Jose Luis Gutierrez

Magnetization Effects on the Superconducting Combined Magnet Prototype for XFEL

The superconducting combined magnets for the main linac are part of the Spanish contribution to XFEL. Each magnet consists of a super-ferric quadrupole for focusing and two dipoles (horizontal and vertical) for steering, glued on the beam tube. The magnets will be operated in a superfluid helium bath. The aperture is 78 mm. The quadrupole gradient is 35 T/m whereas each dipole field is about 0.04 T. This paper reports about the magnetic measurements made on the first prototype. Measured field quality matches calculated values, both at room and cold conditions. Magnetization has been also measured in all the coils, with single or combined powering. Asymmetric and strongly non-linear transfer functions have been observed when quadrupole and dipoles were powered simultaneously. On the other hand, detailed computations were made with ROXIE to understand that issue. Results matched measurements when only one set of coils was powered, but not when two of them were energized. It is likely that the effect of the transport current or the coil-ends-which are not modeled by ROXIE-could explain the difference.

Fabrication and Testing of a Combined Superconducting Magnet for the TESLA Test Facility

An international collaboration at DESY is currently studying the possibilities of a new type of particle accelerator: the superconducting linear collider, developed under the project name TESLA. The TESLA Test Facility is trying to establish a well-developed collider design, which will also be helpful for the design of a superconducting X-ray Free Electron Laser facility (XFEL), a project approved by the German Government and now in its initial stage. Besides, XFEL will be the ideal workbench to improve the necessary components for the next International Linear Collider (ILC). This paper is about the fabrication and testing of the first prototype of a combined superconducting magnet for focusing and steering purposes, in the framework of the Spanish contribution to the TESLA project. It consists of a quadrupole and two dipole concentric coils, one horizontal and another one, vertical. The double pancake winding technique with a ribbon of eight pre-glued wires has been used in order to develop a cheap method for the quadrupole coils in industrial scale, as the accelerator would need about 800 magnets. The coils were fully instrumented with voltage taps to study the quench propagation. The magnet has been successfully tested at DESY and the results are reported in this paper

Development of Radiation Resistant Superconducting Corrector Magnets for LHC Upgrade

Two prototype superconducting corrector magnets, a sextupole and an octupole, have been designed and fabricated by CIEMAT during the preparatory phase for the Large Hadron Collider (LHC) luminosity upgrade, in the framework of the SLHC project. These magnets will be grouped with other correctors in a dedicated cryo-assembly, placed in the LHC insertion regions. The magnets shall be designed to withstand radiation levels up to 10 MGy. Therefore, the nominal aperture will be increased to 140 mm to include a 10-mm-thick steel shielding, and all materials must be radiation resistant. The sextupole has been produced with conventional materials but radiation-resistant ones have been used for the octupole, like polyimide insulated wire and cyanate-ester resin. The nominal integrated strength of the sextupole is 0.055 T · m (0.035 T · m for the octupole) at 40 mm reference radius and overall mechanical length is 160 mm (180 mm for octupole). Due to the moderate peak field, a superferric design is preferred, which also allows placing the coils further away from the aperture. Fabrication techniques and test results are described.

Final Design and Prototyping of the Superconducting Magnet Package for the Linear Accelerator of the European XFEL

The electron beam of the European XFEL will be accelerated to an energy up to 17 GeV in a linear accelerator that is divided into 101 modules. Each module will be equipped with eight superconducting cavities and a superconducting magnet package. That package consists of a main superferric quadrupole and two nested corrector dipoles, horizontal and vertical, enclosed in a stainless steel vessel. Conduction-cooled current leads are used. Up to four prototypes were produced between 2005 and 2009. Some problems were detected, which may complicate the series production, mainly that the wire diameter was too small for the winding process, the solid iron yoke was too expensive to be machined and the magnetization effects on the magnet transfer function were too high. Therefore, it was decided to revisit the design to ease fabrication. The new magnet design is presented in this paper. The fabrication process and test results of the prototype are reported as well. Finally, the helium vessel around the magnet needs to satisfy the European Standard for Pressure Vessels, namely PED 97/23/EC. This paper also describes the modifications necessary in the original design to achieve that specification.

