16.37 Highlights of What’s New in Version 31.0, 1 Oct. 2016

Here is a summary of what’s changed since release 30.1.

16.37.1 Bug Fixes for Elements

• The touschek_scatter command had a bug when random multipoles where used on KQUAD and KSEXT elements. In particular, these multipoles components were re-randomized for each TSCATTER element. This was discovered and fixed by A. Xiao (ANL).
• The implementation of edge effects in the KQUAD element was using x^′ and y^′ in place of q_x and q_y, and so was not symplectic. It also did not have the correct dependence on δ. These issues were reported by R. Lindberg (ANL). A similar error was fixed in the implementation of edge effects for CSBEND; this was fixed by Y.P. Sun (ANL). Practically speaking, we haven’t noticed any significant change in results.
• There was a bug in the evaluation of systematic multipoles when using the second-order integrator for KQUAD and KSEXT. The default fourth-order integrator did not have this issue.
• Higher-order path-length issues were fixed for the BRAT element. This issue was reported by R. Lindberg (ANL).
• The steering kick calibration factors are no longer ignored on the KQUAD element.
• The BMXYZ and BMAPXY elements lacked dependence on the momentum deviation δ. This issue was reported by R. Lindberg (ANL).

16.37.2 New and Modified Elements

• Added the BGGEXP element, which performs tracking through magnetic fields constructed from a generalized gradient expansion [35]. Although the integration is not symplectic, the fields satisfy Maxwell’s equations exactly. A script, computeGeneralizedGradients, is provided to assist in preparing input for this element. Advice from M. Venturini (LBNL) was helpful in performing this work.
• Added separate specification of edge and body multipoles to the KQUAD and KSEXT elements.
• Added steering and steering multipoles to the KSEXT element.
• The BMXYZ element now allows independent specification of the insertion length and field map length.
• The code for the KQUAD, KSEXT, MULT, and FMULT was improved to prevent underflows that might occur in some odd cases, which would negatively affect accuracy.
• The LSRMDLR element now includes an option for a helical device. This was requested by forum user zzhang and implemented by Y.-P. Sun (ANL).
• Two additional parameters, SampledParticles and SampledCharge were added to WATCH files in coordinate mode. These are identical to Particles and Charge, respectively, except when the FRACTION parameter is < 1. In that case, the latter parameters give the values prior to sampling, while the new parameters give the parameters of the sampled fraction of the bunch. Previously, Particles and Charge changed as FRACTION was changed. Note that scripts that use the Particles and Charge may need modification since the meaning has changed. Y. Ding (SLAC) pointed out this issue.

16.37.3 New and Modified Commands

• The analyze_map command can now report the map using canonical variables. It also has a user-controlled accuracy parameter that can be used to eliminate spurious matrix elements. R. Lindberg (ANL) helped with the development and testing.
• The touschek_scatter command now uses averaging of the loss rate over the interval between two TSCATTER elements instead of the local value at the element, which gives more accurate estimates of the distribution of scattered particles. This change requires that TSCATTER elements be inserted at the beginning and end of the beamline, which can be done using add_at_end=1 and add_at_start=1 in the insert_elements command. This was implemented by A. Xiao (ANL).
• The modulate_elements command now offers more control over verbose printouts, to help reduce the volume of uninformative printouts. It also provides user control of the buffer flushing interval for the record output file.
• The insert_elements command now has the option to insert an element at the beginning of the beamline.

16.37.4 Changes to Related Programs and Files

• The script computeGeneralizedGradients was added to assist in preparing input for the BGGEXP element.
• The scripts elasticScatteringLifetime and bremsstrahlungLifetime now support user-specified gas composition. The Z values for carbon and oxygen were mixed up in some places in these and related scripts, as pointed out by S. Tian (IHEP); this was fixed.
• The ionTrapping script now supports user-provided factors for inflating the emittance and energy spread.