Cedric Hönig ; Jochen Dingfelder

2016
University of Bonn Bonn

Abstract: The improved superKEKB accelerator will use a continuous injection scheme. Every 20 ms a e+ or e− bunch will be refilled. The newly injected particles will produce large background and need roughly 3 ms to cool down. The background is caused by the smeared out momentum of newly injected particles. These newly injected particles oscillate around the ideal bunch position or they are lost completely, creating signal while they pass the detector. This poses a special challenge because the integration time of DEPFET is in the order of 20 µs while bunches pass the interaction region every 10 µs. This background from newly injected bunches coupled with the high data rates from the high luminosity could potentially lead to the detector data becoming unreliable and faulty. In order to make the DEPFET detector blind while these noisy bunches pass by a new mode of operation was suggested. This new mode will be called gated mode. Goal of this mode of operation is to suspend normal charge collection whenever a noisy bunch passes the detector. Gated mode is based on the clear process of DEPFET. To put a pixel into gated mode the voltage at the clear contact is raised to a high voltage. At the same time the external gate is switched to off state. This maintains a potential barrier which charge from the internal gate cannot pass. On the other hand charge created in the bulk is not affected by this potential barrier and is extracted into the clear contact. Hence charge within the internal gate is preserved, while newly created charge is removed. This principle was proven to work in measurements by E. Prinker [19]. Switching the detector in and out of gated mode in a time frame which is lower than the integration time poses special challenges. The whole electronics chain needs to be flawless to not corrupt data. The timing for switching in and out of gated mode needs to be precise. Else there is a risk of measuring during the passage of a noisy bunch. Furthermore as few bunch crossings as possible should be gated, to measure as many physic events as possible. Thus optimising the electronics is a first step, before dynamic enabling and disabling of gated mode can be achieved.

Note: Presented on 29 09 2016
Note: MSc