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For LCLS, we will pre-compute the optics from the lattice, to produce the XAL files which include the Twiss params, so each modeling application doesn't have to track a lattice for itself before starting. The online modeling "tracker" will be that in XAL (primarily in the gov.sns.xal.model package). The output of this phase will be the Twiss parameters of each element of the beamline. A second probe can calculate the transfer matrices (R-matrices). The Twiss param outputs will be captured in a series of second XAL files. There is presently no file-handling code in XAL for statically recording the R-matrices or global parameters (path length, energy, betamax), so new output files will be designed for that (either extending the XAL syntax, or creating some other XML file). proposal: adapt probe for coupled R-matrices, and additionally output global parameters to a file.
In the existing XAL API one can track an XAL beamline in either of 2 "modes", i) "design" or ii) "from EPICS PV" - which is to say using settings for each lattice element found either in the XAL input file ("design") or by accessing the EPICS Process Variables of optical and energy components themselves at runtime. The latter produces a model of the optics of the extant machine. We should have file management capability to store a single recognized "design" lattice file, plus a "gold" lattice (the inputs "from PV" that produced good optics (see To Add), plus at least one experimental lattice file. This capability to switch easily between a lattice of the extant machine and an ad-hoc lattice was badly missed in the SLC modeling environment.
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The results of tracking (Twiss, R-matrices, global machine params, k-values of optical components) for each of these beamlines for each of the choices of model (design, gold, experimental) for each source of input data (design, PV), will have to be stored. Put Proposal: put twiss and R-matrix outputs in CVS, primarily to record change history.
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The XAL model includes energy, which it acquires explicitly from klystrons (if running "from PV") at the time the lattice is tracked. Therefore there is no "BDES to KMOD" requirement for online applications as such (see questions ).
Figure 2 shows the workflow of getting from geometry to optics in applications.
Beamline Descriptions
The number of beamline description input files we need depends on the number of beamline geometries the LCLS will be run in (for instance, how many modeled extraction lines for experiments will there be)? It additionally depends on how many energy profiles will there be? Also high-level applications that deal with beamlines (bpm orbit displays, steering etc) will initialize displays based on the end-points of an input XAL beamline description file. So the XAL orbit correction app for instance, will always initialize to steer the whole LCLS unless a separate beamline file is written for smaller regions of interest - such as injection separately from main linac.
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