Design of a HTS Solenoid for a Gyrotron Magnet Upgrade

The design of a HTS cryogen-free solenoid for a gyrotron magnet upgrade is presented. This gyrotron is used to set up and warm the plasma in an experimental fusion device at Ciemat. The solenoid will be wound with BISCCO-2223 tapes. A two stage Gifford-McMahon cryocooler was used to cool down the magnet. A significant operation cost will be saved as the present solenoid is a Nb-Ti magnet cooled down in a helium bath supplied with mobile tanks. The main requirement of the magnet is to reproduce the original magnetic profile in the axis of the solenoid with a peak of 2 T in a 150 mm diameter warm bore. The magnet consists of several stacked double-pancake coils. The outer radii, the axial positions and the number of windings have been optimized by means of a genetic algorithm. Afterwards, the cryostat design is also described, including the heat leakage calculation. Finally, the winding techniques and the results of the tests of a prototype coil are also reported in this paper.

Development of a Test Bench for Magnetic Measurements on E-XFEL Phase Shifters

A test bench has been developed for the magnetic measurements on the Phase Shifters for E-XFEL. It will be part of the Spanish in-kind contribution to this new research facility. The most challenging specification of the phase shifter is given for the variation of the first field integrals (in both horizontal and vertical components), with a tolerance interval of ±4 × 10-6 T·m. Besides, it is necessary to measure the phase integral as a function of gap for the proper operation of the accelerator. Different systems have been analyzed during the conceptual design of the test bench. Finally, the selected configuration is based on a long coil and a voltage integrator, because of its high accuracy and moderate complexity. The objective of this paper is to describe the development of this device (including design, manufacturing, assembly and calibration) and to present the measurements performed on the first phase shifter prototypes. Especial attention has been paid to the treatment of the raw data to compensate the systematic errors and deficiencies of the method.

Development of a Superconducting Magnet for a Compact Cyclotron for Radioisotope Production

The present paper describes the development process of a low critical temperature superconducting magnet to be installed in a compact cyclotron producing single-dose radioisotopes for clinical and preclinical applications. After a brief description of the accelerator, the magnet development process is described, starting from the magnetic, mechanical, quench, and thermal calculations, continuing with the designing process, particularly the support structure of the magnet and the cryogenic supply system, to finish with the fabrication and the first tests than have been performed.

Validation Test of the Forced-Flow Cooling Concept for the Superconducting Magnet of AMIT Cyclotron

Advanced Molecular Imaging Techniques cyclotron is a compact device aimed to produce radioisotopes for medical imaging. A uniform 4-T field is created by means of two NbTi coils in a Helmholtz arrangement. Both coils are embedded in a stainless steel casing that holds the Lorentz forces. The cooling scheme is based on a low-pressure forced internal flow of two-phase liquid-vapor helium through a narrow channel machined in the casing. Preliminary thermohydraulic analysis showed that this concept is capable of cooling the coils, removing a heat load of up to 1 W with just a small amount of mass flow (about 0.1 g/s). In the final application, cold helium will be provided by a cryogenic supply system (CSS), which basically consists of a closed circuit recondenser using a single cryocooler. Previous heat loads are inside the CSS specifications. This paper will present the results of a scaled mock-up of the coils, cooled by a controlled flow of helium provided from a helium Dewar, tested to check the thermal loads, quench training, fluid-solid interaction, and the necessary control system to handle the helium mass flow. It will prove the viability of the concept while advising the potential problems that could arise in the real system.

Further developments on Beth's current-sheet theorem: computation of magnetic field, energy and mechanical stresses in the cross-section of particle accelerator magnets

The design of particle accelerator magnets involves computation of magnetic field and mechanical stresses distribution, together with a quench simulation. First approach is usually 2D, concerning the cross-section, while final calculations include the coil-end effect. Beths current theorem affords a very convenient way to obtain the magnetic field distribution, the magnetic field energy and the Lorentz force distribution, but with one important limitation: the coils must be replaced by a single current-sheet, which is a poor approximation if the coil is somewhat thick. Iron yoke is taken into account by the image method. However, saturation effect cannot be included. In this paper, a further development is proposed. Any winding can be considered as a sum of current sheets, placed at different radii. Results are obtained by the overall contribution: magnetic field distribution and harmonics at a reference radius, self-inductance, magnetic field energy and stress distribution. The main advantage of this analytical method is that the real coil geometry can be modeled. Besides, it is a fast and simple method for the first stage of magnet design, able to provide results not only about magnetic field distribution, but also about self-inductance and Lorentz forces. Calculations are made by means of a Matlab script, and are successfully compared with those obtained with other commercial packages based on FEM method or Biot-Savarts law.