Bernard Gastineau

Design Status of the R3B-GLAD Magnet: Large Acceptance Superconducting Dipole With Active Shielding, Graded Coils, Large Forces and Indirect Cooling by Thermosiphon

The R3B-Glad superconducting Magnet provides the field required for a large acceptance spectrometer, dedicated to the analysis of Reactions with Relativistic Radioactive ions Beams. In the framework of the FAIR Project to GSI and within NUSTAR physics program, the technical study started in 2006, and the engineering design is undertaken. One main feature of this butterfly-like magnet with graded, tilted and trapezoidal racetrack coils is the active shielding. It makes it possible to decreasing the field by two orders of magnitude within a 1.2 m length, despite the large opening on the outlet side of the magnet (around 0.8 square meters). The fringe field is lower than 20 mT in the target area beside the entry, while the main field is larger than 2 teslas, out of 2 m length. The other principal characteristics are as follows: first, a high level of magnetic forces (300 to 400 tons per meter), with little place to block the coils, requiring a very specific mechanical structure; then, the magnet protection system that is based on an external dump resistor, coupled to a strong quenchback effect, to prevent any damage of the coils which could be caused by the 24 MJ of stored energy; lastly, the indirect cooling of the cold mass with a two-phase helium thermosiphon. The overall size of the conical cryostat will be around 3.5 m long, 3.8 m high and 7 m broad.

Progress in Design and Construction of the

The R3B-Glad superconducting Magnet is a large acceptance dipole, dedicated to the analysis of Reactions with Relativistic Radioactive ions Beams. It takes part in the FAIR Project at GSI. As the superconducting NbTi Rutherford cable was under production, detailed studies of the mechanical structure (with both simulation and experiment on a half-scale mock-up) led to revise the magnet design and to abandon the grading of the coils in three stages. Due to the large magnetic forces (up to 400 tons/m), the maximum shear stress level of 20 MPa was impossible to meet in the coils. The main reasons consist in the orthotropic thermo-mechanical behavior of the coils together with the large differential thermal shrinkage between the Cu stabilized coils and their Al alloy casings. Indeed after several studies of different mechanical designs, we decided to simplify the magnet in order to cope with these difficulties. One innovative point is that the coils are not blocked at room temperature, but only at 4.5 K. This paper presents the magnetic calculations of this active shielded magnet, and shows how the new design features meet the specifications. Currently, the 22 tons magnet cold mass, i.e. the 6 coils and their integration in the casings, is ordered and under construction. Meanwhile, the design of the magnet cryostat has evolved into a shape of elliptical cylinder with a lateral satellite. The total weight is expected to be around 50 tons.

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New generation of experiments in Nuclear Physics is requiring large spectrometers with typical width and height at entrance /spl sim/0.36 /spl times/ 0.32 m and /spl sim/1.2 /spl times/ 0.6 m at exit and field integral /spl sim/4.8 Tm. Very low fringe field is requested, especially upstream from the beam. The innovative design of the superconducting magnet for such spectrometers has been extensively studied on the base of active shielding method. The designed magnet is the combination of several tilted and graded racetrack-type trapezoidal windings for creating both main and shielding fields. This requires high mechanical rigidity by use of aluminum containers where windings will be encased. Indirect cooling with thermosiphon is suggested. The internal protection method is discussed. In the paper the details of the magnet design, magnetic field shape, cooling and protection are presented.

