# Re: circular beam

From: Anna Ferrari <anna.ferrari_at_lnf.infn.it>
Date: Sun, 16 Jan 2011 19:23:47 +0100 (CET)

Dear Hamideh,
if I have well understood your needs, it seems to me that you want a
circular source in x-y plane, centered in (0,0,0) and with a certain
radius r, with the particles emitted I guess along z? Is it correct?

Said that, I don't understand why you want to use UBEAM, the tx direction
cosine, to define the radius of your distribution. This is in any case not
correct, the radius r must be defined inside the source.
Moreover, IF I understood correctly your source, I would not touch the
polarization cosines (because tx=0, ty=0 and tz=1 are already the right
choice).
Last: if you want a uniform distribution of the source coordinates in the
circle, take care about the sampling... if you uniformely sample the
radius r between 0 and 1 you get a not uniform particle density, having
more particles originating close to the center.

Hope it helps,
kind regards

Anna

> Dear FLUKA experts
>
> I'm going to define a circular beam in x-y plane ( a beam which
> travels around a circle of radius r and center (0,0,0)). Is it correct
> if I follow these steps:
>
> In BEAMPOS card:
> WHAT(1)-WHAT(3):x,y,z coordinates of the center of the
> circle(XBEAM-YBEAM-ZBEAM)
> WHAT(4): radius of the circle (UBEAM)
>
> Then I modify source.f by adding these command:
>
> r = UBEAM * (FLRNDM(dummy)
> alpha = 2 * PI* (FLRNDM(dummy))
>
>
> XFLK (NPFLKA) = XBEAM + r * COS(alpha)
> YFLK (NPFLKA) = YBEAM + r * SIN(alpha)
> ZFLK (NPFLKA) = ZBEAM
>
> I would be grateful for your help.
> Hamideh
>
>
Received on Sun Jan 16 2011 - 19:56:39 CET

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