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Summary

The charge per macroparticle seems wrongly calculated in case of OPAL-T.

This was discovered by Finn O'Shea, and posted to the OPAL mailing list.

Steps to reproduce

BEAM1: BEAM, PARTICLE=PROTON, PC=P0, NPART=1000, BCURRENT=2.0e-03, BFREQ=50, CHARGE=1;
BEAM2: BEAM, PARTICLE=ALPHA,  PC=P0, NPART=1000, BCURRENT=2.0e-03, BFREQ=50, CHARGE=2, MASS=3.7274;

What is the current bug behavior?

BEAM1:

OPAL> * ************** B U N C H ********************************************************* 
OPAL> * NP              = 1000
OPAL> * Qtot            =       39.500 [pC]         Qi    =       39.500 [fC]

BEAM2:

OPAL> * ************** B U N C H ********************************************************* 
OPAL> * NP              = 1000
OPAL> * Qtot            =       79.000 [pC]         Qi    =       79.000 [fC]

What is the expected correct behavior?

These two beams are expected to have the same charge per bunch and macroparticle (since BCURRENT and FREQ are constant).

Relevant logs and/or screenshots

In TrackRun::setDistributionParallelT():

    // Return charge per macroparticle.
    return beam->getCharge() * beam->getCurrent() / (beam->getFrequency()*1.0e6) / numberOfParticles;

Possible fixes

The factor beam->getCharge() should not be present in the formula. This is correctly calculated for OPAL-Cycl. Ideally the formula should be refactored to a separate function to reduce code duplication.