[3]. x[3] in cm and p[3] in GeV.

The program works by calculating the hits on the TPC rows for the input track, distorts the hits according to the new presciption, and then refits the new hits to find the new track parameters. If the track is a primary track (PrimaryOrGlobal == 0) then x[3] is assumed to be the vertex and it is included in the refit. If the track is a global track (PrimaryOrGlobal == 1) then x[3] is assumed to lie somewhere (anywhere) on the track but it is not included in the fit. For a global track, x[3] must lie on the track because it is used to determine where the track flies (ie. angle phi).

PrimaryOrGlobal = 0 for a primary track. PrimaryOrGlobal = 1 for a global track. You can also use the "Prime" enumeration in the .h file.

The code attempts to be as realistic as possible when it does the refit. Therefore, it asks you for the hit masks from the microDSTs. These masks tell you which TPC rows were used in the original track fit. For future reference, the masks come in two words. The first word covers TPC rows 1-24 and the second word covers rows 25-45. The first 8 bits of the first word are reserved for the FTPC and therefore 0xFFFFFF00, 0x1FFFFF represent all 45 rows of the TPC.

VertexError is quoted in cm (RMS). It is for experts. If you are working with primary tracks, the vertex is included in the fit. The true error bar is multiplcity dependent. (sigma**2 increase linearly with mult). So you can calculate this, external to the function, and then work with a realistic vertex error bar if you wish to do it. 200 microns error is a good average value for central Au-Au events.

Definition at line 3302 of file StMagUtilities.cxx.

References BField(), UndoSpaceChargeDistortion(), and UndoSpaceChargeR2Distortion().

Referenced by StRedoTracks::Make().

Int_t StMagUtilities::GetSpaceChargeMode (  )  [virtual]

Space Charge Correction Mode.

The spacecharge correction is performed using one of a variety of modes. See the UndoSpaceChargeDistortion*() functions for more information on the different shapes used to correct the distortion. Additionally, the magnitude of the correction may be set either manually, or from the database. This routine provides a method to determine which mode is in use at any given time. Return values are as follows:

0 : no correction 10 : uniform, from DB 11 : uniform, manually set 20 : R2, from DB 21 : R2, manually set

Definition at line 557 of file StMagUtilities.cxx.

Referenced by StTpcHitMover::Make().

void StMagUtilities::ManualShortedRing ( Int_t  EastWest,
Int_t  InnerOuter,
Float_t  RingNumber,
Float_t  MissingRValue,
Float_t  ExtraRValue 
) [virtual]

Manually setup a shorted ring in the TPC.

Insert one shorted ring of your choice Side(E=0/W=1) Cage(IFC=0/OFC=1) Ring(# from CM) MissingResistance(MOhm) ExtraResistance(MOhm) For addtional information, see the comments associated with UndoShortedRing().

Definition at line 515 of file StMagUtilities.cxx.

Referenced by StMagUtilities().

Int_t StMagUtilities::PredictSpaceChargeDistortion ( Int_t  Charge,
Float_t  Pt,
Float_t  VertexZ,
Float_t  PseudoRapidity,
Float_t  DCA,
const unsigned int  RowMask1,
const unsigned int  RowMask2,
Float_t  RowMaskErrorR[64],
Float_t  RowMaskErrorRPhi[64],
Float_t &  pSpace 
) [virtual]

PredictSpaceCharge - Input Physical-Signed DCA and get back spacecharge estimate. Includes the SVT and SSD.

Input the parameters for a global track fit and get back an estimate of the spacecharge that distorted the track.

Input for the track includes the Charge, Pt, VertexZ, PseudoRapidity, and measured DCA.

The code attempts to be as realistic as possible when it does the refit. Therefore, it asks you for the hit masks from the microDSTs. These masks tell you which TPC rows were used in the original track fit and whether or not there were hits in the SVT and/or SSD detectors. It the masks have bits set for the SVT then this will affect the track and will pull the fits. For future reference, the masks come in two words. The first 8 bits of the first word describe the vertex, then six layers of the SVT, and finally the SSD. The vertex bit is only set for primary tracks and is not used by this routine. You should only input global tracks. The remaining bits of the first word cover TPC rows 1-24. The second word covers rows 25-45. So, for example 0xFFFFFF00, 0x1FFFFF represent all 45 rows of the TPC and no SVT or SSD hits.

You must provide the hit errors by instantiating with two vectors that include the track errors in both X and Y. RowMaskErrorR[] is the array of hit errors in the radial direction (ie in the direction of a high pt track) RowMaskErrorRPhi[] is the array of hit errors in the r-phi direction (ie tranvsverse to the direction of a high pt track)

pSpace contains the estimate of the space charge in the TPC that caused the distortion on the original track.

The function returns one if it succeeds and pSpace will be finite. The function returns zero if it fails and pSpace will be zero. The function returns zero if there are too few hits in the TPC inner and outer sectors. There are also cuts on Pt and rapdity, etc, that can cause the funtion to return zero.

Definition at line 3900 of file StMagUtilities.cxx.