-GLAD Large Acceptance Superconducting Dipole Spectrometer for GSI-FAIR

Comparison between active and passive shielding magnets for a large acceptance superconducting dipole magnet has been carried out. The two magnet designs have been studied to answer to the new requirements of Nuclear Physics experiments in order to get a momentum resolution of up to 10-3 with 1 GeV/nucleon heavy-ion beams: A field integral of about 5Tmiddotm]], a very low fringe field, especially in the target region about 1 meter upstream from the magnet entrance, and a large acceptance defined by a maximum bending angle of 40deg together with an opening horizontal and vertical angle of +/-80 mrad for the neutrons and the charged fragments. To fulfil these requirements, we find that the iron shielding magnet needs a heavier mass, about 300 tons, compared to the active one, even though the total device volume is not so different (4 meter diameter). With iron the coil volume is divided by two (compared with the same current density value) but the stored energy decreases only of less than 20%. The trajectory reconstruction algorithms give results within the specifications for the kinematical reconstruction at the target in both cases, either with iron pole and yoke or with innovative shielding coils, as shown by the given figures of merit. The conclusion of this study is that we find here the limits of a traditional iron design and that the physics requirements open the way to the choice of an active shielding design

Design study of the superconducting magnet for a large acceptance spectrometer

The Cu-NbTi conductor for the R3B-GLAD spectrometer magnet was manufactured. In order to correctly know the thermo-mechanical behavior of this Rutherford cable after insulation and then impregnation, some impregnated cable stacks have been submitted to mechanical tests at room and cryogenic temperatures. The analysis of these measurements will be presented and compared to a theoretical approach. A half-scale mock-up of a real coil was built with the final conductor. After its cooling down to 80 K, the measurements have given the thermal shrinkage coefficients of this coil in the three directions. They confirmed the really orthotropic behavior of these composite coils. The method and the analysis of these measurements are presented.

Comparison Between Active and Passive Shielding Designs for a Large Acceptance Superconducting Dipole Magnet

The R3B-GLAD magnet is a large acceptance superconducting dipole magnet. It provides the magnetic field needed for the R3B (Reaction studies with Radioactive Relativistic Beams) experiment which will be implemented on the future FAIR Facility (Facility for Antiproton and Ion Research). The cold mass structure of the magnet is designed to hold the six superconducting coils in position and to resist high level magnetic forces. The cold mass assembly consists of coils, coil casings and linking components. It is supported by the three cold to warm supports. It weighs about 20 tons with envelope dimensions of 3 rm(rL) X 5 rm(rW) X 3 rm(rH). Engineering design of the cold mass structure has been carried out through extensive finite element analyses. This paper gives an overview on the mechanical behavior of the cold mass assembly during energizing phase and cool-down phase.

Thermo-Mechanical Measurements on Impregnated Cu-NbTi Cable Stacks and on a Coil Mock-Up of the R3B-GLAD Magnet

The R3B-Glad superconducting Magnet provides the field required for a large acceptance spectrometer, dedicated to the analysis of Reactions with Relativistic Radioactive ions Beams. In the framework of the FAIR Project to GSI and within NUSTAR physics program, the technical study started in 2006, and the engineering fabrication is undertaken. The magnetic field and active shielding are achieved by means of 6 superconducting trapezoidal racetrack coils made of a Rutherford type NbTi superconducting cable. The coils are indirectly cooled at an operating temperature of 4.5 K by a thermo-siphon circuit, and are designed to run at a nominal current of 3.6 kA. The corresponding maximum stored magnetic energy reaches 24 MJ. The quench protection is achieved by discharging the magnet in an external resistor, with a voltage to ground of ±500 V at the beginning of the discharge. The design and the characteristics of the quench protection system are described. The computational results of the quench protection for several scenarii are presented as well as the thermal and electromagnetic behavior of the coil cases.

Mechanical Behavior of the Cold Mass Assembly of the R3B-GLAD Magnet

The cold mass of the R3B magnet consists of a set of six trapezoidal racetrack coils. There are two main coils and two pairs of lateral coils which are connected in series in a butterfly-like shape. The coils are imbedded in the coil-casings and covers which are made of aluminum alloy 5083. There are four coil-casings (two main coil-casings and two lateral coil-casings) and linking components between the coil casings. The cold mass will be placed in a large cryostat. The purpose of the cooling system is to get the R3B-GLAD coils at the proper temperature for running operations under magnetic field. The coils are indirectly cooled. The cool down is ensured by gas helium forced flow. As the coils are imbedded in 5083 (casings + covers) it has been decided to cut off heat loads, like thermal radiation and conduction from room temperature to cold mass, before they can reach the coils. Heat exchangers are thus glued on the casings and covers. There are 20 heat exchanger tubes glued in square grooves in covers and casings over a length of 2 m. In this paper the temperature distribution over all the coils and their support structure during the steady state and transient cooling down process are presented. The orthotropic properties of the thermal conductivity of the winding are taken into account. The non linearity of the thermal properties of the coils and materials constituting the support structure is also considered.

