Since the start of the project, a 2x2x2 prototype LISA array has been constructed, tested, and characterized in beam. This is the first implementation of a solid active target. The array of eight diamond detectors has been constructed from bare electronic grade chemical vapor deposition grown single crystals. After etching, electrodes were deposited, and the detectors were arranged in two layers, of each four detectors.
A dedicated vacuum chamber, signal feed-through, and precision motorized actuator system to position detectors has been designed, and except for the latter construction is finished. For the automatic positioning, the design is finished and components are ordered.
A data acquisition system has been set up. It consists of CSTA2 preamplifiers coupled to FEBEX digitizer cards. This combination gives excellent energy resolution, less than the 1% required by the physics program for the heaviest nuclei.
The detectors and the data acquisition system have undergone extensive testing with an alpha source, where an energy resolution of 0.7% was achieved.
In November and December of 2023, a single detector was tested with a heavy ion beam at GSI. The opportunity arose during the engineering accelerator beam-time and therefore compromises on the experimental setup and conditions (beam species and energy) had to be made. Nevertheless, important observations could be made. The energy loss of 238U fragments as well as fission products were identified with the diamond detector. The energy resolution allowed for unique identification of fragments over a large range of proton numbers.
The prototype was tested and characterized in a test experiment using a 132Xe beam at the HIMAC facility in January 2024. In this test, the first measurements of layer coincidences, particle identification in two layers, as well as first indications for reactions on the diamond detector itself were identified. The data analysis of both experiments has just begun.
In parallel, a GEANT4 based simulation framework is setup and first simulations are used to develop, test, and train the analysis based on neural networks. Accuracies of 90% have been reached and algorithm refinement is ongoing.
Three physics experiments devoted to study the evolution of collectivity and coherence in exotic nuclei have been conduced as preparatory studies for LISA.