References BField(), Undo3DGridLeakDistortion(), UndoGridLeakDistortion(), and UndoSpaceChargeR2Distortion().

Int_t StMagUtilities::PredictSpaceChargeDistortion ( Int_t  Charge,
Float_t  Pt,
Float_t  VertexZ,
Float_t  PseudoRapidity,
Float_t  DCA,
const unsigned int  RowMask1,
const unsigned int  RowMask2,
Float_t &  pSpace 
) [virtual]

PredictSpaceCharge - Input Physical-Signed DCA and get back spacecharge parameter plus a success or failure flag.

Add comments here. TPC Hits only. Does not include SVT or SSD or any other inner tracking detectors.

Definition at line 3683 of file StMagUtilities.cxx.

References BField(), Undo3DGridLeakDistortion(), UndoGridLeakDistortion(), and UndoSpaceChargeR2Distortion().

void StMagUtilities::Undo2DBDistortion ( const Float_t  x[],
Float_t  Xprime[],
Int_t  Sector = -1 
) [virtual]

2D - faster - B field distortions ( no Table ) - calculate the distortions due to the shape of the B field

Distortions are calculated point by point and integrated in real time. This avoids the time required to set up a table of distorted values but is slow for a very large number of points ( > 10,000 ).

Definition at line 1127 of file StMagUtilities.cxx.

References BField().

Referenced by FastUndo2DBDistortion().

void StMagUtilities::Undo3DGridLeakDistortion ( const Float_t  x[],
Float_t  Xprime[],
Int_t  Sector = -1 
) [virtual]

3D GridLeak Distortion Calculation

Calculate the 3D distortions due to charge leaking out of the gap between the inner and outer sectors. Original work by Gene VanBuren, and J. Thomas

Definition at line 4276 of file StMagUtilities.cxx.

Referenced by PredictSpaceChargeDistortion(), and UndoDistortion().

void StMagUtilities::UndoBDistortion ( const Float_t  x[],
Float_t  Xprime[],
Int_t  Sector = -1 
) [virtual]

B field distortions in 3D ( no Table ) - calculate the distortions due to the shape of the B field.

Distortions are calculated point by point and integrated in real time. This avoids the time required to set up a table of distorted values but is slow for a very large number of points ( > 10,000 ).

Definition at line 1085 of file StMagUtilities.cxx.

References B3DField().

Referenced by FastUndoBDistortion().

void StMagUtilities::UndoClockDistortion ( const Float_t  x[],
Float_t  Xprime[],
Int_t  Sector = -1 
) [virtual]

Clock distortion.

The East endwheel of the TPC and the West endwheel of the TPC are not perfectly aligned. They were inserted separately into the TPC field cage tube. They are aligned at the outer diameter (4 meters) to within about 1 mm. This causes a slight misalingment of the relative coordinate systems. By convention, we assume that one end is perfect and attribute all of the error to a rotation of the other end ... however, the method (and the DB) allow you to input a rotation angle for each end, if you wish. Note: this is a coordinate transformation and not a distortion correction. It is here for historical reasons.

Definition at line 1467 of file StMagUtilities.cxx.

Referenced by UndoDistortion().

void StMagUtilities::UndoGGVoltErrorDistortion ( const Float_t  x[],
Float_t  Xprime[],
Int_t  Sector = -1 
) [virtual]

Gated Grid Voltage Error.

This code assumes that information about the GG voltage errors will come from the DB.

Calculate the effect of having an incorrect voltage on the East or West Gated Grids.

Electrostatic Equations from SN0253 by Howard Wieman. Note that we use Howard's funny coordinate system where Z==0 at the GG.

Definition at line 2083 of file StMagUtilities.cxx.

Referenced by UndoDistortion().

void StMagUtilities::UndoGridLeakDistortion ( const Float_t  x[],
Float_t  Xprime[],
Int_t  Sector = -1 
) [virtual]

Grid Leakage Calculation.

Calculate the distortions due to charge leaking out of the gap between the inner and outer sectors as well as the gap between the IFC and the innersector, as well as outersector and OFC. Original work by Gene VanBuren, and J. Thomas NOTE: This routine is obsolete: 10/31/2009 Recommend that you use Undo3DGridLeakDistortion, instead.

Definition at line 4158 of file StMagUtilities.cxx.

Referenced by PredictSpaceChargeDistortion(), and UndoDistortion().

void StMagUtilities::UndoIFCShiftDistortion ( const Float_t  x[],
Float_t  Xprime[],
Int_t  Sector = -1 
) [virtual]

IFC Shift Distortion.

The Inner field cage of the TPC is not perfectly aligned with the outer field cage of the TPC. They are shifted along the Z axis by about 1 mm. This causes a tilting of the equi-potential lines inside the TPC and therefore a DCA error at the vertex. The distortion is anti- symmetric in Z. Electrostatic equations solved in Rectangular Coodinates by Jim Thomas Updated to work in cylindrical coordinates by Jamie Dunlop 11/01/2001

Definition at line 1588 of file StMagUtilities.cxx.

