The muon tracking system for the PHENIX detector at RHIC uses cathode strip chambers (CSC) for the tracking detectors. These detectors must provide 100 μm resolution per measurement plane to give satisfactory mass resolution of the vector mesons. The intermediate station (station 2) must have a very small radiation length, and large acceptance. We have prototyped a full scale CSC chamber to test the use of 25 micron metalized mylar foils for the cathode strips at station 2. The full scale prototype detector is a trapezoid 2.3 meters high and 2.3 meters wide. The foil and wire planes are mounted on thin 3,2 mm thick by 7.5 cm wide laminated frames and the tension of the planes is maintained by the two large 7.5 cm widex3.0 cm thick aluminum support frames. The total radiation length of the active region is 8.5x104

Armijo, V.

Atencio, L.

Brooks, M. L.

Chen, Z.

Clark, D.

Dinesh, B. V.

Fields, Douglas E.

Hart, G.

Kinnison, W. W.

Lee, D. M.

Matousek, H.

Morris, C.

Murray, M. M.

Sondheim, W.

Wang, Y.

Wang, Z.

English

University of New Mexico

University of New Mexico
UNM Digital Repository
Physics & Astronomy Faculty and Staff Publications Scholarly Communication - Departments
11-2-1996
Large CSC chamber for the PHENIX muon
detector with ultra thin cathode foils
Douglas E. Fields
D. M. Lee
V. Armijo
L. Atencio
M. L. Brooks
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Recommended Citation
Fields, Douglas E.; D. M. Lee; V. Armijo; L. Atencio; M. L. Brooks; D. Clark; Z. Chen; B. V. Dinesh; W. W. Kinnison; G. Hart; H.
Matousek; C. Morris; M. M. Murray; W. Sondheim; Y. Wang; and Z. Wang. "Large CSC chamber for the PHENIX muon detector
with ultra thin cathode foils." (1996): 274-278. doi:10.1109/NSSMIC.1996.590958.
Authors
Douglas E. Fields, D. M. Lee, V. Armijo, L. Atencio, M. L. Brooks, D. Clark, Z. Chen, B. V. Dinesh, W. W.
Kinnison, G. Hart, H. Matousek, C. Morris, M. M. Murray, W. Sondheim, Y. Wang, and Z. Wang
This article is available at UNM Digital Repository: https://digitalrepository.unm.edu/phyc_fsp/10
Large CSC Chamber for the PHENIX Muon Detector with Ultra Thin Cathode Foils1 
D.M.Lee2, V.Armijo2, L.Atencio2, M.L.Brooks2, D.Clark2, Z.Chen2, B.V.Dinesh3, D.E.Fields4, 
W.W.knnison2, G.1Hart2, H. Matousek2, C.Morris2, M.M.Murray2, 
W.Sondheim2, Y .Wang5, 2. WangS 
2. Los Alamos National Lab, P.O.Box 1663, Los Alamos, NM 87545 
3. Bhabhar Atomic Research Center, Bombay, In&a 
4. University of New Mexico, Albuquerque, NM 
5. Louisiana State University, Baton Rouge, LA 
Abstract 
The muon tracking system for the PHENUC detector at 
RHIC uses cathode strip chambers(CSC) for the tracking 
detectors. These detectors must provide 100 pm resolution 
per measurement plane to give satisfactory mass resolution 
of the vector mesons. The intermediate station (station 2) 
must have a very small radiation length, and large 
acceptance, We have prototyped a full scale ClSC chamber 
to test the use of 25 micron metalized mylar foils for the 
cathode strips at station 2. The full scale prototype detector 
is a trapezoid, 2.3 meters high and 2.3 meters wide. The foil 
and wire planes are mounted on thin 3.2 mm thick by 7.5 
cm wide laminated frames and the tension of the planes is 
maintained by the two large 7.5cm wide x 3.0 cm thick 
aluminum support frames. The total radiation length of the 
active region is 8.5 x 10'. 
I. INTRODUCTION 
The primary physics goals of the P H E W  Muon 
Spectrometers are to contribute to both the Relativistic 
Heavy Ion Program and to the Spin Physics Program at 
RHIC. The physics requirements have led the muon 
subsystem to choose as the baseline detectors for the 
spectrometers, the cathode strip chamber (CSC) technology. 
The PHENIX muon spectrometers are radial field magnets 
with three detector stations along the axial length at 
approximate locations of 200cm, 350cm, and 600cm. One 
of the PHENK muon spectrometers is shown in Figure 1. 
The spectrometer magnets are eight sided polygons with 
a central piston that is the return yoke and holds the two 
magnet coils. The acceptance for the North Malgnet starts at 
10 degrees at the piston and extends to 37 degrees at the 
outer octogon surface. The physics acceptance is defined to 
be 10 deg to 35 deg. The magnet extends from 200 cm to 
660 cm from the vertex . At 15 deg the field integral is 
0.7 10 tesla-meters. 
