We currently have one SAXS detector for the main beamline (I22), a Pilatus P3-2M detector (the default detector). The Pilatus P3-2M has also become the default detector for microfocus experiments as well. The detector for a given experiment must be discussed well in advance of beamtime and preferably at the time of the proposal so the schedule can be organised accordingly to minimise changeover times between user experiments.
You can also choose to collect data from the WAXS detector. We are currently using a Pilatus P300-KW for this application offering an angular acceptance from 13-51°. A future upgrade will see an L-shaped Pilatus detector replace this, offering some limited anisotropic data in WAXS.
The spatial resolution of the Pilatus detectors are fixed but resolution has been retained for backward compatibility with the old RAPID detector which could be usefully configured between 256 x 256 and 2048 x 2048.
We also have a MarCCD SX-165 but with the fast shutter currently offline it is not available. This also has resolution options which when chosen affect the speed performance.
Collecting single frames of data of any frame time can be achieved by configuring the NCD Detector tab.
Here one frame of 10 seconds has been configured with a 1 millisecond wait before data collection. For Pilatus the minimum collection or run period is 4msec. To change any of the figures in the configuration simply click in the box and replace the number with your own. You must press "return/enter" after making a change for the panel to accept the number. Every time you make a change to the configuration you must also remember to press the "Configure" button.This will send the required information to the TFG to run the next experiment.
Multiple frames are useful if you are collecting data while peperturbing your sample in some way, e.g. a temperature or pressure ramp. The same NCD detector tab is used. In the example below 100 frames of 10 seconds has been set up with a 1millisecond wait between collections, this allows data to be read out. The wait and run time can be configured in units from nanoseconds to hours for RAPID with the same limit as above for Pilatus. 1Gbit of histogramming memory is used to collect all time frames from RAPID and readout is at the end of the experiment. The coloured bar below shows how much of the memory is being used for a particular set up. This will go red if you configure too many frames. Please note that the higher the resolution the smaller the number of frames you can use, e.g. for RAPID data the maximum frame number is 1024 for resolution at 512 x 512. This restriction is not necessary for Pilatus which saves each image as it goes on a PPU unit built into the data acquisition system. The Pilatus P3-2M is however limited to 250Hz, i.e. 4msec frames 3msec run plus 1msec readout
Every time you make a change to the configuration you must also remember to press the "Configure" button. This will send the required information to the TFG to run the next experiment.
The flexibility of this system allows you to have multiple groups where frame times and wait times can be varied. This is useful if you have a reaction you want to follow that has fast and slower regions of interest. The example below has three such groups each running for a different period of time 1, 10 or 100seconds with different wait periods between each frame, in this case 1millisecond, 1 second and 1 hour.
You can see from the example that the time unit for wait can be selected as well as the length. This is also true for the run period and is available in all types of NCD detector configuration.
We routinely use the Time Frame Generator (TFG2) to trigger data collection to ensure synchronisation. In this case a sample environment, for example, the pressure cell can send a TTL pulse to the TFG to trigger the data collection. This can be a rising or falling TTL pulse.
We use LEMO cables from the sample environment plugged into a known port on the patch panel. In the detector CIA, the corresponding patch panel cable is plugged into the correct port on the TFG (your local contact will do this for you). This can be one of four options:
You will need to know which port has been selected! Ask your local contact!
In the detector configure panel in the GDA, you will find several ways to trigger experiment. The simplest is an external trigger to start the experiment but you can also trigger events within a data collection set on either on the Wait Pause or the Run Pause, depending on when you would like to trigger the data collection. For example, we can trigger on the wait pause.
In the Wait Pause box, select a rising pulse (if you are providing a rising pulse!) and then select the trigger port number (i.e. Trig in 2). Press "Configure" and then "Start". The detector should then wait until it receives a TTL pulse before commencing data collection.
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