3. Vacuum and cooling

The DSSC detector is operated in vacuum and at a temperature of -20 degC. This section assumes that the detector is already pumped down, as the latter operation must be done by an expert. The procedure to bring the detector to -20 degC is described below.

3.1. Checking if the detector is in vacuum and at room temperature

Open a Karabo GUI and connect to the project SCS(SQS)_DSSC. There are other subprojects inside. The first thing to check is if the detector is in vacuum.

To check the detector vacuum level, open the DSSC_Main scene (see Fig. 3.1) under the SCS(SQS)_DSSC project. The vacuum scene shows the status of the pressure gauges PCC16 and PCC17. PCC16 is used to measure the pressure in the pipe placed between the DSSC and the sample chamber, while PPC17 measures the pressure inside the DSSC chamber. Since a thin filter is placed between the two, a pressure difference of roughly one order to magnitude is expected at room temperature. The usual vacuum level measured by PCC17 should be lower than 9e-06 mbar (units in the view are in mbar). If this is not the case, please contact DET OCD.

If the vacuum level in the detector is lower than 9e-06 mbar, the detector can be cooled down. Before doing that, please check the temperature of the chiller bath in the DSSC_Main scene. In normal conditions, with the detector warmed up, this temperature shall be around 20 degC, but it can go up to 35 degC in case the chiller is off for more than a few hours.

Fig. 3.1 DSSC_Main scene, showing the two UHV pressure gauges and the cooling bath temperature.

3.2. Cooling down the detector

If the vacuum level in the detector is better than 9e-06 mbar, the detector can be cooled down.

On the DSSC_Main scene find Safety Interlock Boards panel and click on See more, wthis will open the scene SIB (see Fig. 3.2) and check that ‘SIB State’ indicator is equal to 5 for all the Safety Interlock Boards (SIBs). An alternative the :code:`SIB` scene can be accessed from the :code:`SCS_CDIDET_DSSC` or from :code:`SQS_NQS_DSSC` subprojects

Warning

If this is not the case, please contact DOC 98089.

Normally, if the chiller is OFF, the valves on the coolant lines close to the chiller are closed. They are opened automatically when the chiller goes on. Please also check the valves in the hutch, on the wall separating it from the control room, they must also be open. If they are closed, they must be opened by hand.

Check that the chiller device is not in ERROR state in the vacuum scene. The status of the device there should be green. If this is the case, set the bath temperature (Final chiller T setpoint) to -20 degC. The temperature in the scene shall start going down. With a ramp rate of 1 degC/min, roughly 40 minutes will be needed to reach -20 degC.

Note

The temperature of the bath is the temperature of the coolant inside the chiller. Therefore, it takes some time until the cooling blocks reach the same temperature. The temperature of the cooling blocks inside vacuum can be checked in the SIB scene under the same project.

Fig. 3.2 SIB scene.