Preventing, monitoring and curing the ageing in the LHCb Outer Tracker

The modules of the LHCb Outer Tracker have shown to suffer from gain loss under irradiation at moderate intensities, a process known as ageing. The plastifier in the glue with which the detector modules were constructed, Araldite AY103-1, has been shown to be the culprit. In this thesis this is confirmed by irradiating a module constructed with Araldite AY105-1, which does not contain the harmful plastifier. Several methods to prevent and repair the gain loss exist. One preventive measure is the addition of oxygen. However, because of its electronegative nature, oxygen can capture some of the drifting electrons, thereby lowering the gain of the OT. Simulations have been done to investigate the effect of oxygen on the gain and efficiency. One method to remove the ageing is HV training. In this procedure the applied voltage is increased such, that the OT enters the discharge regime. These discharges mostly remove the ageing, but can take place anywhere in the straw tube, not necessarily at the location of the ageing. Curing the module while putting a source near the location of the ageing is shown to always cure the gain loss. Finally, a method has been devised to quantify the amount of gain loss in the OT with the standard OT readout electronics. By performing a threshold scan it is possible to accurately determine the average gain loss of the straws.