Referenced by UndoDistortion().

void StMagUtilities::UndoPad13Distortion ( const Float_t  x[],
Float_t  Xprime[],
Int_t  Sector = -1 
) [virtual]

Pad row 13 distortion.

Remove the effect of the mechanical imperfections between the inner sectors and the outer sectors. There is a gap between the sectors that allow E field lines to leak out of the anode and gated grid region. HHWieman has modelled this effect and his solution is used to remove the distortions.

Definition at line 1356 of file StMagUtilities.cxx.

Referenced by UndoDistortion().

void StMagUtilities::UndoSectorAlignDistortion ( const Float_t  x[],
Float_t  Xprime[],
Int_t  Sector = -1 
) [virtual]

3D Sector Alignment Distortion Calculation

Calculate the 3D distortions due to z displacements caused by mis-alignment of the inner and outer sectors. Original work by Gene VanBuren, and J. Thomas Method: Determine the potential offsets at the innermost and outermost points of the Inner and Outer Sector grids along this phi angle, then interpolate to any poinr between the two. Also interpolate radially to zero out to the field cages.

Definition at line 4502 of file StMagUtilities.cxx.

Referenced by UndoDistortion().

void StMagUtilities::UndoShortedRingDistortion ( const Float_t  x[],
Float_t  Xprime[],
Int_t  Sector = -1 
) [virtual]

Shorted Ring Distortion.

This code assumes that information about shorted rings in the TPC field cage will come from the DB. The DB returns rows from a table and the columns have the following meaning:

Side(E=0/W=1) Cage(IFC=0/OFC=1) Ring(# from CM) MissingResistance(MOhm) ExtraResistance(MOhm)

0 0 169.5 2.0 2.0 0 0 115.5 2.0 0.0 1 1 150.5 1.0 1.0 0 0 0.0 0.0 0.0 etc.

The table indicates that there are two shorted rings on the IFC of the East end of the TPC. One of these shorts has a 2.0 MegOhm compensating resistor installed in the external resistor chain. There is also a short on the OFC of the West end of the TPC. It is a non-standard short of 1 MOhm. It has an external compensating resistor of 1.0 MOhm. The row of zeros indicates that there are no more shorts in the TPC. Counting of the rings starts at the Central Membrane; the CM is ring zero, and 150.5 means the short is between rings 150 and 151.

Electrostatic Equations from SN0253 by Howard Wieman. Note that we use Howard's funny coordinate system where Z==0 at the GG.

Definition at line 1913 of file StMagUtilities.cxx.

Referenced by UndoDistortion().

void StMagUtilities::UndoSpaceChargeDistortion ( const Float_t  x[],
Float_t  Xprime[],
Int_t  Sector = -1 
) [virtual]

Space Charge Correction.

Space Charge distortion assuming a uniform distribution of charge per unit volume in the TPC. We now know that this is not a good assumption but the code is here for legacy reasons. Electrostatic equations solved by Jamie Dunlop 11/01/2001 Updated to include linear increase of charge from endcap to CM by Jim Thomas 12/18/2001

Definition at line 1665 of file StMagUtilities.cxx.

Referenced by FixSpaceChargeDistortion(), and UndoDistortion().

void StMagUtilities::UndoSpaceChargeR2Distortion ( const Float_t  x[],
Float_t  Xprime[],
Int_t  Sector = -1 
) [virtual]

1/R**2 SpaceCharge Distortion

Space Charge distortion using space charge from a real event. Any charge distribution can be simulated by this method. However, the best charge distribution is Howard's fit to HiJet events. It is approximately independent of Z due to the Bjorken Plateau a mid-rapidity. The radial distribution is approximately 1/R**2, however we use a better parameterization in the code. Many different charge distributions are hidden in the comments of the code. All candidate distributions have been integrated over Z to simulate the linear increase of space charge in Z due to the slow drift velocity of the ions. Electrostatic equations solved by relaxtion. Note that on 3/26/2008, we added a new element to the DB so that the space charge in the East and West halves of the TPC can be different by a constant factor. The constant is called "SpaceChargeEWRatio" and is greater than 1.0 when there is more charge in the East half to the TPC. Original work by H. H. Wieman, N. Smirnov, and J. Thomas

Definition at line 1756 of file StMagUtilities.cxx.

Referenced by ApplySpaceChargeDistortion(), FixSpaceChargeDistortion(), PredictSpaceChargeDistortion(), and UndoDistortion().

void StMagUtilities::UndoTwistDistortion ( const Float_t  x[],
Float_t  Xprime[],
Int_t  Sector = -1 
) [virtual]

Twist distortion.

Remove the effects of a simple "twist" of the TPC in the magnet. If there is an angle between the E and B fields, there will be a distortion in the recorded tracks. This routine takes out that distortion.

Definition at line 1323 of file StMagUtilities.cxx.

Referenced by UndoDistortion().

The documentation for this class was generated from the following files:
Generated on Fri Feb 10 04:28:09 2012 for StRoot by  doxygen 1.5.9