The OPAL Discussion Forum

["Dr. Simon Friederich" <s.friederich AT uni-mainz.de>]

Hi Dragos,

I am curious, are all the collimators defined with respect to the Reference Particle frame?

No, the collimators are defined with respect to the lab frame. I have a beam that I bent on a circle with an RFCAVITY and have it fly over a COLLIMATOR, that I've shaped indiviually.

I hope you see this picture (but I've put it in the attachement too): The upper one shows the dumped beam (OUTFN of collimator element), the lower one shows the output of a monitor that is located directly after the collimator counting the particles flying through it.

Here I used 

chop_col: FLEXIBLECOLLIMATOR,
    Z = chopper1->L/2 + 0.34,
    L = 10e-3,
    // rectangle(width, height), centered at the origin of the 2D,
    DESCRIPTION = "intersection(rectangle(30e-3,30e-3), translate(rectangle(7e-3,15e-3),0,-7.5e-3))", // default 7e-3
    // DESCRIPTION = "intersection(rectangle(30e-3,30e-3), translate(rectangle(0e-3,15e-3),0,-7.5e-3))",
    // collimator opening = first entry of second (translated) rectangle, 7e-3 ~ rms_s=9 mm
    OUTFN ="out_chop_col.h5";

If that is the case, how do I define a rectangular aperture in the Lab frame, i.e. an aperture that is FIXED in the Lab Frame? Do I have to modify the code?

I also played a little with the RCOLLIMATOR element. I think this does exactly what you're asking in the upper cite.

(http://amas.web.psi.ch/opal/Documentation/master/OPAL_Manual.html#sec.elements.collimators)

label:RCOLLIMATOR,TYPE=string, APERTURE=real-vector,
      L=real, XSIZE=real, YSIZE=real;

Best regards,
Simon

Am 16.09.2020 um 16:38 schrieb Dragos Constantin:

Hi Andreas,

I was under the impression that the apertures are used as a fixed geometrical boundaries which are defined in the Lab frame.

 

The RF cavity has an aperture associated with it but I know it is not active in v2.2, so I was trying to use ECOLLIMATOR to compensate for it.

 

I am curious, are all the collimators defined with respect to the Reference Particle frame?

 

If that is the case, how do I define a rectangular aperture in the Lab frame, i.e. an aperture that is FIXED in the Lab Frame? Do I have to modify the code?

 

Thanks,

Dragos

 

From: Adelmann Andreas (PSI) <andreas.adelmann AT psi.ch>
Sent: Tuesday, September 15, 2020 11:58 AM
To: Dragos Constantin <Dragos.Constantin AT varian.com>
Cc: opal AT lists.psi.ch
Subject: Re: [Opal] ECOLLIMATOR -- questions/potential issue

 

Dear Dragos, the collimator aperture can not be changed w.r.t. the local reference frame. 

I think you would need to estimate before running the simulation. Certainly one can

implement such a collimator model. If this is very important I can make a feature request

for you.

 

Cheers A

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Dr. sc. math. Andreas (Andy) Adelmann
Head a.i. Labor for Scientific Computing and Modelling 
Paul Scherrer Institut OHSA/ CH-5232 Villigen PSI
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On 12 Sep 2020, at 19:16, Dragos Constantin <dragos.constantin AT varian.com> wrote:

 

Hi All,

I have defined an ECOLLIMATOR like this:

 

BCOL: ECOLLIMATOR, L = 1, Z =0, X = 0, Y = 0, XSIZE = 0.002, YSIZE = 0.002, OUTFN = "BCOL";

 

so I have a circular aperture of 2mm radius. During the simulation the reference particle deviates from the central axis because of fields asymmetries. 

 

Is it possible that the circular aperture is defined with respect to the reference particle local reference frame instead of the laboratory reference frame?

 

It looks like the particles are no longer tracked if they are more than 2mm distance from the reference particle. I have attached two pictures that show the macroparticles bunch and the collimator wall from 2 different orrientations. On the 'cross section' view you can clearly see the circular aperture acting on the bunch but its position is obviously displaced to the right.

 

Thanks,

Dragos

 

<aperture_1.png><aperture_2.png>

 

-- 
Dr. Simon Friederich
Helmholtz-Institut Mainz
Kollaboration B/ACID
Johannes Gutenberg-Universität Mainz
Staudingerweg 18
55128 Mainz, Deutschland

Tel.: +49 (0)6131 39-23160
E-Mail: s.friederich AT uni-mainz.de

Attachment: collimator.png
Description: PNG image