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IBS effect

Posted: 27 Sep 2021, 08:11
by Hossein_Ghasem
Hi everybody,

I have a question regarding with calculation of IBS effects. I used the “ibsEmittance” command to quickly evaluate impact of IBS on the main beam parameters. I assumed 3 nC bunch charge, 1.42MV RF voltage and set the coupling to 3.356% just to have 8 pm vertical emittance including IBS effect, please see below;

ibsEmittance DTBA.twi DTBA.ibs -charge=3.0 -coupling=0.03356 -RF=Voltage=1.42,harmonic=934 -integrate=turns=30000,stepSize=10

To confirm the results provided by “ibsEmittance” command, the "IBSCATTER" element with 10 longitudinal slices has been inserted in the ring definition and a bunch of 5000 particles with Gaussian distribution has been tracked through the ring for 30000 turns. I have also included SREFFECT in the tracking,

RAD : SREFFECTS, QEXCITATION=1, PREF=6849.327668039155, JX=1.872, JY=1, JDELTA=1.128, EXREF= 1.616545e-10, SDELTAREF= 9.35513e-04, DDELTAREF=-2.06705e-04, INCLUDE_OFFSETS=1,coupling=0.0495

As you see above, I have specified all the parameters in the RAD definition and set coupling to 4.95% which provides 8 pm vertical emittance. This coupling has been used in bunch generation but I didn't use it (4.95% coupling) in ibsEmittance method because if I do, final emittance with ibsEmittance will be much higher than 8 pm. Below are the results which compare tracking with ibsEmittance method;
Final parameters provided by ibsEmittance method are close to tracking results but agreement between the methods as a function of turn is not very good. Do you have any idea for improvement of the results?

Many thanks in advance

Re: IBS effect

Posted: 15 Oct 2021, 10:16
by michael_borland

The difference between the methods is that in elegant we use macroparticles and simulation of quantum excitation (which injects noise), whereas in ibsEmittance the calculations are for ideal gaussian distributions. You should see improved convergence of the results as the number of macroparticles is increased.


Re: IBS effect

Posted: 13 Nov 2021, 05:06
by Hossein_Ghasem
Hi Michael,

Many thanks for the reply.