## SBEND3D - Off Momentum beam

Dear all, I have some problems in understanding my result. In bold you can see the two questions I have for you. I will explain you briefly.

The configuration is the following:

- single field map from OPERA
- nominal energy: 185 MeV
- RING definition + Local Cartesian Offset
- Particle distribution from file

From this configuration, the beam envelope looks reasonable and agrees with COSY-Infinity. However, the dispersion seems not to be completely suppressed at the end of the beamline. This means that I need to study more the dispersion and the off-momentum beam.

- 1st Analysis: Dispersion function

In the distribution file, I set one particle with 1% momentum shift (py = 1% p0) with respect to the nominal momentum. The tracking of this particle represents the dispersion function. The result is attached (Dispersion-Test1)

- 2nd Analysis: Off-Momentum Beam

The goal is to study the beamline behaviour with a beam that has 5% momentum shift from the nominal value. Then I have prepared a new distribution, where all the particles (except 2 particles) has a momentum shift of 5% (py = 5% p0). In the OPAL input file, I let 185 MeV as nominal energy (EDES = 0.185), the shift in momentum comes from the beam distribution.

The two not-updated particles are: 1- reference particle: py = 0 2- dispersion function: py = 1% p0

Since the majority of the particles have a different energy, the mean beam energy has been updated to 202 MeV. Has this an influence in the tracking? At the end of this “off-momentum run”, I displayed again the dispersion function, expecting to get the same result as in the first Analysis. The nominal energy, EDES, (185 MeV) did not change and the field map as well. Instead I got a completely different trajectory (see Dispersion-Test2).

Which is the best way to perform this kind of analysis?

Thanks for your help

Regards

Valeria