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T: Fachverband Teilchenphysik
T 55: Silicon Detectors VI
T 55.5: Talk
Wednesday, March 18, 2026, 17:15–17:30, KH 01.022
Fast Shutdown for the Belle II Pixel Detector — •Paula Scholz1, Jannes Schmitz1, Florian Bernlochner1, Jochen Dingfelder1, and Michael Ritzert2 — 1Universität Bonn — 2Universität Heidelberg
During beam loss events at the SuperKEKB accelerator in Japan, large amounts of radiation can severely damage the innermost layers of the Belle II Pixel Detector (PXD). Due to these events, the PXD has remained shut down since May 2024. The PXD consists of silicon pixel matrices based on DEPFET technology. Application-Specific Integrated Circuits (ASICs), known as "switchers", control these matrices by changing voltage levels of 20 V within a few nanoseconds during each 50 kHz readout cycle. Since the detector is safe when the switchers are unpowered, a secure method for rapidly powering down modules during beam loss events is required.
To address this, a modification of the custom-made power supply enabling an immediate pull-down of the switcher channels has been developed. Tests in the laboratory were conducted to verify its reliability and to observe the voltage evolution during the shutdown. The effectiveness of the fast shutdown was further evaluated during a test beam campaign at the MAMI electron facility, where it was triggered before an electron beam reached the sensitive switchers to determine limits for minimum shutdown response times and tolerable beam currents. This upgrade is a key prerequisite for the safe reactivation of the PXD and therefore essential for restoring full vertexing capabilities in the next SuperKEKB run.
Keywords: PXD; Belle II; SuperKEKB