• Improved speed of spectra summing.
• Incorporated spectral peakfit algorithm into X26A_Plot.
• Added ability to do spectral summing in X26A_Plot.
• HDF data format for MED and SDD scans implemented and now default mode. X26A_Plot modified to support it. Also added specplot.pro and fitpeaks_hdf.pro programs for reading and plotting the HDF files.
• Implemented Gzip compression for MCA data within HDF data files.
• Modified syntax for plotting MCA spectra from selected points in X26A_Plot.
• Modified the scan list syntax so that user can input desired file name and title as well.
• Modified widget scan so that timing mode defaults to real time, detector PV names are automatically inserted, and added an MED+SDD scanning mode.

This web page and the ones linked to it hopefully will give you an overview of the beamline control systems at X26A. Currently we use a combination of EPICS and IDL to control the beamline and do data collection, employing the latest EPICS and VME control systems. The system is designed to ensure commonality between our setup at the GSECars sector at the APS and that here at the NSLS. The system uses EPICS as the instrumentation front end, linked to electronics through a VME crate. We still use a CAMAC crate for interfacing with our DXP digital spectrometers from XIA, but it is programmed to boot and receive commands from the EPICS-VME system through a Kinetic Systems K-Bus interface. These web pages are designed to give you a basic understanding of how to navigate the system and is organized top down to follow the general flow of operations you go through in setting up your run. It doesn't come close to addressing all the aspects of the software and beamline operations. That’s always learned best during hands-on operation. This is simply designed to touch on the basics you'll need to get up and running. Reviewing this prior to your arrival will help us get your experiments started more quickly. Topics are grouped by basic concepts using the drop down menu at the top of the page. Clicking on these hyperlinks will take you to the pertinent section. Within the pages all the images shown are linked to larger versions. So if you want to see the picture in big bright bold Technicolor just click on the image.

The PC's

We're currently operating using four computer systems, all networked together. All the systems have access to the outside world, but they also are interconnected on a private network along with our VME crate (which is isolated from the NSLS public subnet). The Macintosh G5 acts as the EPICS boot host, we request that you leave this computer alone since it's the most mission critical. You'll see 3 PC's in operation, the one on the right labeled X26A-Control is the PC we'll be using to operate beamline motors and electronics and do data collection. The one on the left labeled X26A-Cars is the one you'll be using for data processing. The one in the middle, called X26A-XRD, runs the Bruker-AXS SMART software for control of our SMART 1500 CCD area detector. Although it's tempting when a PC gets "hung up" to reboot it, PLEASE DO NOT! Try to get a hold of us first. You'll find that we can resolve most hangs without a reboot and, consequently, we'll get you back up and running faster. All data collected is stored on X26A-Control in the directory X:\data. We will create subdirectories for you that preserve a sequential directory structure we've used since the beamline first came on line (NSLS###). After some time we migrate these directories to X26A-Cars for archival (and then to DVD for backup), but they'll always be available to you. All the data on X26A-Control can be accessed by X26A-Cars or X26A-XRD over the network. Both Control and Cars are loaded with IDL. We also have available CD-R/W, DVD-R/W, and USB Multicard readers for data storage. Although in the past it was possible to retrieve data by telneting or FTPing directly into the system, due to recent changes in BNL computer security, this is no longer convenient for most users. We can, however, on request port these to the NSLS anonymous FTP site for data retrieval. Residence time on the FTP site is roughly a week. But we recommend that you make efforts to take your data with you at the end of your run. Most of our data processing is done using the RSI's IDL software. Since the availability of IDL 6.0, we're striving to make most of our data processing routines available as compiled software that can be run using the IDL Virtual Machine tool. If you wish to purchase your own copy of IDL visit RSI's website at www.rsinc.com.

Logging Your Runs

When you get to the beamline you'll see that we have a logbook for you to record your runs in. You're certainly encouraged to keep your own record of what you do, but it is REQUIRED by NSLS policy that we keep a daily log of what you run. At the very least we'd like you to log file names and type of analysis. No exceptions!

EPICS and VME

The terminology can all get a bit confusing. Luckily, for you as a user this is generally all rather transparent. But a brief description is probably in order...a basic understanding is useful when things go awry. So, what is EPICS anyway? Well, right from the APS EPICS webpage, "EPICS is a set of software tools and applications which provide a software infrastructure for use in building distributed control systems to operate devices." EPICS is really optimized for use with distributed systems over a network and allows for communication between them and provides control and feedback of the various parts of the device from a central control room, or even remotely over the internet. EPICS uses Client/Server and Publish/Subscribe techniques to communicate between the various computers. Most servers (called Input/Output Controllers or IOCs) perform real-world I/O and local control tasks, and publish this information to clients using the Channel Access (CA) network protocol. CA is specially designed for the kind of high bandwidth, soft real-time networking applications that EPICS is used for, and is one reason why it can be used to build a control system comprising hundreds of computers.

In our case, the IOC is sort of split up because we want to operate VME based electronics but also have the main core of the EPICS IOC reside on our Macintosh G5 server. The VME crate is that funky beige box sitting in the top of our electronics rack. It contains things like motor controllers, scalers, etc., but also contains a Power PC processor, so is a computer in its own right, running Wind River's VxWorks realtime operating system. The VME boots up using system files that reside on the Mac. This split personality has some advantages in that things tend not to go crazy if the Mac goes down, since the VME has basic control of motors, detectors, etc. The VME is making frequent backups of motor positions, detector calibrations, etc. onto the Mac, so if we need to reboot the VME for some reason you'll find that most hardware definitions remain intact. With Channel Access, we can then control the system using any client on the network that has the proper host software installed (or me from home if I secure shell into the boot host).