1 /**************************************************************************
2 * Copyright(c) 1998-1999, ALICE Experiment at CERN, All rights reserved. *
4 * Author: The ALICE Off-line Project. *
5 * Contributors are mentioned in the code where appropriate. *
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14 **************************************************************************/
16 ////////////////////////////////////////////////////////////////////////////
18 // AliTPCGGVoltError class //
19 // The class calculates the electric field and space point distortions //
20 // due a Gating Grid (GG) Error voltage. It uses the exact calculation //
21 // technique based on bessel functions. (original code from STAR) //
22 // The class allows "effective Omega Tau" corrections. //
24 // date: 27/04/2010 //
25 // Authors: Jim Thomas, Stefan Rossegger, Magnus Mager //
28 // AliTPCGGVoltError GGerror; //
29 // GGerror.SetOmegaTauT1T2(0.32,1.,1.); // values ideally from OCDB //
30 // GGerror.SetDeltaVGGA(50.); // voltage offset A-side //
31 // GGerror.SetDeltaVGGC(50.); // voltage offset C-side //
32 // GGerror.InitGGVoltErrorDistortion(); // initialization of the look up //
33 // // plot dRPhi distortions ... //
34 // GGerror.CreateHistoDRPhiinZR(1.,100,100)->Draw("surf2"); //
35 ////////////////////////////////////////////////////////////////////////////
39 #include "AliTPCGGVoltError.h"
42 AliTPCGGVoltError::AliTPCGGVoltError()
43 : AliTPCCorrection("GGVoltError","GatingGrid (GG) Voltage Error"),
45 fDeltaVGGA(0.),fDeltaVGGC(0.)
48 // default constructor
52 AliTPCGGVoltError::~AliTPCGGVoltError() {
58 void AliTPCGGVoltError::GetCorrection(const Float_t x[],const Short_t roc,Float_t dx[]) {
61 // Gated Grid Voltage Error
63 // Calculates the effect of having an incorrect voltage on the A or C end plate Gated Grids.
65 // Electrostatic Equations from StarNote SN0253 by Howard Wieman.
68 Int_t order = 1 ; // FIXME: hardcoded? Linear interpolation = 1, Quadratic = 2
70 Double_t intEr, intEphi ;
76 r = TMath::Sqrt( x[0]*x[0] + x[1]*x[1] );
77 phi = TMath::ATan2(x[1],x[0]);
78 if ( phi < 0 ) phi += TMath::TwoPi(); // Table uses phi from 0 to 2*Pi
81 if ( (roc%36) < 18 ) {
83 deltaVGG = fDeltaVGGA; // (TPC End A)
85 sign = -1; // (TPC End C)
86 deltaVGG = fDeltaVGGC;
89 if ( sign==1 && z < fgkZOffSet ) z = fgkZOffSet; // Protect against discontinuity at CE
90 if ( sign==-1 && z > -fgkZOffSet ) z = -fgkZOffSet; // Protect against discontinuity at CE
92 Interpolate2DEdistortion( order, r, z, fGGVoltErrorER, intEr );
93 intEphi = 0.0; // Efield is symmetric in phi
95 // Calculate distorted position
97 phi = phi + deltaVGG*( fC0*intEphi - fC1*intEr ) / r;
98 r = r + deltaVGG*( fC0*intEr + fC1*intEphi );
101 // Calculate correction in cartesian coordinates
102 dx[0] = r * TMath::Cos(phi) - x[0];
103 dx[1] = r * TMath::Sin(phi) - x[1];
104 dx[2] = 0.; // z distortion not implemented (1st order distortions)
109 Float_t AliTPCGGVoltError::GetIntErOverEz(const Float_t x[],const Short_t roc) {
111 // This function is purely for calibration purposes
112 // Calculates the integral (int Er/Ez dz) for the setted GG voltage offset
115 Int_t order = 1 ; // FIXME: so far hardcoded? Linear interpolation = 1, Quadratic = 2
123 r = TMath::Sqrt( x[0]*x[0] + x[1]*x[1] );
124 phi = TMath::ATan2(x[1],x[0]);
125 if ( phi < 0 ) phi += TMath::TwoPi(); // Table uses phi from 0 to 2*Pi
128 if ( (roc%36) < 18 ) {
130 deltaVGG = fDeltaVGGA; // (TPC End A)
132 sign = -1; // (TPC End C)
133 deltaVGG = fDeltaVGGC;
136 if ( sign==1 && z < fgkZOffSet ) z = fgkZOffSet; // Protect against discontinuity at CE
137 if ( sign==-1 && z > -fgkZOffSet ) z = -fgkZOffSet; // Protect against discontinuity at CE
139 Interpolate2DEdistortion(order, r, z, fGGVoltErrorER, intEr );
141 return (intEr*deltaVGG);
145 void AliTPCGGVoltError::InitGGVoltErrorDistortion() {
147 // Initialization of the Lookup table which contains the solutions of the GG Error problem
152 for ( Int_t i = 0 ; i < kNZ ; ++i ) {
154 for ( Int_t j = 0 ; j < kNR ; ++j ) {
156 fGGVoltErrorER[i][j] = 0.0 ;
157 Double_t intz = 0.0 ;
158 for ( Int_t n = 1 ; n < nterms ; ++n ) {
159 Double_t k = n * TMath::Pi() / fgkTPC_Z0 ;
160 Double_t ein = 0 ; // Error potential on the IFC
161 Double_t eout = 0 ; // Error potential on the OFC
163 ein = -2.0 / ( k * (fgkCathodeV - fgkGG) ) ;
164 eout = -2.0 / ( k * (fgkCathodeV - fgkGG) ) ;
166 if ( z == 0 ) continue ;
168 ein = -2.0 / ( k * (fgkCathodeV - fgkGG) ) ;
169 eout = -2.0 / ( k * (fgkCathodeV - fgkGG) ) ;
171 Double_t an = ein * TMath::BesselK0( k*fgkOFCRadius ) - eout * TMath::BesselK0( k*fgkIFCRadius ) ;
172 Double_t bn = eout * TMath::BesselI0( k*fgkIFCRadius ) - ein * TMath::BesselI0( k*fgkOFCRadius ) ;
174 an * TMath::BesselI1( k*r ) - bn * TMath::BesselK1( k*r ) ;
175 Double_t denominator =
176 TMath::BesselK0( k*fgkOFCRadius ) * TMath::BesselI0( k*fgkIFCRadius ) -
177 TMath::BesselK0( k*fgkIFCRadius ) * TMath::BesselI0( k*fgkOFCRadius ) ;
178 Double_t zterm = TMath::Cos( k*(fgkTPC_Z0-TMath::Abs(z)) ) - 1 ;
179 intz += zterm * numerator / denominator ;
180 // Assume series converges, break if small terms
181 if ( n>10 && fabs(intz)*1.e-10 > fabs(numerator/denominator) ) break;
183 fGGVoltErrorER[i][j] = (Double_t) intz ;
191 void AliTPCGGVoltError::Print(Option_t* option) const {
193 // Print function to check the settings (e.g. voltage offsets)
194 // option=="a" prints the C0 and C1 coefficents for calibration purposes
197 TString opt = option; opt.ToLower();
198 printf("%s\n",GetTitle());
199 printf(" - GG Voltage offset: A-side: %3.1f V, C-side: %3.1f V \n",fDeltaVGGA,fDeltaVGGC);
200 if (opt.Contains("a")) { // Print all details
201 printf(" - C1: %1.4f, C0: %1.4f \n",fC1,fC0);