Message: Re: Different radii for the 'same' electron in B-field Not Logged In (login)
 Next-in-Thread Next-in-Thread
 Next-in-Forum Next-in-Forum

None Re: Different radii for the 'same' electron in B-field 

Keywords: GEATN4 magnetic field electrons curve
Forum: Fields: Magnetic and Otherwise
Re: None Different radii for the 'same' electron in B-field (Valentin)
Re: None Re: Different radii for the 'same' electron in B-field (John Apostolakis)
Date: 16 May, 2005
From: Valentin <Valentin.Kozlov@fys.kuleuven.ac.be>

Thank you for your answer. 

Indeed when I switched to store position points 
in SteppingAction (via track->GetPosition().x() etc) the situation has changed:

Since the electrons are produced in vacuum, in order to see the tracks I have to 
limit the step size (via UserLimits process). When it was done, I could see 
more or less only one circle of right diameter in XY plane (just to remind:
e- start in direction (0,1,0), while B-field is (0,0,9)T). But.. 
in  3D(XYZ) it's a cylinder! and quite long cylinder (few 10s cm along Z). This 
means particle drifts in Z direction while it should not. The following was tried:

1) different EpsilonStep (1e-5 : 1e-7), no visible change 
2) fMinStep for G4ChordFinder(), no visible change 
3) stepMax (step size of track). this one is sensitive parameter: 

_stepMax=10mm_ : 
EkinInit[keV]=3000, p(0,1,0) 
Ekin[keV]=3000, m(e-)[keV]=510.999 
p=sqrt{Ekin*(Ekin+2m(e-))}[keV]=3473.61, p[keV]=3473.61: p(-3.46044,0.302211,7.87798e-07)
(-1.17539,1.28275,-323): 9

here:
- first row is Initial Ekin and direction;
- second row is Ekin in step, m(e-);
- third row is momentum calculated via GetKineticEnergy() and via 
  GetMomentum().x(): sqrt(px^2+py^2+pz^2), and momentum as (px,py,pz)
- third row is (x,y,z) and field there.

so, as one can see pz.neq.0 over sudden appears.

_stepMax=1mm_ : 
EkinInit[keV]=3000, p(0,1,0)
Ekin[keV]=3000, m(e-)[keV]=510.999
p=sqrt{Ekin*(Ekin+2m(e-))}[keV]=3473.61, p[keV]=3473.61: p(-2.43488,2.47737,6.43e-09)
(-0.369229,0.902438,-323): 9

but...

_stepMax=0.1mm_ :
EkinInit[keV]=3000, p(0,1,0)
Ekin[keV]=3000, m(e-)[keV]=510.999
p=sqrt{Ekin*(Ekin+2m(e-))}[keV]=3473.61, p[keV]=3473.61: p(-0.269542,3.46314,7.60947e-08)

i.e. pz became larger than for stepMax=1mm;

and if there is no "UserLimit":

_no UserLimit_:
EkinInit[keV]=3000, p(0,1,0)
Ekin[keV]=3000, m(e-)[keV]=510.999
p=sqrt{Ekin*(Ekin+2m(e-))}[keV]=3473.61, p[keV]=3473.61: p(-2.8789,-1.94369,0)
(-2.02679,1.09512,-323): 9

i.e. pz exactly equals zero, how it has to be!

well, I think I am satisfied in my "research" but curious from where 
the inprecision comes from in case of UserLimit process?

Best regards,
Valentin

Inline Depth:
 1 1
 All All
Outline Depth:
 1 1
 2 2
 All All
Add message: (add)

 Add Message Add Message
to: "Re: Different radii for the 'same' electron in B-field"

 Subscribe Subscribe

This site runs SLAC HyperNews version 1.11-slac-98, derived from the original HyperNews


[ Geant 4 Home | Geant 4 HyperNews | Search | Request New Forum | Feedback ]