In 2015, 3 R&D projects have been funded by P2IO: the DRUM project, the 511 keV gamma detector project with high temporal resolution and the nuclear fragment detector project for CLAS 12.
Nuclear fragments detector for CLAS12
R. Dupré (IPNO), D. Attié (Irdu/DEDIP)
The "Nuclear Fragment Detector for CLAS12" project aimed to finalize the R&D for a drift detector to be installed at the Jefferson Laboratory (USA) in the CLAS12 experiment. In this project, the team focused on two issues: the possibility of placing wires every two millimeters in the full volume of the detector and the possibility of using alternative lighter materials for the wires, especially carbon.
On the subject of high wire density, two main issues were addressed: the method of wire attachment and mechanical strength. There are indeed several methods for attaching wires in drift chambers (soldered, glued or crimped), these methods being themselves variable with different types of solders, glues and crimps. These methods have been tested on different types of carbon, aluminum and gold tungsten wires to determine the best possible fastening methods. This, always with the important space constraint related to the high density of detector wires. As each wire has a tension ranging from a few grams to a few tens of grams, the cumulative stresses on the chamber structure are important and have also led to work to determine the best possible geometry and the best materials to use.
A simple prototype was built and tested and allowed to fully validate the possibility of using carbon wires from an instrumental point of view (G. Charles et al. Nucl. Instrum. Meth. A855 (2017) 154). In addition, as an extension of the project, the study of certain types of lightly resistant carbon wires offers prospects for certain applications that are now being researched in the IJCLab laboratory. Nevertheless, mechanical constraints related to the brittleness of the wires during handling remain a major concern for the use of carbon wires in large detectors.
Finally, this project has been the occasion of collaborations between IJCLab and CEA for the use of the DREAM chip for reading wire chambers. The use of this chip, previously used for micromegas detectors, has proved to be a success and has enabled a test bench to be set up for a succession of prototypes tested at IJCLab within the framework of the project and beyond. In addition, the R&D developed during the project was largely responsible for the European PartonicNucleus project (ERC starting grant) which includes funding for the construction of the complete detector.
In conclusion, the project has been a success and has resolved several critical R&D issues, published an article on the use of carbon wires in drift chambers, improved collaboration between IJCLab and CEA on gas detectors, and initiated significant funding for the construction of the complete detector within the LabEx P2IO.
511 keV gamma detector with High Time resolution
D. Breton (LAL), V. Sharyy (Irfu/DPhP)
In this project, the possibility of using a Cherenkov light for efficient detection of 511 keV photons was investigated. The goal is to use it for Time of Flight (TOF) Positron Emission Tomography (PET). Indeed, PET scanners are widely used for research in oncology and neurobiology and using improved detectors with TOF capabilities would allow to drastically reduce the dose received by the patient.
In this study, the researchers explored the possibility of creating a large Cherenkov detector module using a PbF2 crystal coupled with a commercial microchannel disk photomultiplier with very good detection efficiency, compatible with the use of a PET scanner. Two detection modules have been developed and tested: the 32 signals from each detector are read by the SAMPIC fast digitizing module, developed in collaboration between LAL, IN2P3, CNRS and CEA's Irfu.
This module measures the shape of each signal and determines the time signal with a precision of 5 ps. Using a 22Na radioactive source, the detection efficiency of the 511 keV photons is measured at 24% and a coincidence resolution time between two detectors of 280 ps. Several factors limiting the temporal resolution of the module's large detection area have been identified, thus limiting the interest of its use in the PET scanner. Appropriate solutions to improve the technique have been proposed and are currently being tested.
Bibliography :
The DRUM project
C. Bruni (LAL)
The DRUM project aims to generate ultrashort packets with LASERIX, an essential step for the proper functioning of the ESCULAP project.
The ESCULAP project is a continuation of the reflection carried out since the 1990s by part of the scientific community on the possibility of injecting electron packets from a photo-injector into a plasma wake wave created by a laser, in order to be able to combine the optimal characteristics of the beam from the accelerator with the strong gradients and femtosecond pulse duration available with laser plasma acceleration. The aim of the project, through the control of ultrashort electron packets with high peak currents, as well as that of the optimisation parameters of the plasma accelerator, is to be able to respond to the demand of the "accelerator" and "power laser" communities for the development of new electron acceleration solutions, as well as new means for characterising them.
The production of short packets of electrons by femtosecond irradiation of the PHIL photocathode was made possible in part by the DRUM project. The device consists of using a 3 mJ leak at 10 Hz, stretched to 500 ps, which is sent to an optical table as close as possible to the photocathode. This optical table is used initially to house the pulse compressor, which allows an ultimate duration of 30 fs to be achieved in the infrared, and the frequency tripler, which allows pulses to be generated in the ultraviolet with an estimated duration of 100 fs.