CBM Progress Report 2006 - GSI

Detector Developments CBM Progress Report 2006
Development of straw tubes for high rate capability application ∗
K. Davkov 1 , V. Davkov 1 , J. Marzec 2 , V. Myalkovskiy 1 , L. Naumann 3 , V. Peshekhonov 1 ,
A. Savenkov 1 , D. Seliverstov 4 , V. Tikhomirov 5 , K. Viryasov 1 , P. Wintz 6 , K. Zaremba 1 , and I. Zhukov 1
1 JINR Dubna, Russia; 2 University of Technology, Warszaw, Poland; 3 FZ Dresden-Rossendorf, Germany; 4 Institut of
Nuclear Research, Gatchina, Russia; 5 Lebedev Institut, Moscow, Russia; 6 FZ Jülich, Germany
The construction of a large size straw tube particle tracking
detector for the Compressed Baryonic Matter Experiment
at FAIR is under consideration [1]. Drift chambers
on the basis of thin-walled drift tubes (straws) have been
widely used as tracking detectors in high rate environments
[2,3,4]. In the inner part of the first CBM tracker station the
expected hit density of charged particles for central Au+Au
collisions at 25 AGeV amounts to 0.05 /cm 2 . To guarantee
a sufficient efficiency of the tracking system, the occupancy
of a single drift tube element should be below five
percent and the active detector cross-section yields 1 cm 2
for the expected hit density. To realise small area drift detectors
long straw tubes with subdivided anodes of different
length have been developed. The readout of a section
should be independent of each other. Consequently it is
possible to reduce the active cross-section of a straw tube
to few cm 2 . The low-mass inner straw elements and the
technology of the multi-anode straw assembly have been
devised and checked. A prototype of 19 straws with 57
readout channels has been manufactured. The straws are
500 mm long and 4 mm in diameter. The anodes are subdivided
in two, three or four parts of different length. Fig. 1
shows a straw tube layout with four anode segments.
Figure 1: Schematical drawing of the straw tube design
with four anodes.
Different readouts have been tested. The front-end readout
of the outer anodes has been provided close to the endplugs.
For the inner sectors cables of 15 cm length connect
the anode wires with the front-end electronics. In the
threefold segmented anode the single glas joint has been removed
to investigate the double-sided readout. The current
sensitive preamplifiers with an input impedance of 300 Ω
are connected to the anodes by a capacitive coupling of
200 pF. Each anode has been supplied with high voltage
∗ Work supported by INTAS 03-54-5119
38
through a resistor of 1 MΩ. A gas mixture of Ar/CO2
(70/30) at atmospheric pressure has been supplied through
the two end-plugs of each straw. Collimated Gammas
( 55 Fe) irradiated the straws along the anodes with a width
of 1 mm perpendicular to the wires. Fig. 2 shows the anode
signal amplitude distribution in a threefold subdivided
wire. The collimator was moved along the straw. The information
from the inner sector is read out over the contact
wire fed through the spacer supporting the capillary tube
and the hole in the straw wall. To compare the signals going
through the straw wall and the end plug, the readout of
the right anode has a double-sided layout.
Figure 2: Amplitude distribution of the anode signals (A)
along the threefold subdivided straw of 500 mm length (L).
The result shows, that detector inefficiencies are only evident
in small regions of 7.2 mm length around the spacer
units. The straws work stably, no discharges were observed
between any construction elements placed inside
the straws. The radiation length of the spacer amounts to
0.4 %. For minimum ionizing particles the rate capability
amounts up to 4.5 MHz/cm 2 in single straws of 4 mm in
diameter with a gain of 5×10 4 [5].
References
[1] CBM Experiment, Techn. Status Report, GSI Darmstadt
(2005)
[2] Y. Arai et al., NIM A381 (1996) 355
[3] ATLAS Inner Tracker Design Report, CERN/LHCC/97-16
[4] V. Bytchkov et al., Particles a. Nuclei, Letters N.2 (2002) 75
[5] I. Zhukov et al., JINR Preprint P13-2005-126