C. Magsig

The Superferric Cyclotron Gas Stopper Magnet Design and Fabrication

The Facility for Rare Isotope Beams under construction and the existing National Superconducting Cyclotron Laboratory at Michigan State University will provide exotic low-energy rare isotope beams (KeV-MeV) by stopping relativistic fragments produced by projectile fragmentation at high energies (<; 50 MeV/u). The stopped radioactive ions using the cyclotron gas stopper magnet system will feed the existing program centered on precision mass measurements of exotic nuclei and laser spectroscopy. Later on, stopped radioactive ions will be available as reaccelerated low-energy beams ( <; 15 MeV/u) using compact linear accelerator currently under construction. The cyclotron gas stopper magnet is a warm iron superconducting cyclotron sector dipole. The maximum field in the gap (0.18 m) is 2.75 T. The outer diameter of the magnet yoke is 4.0 m, with a pole radius of 1.1 m and Br = 1.8 T m. The desired field shape is obtained by a pole profile. Each coil of the two halves is in a separate cryostat and connected in series through a warm electrical connection. The entire system is mounted on a high voltage platform, and will be cooled by six cryocoolers. This paper presents the magnet design and discusses various design aspects of the magnet.

Lessons learned from the cool down of a superconducting magnet using a thermal-siphon cooling-loop

The two Michigan State University (MSU) cyclotron gas-stopper magnet superconducting-coils were designed to be cooled down and to be kept cold using three pulse-tube coolers per coil cryostat. These coolers are designed to produce from 1.3 to 1.7 W per cooler when the cooler first-stage is at 40 K. The cyclotron gas stopper coils can be separated while cold, but unpowered. The two coil cryostats were cooled down separately in 2014, and room temperature helium gas was liquefied into the coil cryostats. The magnet temperature at the end of the cool-down was 4.55 K for one coil and 4.25 K for the other with and added 1.6 W of heat. The coil-down time for the coils was three and a half times longer than expected. The time to liquefy the helium was also much longer. The reasons for the disparity between the calculated cool-down time and measured cool-down time are discussed in the paper.

Construction and testing of A &#177; 16&#176; superconducting beamline magnet

A prototype of the beamline switching magnets needed for operation of the National Superconducting Cyclotron Labs 1.6 GeV/c heavy ion beam transport system has been constructed and is undergoing tests. The device features a compact design, as well as good cryogenic and magnetic efficiency. In the operational range of 1.0 to 1.75 T the required field uniformity of ± 0.1% has been obtained. The design current density in the potted coils is 17 kA/cm2at 1.75 T, and the magnet has operated at a current density of 20 kA/cm2at 1.8 T without a quench.

Slow Current Discharges and Quenching of the MSU Superconducting Cyclotron Gas-Stopper Magnet

The Michigan State University cyclotron gas-stopper magnet generates a strong focusing cyclotron magnetic field that permits an ion beam of up to 100 MeV/u to enter the magnet and have most of its energy reduced by low-pressure helium gas. The magnet has two superconducting coil cryostats mounted within warm iron poles and a warm split iron return yoke. The coils are connected in series using room temperature cables. The peak magnet stored energy is 3.5 MJ. The magnet has been tested to its full operating current of 180 A. During tests, the magnet discharged inadvertently three times. Two low-current discharges caused the magnet current to decay through the power supply system. A discharge at 180 A quenched the magnet, because the quench protection system caused the magnet to discharge across a 1.25-Ω resistor. This fired the cold quench protection diodes within the cryostat, quenching both coils. The magnetic field in the gap was measured as the magnet discharged. For the two low-current discharges, the magnetic field followed the current in the external magnet circuit. During a quench, the magnetic field decay rate was much slower than the external circuit current decay rate.

Cold Mass Support System for the MSU Superconducting Cyclotron Gas-Stopper Magnet

The cyclotron gas-stopper magnet at Michigan State University consists of two superconducting coils, each in its own cryostat. The two cryostats are mounted in the two warm iron poles of a sector cyclotron magnet used to control the orbit of heavy ions as the particle energy is being removed by circulating the ions through helium gas. Because the two poles of the magnet must be separated to install the gas chamber and beam extraction system, the magnet coils cannot be connected together. As a result, the magnet cold mass support system must carry the forces pushing the magnet into the iron pole as well as any decentering forces that occur from coil placement errors. The cold mass support system for each magnet coil consists of six compression supports that support magnet forces in the axial direction. In addition, there are three radial supports to center the coil axis coaxial with the axis of the iron poles. This paper presents an analysis of the superconducting magnet cold mass support system, which must be designed to have a spring constant that is higher than the magnet force constant at the full design current for the magnet.

Fabrication of the Superferric Cyclotron Gas-stopper Magnet at NSCL at Michigan State University

The magnet for the cyclotron gas stopper is a newly designed, large warm-iron superconducting cyclotron sector gradient dipole. The maximum field in the centre (gap = 0.18 m) is 2.7 T. The outer diameter of magnet yoke is 4.0 m, with a pole radius of 1.1 m and B*ρ = 1.8 T m. The fabrication and assembly of the iron return yoke and twelve pole pieces is complete. Separate coils are mounted on the return yokes that have a total mass of about 167 metric tons of iron. This paper illustrates the design and the fabrication process for the cyclotron gas-stopper magnet that is being fabricated at MSU.

Effects of insulation on potted superconducting coils

The authors studied the effects of the insulation on potted superconducting coils wet-wound with Stycast 2850 FT epoxy. The wire was insulated with one or two insulating varnishes: Formvar (a polyvinyl formal resin) or Polyesterimid (a phenolic resin). Although differences in maximum currents were observed, it was found that the type of insulation did not affect the training behavior. >

Cooling and Operation of the MSU Cyclotron Gas-Stopper Magnet

The two coils of the cyclotron gas-stopper magnet at Michigan State University (MSU) were each cooled down and filled with liquid helium made from 300-K gas separately using three PT415 coolers in the fall of 2014. The magnet was first powered in late 2014. During the process of powering the magnet, discharges occurred because the interlock system caused the magnet to discharge. As the magnet was powered to higher currents, the coil positions were changed using the cold mass support adjustments to ensure that forces on the cold mass supports were within the design limits. The force pattern on the cold mass supports was expected to change as the iron pole pieces saturated. Changes in the coil inductance were expected and observed as the iron pole pieces saturated. This paper describes the process that brings the magnet current up to its full current.

Superconducting beamline elements for the NSCL spectrograph

The superconducting beamline elements for a magnetic spectrometer at the National Superconducting Cyclotron Laboratory are being constructed. There are four dipoles, which produce a peak field of 1.7 T in a 7 cm gap, and fifteen quadrupoles, which have peak gradients of 25 T/m in a 20 cm diameter bore. A quadrupole has been tested to higher than the required current. All of the devices are being assembled into their cryostats.<<ETX>>

The superconducting beam transport system at the NSCL

The beam transport system at the National Superconducting Cyclotron Lab (NSCL) consists of 22 cryostats containing superconducting quadrupole doublets or triplets, and 9 superconducting dipoles. The quads achieve gradients of up to 35 T/m in the 10-cm-diameter warm bore. Operating at a maximum current of 20 A allows the helium consumption rate to be kept to less than 0.3 L/h. The dipoles produce fields in the 5-cm gap of over 1.9 T at a current of 100 A, and the two types produce bends of either +or-16 degrees or 22.5 degrees at 1.75 T for the 1.6-GeV/c heavy ion beams produced by the K1200 superconducting cyclotron. One years operations experience demonstrates their efficiency and reliability.