&uh"L 1% bv fie US D e D m  
W-7405. 
274 
0-7803-3534-1/97 10.0001 997IEEE 
Figure 1. PHENM North Muon Arm Spectrometer 
Because of the need to maintain good momentum 
resolution down to 1.5 GeV, the second detector station has 
to have as small a radiation length as possible to minimize 
multiple scattering. To Be able to separate the Y and the Y 
vector mesons, three CSC detectors with 100 p resolution 
at each detector station were required to give a momentum 
resolution of 200 MeV. The requirements of good resolution 
and low radiation length led to the adoption of thin copper 
metalized mylar foils as the cathode strip structure for 
station 2 rather than the more conventional etched cathode 
printed circuit boards. The mylar foils are 25 p thick 
with 600 angstroms of copper on one side. A large etching 
table was constructed to handle the large foils. The 100 pm 
detector resolution and 58 pn station resolution require 
precisely constructed chambers, frames and support 
structures that are designed to be insensitive to 
environmental vibrational forces. The goals of the 
construction program are to maintain assembly tolerances 
and vibrational tolerances to less than 25 pm. 
II. Station 2 Mechanical Design 
A. Station 2 Octant Assembly 
The station 2 octant detector assembly is shown in 
Figure 2. A cross section of the CSC octant assembly is 
shown in Figure 3. The station 2 design is a laminated 
structure of thin frames for the wire and foil planes and two 
thick aluminum support frames. Each assembly contains 
three CSC detectors. The total cathode to cathode gap is 
6.35 mm for each CSC detector. The anode plane is an 
alternating structure of 20 pn gold plated tungsten sense 
wires and 75 pn CuBe field wires with the sense wire 
spacing of 10 mm. The anode wires follow the chord in 
each 22.5 degree segment. 
Figure 2. Station 2 octant detector assembly 
I 1 .ae+I-a.23- 
' - - ! !  
LAYER 
I I I I  I 
Figure 3. Cross section of the station 2 octant assembly 
pm. The 5mm wide spoke is constructed to fom a 
laminate with one piece grooved to define the the anode-to- 
275 
is held fixed in an aluminum channel. The CSC chamber 
frames are held rigid and in proper shape and tension by 2 
aluminum support frames which are 3 cm thick and 7.5 cm 
wide. Nine alignment pins, 3 on each long edge properly 
locate the thin frames during the assembly process. A 
single support frame is used during the etching and wiring 
process to pin the thin chamber planes to insure proper 
tension. A number of detailed finite element calulations 
were performed to verify this design. 
B. Station 2 Mounting Structure 
define the natural frequencies of vibration and the static 
distortions due to gravity. The maximum static distortions 
due to gravity is 0.362 mm, less than the frame alone 
indicating that the chamber frames provide structural 
rigidity. The alignment system will be used to correct for 
distortions due to gravity and temperature. 
Vibrations due to ground motion coupling into the 
station 2 assembly require a knowledge of the natural 
frequencies of the structure. The natural frequency modes 
are shown in Table 1. 
Table 1 
The mounting structure for the station 2 octants in the 
magnet must hold the octants rigidly to 25 p over the 
environmental forces could move the chambers. The 
mounting structure is shown in Figure 4. Freq( Hz) 7.9 12.4 16.6 25.5 27.9 
Station 2 natural frequencies 
short period of time (< 15 min) when vibrational and ~ 1 2 3 4 5 
le M -- 
Figure 4. Station 2 Mounting structure, front view. 
It consists of stainless steel tubing, rectangular in shape, 
on the front and back of the octants with a truss structure at 
the top and mounting ring at the inner radius. The 
mounting ring does not come in contact with magnet piston. 
The mounting structure is mounted to the magnet at four 
points at the bottom of the magnet and at four points at the 
top, The mounting structure and therefore the chamber 
octants are electrically isolated from the magnet. The 
mounting structure design criteria was to have vibrations 
from natural frequencies less than 25 p. Static distortions 
due to gravity, thermal, and magnetic effects were 
minimized but allowed. The active alignment system is 
designed to account for static distortions. An analytic 
calculation of the weight and maximum distortions of the 
