Enrique Rodriguez

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.

Experience on Series Production of the Superconducting Magnet Package for the Linear Accelerator of the European XFEL

The procurement of 103 superconducting magnet packages is part of the Spanish in-kind contribution to the European X-FEL. Each package consists of a main superferric quadrupole and two steerers, vertical and horizontal, fed by conduction-cooled current leads and enclosed in a stainless steel vessel. The operation temperature is 2 K, as they are embedded in a superfluid helium bath. The magnetic and mechanical designs are published elsewhere. The magnets are being produced in the Spanish company ANTEC, while the vessels are fabricated by another Spanish company, Trinos Vacuum-Projects, which is also responsible for the integration, under the supervision of CIEMAT. The helium vessel manufacturer needs to accomplish the requirements given by the European Pressure Equipment Directive, namely PED 97/23/EC. This paper describes the series fabrication techniques, the production follow-up, the quality assurance, and the magnet testing at the manufacturer site. Cold tests are realized at DESY premises. The main problems found during the fabrication of the first half of the series are also reported: 1) the reproducibility of the quadrupole coil dimensions; 2) the accuracy of the beam position monitor housing after final welding of the vessel; and 3) the minimization of the magnetization effects on the transfer function of the magnets.

Switching losses reduction in current-controlled single-phase inverters

This paper introduces an effective technique for reducing semiconductor switching losses, and evenly distributing them, in current-controlled single-phase inverters. The current switching frequency is reduced taking advantage of three-level commutation by a double hysteresis-band current-control strategy imported from multilevel converters studies. Furthermore, an additional reduction of the semiconductor switching frequency is accomplished by modifying the standard semiconductor switching pattern for balancing power dissipation between upper and lower devices. An overall reduction of switching losses in a factor of 2 to 4 is achieved in this manner. The system control strategies are exposed in detail and experimental results for a 200 kVA grid-side converter of a switched reluctance drive are presented to better show the concepts involved.