The R3B-GLAD Quench Protection System

The SEPAGE spectrometer (Spectromètre Electrons Protons A Grandes Energies) was realized within the PETAL+ project funded by the French ANR (French National Agency for Research). This plasma diagnostic, installed on the LMJ-PETAL laser facility, is dedicated to the measurement of charged particle energy spectra generated by experiments using PETAL (PETawatt Aquitaine Laser). SEPAGE is inserted inside the 10-meter diameter LMJ experimental chamber with a SID (Diagnostic Insertion System) in order to be close enough to the target. It is composed of two Thomson Parabola measuring ion spectra and more particularly proton spectra ranging from 0.1 to 20 MeV and from 8 to 200 MeV for the low and high energy channels respectively. The electron spectrum is also measured with an energy range between 0.1 and 150 MeV. The front part of the diagnostic carries a film stack that can be placed as close as 100 mm from the target center chamber. This stack allows a spatial and spectral characterization of the entire proton beam. It can also be used to realize proton radiographies.

Temperature Distribution During the Cooling Down of the R3B Magnet Cold Mass

SNRC and CEA collaborate to the upgrade of the SARAF accelerator to 5 mA CW 40 MeV deuteron and proton beams (Phase 2). CEA is in charge of the design, construction and commissioning of the MEBT line and the superconducting linac (SARAF-LINAC Project). The prototypes of the 176 MHz NC rebuncher, SC cavities, RF coupler and SC Solenoid-Package are under construction and their test stands construction or adaptation is in progress at Saclay. Meanwhile, the cryomodules and the global system just passed their Critical Design Reviews. This paper presents the status of the SARAF-LINAC Project at April 2018. INTRODUCTION The SARAF-LINAC project, managed by CEA (France), integrated to the SARAF-Phase 2 project managed by SNRC (Israel) has been introduced in [1]. In 2014, a first System Design Report was presented and served of basis on an agreement between CEA and SNRC. The < 8 year project can be simplified in 3 overlapping phases (Fig. 1):  ~3 years of detailed design, including prototyping,  ~4 years of construction, assembly and test at Saclay,  ~2 years of installation and commissioning at Soreq. Figure 1: SARAF-LINAC major schedule. Following the IPAC 2017 status [2], this paper presents the status of these developments after the third year of detailed design phase. In March 2018, three Design Reviews (DR) took place at Saclay:  System CDR2.  MEBT DR.  Cryomodule Critical DR (CDR). SYSTEM The linac layout is given on Fig. 2. A systematic engineering process is applied to derive and follow requirements, specifications, solutions and acceptance of each subsystems (from SARAF-LINAC to small components). The proton or deuteron beam dynamics, from 40 μA to 5 mA, from 1.3 MeV/u to 40 MeV final energy have been calculated (including the error studies) with TraceWin code package [3]. The linac tuning strategy [4] and associated performances [5] have been studied, see Fig. 3. Figure 3: Beam statistical longitudinal distribution with errors. Blue tails represent unhooked particles with very low probability (<10-7). Figure 2: SARAF-LINAC layout, side view (left) and beam view (right). MEBT CM1 Linac 2015 2022 9th International Particle Accelerator Conference IPAC2018, Vancouver, BC, Canada JACoW Publishing ISBN: 978-3-95450-184-7 doi:10.18429/JACoW-IPAC2018-TUPAK015