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H. J. Hilke and W. Riegler
of 40 μm carbon doped polyimide (Kapton-XC), the outer is a laminate of 25 μm
polyimide, to enhance the gas tightness, and 12.5 μm aluminum, to ensure fast
signal transmission and good shielding. The tubes are up to 2.5 m long and have the
25 μm wire supported every 80 cm.
Staggered double layers tubes are glued to light support panels to form modules
up to 5 m long. An average spatial resolution of a double layer below 200 μm was
measured with Ar/CO 2 (70/30%). In a station, 4 double layers are aligned along
0, + 5, − 5, 0
◦ , thus providing a crude second coordinate measurement.
In another design for ATLAS [15], mechanical strengthening of 4 mm straws is
achieved with carbon fibers wound around the tubes and straightness by supporting
them every 25 cm with alignment planes vertical to the straws. This construction
reduces the material along the radial tracks, which is essential for the role of the
straws to detect transition radiation originating in fibers stacked in between the
tube layers. This role also determines the need for Xe in a mixture of Xe/CO 2 /O 2
(70/27/3%), the oxygen addition increasing the safety margin against breakdown.
Another quasi-single wire design is that of plastic streamer tubes usually called
Iarocci tubes. Because they are easy to construct in large size and cheap, they have
been widely used, especially as readout planes in hadron calorimeters.
A plastic extrusion with an open profile with typically 8 cells of lxl cm 2 and a
PVC top plate, is coated on the inside with graphite with a minimum resistivity of
200 k/square. All this is slid into a plastic box, which serves also as gas container.
For stability, wires are held by plastic spacers every 50 cm. Using a thick wire
of 100 μm, self-quenching streamers are initiated in a gas containing a strong
quencher, typically isobutane in addition to Ar. Electrodes of any shape placed on
one or both external surfaces pick up the rather strong signals. The dead time is long
but only locally, so that particle rates up to 100 Hz/cm 2 can be handled.
4.3.2 Multiwire Proportional Chambers (MWPC)
Already 1 year after the invention of the multiwire proportional counter (MWPC)
by Charpak in 1968, a system of small chambers was used in an experiment [58],
another year later a large chamber 2 m × 0.5 m had been tested with Ar/Isobutane
[59]. A number of developments like bi-dimensional readout were discussed [60].
In 1973 already, a large system of MWPC containing 50,000 sense wires had been
constructed for an spectrometer at the ISR, the Split-Field Magnet (SFM) [61].
All these chambers had a geometry for the sense wires and gap size similar to the
original design, shown in Fig. 4.18.
The SFM chambers of 2 × 1 m 2 contained three light support panels forming two
amplification gaps of 2 × 8 mm each, one with vertical, the other with horizontal
wires of 20 μm diameter. The cathodes on the panels were sprayed with silver paint
to provide readout strips 5.5 cm wide and at angles of ±30
◦ , to resolve ambiguities.
Special emphasis was put on high precision with a light construction, including
frames of only 5 mm thickness. A total thickness of 1.7% of a radiation length
H. J. Hilke and W. Riegler
of 40 μm carbon doped polyimide (Kapton-XC), the outer is a laminate of 25 μm
polyimide, to enhance the gas tightness, and 12.5 μm aluminum, to ensure fast
signal transmission and good shielding. The tubes are up to 2.5 m long and have the
25 μm wire supported every 80 cm.
Staggered double layers tubes are glued to light support panels to form modules
up to 5 m long. An average spatial resolution of a double layer below 200 μm was
measured with Ar/CO 2 (70/30%). In a station, 4 double layers are aligned along
0, + 5, − 5, 0
◦ , thus providing a crude second coordinate measurement.
In another design for ATLAS [15], mechanical strengthening of 4 mm straws is
achieved with carbon fibers wound around the tubes and straightness by supporting
them every 25 cm with alignment planes vertical to the straws. This construction
reduces the material along the radial tracks, which is essential for the role of the
straws to detect transition radiation originating in fibers stacked in between the
tube layers. This role also determines the need for Xe in a mixture of Xe/CO 2 /O 2
(70/27/3%), the oxygen addition increasing the safety margin against breakdown.
Another quasi-single wire design is that of plastic streamer tubes usually called
Iarocci tubes. Because they are easy to construct in large size and cheap, they have
been widely used, especially as readout planes in hadron calorimeters.
A plastic extrusion with an open profile with typically 8 cells of lxl cm 2 and a
PVC top plate, is coated on the inside with graphite with a minimum resistivity of
200 k/square. All this is slid into a plastic box, which serves also as gas container.
For stability, wires are held by plastic spacers every 50 cm. Using a thick wire
of 100 μm, self-quenching streamers are initiated in a gas containing a strong
quencher, typically isobutane in addition to Ar. Electrodes of any shape placed on
one or both external surfaces pick up the rather strong signals. The dead time is long
but only locally, so that particle rates up to 100 Hz/cm 2 can be handled.
4.3.2 Multiwire Proportional Chambers (MWPC)
Already 1 year after the invention of the multiwire proportional counter (MWPC)
by Charpak in 1968, a system of small chambers was used in an experiment [58],
another year later a large chamber 2 m × 0.5 m had been tested with Ar/Isobutane
[59]. A number of developments like bi-dimensional readout were discussed [60].
In 1973 already, a large system of MWPC containing 50,000 sense wires had been
constructed for an spectrometer at the ISR, the Split-Field Magnet (SFM) [61].
All these chambers had a geometry for the sense wires and gap size similar to the
original design, shown in Fig. 4.18.
The SFM chambers of 2 × 1 m 2 contained three light support panels forming two
amplification gaps of 2 × 8 mm each, one with vertical, the other with horizontal
wires of 20 μm diameter. The cathodes on the panels were sprayed with silver paint
to provide readout strips 5.5 cm wide and at angles of ±30
◦ , to resolve ambiguities.
Special emphasis was put on high precision with a light construction, including
frames of only 5 mm thickness. A total thickness of 1.7% of a radiation length