Magnet Cold Mass Research Articles

Numerical Assessment of the Inhomogeneous Temperature Field and the Quality of Heat Extraction of Nb3Sn Impregnated Magnets for the High Luminosity Upgrade of the LHC

The High Luminosity upgrade of the Large Hadron Collider (HL-LHC) at CERN foresees the installation of Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn-based quadrupole magnets at selected interaction points of the accelerator. The precise knowledge of each magnet's thermal characteristics and heat extraction performance in response to power depositions during both nominal and ultimate conditions is essential in determining safe operating margins. A 2D numerical framework has been developed to systematically assess the temperature distribution in the combined magnet structure-superfluid He system of each magnet and enveloping cold mass using open-source software. Here a full cross-section of a magnet cold mass is modelled, under the power density distribution expected at the most exposed longitudinal position during accelerator operation at an instantaneous luminosity of 5.0x10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">34</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , corresponding to the nominal conditions for HL-LHC. Temperature maps and margins are presented for the inner triplet magnets (MQXF) for both horizontal and vertical beam crossing conditions, along with the validation of the design of cold mass cooling channels for heat extraction.

Application of Distributed Fiber Optic Strain Sensors to LMQXFA Cold Mass Welding

The future High Luminosity upgrade of the Large Hadron Collider (HL-LHC) at CERN will include the low-beta inner triplets (Q1, Q2a/b, Q3) for two LHC insertion regions. The Q1, Q3 components consist of eight 10 m-long LMQXFA cryo-assemblies fabricated by the HL-LHC Accelerator Upgrade Project. Each LMQXFA Cold mass contains two Nb3Sn magnets connected in series. A stainless-steel shell is welded around the two magnets before the insertion into the cryostat. There is a limit on how much coil preload increase induced by the shell welding is allowed. Distributed Rayleigh backscattering fiber optics sensors were used for the first time to obtain a strain map over a wide area of a Nb3Sn magnet cold mass shell. Data were collected during welding of the first LMQXFA cold mass and the results confirm that the increase of the coil pole azimuthal pre-stress after welding do not exceed requirements.

Thermohydraulic simulation of quenches and quench recovery for the HL-LHC IT String test bench at CERN

In the framework of the High Luminosity LHC (HL-LHC) project, a new test system - the Inner Triplet (IT) magnets String - for the characterization and validation of the collective behaviour of a 60 m long string of magnets is being built in the SM18 cryogenic test facility at CERN. Among the main objectives of the IT String is the assessment of the magnet performance during the resistive transition from the superconducting to the normal state (quench) when energies up to 39.1 MJ are released into the magnet cold mass and into the helium. In this paper we present the thermohydraulic study performed to design the quench recovery system of the IT String, which limits the pressure rise in the magnets during a quench and ensures the recovery of the operating conditions within the required timeframe. As a new design method, a 1-D thermohydraulic model of the quench relief system has been created using the EcosimPro software with the CRYOLIB library developed at CERN.

Mechanical Behavior of the Shielded HL-LHC Beam Screen During a Magnet Quench

In the framework of the High-Luminosity Large Hadron Collider (HL-LHC) project, larger and shielded beam screens will be installed in the beam pipe of the superconducting magnets of the insertion next to the ATLAS and CMS detectors. The beam screen is a complex assembly that guarantees the vacuum requirements while shielding the magnet cold mass from the induced heat loads. Such an assembly has to withstand high intensity electromagnetic forces induced during magnet quenches. The mechanical stability was verified in a dedicated quench test campaign performed at the magnet test station of CERN. Strain gauges, custom-made probes, and optical fibers were installed in the beam screen to measure deformations during a quench. Magnetic field measurements were also carried out by means of pick-up coils mounted within the assembly. The main outcomes of this work are the elastic behaviour of the beam screen after 52 quenches and a satisfactory agreement between measurements and simulations.

Busbar technology development for the HL-LHC inner triplet magnets

The busbars for the HL-LHC magnets are made of Nb-Ti/Cu conductor, the insulation system, and the auxiliary equipment to align the busbars with respect to the magnet coldmasses. This paper presents design options concerning the integration of the busbars inside the coldmass with a fixed point, and a reinforced insulation system for the flexible busbar part using thin PEEK tubes. Prototype splices for interconnecting Nb3Sn and Nb-Ti Rutherford cables, and round and flat 18 kA Nb-Ti cable have been produced and first test results are presented.

