Introducing a Uniform Magnetic Field in the simulation

Geometry, Fields and Transportation
1

Hello,

I am a beginner and currently I am trying to introduce a uniform magnetic field in my simulation by following the instructions in this doccument.

I tried to introduce the field within a G4Box made of vacuum. Here is a part of my code:

void MyDetectorConstruction::ConstructSDandField()
{
    G4MagneticField *magField = new G4UniformMagField(G4ThreeVector(0.5*tesla, 0., 0.));
    G4FieldManager *globalFieldMgr = G4TransportationManager::GetTransportationManager()->GetFieldManager();
    globalFieldMgr->SetDetectorField(magField);

    auto localFieldMgr = new G4FieldManager(magField);
    Region->SetFieldManager(localFieldMgr);
    logicVacuum->SetFieldManager(localFieldMgr, true);
}

My problem is, when trying to open the simulation, I always receive: Segmentation fault (core dumped). What could be the reason for that?

Thank you.

2

Are both Region and logicVacuum data members of your class? Are you sure that they are both set to non-null values when this function is called (i.e., after you’ve built your geometry)?

3

Thank you for the response.

My program is compiling normally, after a while I managed to make it work by copying the same geometry from example B5, that uses G4Tubs, and creating my own MagneticField class. However, I am still having difficulties in realizing why in my program the magnetic field only works along with this specific geometry and how do I adapt to make it work with other types of geometry that I wish to choose.

4

Hi

As Michael wrote in the code segment which you showed it was not clear whether ‘Region’ and ‘logicVacuum’ were valid pointers: that they are NOT null, and that they point to valid objects of each type.

So, to check this, you can add a couple of lines to your program, such as

G4cout << " Value of Region= " << Region << G4endl;
G4cout << " and its name is " << Region->GetName() << G4endl;
G4cout << " Value of logicVacuum= " << logicVacuum << G4endl;
G4cout << " and its name is " << logicVacuum->GetName() << G4endl;

This will likely help you to identify whether one of these variables does not hold the value which you expect, and to correct it.

Best regards,
John