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- From: Daniel Winklehner <winklehn AT mit.edu>
- To: Snuverink Jochem <jochem.snuverink AT psi.ch>, Malek Haj Tahar <malek AT transmutex.com>
- Cc: "opal AT lists.psi.ch" <opal AT lists.psi.ch>
- Subject: RE: [Opal] Transit time factor calculation in OPAL
- Date: Wed, 8 Mar 2023 16:34:26 +0000
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Hi Malek,
I know you know this, but if anyone else follows the thread: The transit time correction or transit time factor (TTF) is a modifying factor to the energy gain in the idealized cavity that depends on gap length, frequency, and particle velocity like this : TTF = sin(omega*d/2*v)/( omega*d/2*v). It stems from the voltage changing while the particle traverses the finite-length gap. Energy gain is calculated as q*V*TTF*cos(phi) where phi is the cavity phase.
You might be looking for the following snippet of code in /src/Classic/AbsBeamline/RFCavity.cpp:
if (gapwidth_m > 0.0) { double transit_factor = 0.5 * frequency * gapwidth_m * Units::mm2m / (Physics::c * beta); Ufactor = std::sin(transit_factor) / transit_factor; }
Also here: https://gitlab.psi.ch/OPAL/src/-/blob/master/src/Classic/AbsBeamline/RFCavity.cpp#L363
Cheers, Daniel
From: opal-request AT lists.psi.ch <opal-request AT lists.psi.ch>
On Behalf Of Snuverink Jochem
Dear Malek
Apologies for the late answer.
The correction is done when a particle step crosses an RF cavity. In this case the step is split in two, one with the old particle energy up to the cavity, and one with a step after the cavity with the new particle energy. I believe this is what is meant with the transit time correction.
To see the code, this is implemented twice (in the same way) at: and
Best wishes, Jochem Von:
opal-request AT lists.psi.ch <opal-request AT lists.psi.ch> im Auftrag von Malek Haj Tahar <malek AT transmutex.com>
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AW: [Opal] Transit time factor calculation in OPAL,
Snuverink Jochem, 03/08/2023
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RE: [Opal] Transit time factor calculation in OPAL,
Daniel Winklehner, 03/08/2023
- Re: [Opal] Transit time factor calculation in OPAL, Malek Haj Tahar, 03/09/2023
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RE: [Opal] Transit time factor calculation in OPAL,
Daniel Winklehner, 03/08/2023
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