Cryogenic management of the LHC run 2 dynamic heat loads

During the LHC (Large Hadron Collider) Run 2 between 2015 and 2018 inclusive, significant dynamic heat loads have been generated and successfully managed by the LHC cryogenic system. These dynamic heat loads are generated by several physical phenomena occurring at two temperature levels and with different time constants. On the magnet cold-mass maintained at 1.9 K, dynamic heat loads are coming from eddy currents generated during the magnet transients, resistive heating in welds of superconducting electrical circuits, beam gas scattering, beam losses, and secondary particles escaping from collisions (debris). On the beam screens, actively cooled between 4.6 K and 20 K, the circulating beams produce also dynamic heat loads due to synchrotron radiations, image current and photo-electron clouds. This paper presents the measurements inventory performed during the Run 2 to assess these dynamic heat loads as a function of the different accelerator parameters (beam energy, beam intensity, injection scheme, etc.). Then, the related compensation measures and adapted cryogenic operation modes applied to manage the induced transients at the different time scales will be presented.

Mechanical Design and Analysis of the Baby-IAXO Magnet Cold Mass, Cryostat and Support System

According to the so-called Primakoff effect, axions and axion-like particles can transform into photons in the presence of a strong magnetic field. To continue the search for these hypothetical particles, a new helioscope called the International Axion Observatory IAXO, and its subscale but fully functional demonstrator Baby-IAXO, are being designed. To increase the detector's sensitivity by a factor of 10 compared to the present CAST helioscope, the experiment needs a stronger magnetic field and in a much larger volume. The superconducting magnet of Baby-IAXO features two 10 m long flat racetrack coils spaced by 0.8 m, arranged in a common coil configuration and generating an average magnetic field of 2.1 T in the two 700 mm detection bores positioned in between the coils. The cold mass structure based on using mainly Al6061-T651, is designed to guarantee pre-stress of the coils during curing and sustain the magnetic loads by the Lorentz force. At ultimate current of 12 kA, the repelling force between the two coils is 33 MN. Furthermore, the supporting structure has to keep the coils in position as they are in an unstable equilibrium in the plane parallel to the racetracks. To support the cold mass in the cryostat, an arrangement of rods was chosen in order to minimize the cryogenic load. The system is composed of 16 titanium rods, which in addition to supporting the expected force loads also keeps the magnet centered. The total mass of the magnet is 35 t comprising an 18 t cold mass and a 15 t cryostat. The magnet is installed on an elevated 360° rotating platform further constraining the cryostat design. Here the mechanical design of cold mass, cold mass supporting system and cryostat of the Baby-IAXO magnet are presented.

Magnetic and Thermal Design of HTS Quadrupole Magnet for Newly Developed Superconducting Proton Cyclotron Beam Line

A magnetic and thermal design of high-temperature superconducting (HTS) quadrupole magnet for newly developed superconducting proton cyclotron was presented in this research. With superconducting technology, the design can reduce the magnet size and remove the heat loads more efficiently. Calculations are conducted with finite element method (FEM) to study the quadrupole magnet’s magnetic and thermal properties. For the magnet cold-mass and cryostat system, the heat load is mainly generated by conduction and radiation. Multilayer thermal insulation and G10 supports are used to restrict them. The magnetic field distribution in the HTS coils is calculated to consider the critical current degradation of the YBCO tapes. The effects on the field gradient quality in relation to the pole tip profile and end chamfer are analyzed. The sixth multipole component in the integral field can be improved with end chamfer. Finally, a 20 T/m HTS quadrupole magnet with integral field uniformity less than 0.05% out to 75% of the inscribed radius is proposed.

Adaption of the LHC cold mass cooling system to the requirements of the Future Circular Collider (FCC)

The cooling of the superconducting magnet cold masses with superfluid helium (He II) is a well-established concept successfully in operation for years in the LHC. Consequently, its application for the cooling of FCC magnets is an obvious option. The 12-kW heat loads distributed over 10-km long sectors not only require an adaption of the magnet bayonet heat exchangers but also present new challenges to the cryogenic plants, the distribution system and the control strategy. This paper recalls the basic LHC cooling concept with superfluid helium and defines the main parameters for the adaption to the FCC requirements. Pressure drop and hydrostatic head are developed in the distribution and pumping systems; their impact on the magnet temperature profile and the corresponding cooling efficiency is presented and compared for different distribution and pumping schemes.

Mu2e Transport Solenoid Cold-Mass Alignment Issues

The muon-to-electron conversion experiment (Mu2e) at Fermilab is designed to explore charged lepton flavor violation. It is composed of three large superconducting solenoids: the production solenoid, the transport solenoid (TS), and the detector solenoid. The TS is formed by two magnets: TS upstream and TS downstream. Each has its own cryostat and power supply. Tolerance sensitivity studies of the position and angular alignment of each coil in this magnet system were performed in the past with the objective to demonstrate that the magnet design meets all the field requirements. The alignment of the cold masses is critical to maximize the transmission of muons and to avoid possible backgrounds that would reduce the sensitivity of the experiment. Each TS magnet cold mass can be individually aligned. In this paper, we discuss the implications of the alignment of the TS cold masses in terms of the displacement of the magnetic center. Consideration of the practical mechanical limits is also presented.

