Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 53

Development status of long data cable for sPHENIX-INTT detector
T. Hachiya,∗1,∗2 Y. Akiba,∗1 D. Cacace,∗3 K. Cheng,∗4 E. Desmond,∗3 S. Hasegawa,∗5 T. Kondo,∗6 C. Kuo,∗4M. Lenz,∗3 E. Mannel,∗3 C. Miraval,∗3 M. Morita,∗2 I. Nakagawa,∗1 R. Nouicer,∗3 R. Pisani,∗3 M. Shibata,∗2C. Shih,∗4 A. Suzuki,∗2 T. Todoroki,∗2 X. Wei,∗7 and R. Xiao∗7
The intermediate tracker (INTT) is a silicon strip
barrel detector for the sPHENIX experiment.1) INTT
requires a special extension cable for data transfer between the INTT module and readout electronics. The
data cable must satisfy the following requirements toﬁt the tight space available for INTT at the sPHENIX
detector: (1) ﬂexibility, (2) a very long length ofat least 120 cm, (3) high-density signal lines (128lines/5 cm width), and (4) high-speed signal transfer(by LVDS).2) The development of the cable is the mostchallenging part of the INTT project.
We performed research and development of the cable in the past two years. The design of the cable was
optimized using a signal-transfer simulation with thestrip-line structure. We then made a prototype of thecable using a ﬂexible printed circuit board (FPC) witha liquid crystal polymer (LCP) as the substrate. TheLCP realizes a small signal loss because of its small
dielectric constant. The electrical and mechanical performance of the prototype were tested.2) Based on thisknowledge, we made a 120-cm-long prototype cable.
We measured the eye diagram to study the transfer
performance of the cable. Figure 1 shows the input(left) and output (right) shapes of the eye diagrams.
The signal height is 30% attenuated, and the waveformis rounded. This change in waveform is consistent withthe expectation from simulation. We found that theeye is clearly open. To quantify the performance, wewill measure the bit error rate.
In June 2019, we performed a beam test with a
120 GeV proton beam at the Fermilab Test Beam Facility (FTBF). The performance of the INTT module
Input signal

Output from the data cable

Fig. 1. Eye diagram with (right) and without (left) thecable.
∗1∗2∗3∗4∗5∗6∗7RIKEN Nishina Center
Nara Women’s University
Brookhaven National Laboratory
National Central University
Japan Atomic Energy Agency
Tokyo Metropolitan Industrial Technology Research InstitutePurdue University- 120 -Sensors in a dark box

Readout Electronics

Long data cables

Fig. 2. Setup for testing the cable during the beam test atFTBF.

was evaluated in terms of the detection eﬃciency andminimum ionizing particle (MIP) peak.3) In addition,
the prototype cable was tested under a beam environment. The data were taken using the cable together
with the INTT module and, later, readout electronics. Figure 2 shows the test setup at the beam test.
The INTT modules are installed in a dark box, andthe readout electronics are placed. The cable, shownas an orange ﬂat cable that makes loops, is connectedto them. This was the ﬁrst attempt to take data withthe full readout chain of the INTT detector. Further
investigation is ongoing to quantify the performance
under the beam environment.
An issue was found in the production of throughholes on the cable. We found that the through holes
have nodules caused by the residue of the adhesive
sheet used to laminate the FPC layers. Several attempts to clean the through holes by changing the drill
process and desmear process were unsuccessful. We
will test new adhesive sheets from diﬀerent manufacturers. These sheets are suitable for LCP according tothe catalog.
In summary, the development of an extremely longand high-density cable is in progress. The production
version of the cable was made and tested under a beam
environment. An issue is under investigation. We will
test new adhesive sheets, and a new prototype will bemade using a new adhesive sheet and tested during thebeam test in May 2020.
References

1) I. Nakagawa et al., in this report.
2) T. Hachiya et al., RIKEN Accel. Prog. Rep. 52, 128 (2019).
3) A. Suzuki et al., in this report.