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     Geant4 - an Object-Oriented Toolkit for Simulation in HEP
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                            field05 Example
                            ---------------

     This example checks so-called "spin-frozen" condition
     There is a good example article hep-ph/0012087v1.
     This article discusses about how to cancel the muon g-2 precession by
     applying an electric field.

     1) beta is muon velocity,
     2) B is an uniform magnetic field and \vec{beta}.\vec{B}=0,
        "." means scalar product,
     3) Radial electric field (E) in the lab frame and \vec{beta}.\vec{E}=0,
     4) a=(g-2)/2 is muon anomalous magnetic moment.

     The required electric field to cancel the g-2 precession is,
     E=a*B*light_c*gamma**2*beta.

     In case of gamma=5 and B=0.24 Tesla, the required electric field is
     E=2 MV/m.

     "Spin-frozen" happens when spin rotation cycle and muon rotation cycle
     are same. In this case, both cycles should be 149.5 nsec.

     See also:
     http://research.kek.jp/people/hiromi/MyHomePage/G-2_work_files/SpinStudyinEMfieldByGeant4.pdf


     Credit goes to Hiromi Iinuma from KEK.

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*Classes Used*
**************

 1 - main()

    See field05.cc.

 2- GEOMETRY DEFINITION

    as simple world G4Box with a G4ElectroMagneticField
    propagating both spin and momentum (G4EqEMFieldWithSpin)
    with G4ClassicalRK4(fEquation,12) and
    Bz = 0.24*tesla;
    Er = 2.113987E+6*volt/m;

 3- AN EVENT: THE PRIMARY GENERATOR

    use mu+ G4ParticleGun with Pmu = 517.6*MeV/c
    and aligned spin and momentum direction

 4- PHYSICS

    RegisterPhysics(new G4SpinDecayPhysics());
    RegisterPhysics(new G4StepLimiterPhysics());

    G4SpinDecayPhysics defines muon decay modes with spin,
    G4StepLimiterPhysics defines G4StepLimiter and G4UserSpecialCuts.

 5- User Action Classes

        SteppingAction:
            G4Exception when the cosine of the angle between
            the spin and the momentum is < (1.-1.E-7)

 6- HOW TO START ?

        - Execute field05 in 'batch' mode from macro files e.g.
                % field05 field05.in > field.out &

        - Execute field05 in 'interactive' mode with visualization e.g.
                % field05
                ....
                Idle> type your commands, for example:
                Idle> run/beamOn 1
                ....