The OPAL Discussion Forum

["Snuverink Jochem (PSI)" <jochem.snuverink AT psi.ch>]

Dear Simon,

The SIGMAPX formula is what it should be. I think the reason why you don't see an increase in beam size of 5 mm is because you don't start with a point source, but with SIGMAR = 1e-3. If you would start with SIGMAR=0.0, then I believe you should get an increase of 5mm.

Hope that helps,

Jochem

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From: opal-request AT lists.psi.ch <opal-request AT lists.psi.ch> on behalf of Dr. Simon Friederich <s.friederich AT uni-mainz.de>
Sent: Wednesday, February 24, 2021 1:47:38 PM
To: opal AT lists.psi.ch
Subject: [Opal] OPAL-T: Distribution SIGMAPX and SIGMAPY

 

Dear Opal-Team,

I simulated only an injected GAUSS-type distribution with a non-zero SIGMAPX and SIGMAPY:
distr_gauss_injected: DISTRIBUTION,
    TYPE = GAUSS,
    SIGMAR = 1.0e-3, CUTOFFR = 3,
    SIGMAPX = 5.0e-3*beta*gamma, SIGMAPY=5.0e-3,
    SIGMAZ = 1e-6, CUTOFFLONG = 4,
    EMITTED = false;

I thought, I could use these paramters to have the distribution start with a transverse divergence of 5 mrad,
i.e. after Δs=1 m the rms size increases by Δσ=5mm (maybe this is where I am already mistaken).

I did not change INPUTMOUNITS (default = NONE) but neither
    SIGMAPX = 5.0e-3*beta*gamma  // this I would expect from the explanation in the manual, right?
    nor
    SIGMAPY=5.0e-3
show the expected divergence (see screenshot in the attachement). At least SIGMAPX leads to Δσx=4mm though.

Beta and gamma are defined by:
REAL Ekin_GeV = 1e-4; // 100 keV
REAL gamma = (EMASS + Ekin_GeV)/EMASS;
REAL beta = sqrt(1-1/gamma^2);

Did I missinterpret SIGMAPX and SIGMAPY?

Best regards
Simon

-- 
Dr. Simon Friederich
Helmholtz-Institut Mainz | Insitut für Kernphysik
Kollaboration ACID       | B
Johannes Gutenberg-Universität Mainz
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55128 Mainz, Deutschland

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