space frame were carried out for a variety of tubing sizes 
and for stainless steel and aluminum. The results pointed to 
stainless steel with a cross section of 7.5 cm x 5.0 cm x 
0.3175 cm wall as an acceptable material. The maximum 
displacement under gravity load is 0.399 mm. A finite 
element analysis of the mounting structure with the octants 
in place was carried out with the program COSMOSM to 
The first three modes correspond to displacements in the 
z direction. The fourth and fifth modes are displacements in 
the phi and r direction and therefore are of greatest concern. 
To determine the maxi" displacements expected from 
these and all frequency modes, a dynamic analysis was done 
using the finite element analysis program ABAQUS. The 
excitation to the station 2 structure was based on 
measurements made at four laboratory facilities [2]. It was 
considered roughly typical of what one would expect at the 
PHENIX facility. No site specific ground motion 
measurements have been made and the excitation function 
does not represent vibrational forces that could be generated 
by equipment ( e.g. vacuum pumps,etc.) attached directly to 
the magnet. In the calculation, the sagitta error was 
determined under the assumption that stations 1 and 3 are 
fixed. The frequency analysis for the magnet suggests that 
motion in the x and y coordinates of stations 1 and 3 is 
negligable owing to the large massive back plate and tea 
cup to which they are attached. The response power 
spectral density for x and y components of the sagitta at the 
node at the top of the frame is shown in Figure 5. 
This no& corresponds to the vertical frame of the 
octant at the top of the magnet at the 12:OO o'clock location. 
The peaks in the spectrum correspond to the frequencies 
where the coupling is the largest. The z component is added 
for reference but does not effect the sagitta. The largest x 
component of the sagitta rms response is 0.17 p. The 
largest Y component of the rms response is 0.11 pm and 
occurs at the horizontal frame of the octant on the side of 
the magnet at the 3:OO o'clock location. The largest Z 
component of the rms motion relative to the base is 1.1 p 
at the horizontal member on the top of the octant at the top 
of the magnet. The results show that the largest sagitta error 
introduced because of ground motion is approximately 0.2 
p. We expect to measure the ground motion at the 
PHENIX site and redo this calculation but the results 
indicate that we have two orders of magnitude margin 
before ground motion becomes a problem. 
276 
1 0  - 2  
10 -’ I 1 1 1 1 1 1 1 1  I I I I I I l l !  
10 * l o 1  10 10’ 
FREQUENCY 
Figurc 5. Power Spectral Density sagitta response for x 
and y directions at the top of the frame 
C. Foil Etcher 
A technique to etch the thin mylar foil has been 
developed that allows the etching process to be done on the 
foil after the foil has been stretched on the support frame. 
This process involves electroetching the copper coated 
1 ‘-i 1 
frame distortion occurs when all of the foils and wires are in 
place the cathode strips will be positioned correctly. 
Creep of mylar foils occurs in the fiist few days after 
stretching. Experience with full size stretched mylar foils 
have shown no unacceptable loss in foil tension due to 
creep over 6 months. Previously stretched 1 meter foils 
have shown no loss in tension over 4 years. Our experience 
has shown relaxation appears not to be a problem. 
The alignment of the etcher lead screws to the structural 
frame via the 9 alignment pins is fist determined [l] and a 
file is produced that includes the alignment information and 
lists the location of all the strips, For each strip the pen is 
moved in the up position to the beginning of the strip to be 
etched, lowered to the foil, moved to the end of the strip,and 
then raised to the up position, ready to be moved to the next 
strip. This process is repeated for each strip to be etched. 
The pen is moved at the rate of -100cdmin. At each move 
the computer incorporates a search procedure to locate the 
lead screws and remove any backlash. We rely on the linear 
optical encoders rather than the stepping motors to locate 
the actuators. The quality of the etch depends on the pen 
voltage and the speed of pen motion as well as the presence 
of an insulating gas. The quality of the etched line was 
