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Use Case: A beamline physicist will provide MAD, Parmela or Elegant files 3. Some designated person will update the Oracle DB with relevant information from these files, and run some process (presumably a SQL script) which outputs an XAL lattice input file in XML - the file containing the lattice description of the machine Test page(See questions). Given this input lattice file, software in the XAL package library can then be used by applications to compute optics (Twiss, R-matrices, etc), which they can then use to calculate bumps, orbit corrections, beta-match settings etc.
Systematics of Optics Computation
Presently in XAL each application which uses optical parameters (Twiss and R-matrices) must track a lattice. That is, it must acquire the k-value of optical components and track the lattice (which XAL calls "probe"). One of the apps, the Model Optics application, allows a user to browse optics so calculated.
For LCLS, we will pre-compute the optics from the lattice, so each modeling application doesn't have to track a lattice for itself before starting. The online modeling "tracker" will XAL 1. XAL has a number of components, one part of which be that in XAL (primarily in the gov.sns.xal.model package) can be used to "track" a lattice description (which XAL calls "probe"), defined in an XML file.xal.model package). The output of this phase will be the Courant-Snyder (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 (XAL, or some other XML).
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 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 #td_GW1 (the inputs "from PV" that produced good optics 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.
Store the optics in a well known place
The results of tracking (twissTwiss, R-matrices, global machine params, optical component settingsk-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. This could all be handled by careful filenaming if it's sufficient to do tracking in the initialization stage of each modeling program's startup. But if that proves too slow then we'll need to persist the outputs into the Oracle DB and programs will go to the db to get optical parameters. See figure 2.go to the db to get optical parameters. See figure 2.
"KMOD to BDES"
Presumably only the Model Optics application presently allows a used to implement new k-values of optical components following tracking -see questions.
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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Create a Skills Matrix for applications, eg, XML and associated technologies (DOM, XSL etc), Oracle and associated technologies (SQL, PHP, persistence).
H2. QUESTIONS
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Verify AFS client for Windows is not workable.
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Is this as simple as it sounds? Will the db contain enough to emit a lattice as opposed to only the geometry - what does Mark Woodley have to do now given a MAD geometry description to convert it to a lattice suitable for Dimad?
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Which XAL applications allow one to update the EPICs magnet k-values after a successful model run?
Does XAL really not model acceleration? If not how is it useful for SNS?
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What is the canonical list of XAL physics apps?
Does LCLS need SVD based orbit minimization? Is there an orbit minimization in XAL?
R&D
This section outlines some constrained R&D we should do to check architecture decisions.
Matlab
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Accelerator Toolkit (AT)
See what applications are available in Accelerator Toolkit (AT). Use of matlab for applications depends on desirability of the functionality offered, responsiveness of the application in the context of a large accelerator's operations, and importantly, ability to secure licensing with manageable cost/benefit.
Specifically: Do AT applications appear to offer support for configurations necessary in a large machine (e.g. choosing from available bpms and correctors in an orbit correction package). How does it handle errors? Are bpm statuses communicated to the user interface and graphics?
Matlab Plotting
Can Matlab be used as a general purpose charting engine? This would be very much more desirable than XAL's charting if having charted the data for a plot one could easily "drop into matlab" to further analyse the data just plotted.
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Filesystem and distributing software releases
Should the production executables (XAL java jar files etc) and configuration files be on AFS or NFS? Operative points in the question are that both XAL and Eclipse require that the user specify a "workspace" at startup, which defines their particular configuration. This workspace must always be writable, so AFS token expiry after 25 hrs use, can be problematic. Simplest solution is makefile "install" to a mounted NFS directory - but that directory has to be accessible by all head nodes (that is, all linux desktops running the applications).
Eclipse includes two software distribution mechanisms: first requires "pull" (the user initiates the update), 2nd is Java Web Start, which checks for updates at predefined intervals.
DETAILS
This section gives details behind architectural statements made above.
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Why so definite about x86 Linux RH with KDE/GTK-2?
To create a high performance user interface we should lock down the desktop hardware. We can support more than one such configuration, such as x86 Windows and x86 Linux with GTK, but for high performance UIs we need to build for specific desktops, so we have to know what they will be a-priori. Eg, when building SWT/Jface apps, one has to target a gives set of desktops so the appropriate libraries can be included in the build.
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ERROR HANDLING, LOGGING AND VIEWING
A programmer spends half their time handling errors, so making that as easy as possible is a productivity priority. For LCLS we will use the following technology stack:
Err package.
Err (see http://www.slac.stanford.edu/grp/cd/soft/err/
) makes the process of rigorously handling errors easy. It allows a programmer to define an error code in a structured, recorded global way; and to use that code to issue errors and associated diagnostics from or linux, solaris, windows platforms in either java or C/C++, and issue them directly to CMLOG (or some other message logger). It includes support for exception chaining ("caused-by") and exception translation, so the end user can see what systematic thing caused their functional problem (E.g. of a error logged by Err in cmlog might be "UnableToTrackBeamlineException: LCLS ; caused by FileNotFoundException: LCLS.XML when attempting to steer LCLS".
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