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.

A Cyclotron Magnet Case Study: Would Replacing the LTS Coils With HTS Coils Make Sense?

The cyclotron gas-stopper magnet (CGSM) at Michigan State University (MSU) was used as model for a study for whether HTS conductor is feasible for use in cyclotrons. The outside diameter of the CGSM split warm iron magnet yoke is 4 m, with a pole radius of 1.1 m. The desired field shape is obtained by shaping the iron pole profile. Each superconducting coil is in a separate cryostat. The two coils are connected in series through the warm electrical connection. Each coil is wound and potted within an 80 mm × 80 mm cross section and mounted within a 304 stainless steel helium vessel that is designed to carry magnetic forces to the magnet cold mass supports without excessive deflection. The iron is split, so that the cyclotron chamber and RF extraction system can be mounted between the two poles. This magnet has been successfully cooled down and tested at MSU to its 180-A operating current. One can ask the following question, “If one built a cyclotron magnet the size of the MSU cyclotron gas-stopper magnet, would replacing the existing LTS coils with HTS coils using a standard second generation HTS tape make technical sense or economic sense?” The report will explore the technical and economic issues of replacing an existing LTS coil with an HTS coil of the same size and shape, using 2G YBCO tape conductor commercially available in 2015 in place of the Nb-Ti used in the magnet.

MO‐F‐CAMPUS‐J‐04: Radiation Heat Load On the MR System of the Elekta Atlantic System

Purpose:The Elekta Atlantic system combines a digital linear accelerator system with a 1.5T Philips MRI machine.This study aimed to assess the energy deposited within the cryostat system when the radiation beam passes through the cryostat. The cryocooler on the magnet has a cooling capacity which is about 1 Watt in excess of the cryogenic heat leak into the magnet's cold mass. A pressure‐controlled heater inside the magnet balances the excess refrigeration power such that the helium pressure in the tank is kept slightly above ambient air pressure. If radiation power is deposited in the cold mass then this heater will need less power to maintain pressure equilibrium and if the radiation heat load exceeds the excess cryocooler capacity the pressure will rise.Methods:An in‐house CAD based Monte Carlo code based on Penelope was used to model the entire MR‐Linac system to quantify the heat load on the magnet's cold mass. These results were then compared to experimental results obtained from an Elekta Atlantic system installed in UMC‐Utrecht.Results:For a field size of 25 cm × 22 cm and a dose rate of 107 mu.min‐1, the energy deposited by the radiation beam led to a reduction in heater power from 1.16 to 0.73 W. Simulations predicted a reduction to 0.69 W which is in good agreement. For the worst case field size (largest) and maximum dose rate the cryostat cooler capacity was exceeded. This resulted in a pressure rise within the system but was such that continuous irradiation for over 12 hours would be required before the magnet would start blowing off helium.Conclusion:The study concluded that the Atlantic system does not have to be duty cycle restricted, even for the worst case non‐clinical scenario and that there are no adverse effects on the MR system.Stephen Towe and David Roberts Both work for Elekta; Ezra Van Lanen works for Philips Healthcare; Johan Overweg works for Philips Innovative Technologies

Energy deposition studies for the high-luminosity Large Hadron Collider inner triplet magnets

A detailed model of the High Luminosity LHC inner triplet region with new large-aperture Nb3Sn magnets, field maps, corrector packages, and segmented tungsten inner absorbers was built and implemented into the FLUKA and MARS15 codes. In the optimized configuration, the peak power density averaged over the magnet inner cable width is safely below the quench limit. For the integrated luminosity of 3000 fb-1, the peak dose in the innermost magnet insulator ranges from 20 to 35 MGy. Dynamic heat loads to the triplet magnet cold mass are calculated to evaluate the cryogenic capability. In general, FLUKA and MARS results are in a very good agreement.

Cryogenic Operation on the R3B-Glad Large Acceptance Superconducting Dipole Spectrometer at CEA Saclay

The R3B-Glad magnet cold mass has been tested in the test facility at CEA Saclay previously used for testing W7X coils. This superconducting dipole has been cooled down by indirect cooling, and its 21 tons were maintained at around 4.8K by means of helium thermosiphon. For this, the facility was adapted and connected to the cold mass to approximate actual conditions in its final configuration at GSI (Darmstadt, Germany). The magnet cooling down as well as the two-slope current ramping up to the nominal current of 3584 A was successfully achieved in December 2013. This paper presents the cryogenic distribution process, and shows the relevant results.