investigated by varying the voltage between 12 and 30 volts 
DC and the speed of the pen. The optimum was achieved 
for 16 volts and a pen speed of 100 cdmin. We have used 
nitrogen as the insulating gas. The etcher head is shown in 
Figure 7. The etcher head holds the pen which is controlled 
by a solenoid, the nitrogen gas nozzle, and the alignment 
telescope. An example of the etched line is shown in Figure 
8. The width of the etched line is approximately 250 
microns. The line width increases with the applied voltage 
and the edge definition worsens with increased voltage. 
I I 
Figure 6. Etching setup for etching stretched cathode 
mylar foils in the presence of an insulating gas with a probe 
tip attached to a low voltage source. The tip is mounted on a 
computer controlled x-y table and positioned with an 
accuracy of 10 pm by a linear slide. A drawing of this setup 
is shown in Figure 6. 
The high resolution cathode foil is prestressed on the 
support frame during the etching process so that when the 
Figure 7. The etcher head with the etcher pen on the right and the 
alignment telescope on the left. 
277 
Figure 8. TV image of etched line. 
D. Anode Wire Stringing and Tensioning 
All of the anode wires were stretched and attached by 
hand. A support frame held the wire frame in position and 
prevented distortion of the frame due the wire load. The 
central support spoke was held fixed by a metal groove. 
The wires were located by precision combs and tensioned 
by hanging weights. Before soldering, the tension of each 
wire was measured by a simple tension measuring device to 
insure any friction in the spoke or frame did not alter the 
tension of the wire. The tension measuring procedure 
consisted of inducing a standing wave in the wire by passing 
an alternating current through the wire in the presence of a 
magnetic field. A capacitive pickup sensed the oscillation. 
The correct frequency was observed by looking at Lissigous 
figures on an xy oscilloscope. 
Figure 9. 
support Game. 
A rate of 200 wires per day were soldered and measured. 
A more automated procedure for stringing the wires is being 
studied. Removing the completed anode plane from the 
wiring table required a transfer support frame to keep the 
wires under modest tension so that during transfer the wires 
did not wrap around adjacent wires. No problem was 
encountered because of the support spoke. 
A completed wire plane with spoke attached to the 
111. ASSEMBLY AND TESTING 
The anode and cathode planes were assembled with the 
sutructural frames to complete one CSC detector. No 
problems were encountered in the assembly process. The 
completed assembly is shown in Figure 10. Clearly visible 
are the 9 alignment pins that hold the thin foil and wire 
planes. The gas window visible is single sided 25 pm 
aluminized mylar. Also visible is the support tie bar that 
aids in maintaining the shape of the side members. The 
maximum deflection of the side bars is 30 pm. 
Figure 10. Complete CSC chamber assembly. 
A. Preliminary Testing 
The detector assembly was connected to an argon- 
isobutane ( 70:30) gas system and brought up to 1900 volts. 
Leakage currents were less than 30 nanoamps for the entire 
chamber. We connected a 16 channel section of the 
cathode strips to a transimpedence amplifier with a transfer 
gain of 0.3 volts/pAmp and observed signals reaching 500 
mVolts with noise levels < 2 mvolts. These are fast 
amplifiers and are not optimized for the CSC chamber. 
Tests are now underway to measure the the efficiency 
plateau and resolutions and uniformity across the chamber. 
When better electronics become available the final 
resolution measurements will begin. Preliminary results 
indicate that the resolution without adequate calibration and 
amplifiers is e 130 p. We find this very encouraging and 
expect these chambers to reach the design goal of 100 pm. 
IV. REFERENCES 
[l] M.L.Brooks, D.M.Lee, W.E.Sondheim, “Alignment 
System for the PHENIX Muon Tracking Chambers”, 
this conference proceedings. 
121 Sawicki, R, Lawrence Livermore Laboratory Report, 
LLNL-93-260.1993 
278 


Large CSC chamber for the PHENIX muon detector with ultra thin cathode foils

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Large CSC chamber for the PHENIX muon detector with ultra thin cathode foils

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