RIKEN Accel. Prog. Rep. 48 (2015)

Ⅱ-9. Instrumentation

Status of SπRIT-TPC
M. Kurata-Nishimura,∗1 R. Shane,∗2 A. McIntosh,∗3 T. Isobe,∗1 J. Barney,∗2 J. Estee,∗2 G. Jhang,∗1∗4W. Powell,∗5 W.G. Lynch,∗2 M.B. Tsang,∗2 T. Murakami,∗6 S. Tangwancharoen,∗2 S.J. Yennello ,∗3for SπRIT-TPC collaboration
The SAMURAI Pion-Reconstruction and IonTracker Time-Projection Chamber (SπRIT-TPC)1)
was constructed at Michigan State University andtransferred to RIKEN RIBF-SAMURAI in February
2014. The main aim of this project is to constrainthe symmetry energy term in the nuclear-matter equation of state (EoS) at supra-saturation density. TheSπRIT-TPC is capable measuring the momentum ofpions and light particles emitted in heavy nuclear collisions, such as 132 Sn + 112 Sn at beam energies of hundreds of MeV/nucleon.
In summer 2014, an installation procedure for theSπRIT-TPC into the SAMURAI magnet chamber wasdeveloped and verified. The SπRIT-TPC is designed
to maximize the coverage in the SAMURAI magnetchamber. The internal height of SAMURAI chamber isdesigned to be 800 mm. Bolts, covered by 25 mm highcaps, surround the magnet pole on top and bottom toprevent the chamber from crushing due to the pressure
difference when the chamber is under vacuum. On theother hand, the design height of the SπRIT-TPC is742 mm and thus there is a very small margin of error
for installing it into the SAMURAI chamber. Thus
the confirmation of the installation is one of the mostimportant issues in this project. Also confirmation ofsafe operation in the magnetic field is critical.
The setup for installation of the SπRIT-TPC in thechamber is shown in Fig.1. In this figure, the SAMURAI magnet was oriented at 30 degrees, it is most common experimental configuration. However, the SpiRIT
TPC was designed to sit inside the SAMURAI magnet
chamber when it is oriented at zero degree. To test
the installation procedure without expending a lot ofresources to reconfigure the SAMURAI magnet, theSπRIT-TPC was inserted from one half side of theexit window with the oblique angle. Rails placed in
the chamber extended toward the downstream window where additional rails were located on tables. TheSπRIT-TPC was set on a slider which moves along
rails with negligible friction. It was able to be pushed
and pulled in the chamber using dual hydraulic jacks.
When the SπRIT-TPC was installed inside the chamber, it was raised up about 25 mm to the beam height.
Installing and dismounting the SπRIT-TPC was com∗1
∗2

∗3
∗4
∗5
∗6RIKEN Nishina Center
National Superconducting Cyclotron Laboratory and Department of Physics and Astronomy, Michigan State University
Cyclotron Institute, Texas A&M University
Department of Physics, Korea Universtiy
Department of Physics, University of Liverpool
Department of Physics, Kyoto University

pleted in about 20 minutes.
An operational test in the magnetic field was also
performed. Before hand, all magnetic material itemson the SπRIT-TPC were removed. The read out
electronics described in Ref.2) were set up. Finally,
charged particle tracks of cosmic rays and beta source
were detected in a magnetic field ranging from 0.1 to0.5 T. Figure 2 shows a part of a helical track produced
by a cosmic ray was observed within the detection area
read out by one AsAd electronics board.
Furthermore, a remote controlled target ladder wasmounted inside the TPC-enclosure. The target position is determined by reading the voltage drop between
the fixed and movable contacts on a resistive strip.
The overall geometry and position of the field cage
and the target ladder relative to the enclosure were
measured using photogrammetry2) . The deviationfrom the design value was evaluated as less than 200µm.
In summary, significant progress on the preparation
for the SπRIT-TPC experiment has been achieved.

Fig. 1. Picture of the SπRIT-TPC inserted into the SAMURAI chamber. Left top: picture in the chamber. Leftbottom: schematic view of the installation method.

Fig. 2. Event display for a cosmic ray detected by theSπRIT-TPC in the SAMURAI magnet at 0.3 T. Enlarged view of the track is on the right.

References
1) R. Shane at al.: Nucl. Instr. Meth. A 784 (2015) 513.
2) http://www.geodetic.com/products/systems/v-stars-s.aspx
3) T. Isobe et al.: in this report.

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