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https://www-ssrl.slac.stanford.edu/webxas/xdc_v2/help_guide.php


XAS Data Collector Getting Started.pdf


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Overview

Web XAS is a browser-based interface for the XAS Data Collector on the beam line computer. Web XAS executes a queue of various item types (XAS experiments, time scans, motor moves, etc.) and provides the tools to edit the queue items as needed for the user's experiment.

If Web XAS freezes, is not behaving as expected, or is displaying a lot of errors, you can try following these directions to restart things: Restarting Web XAS

Logging In

Using your web browser, navigate to: https://www-ssrl.slac.stanford.edu/webxas and click Continue to XAS Data Collector.

Enter the email address and password associated with your SLAC User Portal account and press Login.

After you successfully log in with your User Portal credentials, you will be asked to enter your beam line computer account. This is the username that your group has been given and typically starts with "b_". You will also need to select the beam line that you are running on.



Queue Setup

Using Web XAS, you can execute a series of items in queue. Queue items can be an experiment ("EXP") of various types (XAS, alignment scan, or time scan) or ICS commands ("ICS").

To define an XAS experiment, create a new EXP item using the + button in the Queue Manager section. Make sure EXP is selected in the Add Type select list. If you have existing experiment files, you can select one of those. If not, select Create New, enter a name for the item (this can be descriptive of the experiment and should contain no special characters), and press Add Item. Press Close when you are done adding items to the queue.


Setting up an XAS Experiment

Select the experiment item in the Queue Manager item list. Under the Queue Manager is the Item Editor. In this section, you can define your XAS experiment by selecting a detector file, region file, and scan device.

  • Type - Select XAS to define an XAS experiment. Other options include: TIME or ALIGN
  • Num Sweeps - Number of times to repeat the scan.
  • Detector - Detector files define what detector will be used and what data channels will be collected. Select a predefined detector file for transmission or fluorescence. If you have questions about which detector file is appropriate for your experiment, please ask beam line staff.
  • Region - Region files define the scan energy, number of points in the scan, and count time per point. If you do not have a region file and want to learn how to set up a region file, click here: Define a Region
  • Scan Device - the motor that will be moving, typically MONO, for an XAS experiment. (Exception: BL 2-2 uses MONOT1)

Once you've set these parameters, enter a file name and any comments (will be saved in the output data file), and press Apply.


Defining a Region

To define a new region (or edit an existing one), click on the Regions box at the bottom of the Web XAS window. In the Region editor, press the New button to create an EXAFS region with basic defaults. There is also a Region Wizard available if you press the Wizard button. The wizard will allow you to enter more detailed information about your sample and experiment to generate a more customized region.

Once you've created a new region, you can select it in the list and edit Start, Stop, Incr/Num Points, Count Time, Max Time, Power, and Edge for each segment. Press Save to save your changes. With your new region defined, you can go back up to the Item Editor and select it in the list of regions. (Use the Filter button to refresh the list of regions.)


Basic Region Generator


Region Wizard



Executing the Queue

To start the queue, press the  Queue Controls button at the top of Web XAS. There will be a lightbox displaying information about the queue. If there are no errors, press Start to execute the queue. It may take a few seconds, but you should eventually see the Status field go from INACTIVE to ACTIVE. If there are errors, check the Queue Manager for more detailed error messages. If you need help resolving errors, please ask beam line staff.


Once the queue is active, press the Queue Controls button to bring up a panel with the following controls:

  • Repeat the current sweep
  • Stop queue execution
  • Pause/continue queue execution
  • Skip to the next sweep
  • Skip to the next queue item
  • Increase/decrease the number of sweeps


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