default_order=1 in Chicane bunch compression

[Biaobin]

Hi Michael,

I am a graduate student and is doing some work related to bunch compression with four rectangular dipole chicane. I have a confusion about the default_order in run_setup.

Seeing from the manual, when default_order=1, the transfer matrices are all first order, which means that the longitudinal phase space after the chicane can be simply calculated as: z = z0 + R56*delta, no consideration about the higher order terms, such as T566.

So with a linear chirp beam input, the final longitudinal phase space should be still linear, just have a rotation. But the simulation result is curved as the Figure.

I interpret it as there can be two methods to use Transfer Matrix, all particles one transfer matrix which is determined by the reference particle, or one particle one transfer matrix. If R56 is calculated by the reference particle, so it is the same to all particles with different energy, the phase space should just have a rotation, being linear. But if one particle corresponds to one R56 (one transfer matrix), the final space should be curved. I have verified it by Matlab. Is Elegant also tracking by this method or somewhere I misunderstand ?

The .lte and .ele files are also attached. Looking forward to your kind reply.

Best regards,
Biaobin

[michael_borland]

Biaobin,

The problem is that the CSBEND elements do not respect the default_order parameter in &run_setup. The reason is that the default_order parameter only controls modeling of elements that is performed using a transport matrix. CSBEND is implemented with a symplectic integrator. You can get a linearized model from CSBEND by setting NONLINEAR=1 on the CSBEND element definitions. Or, you can use SBEND elements instead.

--Michael

[Biaobin]

Dear Michael,

Thank you very much! I get what I want using SBEND. I had neglected the differences between SBEND and CSBEND, for misunderstanding the so-called "symplectic bending magnet". Now I am reading the references about it.

Thank you again!

Biaobin