Solenoid Detectors
we're gonna need a bigger magnet!

Working Group Conveners

Ben Kay (ANL)


This long-running working group has focused on designing, constructing and utilizing a solenoidal spectrometer system for the measurement of reactions in inverse kinematics at FRIB. Their activities have culminated in the Solenoidal Spectrometer Apparatus for Reaction Studies, or SOLARIS. The group also explores opportunities and concepts to evolve the solenoidal spectrometer technique and discusses the status of the HELIOS spectrometer at Argonne National Laboratory (ANL) and the ISOLDE Solenoidal Spectrometer (ISS) at CERN.

A white paper on SOLARIS was published in 2017, proposing a dual-mode solenoidal spectrometer operating in a Si-array mode and an active target time projection chamber (AT-TPC) mode. The white paper detailed the outstanding physics opportunities made available by the coupling of SOLARIS and the ReA facility at FRIB, along with conceptual designs.

The main componentof the SOLARIS spectrometer is a 4 T superconducting solenoid. Such a magnet was acquired by Argonne prior to the start of the SOLARIS project. The magnet was cooled, tested, and moved to the ReA6 vault in 2019.

SOLARIS was funded by FRIB in 2020 and is currently under construction. Phase 1, which included all mechanical infrastructures, was completed in late 2022. SOLARIS operated in both AT-TPC mode and Si-array mode, using the HELIOS detector system, in 2021, using beams of long-lived radioisotopes provided by ReA in standalone mode. The first publications are in preparation.

SOLARIS builds upon the success of the HELIOS spectrometer at ANL, which celebrated 15 years of operation in August 2023. It has recently undergone an upgrade of the Si detector system and is now implemented with a digital data acquisition. A subset of the working group is also involved in the development of the ISS at the HIE-ISOLDE facility at CERN.

In 2023, the AT-TPC was used in HELIOS for a campaign of experiments, following an upgrade to the mechanical infastructure of HELIOS so it shares common features with SOLARIS.