Charge Transfer and Charge Broadening of GEM Structures in High Magnetic Fields

• Main Authors: Killenberg, M, Lotze, S, Mnich, J, Muennich, A, Roth, S, Sefkow, F, Tonutti, M, Weber, M, Wienemann, P
• Format: Journal Article
• Language: English
• Published: 25-02-2004
• Subjects: Physics - Instrumentation and Detectors
• DOI: 10.48550/arxiv.physics/0402121

We report on measurements of charge transfer in GEM structures in high
magnetic fields. These were performed in the framework of the R&D work for a
Time Projection Chamber at a future Linear Collider. A small test chamber has
been installed into the aperture of a superconducting magnet with the GEM
structures mounted perpendicular to the B field direction. The charge transfer
is derived from the electrical currents monitored during irradiation with an
^{55}$Fe source. No severe loss of primary ionisation charge is observed,
but an improved ion feedback suppression is achieved for high magnetic fields.
Additionally, the width of the charge cloud released by individual ^{55}$Fe
photons is measured using a finely segmented strip readout after the triple GEM
structure. Charge widths between 0.3 and 0.5 mm RMS are observed, which
originate from the charge broadening inside the GEM readout. This charge
broadening is only partly suppressed at high magnetic fields.