#include <G4VUserDetectorConstruction.hh>
#include <G4GlobalMagFieldMessenger.hh>
#include <G4tgbVolumeMgr.hh>
class Detector : public G4VUserDetectorConstruction, G4GlobalMagFieldMessenger
{
public:
G4VPhysicalVolume* Construct() {
G4tgbVolumeMgr::GetInstance()->AddTextFile("detector.tg");
return G4tgbVolumeMgr::GetInstance()->ReadAndConstructDetector();
} ///< load detector definition from a text file "detector.tg"
};
Since G4GlobalMagFieldMessenger is initiated before Detector, /globalField is indeed created. I can use it to set field values and to change output verbosity. I can also use /vis/scene/add/MagneticField to draw the field.
However, no particle can be bent in the field. I’ve tried e-, proton, with different energies, (from MeV to GeV), even though /globalField/verbose 2 shows
G4ChordFinder: stepperDriverId: 2
Magnetic field is active, fieldValue = (0 0 0.1 T ).
To see the curvature of tracks in a field you have to ask for smooth (or rich) trajectories:
/vis/scene/add/trajectories smooth
Otherwise the trajectory contains only the start point and end point (when it reaches a boundary or interacts). Even if the track spirals, you might only see the start and end of the spiral.
Is this the issue? Let us know. Otherwise, there’s something wrong with your field setup, and we would have to investigate further.
And below is what I got. I can see step points of an e- trajectory when it goes through boundaries. It starts from somewhere on the negative x-axis and goes to the positive direction of x. The field is along the z axis. I expect the trajectory to bend to negative y direction. But it simply follows the x axis. The material of all volumes is set to G4_Galactic.
I also tried to new G4GlobalMagFieldMessenger in the main function more explicitly. The result is the same. The code I modified is a simple file with 60-ish lines of C++: https://github.com/jintonic/mingle.
The G4GlobalMagFieldMessenger must be created in UserDetectorConstruction::CreateSDandField, see e.g. basic/B2 examples.
You need to remove it from inheritance, as while the UserDetectorConstruction is instantiated only on master, the field messenger has to be created on thread workers, that’s why it should go in the :CreateSDandField method, that was added to G4VUserDetectorConstruction for this purpose.
