Susceptibilty characterization of DEPFET Pixel Systems
Hans-Günther Moser (Max-Planck-Institut für Physik), 28/02/2017
PXD test set-up during the susceptibility test campaign at ITAINNOVA EMC Lab. Pictured, from left to right: Fernando Arteche, Hans-Günther Mosser, Felix Müller, Ivan Echeverria , Philipp Leitl and Mateo Iglesias. (Image: ITAINNOVA)
In summer 2016, researchers from the Max-Planck-Institute of Physics in Munich, Germany visited the Instituto Tecnológico de Aragón (ITAINNOVA) in Zaragoza, Spain to perform measurements on prototype DEPFET pixels to be used in the Belle II experiment at the KEK facility in Tsukuba, Japan.
Belle II will be equipped with a novel pixel detector (PXD) based on the DEPFET principle. This small detector is located in the innermost region of the detector directly around the beam pipe. It will measure the trajectories of charged particles with a precision of a few µm.
The signals DEPFET pixels can detect are small: an ionizing particle releases about 6000 electrons in the sensitive volume, or 9.6 fC. The signal can then be converted to up to 25 µA by built-in transistor. As this signal is still small, it must be studied against noise.
In big experiment like Belle II noise is generated almost everywhere. The most prolific sources are the detector’s power supplies, cables from subdetectors and noise from accelerator components propagating along the beam pipe. As such, studying noise sources and determining the sensibility of the DEPFET detector is crucial.
The Transnational Access programme offered by the AIDA-2020 project allowed the Max-Planck researchers to perform such measurements at the electromagnetic compatibility (EMC) facility at ITAINNOVA with a DEPFET prototype.
With the assistance of scientists from ITAINNOVA, the team performed a series of noise susceptibility tests. A specific test set-up was developed to evaluate the susceptibility of the PXD system to radiated noise coming from the beam pipe.
The data analysis demonstrated that the sensitivity of the DEPFET detector to noise was low enough to be able to cope with the typical noise sources of a HEP detector. In addition, the knowledge acquired on the response characteristics of the DEPTFET to noise will allow countermeasures to be employed in case problems occur.
This test campaign marked the first instance such measurements were performed with a pixel detector, including those related to the beam pipe radiation.
The access to the ITAINNOVA facilities provided by AIDA-2020 which allowed the Max Planck team to collect important information on the performance of the Belle II PXD, which would have been difficult to obtain otherwise.