Eric Sun

Design of the Super Conducting Super High Momentum Spectrometer (SHMS) for the JLAB 12 GeV Upgrade

The 12 GeV Upgrade at Jefferson Lab requires a new particle spectrometer for precision Nuclear Physics studies at the highest electron momentum available. This new spectrometer the Super High Momentum Spectrometer (SHMS) operating at 11 GeV/c will be built in Hall C to work in coincidence with the present device, the 7.5 GeV/c High Momentum Spectrometer (HMS). The SHMS design requires five new SC magnets arranged as dipole, quad, quad, quad, dipole or dQQQD. The ldquodrdquo is a small 3.1 T, SC dipole providing an initial 3.5 degree bend which allows the SHMS to reach a 5.5 degree scattering angle and provide enough clearance for the other much larger magnets of the SHMS. The first SC quad is an upgraded version of the HMS Q1 quad running at 10.7 T/m in a 40 cm warm bore with a 1.86 m EFL. The second and third quads are a pair of a completely new design, 60 cm warm bore, 14.4 T/m, 1.6 m EFL cosine2Theta SC quadrupole. Finally, the main dipole is a 60 cm warm bore 4.5 T, 2.85 m EFL magnet that provides the momentum analysis for the SHMS. This project is on schedule for the start of commercial procurement beginning in FY2009 to support start of Physics with the SHMS in 2014. The final design details of these four unique magnets will be presented including the coil design, magnetic design, force collar, and cryostat.

JLAB's Super High Momentum Spectrometer's Superconducting Q1 Magnet

The commissioning and test results of a superferric superconducting quadrupole magnet constructed by Scientific Magnetics, Inc., for Thomas Jefferson National Accelerator Facility (TJNAF also known as JLAB) will be presented. The quadrupole magnet, named Q1, is the first focusing element in the Super High Momentum Spectrometer (SHMS). The SHMS, which is located within JLABs experimental Hall C, consists of all superconducting magnets in a dQQQD configuration and is part of the JLABs 12-GeV upgrade. Here, “d” refers to the small horizontal bend dipole, “Q” stands for focusing quadrupole magnets, and “D” is the vertical-bending momentum-selecting dipole magnet. Characterization of the magnets cryogenic heat loads and magnetic field quality will be presented along with descriptions of the magnets control system, power supply, and quench detection system.

Structural Analysis of the SHMS Cosine Theta Superconducting Dipole Force Collar

Jefferson Laboratory is developing a set of innovative superconducting magnets for the 12 GeV upgrade in JLAB Hall C. We will report on the finite element analysis (FEA) of the force collar for the Super High Momentum Spectrometer Cosine Theta Dipole magnet. The force collar is designed with an interference fit and intended to provide enough pressure after cool down to operating temperature to counteract Lorentz forces acting on the dipole coil during operation. By counteracting the Lorentz forces and keeping the coil pack in overall compression, movement of the coils is expected to be minimized. The dimensional geometry of the cold mass is maintained in the commercial solid modeling code UG/I-DEAS while the magnetic field design is maintained in the commercial TOSCA code from Vector Fields. The three dimensional FEA was conducted in the commercial codes ANSYS and IDEAS. The method for converting the models and calculating the loads transferred to the structure is discussed. The results show the cold mass response to: force collar assembly preload, differential thermal contraction, and operational Lorentz loads. Evaluations are made for two candidate force collar materials and two candidate force collar designs.

Design and Fabrication of the Superconducting Horizontal Bend Magnet for the Super High Momentum Spectrometer at Jefferson Lab

A collaboration exists between NSCL and JLab to design and build JLabs Super High Momentum Spectrometer (SHMS) horizontal bend magnet that allows the bending of the 12 GeV/c particles horizontally by 3° to allow SHMS to reach angles as low as 5.5°. Two full size coils have been wound and are cold tested for both magnetic and structural properties. Each coil is built from 90 layers of single-turn SSC outer conductor cable. An initial test coil with one third the turns was fabricated to demonstrate that the unique saddle shape with fully contoured ends could be wound with Rutherford superconducting cable. Learned lessons during the trial winding were integrated into the two complete full-scale coils that are now installed in the helium vessel. The fabrication of the iron yoke, cold mass, and thermal shield is complete, and assembly of the vacuum vessel is in progress. This paper presents the process and progress along with the modified magnet design to reduce the fringe field in the primary beam region and also includes the impact of the changes on coil forces and coil restraint system.

