CCD

The use of the CCD detectors at ID1   (PDF document)

Overview:
One of the 2D detectors available at ID1 is a 1242 x 1152 pixel fiber-optic taper CCD camera from Princeton with a resolution of 110 microns. X-rays pass through a Beryllium window and are absorbed by a  circular phosphor screen of diameter 80mm. This emits visible light and the image is reduced and directed to the CCD chip by a system of fiber-optics. The CCD detects one or more visible photons per X-ray photon that is absorbed. The detector system consists of five components: the CCD camera head, the PPS-1 power supply, the STS-138 controller, a Neslab digital circulator and a PC with software to control the camera and read the data. The camera, the cables and the controller have been modified so that the CCD may be used in vacuum and so these components are unique at the ESRF (although similar Princeton CCD cameras are used at BM2 and ID24.) The CCD is always used with a fast-shutter system so that the sample and CCD is only exposed during the acquisition. This is necessary for the correct readout of the CCD and it protects the sample from radiation damage. The CCD head is easily mounted on the detector arm of the 6 circle diffractometer at a distance from the sample of 10cm to 1m according to the Q-range and resolution that is required.

Switching on/off:
The CCD chip itself is cooled to a temperature of -60 C or warmed to room temperature under careful control. Liquid coolant at a temperature of about 0 C (a mixture of 50% water and 50% ethylene glycol) must always be passed through the camera head to remove the heat from the thermoelectric Peltier cooler.  The CCD camera is very sensitive and several precautions must be taken. Cooling or warming of the CCD must always be done under control to avoid damage. Never connect or disconnect any cable while the system is turned on.
To switch on: Make sure that the 2 cables and cooling pipes are firmly connected to the CCD via the vacuum feedthroughs. Turn on (in this order) the Neslab circulator, the PPS-1 (switch on the back of the black box) and then the power and cooler switch of the grey STS-138. The dial of the STS-138 should be set to -60 C. There is no need to adjust the settings of the Neslab circulator as this is controlled remotely. A red LED on the PPS-1 (black box) shows the status of the cooling/warming process. The LED should be on continuously once the camera is ready for operation. If the LED is off there is a fault.
To switch off: Turn off the cooler and then main power switch on the grey STS-138. Do not turn off the PPS-1 or Neslab circulator. Wait for the red LED on the PPS-1 to flash with the off part of the cycle longer than the on. This shows that the camera is warm and the PPS-1 and circulator can be switched off and the cables removed.

Operation:
The CCD is connected to an ISA interface card in a PC in the beamline control room. It can be controlled from this PC using Princeton's Winview software or from the beamline workstation using SPEC or indeed with both. There are advantages in each case. For SPEC to be able to control the CCD and read the data the TACO device server (written by the ESRF BLISS group) and PORTMAP must be running (contact the beamline BLISS representative in case of problems). The use of the PC for other tasks should be avoided while it is in use with the CCD as it would adversely affect the data transfer. This includes setting a screensaver. In general the PC and Winview should be used when speed is important. It is simple to set a ROI and to reduce the resolution by grouping the pixels giving a fast readout. This is not possible with SPEC. The data transfer to the workstation also slows down the time acquisition time. A common example is for beamstop alignment. An ROI can be set in the center of the image (as the beamstop is located roughly in the center of the camera). By choosing the focus mode with a small ROI the image is refreshed every second. It is easy to see the beam disappear behind the beamstop in realtime as the CCD is moved using DEL or GAM.
The use of SPEC is necessary in order to permit use of the CCD in combination with a motor scan or a macro and to allow the CCD image to be correlated with the monitor count. Some specific settings:
SPEC: To start the CCD in SIXC type> ccdon and >ccdsetup to set the ADC, trigger and data saving options. ct 1 or ccdtake 1 give a 1 second acquisition.
ADC: The speed of the ADC must be chosen between 50 Hz and 430 Hz in Winview or SLOW and FAST in SPEC. The slower setting gives a longer readout but a lower noise level and vice-versa.
TRIGGER: In SPEC the CCD is triggered externally (VCT6) in order to work together with the monitor diodes. The SIGNAL mode must be chosen as it will not work with the GATE mode. (Set this in menu> ccdsetup)
DATA: The data is saved either on the PC and so must be backed up by the user or in the experiment directory on NICE if using SPEC. The file name and location is set by typing >ccdsetup in SPEC.
FAST SHUTTER:  The CCD must be operated with the fast shutter that is located just upstream of the diffractometer vacuum vessel. The commands are fsin to put the fast shutter device into the beam and fsout to remove it completely. In the case of SPEC the fastshutter should be set to work with the CCD by the command fs ccd. The fast shutter controller must be switched on. This is located next to the diffractometer vacuum vessel. (Please contact Peter Boesecke the beamline BLOM for help with the fast shutter or cabling.) A spare shutter and controller is available in the detector group.