Elegant users forum

Hello all,

I am still learning the ropes of Elegant and just want to check if I am doing correctly the following:

Suppose that I have calculated the electric and magnetic field in the reference frame and want to find a change in momentum due to the Lorentz force.
First, I define delta t as:

set t [ expr "$L" / 299792458.0] ;

where L is the length of my drifting element.

Then change in momentum in SI units can be calculated as following (assuming that there is no B-field in the beam frame, so B-field in the rest frame can be expressed in terms of E). We will use sddsprocess for that.
#Calculating change in momentum:
"-def=col,dpx,Charge Particles / Ex * MeanGamma / MeanGamma / $t *"
"-def=col,dpy,Charge Particles / Ey * MeanGamma / MeanGamma / $t *"
"-def=col,dpz,Charge Particles / Ez * $t *"

Now I can convert change in momentum into Elegant units where the new xp will be (px+dpx)/pz. Let's assume for now that pz=p, so then I can write:

"-redef=col,xp,dpx 1.60218e-19 / 0.511e+6 / p / xp +"
and same for yp, and p.

I would like to check a few things.

1. Is the conversion from SI units correct?
2. Should I flip the sign for dpz since the tail and head of the bunch are flipped in Elegant?

Thanks.

The quantity "p" in elegant is the momentum in SI units (call it "P") divided by m*c: p = P/(mc).

So you should use
"-redef=col,xp,dpx me_mks / c_mks / pz / xp +"
and similarly for yp.

--Michael

Thanks for your reply!

But it looks like in my case I need to use the mass of the macroparticle, not the electron mass.
So something like this:

"dpx 1.60218e-19 * me_mks / c_mks / Particles * Charge / pz / xp +"

Thanks again.

Yes, if the Charge quantity pertains to the macro particle, then that would seem to make sense.

--Michael