Optics Calculation

(return)

All the existing GSI optics were calculated using MIRKO optics program. It is a very good program, containing lot of functionalities not present in other optics programs. However it is not officially supported by GSI, has relatively small user base and in principle it only runs on outdated versions of Windows.

LSA optics import needs two files for each optics: so called csv-strength file and csv-twiss file. The csv-strength file contains two columns with element name and magnetic strength (k0l, k1l, k2l...) for each active beam element. The csv-twiss file is more complex and has structure similar to twiss file as produced by MADX optics program.

Currently there are two ways to obtain LSA input files:

  1. using MIRKO export to twiss file and converting this twiss file to csv-twiss input to LSA; this was is partly automoatized, but needs a lot of manual editing because LSA input requires very specific format and markers not present in MIRKO->twiss export.

  2. using MADX;

The final workflow is the following:

  1. open optics MAK file in MIRKO;
  2. export twiss file and MADX thin sequence file (beamline sequence); the twiss file can be used to generate LSA input files;
  3. carefully correct manually the beamline sequence file by removing drifts spaces with negative length, which are not allowed in MADX;
  4. check, running MADX, if the beamline sequence is okey;
  5. in MADX save beamline sequence as normal sequence file (save, sequence=beamline, file=optics.seq, bare;), where there are no drift spaces and each element is laced using 'at=' command;
  6. edit the normal sequence file, add element type and corresponding parameter (angle, k1, k2); mark the beginning and the end of each dipole with MARKER;
  7. run genLSA.py script, which generates both files required for LSA import.

A work of converting MIRKO files to MADX has been reported before (R. Cee et al, A MAD-X MODEL OF THE HIT ACCELERATOR). These results were used widely for HEST optics, however some differences exist due to differen MIRKO version used etc.

Additional Remarks:

  1. typical MIRKO envelope calculation takes into account 2 beam sigma: ex=pi*(2*sigma^2)/beta
  2. typical half-apertures are:

    • 54.5 mm- beakable chambers
    • 60 mm - normal quadrupole chambers
    • 75 mm - sometimes in steerers and drift spaces

2020-06-17 16:00