Coupled Transient Finite Element Simulation of Quench in Jefferson Lab's 11 GeV Super High Momentum Spectrometer Superconducting Magnets

This paper presents coupled transient thermal and electromagnetic finite element analysis of quench in the Q2, Q3, and dipole superconducting magnets using Vector Fields Quench code. Detailed temperature distribution within coils and aluminum force collars were computed at each time step. Both normal (quench with dump resistor) and worst-case (quench without dump resistor) scenarios were simulated to investigate the maximum temperatures. Two simulation methods were utilized, and their algorithms, implementation, advantages, and disadvantages are discussed. The first method simulated the coil using nonlinear transient thermal analysis directly linked with the transient circuit analysis. It was faster because only the coil was meshed and no eddy current was modeled. The second method simulated the whole magnet including the coil, the force collar, and the iron yoke. It coupled thermal analysis with transient electromagnetic field analysis which modeled electromagnetic fields including eddy currents within the force collar. Since eddy currents and temperature in the force collars were calculated in various configurations, segmentation of the force collars was optimized under the condition of fast discharge.

The Superconducting Horizontal Bend Magnet for the Jefferson Lab's 11 GeV/c Super High Momentum Spectrometer

A collaboration between NSCL and Jlab has developed the reference design and coil winding for Jlabs Super High Momentum Spectrometer (SHMS) horizontal bend magnet. A warm iron ¿C¿ type superferric dipole magnet will bend the 12 GeV/c particles horizontally by 3° to allow the SHMS to reach angles as low as 5.5°. This requires an integral field strength of up to 2.1 T.m. The major challenges are the tight geometry, high and unbalanced forces and a required low fringe field in primary beam path. A coil design based on flattened SSC Rutherford cable that provides a large current margin and commercially available fiberglass prepreg epoxy tape has been developed. A complete test coil has been wound and will be cold tested. This paper present the modified magnet design includes coil forces, coil restraint system and fringe field. In addition, coil properties, quench calculations and the full mechanical details are also presented.

Commissioning of Horizontal-Bend Superconducting Magnet for Jefferson Lab's 11-GeV Super High Momentum Spectrometer

Commissioning of the characteristics of the superconducting high momentum spectrometer horizontal-bend (HB) magnet was presented. The precommissioning peer review of the magnet uncovered issues with eddy currents in the thermal shield, resulting in additional testing and modeling of the magnet. A three-stage test plan was discussed. A solution of using a small dump resistor and a warm thermal shield was presented. Analyses illustrated that it was safe to run the magnet to full test current. The HB magnet was successfully cooled at 4 K and reached its maximum test current of 4000 A.

Analysis of Superconducting Dipole Coil of 11 GeV Super High Momentum Spectrometer

Jefferson Lab is constructing five Super High Momentum Spectrometer (SHMS) superconducting magnets for the 12 GeV Upgrade. This paper reports measured coil material properties and the results of the extensive finite element analysis (FEA) for the dipole coil. To properly define the smeared orthotropic material of the coil, a detailed coil model is set up to compute material parameters because not all parameters were measured. Stress and strain acceptance criteria are discussed. Eight load steps are defined. The preheat temperature of the force collar is optimized under two loading scenarios so that the positive pressure between the inner coil and central spacer is maintained while there is not too much squeeze to the coil.

CRYOSTAT DESIGN AND ANALYSIS OF THE SUPERCONDUCTING MAGNETS FOR JEFFERSON LAB’S 11 GEV/C SUPER HIGH MOMENTUM SPECTROMETER

This paper describes the mechanical design and analysis of the cryostats for the two cos(2θ) quadrupoles and the cos(θ) dipole. All the magnets are currently being bid for commercial fabrication. The results of finite element analysis for the magnet cryostat helium vessels and outer vacuum chambers which investigate the mechanical integrity under maximum allowable internal working pressure, maximum allowable external working pressure, and cryogenic temperature are discussed. The allowable stress criterion is determined based on the allowable stress philosophy of the ASME codes. The computed cryogenic heat load of the magnets is compared with the allowable cryogenic consumption budget. The presented cool‐down time of the magnets was studied under the conditions of a limited supply rate and a controlled temperature differential of 50 K in the magnets.

THE ANALYSIS AND MEASUREMENT OF COMPOSITE COIL PROPERTIES OF JEFFERSON LAB’S SUPER HIGH MOMENTUM SPECTROMETER (SHMS) SUPERCONDUCTING MAGNET COILS

Jefferson Lab’s 11 GeV/c Super High Momentum Spectrometer’s superconducting cosine(2θ) quadrupole magnets and the cosine(θ) dipole use a Nb‐Ti, 36‐strand Rutherford style cable wave‐solder to a copper extruded substrate as their conductor. These magnets will operate at 4.4 K. Accurate analysis of the mechanical performance of the magnets under Lorentz forces and thermal stresses requires that the composite coil’s physical properties at cryogenic temperatures be known. The composite coil design details including the geometry, components, epoxy glass, and its electrical insulation will be presented. The derivation of the composite coil’s calculated physical properties values, using a mixing rule and by Finite Element Analysis (FEA) modeling of a sample coil will be given. The calculated values will be compared to recent measured values of representative samples of the composite coils. Comparison of the composite built up coil sample, measurements and calculated values will be discussed.