MAKETHIN

EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH

MAKETHIN: Slice a sequence into thin lenses

This module converts a sequence with thick elements into one composed of thin (zero length) element slices or simplified thick slices as required by MAD-X tracking or conversion to SIXTRACK input format.

Slicing to thin elements

The slicing is performed by the command:

MAKETHIN,SEQUENCE=seq_name, STYLE=slicing_style,
         MAKEDIPEDGE= logical; 
         MINIMIZEPARENTS= logical, 
         MAKECONSISTENT= logical;

The parameters are defined as:

SEQUENCE= seq_name is the name of the sequence to be processed to thin slices. The sequence must be active, i.e. it should have been previously loaded with a USE command. The sequence must use the default positioning of elements (REFER=centre)
STYLE= slicing_style where the argument is optional, selects the slicing style. Available slicing styles are:
- SIMPLE : produces equal strength slices at equidistant positions with the kick in the middle of each slice.
  It is the default if the number of slices is larger than 4.
- TEAPOT : improves the slice positioning using the algorithm described in IPAC'13 MOPWO027
  It is the default if the number of slice is less or equal to 4.
- COLLIM : is the default slicing for collimators. If only one slice is chosen it is placed in the middle of the old element. If two slices are chosen they are placed at either end. Three slices or more are treated as one slice.
- (parameter not given): The standard default slicing for all elements (except collimators). It uses TEAPOT if the number of slices is less or equal to 4, and SIMPLE otherwise.
Note: It is strongly recommended to always specify STYLE=teapot to use the improved slicing for any number of slices.
MAKEDIPEDGE is a flag that controls the generation of DIPEDGE elements at the start and/or end of bending magnets, to conserve edge focusing from pole face angles e1, e2 or extra fields described by fint, fintx, in the process of slicing bending magnets to thin multipole slices. Selection with THICK=true will translate a complex thick RBEND or SBEND, including edge effects, to a simple thick SBEND with edge focusing transferred to extra DIPEDGE elements.
(Default: MAKEDIPEDGE= false)
Example:
```
!  keep translated rbend as thick sbend
select, flag=makethin, rbend, thick=true;
```
MINIMIZEPARENTS is a flag that controls the removal of inconsistent numbers of slices for parent elements.
(Default: MINIMIZEPARENTS= true)
MAKECONSISTENT is a flag to ensure an equal number of slices for parent and children elements, using the larger value.
(Default: MAKECONSISTENT= false)

Number of slices

The number of slices can be set individually for elements or groups of elements using SELECT commands

SELECT, FLAG=makethin, 
        RANGE=range, CLASS=class, PATTERN=pattern[,FULL][,CLEAR],
        THICK=logical, SLICE=integer;

where the argument to the parameter SLICE is the number of slices for the selected elements.
The default is one slice and THICK=false for all elements, i.e. conversion of all thick elements to a single thin slice positioned at the centre of the original thick element.

Note that THICK=true only applies to dipole or quadrupole magnet elements and is ignored otherwise.

MAKETHIN allows for thick quadrupole slicing with insertion of markers between thick slices. Positioning is done with markers between slices, here however with thick slice quadrupole piece filling the whole length.
Examples:

! slice quadrupoles thick, insert 2 markers per quadrupole
select, flag=makethin, class=quadrupole, thick=true, slice=2; 

! thick slicing for quadrupoles named mqxa, insert one marker in the middle
select, flag=makethin, pattern=mqxa\., slice=1,  thick=true;

Slicing can be turned off for certain elements or classes by specifying a number of slices < 1. Examples:

! turn off slicing for sextupoles
select, flag=makethin, class=sextupole, slice=0; 

! keep elements unchanged with names starting by mbxw
select, flag=makethin, pattern=mbxw\., slice=0;

This option allows to introduce slicing step by step and monitor the resulting changes in optics parameters.
Keep in mind however that subsequent tracking generally requires full slicing, with possible exception of quadrupoles and bending magents.

Additional Information

The generated thin lens sequence has the following properties:

The new sequence has the same name as the original. The original sequence is replaced by the new one in memory. If the original sequence is needed for further processing in MAD-X, it should be reloaded.
The algorithm also processes any sub-sequence inserted in the main sequence. These sub-sequences are also given the same names as the original ones.
Any element transformed into a single thin lens element has the same name as the original.
If an element is sliced into more than one slice, the individual slices have the same basename as the original element plus a suffix ..1, ..2, etc. and a marker, with the name of the original element, is placed at the location of the center of the original element.

Hints:

Compare the main optics parameters like tunes before and after slicing with MAKETHIN. Rematch tunes and chromaticity as necessary after MAKETHIN.
In tests, turn off slicing for some of the main element classes to identify the main sources of changes.
For sextuples and octupoles, a single slice should always be sufficient.
Increase the number of slices for critical elements like mini-beta quadrupoles. Even there, more than four slices should rarely be required.
In case of problems or doubts, consider to flatten the sequence before slicing.
See the examples for makethin.
See also the presentations on the upgrade of the makethin module:
LCU_makethin_2012_09_18.pdf, and
LCU_makethin_2013_04_19.pdf.
TEAPOT is documented in IPAC'13 MOPWO027

Helmut Burkhardt, May 2014