Paper |
Title |
Other Keywords |
Page |
PT07 |
Cavity Beam Position Monitor For The TESLA Energy Spectrometer
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diagnostics, electro-magnetic fields, linear-collider, monitoring, radio-frequency |
184 |
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PT26 |
Cryogenic Current Comparator for Absolute Measurement of the Dark Current of the Superconducting Cavities for Tesla
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cryogenics, diagnostics, monitoring, pick-up, shielding, superconductivity |
234 |
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- K. Knaack, M. Wendt, K. Wittenburg
DESY, Deutsches Elektronen-Synchrotron, Hamburg, Germany
- R. Neubert, S. Nietzsche, W. Vodel
FSU Jena, Friedrich-Schiller Universität, Jena, Germany
- A. Peters
GSI, Gesellschaft für Schwerionenforschung, Darmstadt, Germany
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A newly high performance SQUID based measurement system for detecting
dark currents, generated by superconducting cavities for TESLA is
proposed. It makes use of the Cryogenic Current Comparator principle and
senses dark currents in the nA range with a small signal bandwidth of 70
kHz.
To reach the maximum possible energy in the TESLA project is a strong
motivation to push the gradients of the superconducting cavities closer
to the physical limit of 50 MV/m. The field emission of electrons (the so
called dark current) of the superconducting cavities at strong fields may
limit the maximum gradient. The absolute measurement of the dark current
in correlation with the gradient will give a proper value to compare and
classify the cavities.
This contribution describes a Cryogenic Current Comparator (CCC) as an
excellent and useful tool for this purpose. The most important component
of the CCC is a high performance DC SQUID system which is able to measure
extremely low magnetic fields, e.g. caused by the extracted dark current.
For this reason the SQUID input coil is connected across a special
designed pick-up coil for the electron beam. Both the SQUID input coil
and the pick-up coil form a closed superconducting loop so that the CCC
is able to detect dc currents down to 2 pA/√Hz. Design issues and the
application for the CHECHIA cavity test stand at DESY as well as
preliminary experimental results are discussed.
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