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Forum: Event and Track Management
Re: None Ion beam disappears entering in quadrupole field (Jorge Gallardo)
Date: 13 Mar, 2014
From: Gumplinger Peter <Gumplinger Peter>

> I'm trying to simulate a beamline with a quadrupole field, the code seems
> to work fine with very low gradient ( < 0.001 T/m ) and is possible to
> track the beam across the quadrupole, traversing it and appearing in the
> other side (for that gradient value, the effect of the quad. field is
> negligible ) ...  but when the gradient increases, the beams (there are 8
> parallel beams really) begin to disappear inside the quadrupole... When my
> maximum working gradient (11.3 T/m) is reached the beam disappears in the
> middle of the "quadrupole zone",

You probably have to reduce the step size manually. Runge Kutta should reduce the tracking steps automatically until they are short enought for accurate integration but perhaps in such strong fields/gradients this doesn't work adequately. Please, read about 'StepLimiter' etc. in the Application Dev. Manual. Also, how fine do you specify the field - in case it's a map - or do you calculate it from a quadrupole field equation. The latter is best, of course, because you must avoid field discontinuities.

> as if the particles vanished in the vacuum
> (galactic)... In the vis.mac file the line "/tracking/verbose 1"  is
> enabled, but the output seems to be normal, and no error message appears...
> any idea?

There is an explanation, but anyway, there can be issues with your visualization. What is important is the tracking verbose. Look at it carefully, what are the step sizes, where is the track going - all of this is documented with the verbosity. What's also important is what your field returns for each step. You can put a G4cout into your code.

You'll have to try harder and can't rely on being tutored via this Forum as soon as you don't understand something.

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1 None: Re: Ion beam disappears entering in quadrupole field   (jorge gallardo - 21 Mar, 2014)
(_ Feedback: Re: Ion beam disappears entering in quadrupole field   (Gumplinger Peter - 21 Mar, 2014)
(_ None: Re: Ion beam disappears entering in quadrupole field   (jorge gallardo - 21 Mar, 2014)
(_ Feedback: Re: Ion beam disappears entering in quadrupole field   (Gumplinger Peter - 21 Mar, 2014)
(_ None: Re: Ion beam disappears entering in quadrupole field   (jorge gallardo - 01 Apr, 2014)
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