The OPAL Discussion Forum

[jjyang <jianjun.yang AT psi.ch>]

在 2011-8-24，下午12:04， Suzie Sheehy 写道：

Hi there,

Thanks for getting back to me about pp.43 of the manual. To make sure, here is an example to test out the conversion:

If I want to convert straight fro mrad to eV, all I'm doing is recognising that my beam has a total momentum P and is travelling at an angle (theta) from the midplane. Then the transverse momentum Px[eV/c]=theta[rad]*P[eV/c] if theta is small. 

For a 1 mrad angle for a KE=250 MeV/c2 proton beam then Pc=729.13E+6 [eV]. 

Therefore I have to put in sigmapx= 729.13E+6 * 1E-3 / 3E+8 = 0.00243 eV.   Is this correct?

(If this is the case I would not technically call this a momentum, as momentum should be in units of eV/c!!) 

Your calculation is correct.  Maybe it is clearer to call sigmapx as eV/c.

Could you also clarify what the units are in the longitudinal direction? Specifically, what are the units when defining sigmat and sigmapt in the Distribution command?

The units in the longitudinal direction is the same as in the other directions.

 

Finally, I think that when you say that in the h5 file:

x,px are horizontal,   y,py are longitudinal  and z,pz are vertical

Do you actually mean:

x,px are horizontal, y,py are vertical and z,pz are longitudinal?

No, I repeat,  if you are using OPAL-CYCL (METHOD = "CYCLOTRON-T"  in TRACK command),  y, py in h5 file are longitudinal. 

Certainly this is what changes when I vary the input distribution for x, y, and t in my input file.

Suzie

Jianjun