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The Spin Physics Detector (SPD) at the NICA collider at JINR is being developed to study the nucleon spin structure. Polarized proton and deuteron beams will collide at center-of-mass energies up to 27 GeV in proton-proton collision mode, with the instantaneous luminosity up to 10³² cm⁻²s⁻¹. Tracks of charged particles will be measured in the magnetic field of a superconducting magnet using a straw tube tracking system. In addition to the coordinate measurements, the tracker will be used as a part of the particle identification (PID) system by registering ionization losses (dE/dx) for low momentum particles.
The barrel part of the tracker will consist of thin-wall tubes manufactured by ultrasonic welding of metallized polyethylene terephthalate (PET) film. The straws have the diameter of 1 cm and will be assembled into self-supporting octants, each containing 31 double layers, resulting in a total of approximately 25,000 readout channels. The readout electronics is being developed aiming the high spacial resolution of the tracker along with accurate measurements of ionization energy losses.
Ultrasonic welding technology is an alternative to traditional winding approach and has recently achieved the required level of quality. The key advantage of welded straws is their high elasticity, which makes it possible to create large tracking systems without additional reinforcing elements (as, for example, in ATLAS TRT) or complex load-bearing structures (as in the PANDA project). In trackers made of welded straw, the precise straw positioning is ensured by self-supporting of inflated straws filling a limited tracker envelop
Successful experience of the NA62 experiment (CERN) which operates in vacuum a large-scale tracker made of welded straws, confirms the high reliability and stability of this technology. Together with continuous enhancement of the straw welding process and quality control methods, the NA62 experience makes the straw welding technology attractive for future experiments such as SHiP, DUNE, FCCee and, particularly, SPD.
This report presents specific features of the straw production using ultrasonic welding, compares requirements for straw trackers in a number of future experiments, and showcases first prototypes of the SPD barrel tracker. In addition, possible concepts of the tracker readout electronics are discussed, and results of straw response simulation studies are compared to test beams measurements.
