[ALICE3] Add V3 magnet map

Author: njacazio

Detectors/Upgrades/ALICE3/macros/ALICE3FieldV3Magnet.C

@@ -0,0 +1,91 @@
+// Copyright 2019-2020 CERN and copyright holders of ALICE O2.
+// See https://alice-o2.web.cern.ch/copyright for details of the copyright holders.
+// All rights not expressly granted are reserved.
+//
+// This software is distributed under the terms of the GNU General Public
+// License v3 (GPL Version 3), copied verbatim in the file "COPYING".
+//
+// In applying this license CERN does not waive the privileges and immunities
+// granted to it by virtue of its status as an Intergovernmental Organization
+// or submit itself to any jurisdiction.
+//
+// Author: J. E. Munoz Mendez jesus.munoz@cern.ch
+
+std::function<void(const double*, double*)> field()
+{
+  return [](const double* x, double* b) {
+    const double Rc = 185.;                                  //[cm]
+    const double R1 = 220.;                                  //[cm]
+    const double R2 = 290.;                                  //[cm]
+    const double B1 = 2.;                                    //[T]
+    const double B2 = -Rc * Rc / ((R2 * R2 - R1 * R1) * B1); //[T]
+    const double beamStart = 370.;                           //[cm]
+    const double tokGauss = 1. / 0.1;                        // conversion from Tesla to kGauss
+
+    const bool isMagAbs = true;
+
+    const double r = sqrt(x[0] * x[0] + x[1] * x[1]);
+    if ((abs(x[2]) <= beamStart) && (r < Rc)) { // We are inside of the central region
+      b[0] = 0.;
+      b[1] = 0.;
+      b[2] = B1 * tokGauss;
+    } else if ((abs(x[2]) <= beamStart) && (r >= Rc && r < R1)) { // We are in the transition region
+      b[0] = 0.;
+      b[1] = 0.;
+      b[2] = 0.;
+    } else if ((abs(x[2]) <= beamStart) && (r >= R1 && r < R2)) { // We are within the magnet
+      b[0] = 0.;
+      b[1] = 0.;
+      if (isMagAbs) {
+        b[2] = B2 * tokGauss;
+      } else {
+        b[2] = 0.;
+      }
+    } else { // We are outside of the magnet
+      b[0] = 0.;
+      b[1] = 0.;
+      b[2] = 0.;
+    }
+  };
+}
+
+void ALICE3V3Magnet()
+{
+  auto fieldFunc = field();
+  // RZ plane visualization
+  TCanvas* cRZ = new TCanvas("cRZ", "Field in RZ plane", 800, 600);
+  TH2F* hRZ = new TH2F("hRZ", "Magnetic Field B_z in RZ plane;Z [m];R [m]", 100, -10, 10, 100, -5, 5);
+  hRZ->SetBit(TH1::kNoStats); // disable stats box
+  for (int i = 1; i <= hRZ->GetNbinsX(); i++) {
+    const double Z = hRZ->GetXaxis()->GetBinCenter(i);
+    for (int j = 1; j <= hRZ->GetNbinsY(); j++) {
+      const double R = hRZ->GetYaxis()->GetBinCenter(j);
+      const double pos[3] = {R * 100, 0, Z * 100}; // convert to cm
+      double b[3] = {0, 0, 0};
+      fieldFunc(pos, b);
+      hRZ->SetBinContent(i, j, b[2]);
+    }
+  }
+
+  hRZ->Draw("COLZ");
+  cRZ->Update();
+
+  // XY plane visualization
+  TCanvas* cXY = new TCanvas("cXY", "Field in XY plane", 800, 600);
+  TH2F* hXY = new TH2F("hXY", "Magnetic Field B_z in XY plane;X [m];Y [m]", 100, -5, 5, 100, -5, 5);
+  hXY->SetBit(TH1::kNoStats); // disable stats box
+
+  for (int i = 1; i <= hXY->GetNbinsX(); i++) {
+    const double X = hXY->GetXaxis()->GetBinCenter(i);
+    for (int j = 1; j <= hXY->GetNbinsY(); j++) {
+      const double Y = hXY->GetYaxis()->GetBinCenter(j);
+      const double pos[3] = {X * 100, Y * 100, 0}; // convert to cm
+      double b[3] = {0, 0, 0};
+      fieldFunc(pos, b);
+      hXY->SetBinContent(i, j, b[2]);
+    }
+  }
+
+  hXY->Draw("COLZ");
+  cXY->Update();
+}