The GLAD superconducting spectrometer for R3B

The European Reactions with Relativistic Radioactive Beams of Exotic Nuclei (R3B) collaboration brings together 230 physicists from 63 institutes in 21 countries. The group has set up a study at GSI in Darmstadt, Germany to investigate the emerging physics of exotic nuclei with relativistic energies. This program requires the construction of a number of high performance experimental installations in the fields of inverse kinematic reactions, total detection of the reaction products, and momentum resolution. The GSI Large Acceptance Dipole (GLAD), a superconducting spectrometer, will be an essential component of the R3B detector assembly. The preliminary design for the project was carried out as part of the 5th European research and development framework program (FP5). The decision to fund the construction of the GLAD magnet was taken in October 2005 as part of FP6.

 
The GLAD superconducting spectrometer for R3B

Left: The magnetic structure consisting of six trapezoidal coils. Center: The cold mass of the magnet consisting of the four coil enclosures, connecting plates and cryogenic supports. The electrical junction boxes connecting the superconducting cables are seen here against a blue background. In yellow: The 460 liter tank supplying the 4.5 K indirect cooling tubes in the convection circuit. Right: The cryostat next to its cryogenic satellite providing the external connections. It moves on an air cushion. The total mass of the magnet is 55 tonnes.

 

 

 

Specifications of the spectrometer

 

The GLAD dipole will have to take numerous constraints into account when analyzing the particles from reactions between radioactive ions and the secondary target. These include:

  • A field integral of 4.8 tesla.meters, making it possible to deflect the high magnetic rigidity heavy ions by 18° (typically 15 T.m for 132Sn50+), and protons by up to 50°.
  • A wide angle inlet opening of ± 80 milliradians in both the horizontal and vertical axes, which also provides greater transparency to neutrons that are not deflected by the magnetic field.
  • A large momentum acceptance, making it possible to detect protons and heavy relativistic nuclei, at individual nucleon energies of the order of a GeV.
  • A negligible leakage field (< 20 mT), especially around the target zone located one meter upstream from the magnet entry face.
  • A momentum resolution of 10-3 and an angular resolution of 1 mrad reconstructed at the target.
 
The GLAD superconducting spectrometer for R3B

Installation of a coil in its housing.

Progress of the GLAD magnet tests

 

Since the end of 2005, the construction of this magnet has been being partly funded by the European Construction of New Infrastructure – Darmstadt Ion Research and Antiproton Center (CNI-DIRAC) contract under FP6. The design has resulted in a compact and innovative magnet using an active shielding magnetic configuration.

 

Following a series of mechanical tests carried out on samples of the conductors and a half-scale mock-up of the winding, the mechanical design was finalized and the construction of the coils began in 2009. A prototype coil was built during that year, and six production coils were manufactured during 2010 and installed in their aluminum alloy housings. Electrical and cryogenic tests on the mock-up, also carried out during 2010, confirmed the performance of the conductor and the thermo-mechanical behavior of the winding.

 
The GLAD superconducting spectrometer for R3B

Half of the connections, stabilized, brazed, insulated and installed on their cooling plate.

The first coil was delivered at the end of 2010, enabling the start of the cold mass assembly. In addition to the mechanical assembly itself, one of the most important tasks has been to make the electrical interconnections between the 28 double pancake coils. The resistance of each connection must be of the order of a few nano-ohms, and each connection must be made with particular care using specific tooling developed for this task. Numerous electrical insulation tests have been carried out on these connections in order to ensure that they have been made correctly. The aluminum heat exchangers were glued to each coil prior to assembly.

 

The natural circulation of liquid helium in the tubes of the heat exchangers will provide indirect cooling to the entire cold mass. The coil housings are thermally linked to the coils by a total of 344 copper braids for cooling purposes.

 

The cold mass was placed on its three supporting legs at the end of 2011. Two of the legs are articulated so that the mass is free to retract during the initial cooling process. This assembly was then installed in one of the test cryostats in the W7-X test station in order to verify its behavior during all phases of the operation of the magnet, including initial cooling, current ramping, quench, and warming. The W7-X test station was extensively modified during 2011 in order to accept the cold mass and carry out these functions. A large number of tests have been carried out in order to confirm that its cryogenic capacity was sufficient to allow the operation of the magnet.

 

The cold mass was connected to the test station in 2012 and a full range of tests were carried out in order to confirm that the magnet would operate correctly and safely during testing. The first tests with a current flowing were carried out at the end of 2012 and will continue through early 2013 until the nominal current of 3584 A is reached.

 
The GLAD superconducting spectrometer for R3B

The cold mass installed in one of the cryostats in the W7-X test station at Saclay for acceptance testing at the nominal current.

Last update : 06/22 2018 (3374)

 

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