Engineering Study of the Sector Magnet for the Dae&lt;formula formulatype="inline"&gt;&lt;tex Notation="TeX"&gt;$\delta$&lt;/tex&gt;&lt;/formula&gt; alus Experiment

The Daeδalus experiment seeks to evaluate neutrino scattering effects that go beyond the standard model. Modular accelerators are employed to produce 800 MeV proton beams at the megawatt power level directed toward a target, producing neutrinos. The Superconducting Ring Cyclotron consists of identical sectors (currently 6) of superconducting dipole magnets with iron return frames. The Daeδalus Collaboration has produced a conceptual design for the magnet, which, after several iterations, is the current best design that achieves the physics requirements of the experiment. The main purpose of the analytical effort, results of which are presented here, is to develop a viable engineering design satisfying requirements to the superconductor, as well as structural and cryogenic requirements. The work includes proposed conceptual approaches, solid modeling and analyses for the conductor and winding pack design, high-temperature superconductor and copper current leads for the magnet, structural design of the magnet cold mass, cryostat and warm-to-cold supports, cryogenic design of the magnet cooling system, and magnet power supply sizing. A description of the winding pack design, structural analysis, and cryogenic system is reported.

R3B-Glad Magnet R&amp;D Tests Program: Thermosiphon Loop With Horizontal Section, Superconducting Cable Joints at 3600 A, and Reduced Scale “Coil in its Casing” Mock-Up

The R3B-Glad magnet is part of a large acceptance spectrometer devoted to the physics of exotic nuclei, under construction at CEA Saclay (France) for the future FAIR facility at GSI (Darmstadt, Germany). The R3B-Glad project is in its final phase where the magnet cold mass is achieved and will be tested at 4.6 K and nominal current in the fall of 2011. We present the results of the R&D tests programs that were implemented to answer some issues raised after the technical design review. First, this superconducting dipole will be cooled down by indirect cooling, and its 22 tons cold mass maintained at 4.6 K by means of a two-phase helium thermosiphon loop. An experimental model set-up has been specifically built to demonstrate the cooling efficiency despite the presence of large quasi-horizontal sections in the circuit. Then the superconducting Rutherford cable joints, required between the 26 coil double pancakes, were designed and tested to minimize their electrical resistance. Finally a reduced scale mock-up of a coil in its casing, with a general design similar to the final magnet, was tested at low temperature to validate the indirect cooling and the mechanical blocking system of the coil in its casing by differential thermal shrinkage. This test was performed at a higher current (8800 A) than the nominal one (3600 A) to reach the same value of temperature margin before quenching, together with similar high level of magnetic forces on the coil (100 to 200 t/m in final magnet).

R3B-Glad Magnet Cold Mass Manufacture: Coils and Casings Fabrication and Integration

The R3B-Glad magnet is part of a large acceptance spectrometer devoted to the physics of exotic nuclei, under construction at CEA Saclay (France) for the present GSI and the future Fair facilities (Darmstadt, Germany). In this paper is presented the fabrication of the cold mass (22 t), divided into three batches (coil manufacture, machining of coil casings, and integration of the coils inside their casings). The work began in January 2009 and ended in December 2010. A real size prototype coil, was developed to validate the winding process, with double pancakes assembled in a stacking tool, and the procedure for impregnating coils, inserted into a mold. After impregnation of the prototype and the first coil, a failing (short circuit between turns) was detected in both coils by electrical testing. The repair of various defects has been a success. Insulation reinforcements were performed on the following coils to avoid any further electrical default. The whole set of coils was wound and impregnated in 2010 (6 coils, about 3 meter long each). The casings are made of aluminum alloy 5083 (with the exception of a few pins, screws and bolts made of stainless steel) and machined from single blocks without welding. All parts were machined in two stages. The first step was a premachining to perform a blank assembly of the whole cold mass (performed in February 2010). The final machining was performed according to the actual dimensions of the manufactured coils, in order to get a perfect fit of the coils within their casings. The integration of the coils inside their casings (including shims setting, adjusting of pushing systems, bonding of drains and thermal sensors) occurred in autumn 2010. The set of coils in their casings was delivered to Saclay in December 2010.

Novel Ways of Heat Removal from Highly Irradiated Superconducting Windings in Accelerator Magnets

Novel ideas of heat removal from superconducting windings in accelerator type magnets are investigated with the help of a recently developed and validated thermal model of a magnet cold mass implemented in COMSOL Multiphysics. Here the focus is on how to improve heat removal from the midplane of a superconducting quadrupole magnet, the area exposed to the highest radiation heat load. In addition, this part of the coil windings has the longest thermal path towards the heat sink and several thermal design improvements proposed in the past are not very effective here. It is shown that with minor changes in the geometrical design, the cooling of the midplane conductors can be strongly increased

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

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.