The CLAS12 Spectrometer at Jefferson Laboratory

The CEBAF Large Acceptance Spectrometer for operation at 12 GeV beam energy (CLAS12) in Hall B at Jefferson Laboratory is used to study electro-induced nuclear and hadronic reactions. This spectrometer provides efficient detection of charged and neutral particles over a large fraction of the full solid angle. CLAS12 has been part of the energy-doubling project of Jefferson Lab's Continuous Electron Beam Accelerator Facility, funded by the United States Department of Energy. An international collaboration of 48 institutions contributed to the design and construction of detector hardware, developed the software packages for the simulation of complex event patterns, and commissioned the detector systems. CLAS12 is based on a dual-magnet system with a superconducting torus magnet that provides a largely azimuthal field distribution that covers the forward polar angle range up to 35∘, and a solenoid magnet and detector covering the polar angles from 35° to 125° with full azimuthal coverage. Trajectory reconstruction in the forward direction using drift chambers and in the central direction using a vertex tracker results in momentum resolutions of <1% and <3%, respectively. Cherenkov counters, time-of-flight scintillators, and electromagnetic calorimeters provide good particle identification. Fast triggering and high data-acquisition rates allow operation at a luminosity of 1035 cm−2s−1. These capabilities are being used in a broad program to study the structure and interactions of nucleons, nuclei, and mesons, using polarized and unpolarized electron beams and targets for beam energies up to 11 GeV. This paper gives a general description of the design, construction, and performance of CLAS12

Direct three-dimensional microfabrication of hydrogels via two-photon lithography in aqueous solution

Hydrogels capable of releasing growth factors from very precise 3D structures to be placed on neural electrodes were microfabricated by two-photon lithography in aqueous solution. Hydrophobic chromophores with a large two-photon absorption cross section were solubilized using a nonionic surfactant and the resulting complex were applied with an oil soluble photoradical initiator to fabricate hydrogel microstructures. The results show that hydrogel microstructures are formed when the initiator 2,2-dimethoxy-2-phenyl acetophenone (Irgacure 651) and the 2-photon sensitive chromophore are present in the polymerizable mixture. The presence of water in the prepolymer solution helps in controlling important properties of the resulting structure such as modulus and the pore size which can be fine-tuned for its intended application