SolenoidBField.hpp

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// This file is part of the Acts project.
//
// Copyright (C) 2017-2018 CERN for the benefit of the Acts project
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.

#pragma once

#include "Acts/MagneticField/MagneticFieldContext.hpp"
#include "Acts/Utilities/Definitions.hpp"

namespace Acts {

//
class SolenoidBField {
 public:
  struct Cache {
    Cache(std::reference_wrapper<const MagneticFieldContext> /*mcfg*/) {}
  };

  struct Config {
    double radius;
    double length;
    size_t nCoils;
    double bMagCenter;
  };

  SolenoidBField(Config config);

  Vector3D getField(const Vector3D& position) const;

  Vector3D getField(const Vector3D& position, Cache& /*cache*/) const;

  Vector2D getField(const Vector2D& position) const;

  Vector3D getFieldGradient(const Vector3D& position,
                            ActsMatrixD<3, 3>& /*derivative*/) const;

  Vector3D getFieldGradient(const Vector3D& position,
                            ActsMatrixD<3, 3>& /*derivative*/,
                            Cache& /*cache*/) const;

 private:
  Config m_cfg;
  double m_scale;
  double m_dz;
  double m_R2;

  Vector2D multiCoilField(const Vector2D& pos, double scale) const;

  Vector2D singleCoilField(const Vector2D& pos, double scale) const;

  double B_r(const Vector2D& pos, double scale) const;

  double B_z(const Vector2D& pos, double scale) const;

  double k2(double r, double z) const;
};

}  // namespace Acts