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 over 40 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 10 35 cm −2 s −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.
The Super High Momentum Spectrometer (SHMS) of Hall C, part of the 12 GeV Upgrade at Jefferson Lab, was successfully commissioned in 2017. Early operation shows that fast dumps of the SHMS Q2/Q3 and Dipole superconducting magnets triggered quenches, causing some level of operational difficulty. Tests and detailed analyses indicate that a fast discharge produces a fast current decay, which results in substantial AC loss in the conductor and subsequently triggers a quench-back effect. The OPERA/ELECTRA software package was used to calculate the amount of heat deposited in the copper stabilizer from a fast current decay. The magnets' external protection dump resistor values were lowered to slow the fast dumping of the magnet's current, which therefore reduces or eliminates the quench-back effects. A worst-case adiabatic quench scenario was analyzed, assuming no external dump resistor and no liquid helium surrounding the coil, to ensure the safety of the magnets. The stress levels in the coil imposed by winding, collaring preload, Lorentz force, and temperature gradient during a quench, were also examined. The Tsai-Wu material failure criterion was used to determine the acceptable combined stress level. Linear orthotropic analysis of the coil indicates that the magnets can be operated safely with appropriately sized dump resistors. Fast dump tests with the modified dump resistors have been planned to verify the performance and suitability. Index Terms-Magnet, fast discharge, superconducting, AC loss, quench-back, dump resistor, Tsai-Wu criterion I. INTRODUCTION Jefferson Lab's 11 GeV Super High Momentum Spectrometer (SHMS), consisting of Horizontal Bend (HB), Q1, Q2, Q3, and Dipole magnets has been commissioned successfully [1]-[5] with all magnets achieving the required 11 GeV specifications. Fig. 1 indicates the layout of all five superconducting magnets in experimental Hall C [5].Table 1 summarizes the key design parameters for the magnets. The magnet design employs 36-strand NbTi-Rutherford cable, originally manufactured for the dipoles of the now abandoned Superconducting Super Collider (SSC) [5]. The HB and Q1 used bare SSC cable while the Q2, Q3, and the Cos θ Dipole used copper stabilized SSC cable. During pre-commissioning, the HB experienced a series of training quenches, starting at 2640 A, before reaching 4000 A (3900 A is required for 11 The Manuscript received XXXXXX.
As part of the Jefferson Lab 12 GeV accelerator upgrade project, Hall B requires two conduction cooled superconducting magnets. One is a magnet system consisting of six superconducting trapezoidal racetrack-type coils assembled in a toroidal configuration and the second is an actively shielded solenoidal magnet system consisting of five coils. Both magnets are to be wound with Superconducting Super Collider-36 NbTi strand Rutherford cable soldered into a copper channel. This paper describes This paper describes a failure modes and effects analysis (FMEA) that was done on these magnets to identify their various failure modes, which were assessed in terms of their Risk Priority Numbers (RPN). Mitigating actions were identified that would reduce the RPNs to acceptable values.Index Terms-Conduction cooled, failure modes and effects analysis (FMEA), magnet quench protection, SSC-NbTi rutherford cable, superconducting magnet, torus.
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