From November 16 to 27, 2020, a prototype of the ALERT drift chamber was characterized in beam at ALTO. This was the first experience on the ALTO platform since its re-launch. Thanks to the combined efforts of the ALERT and ALTO teams at IJCLab, more than 11.5 million events were recorded during these two weeks. ALERT will be the central tracker for the CLAS12 experiment in Hall B of Jefferson Lab in Virginia (United States). Its detectors will be tasked with tracing and identifying recoil nuclei whose mass is between that of the proton and that of the alpha. The energies will be from a few MeV to several tens of MeV. To best meet these requirements, the ALERT detector is composed of a drift chamber entirely designed by IJCLab and scintillators designed by Argonne National Laboratory. The design of the drift chamber is demanding, combining for the first time several delicate technologies. The chamber will be equipped with 3,000 aluminum wires spaced only 2 millimeters apart at an angle of 20 degrees.
After several tests, a first prototype was assembled with 100 threads thanks to a work of goldsmith then tested on ALTO. The ALTO facility was ideal for this characterization. Under conditions almost identical to those which will prevail during the experiment at the Jefferson Lab, it indeed received beams of protons and alphas ranging between 6 MeV and 18 MeV. Throughout the testing period, the detector's behavior met expectations perfectly. The data analyzes will make it possible to determine the resolutions in energy and in resolution as well as the efficiency of the chamber according to the type of particles, the energy and the parameters of the electronics. These studies will help IJCLab members participating in ALERT to improve the design and performance of this detector.
View of the wire chamber in the gas chamber during tests at ALTO. The wires are visible in the center in the top first quarter of the photo. The rest is hidden by a silicon detector used as an external trigger.