Search

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.

The European X-ray Free Electron Laser facility (XFEL) is currently under construction at DESY in the Hamburg area in Germany. A linear accelerator consisting of 102 accelerator modules is used to accelerate the electron beam. Each module contains eight superconducting RF cavities and one magnet package, all operating in a 2 K super-fluid helium bath. Each magnet package consists of three nested magnets. Two cos θ-type correction dipole magnets horizontal and vertical deflecting are glued onto the surface of the beam pipe being the inner wall of the cryostat vessel. They are inside of a superferric quadrupole magnet. Each magnet package together with a conduction cooled current lead assembly, based on a CERN design, will be tested at room temperature and at 2 K in a special cryostat XMTS at DESY. It allows access for the field measurement equipment into the magnet bore at room temperature by using an anti-cryostat. The cold magnet project is realized by three groups as in kind contributions to the XFEL project. CIEMAT designs and provides the magnets and DESY the current leads. Magnet testing at DESY is performed together with IFJ PAN. A description of the XMTS facility, the magnetic field measurement systems used (harmonic coils and stretched wire setups) are given. Finally a short discussion of the results obtained for the first third of the magnets is presented. All magnets tested so far perform very well up to the design current. The quality and strength of the magnetic field are as designed.

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.

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.

For HERA (Hadron Electron Ring Accelerator) a total of 453 superconducting dipoles and 246 superconducting quadrupoles has been built by European industry. During the first stage of the fabrication period several technical improvements turned out to be necessary. All magnets have been carefully checked mechanically, optically, and electrically, and have been cold-tested at DESY. The result of these checks gives a good overview of the fabrication quality and gives hints for possible improvements for future superconducting accelerator magnet fabrication. The reproducibility achieved during mass production is very high. The rejection rate for nonconformity with specification was 7.2% overall. >

The conceptional design of the proposed linear electron-positron collider TESLA is based on 9-cell 1.3 GHz superconducting niobium cavities with an accelerating gradient of ${E}_{\mathrm{acc}}\ensuremath{\ge}25\mathrm{MV}/\mathrm{m}$ at a quality factor ${Q}_{0}\ensuremath{\ge}5\ifmmode\times\else\texttimes\fi{}{10}^{9}$. The design goal for the cavities of the TESLA Test Facility (TTF) linac was set to the more moderate value of ${E}_{\mathrm{acc}}\ensuremath{\ge}15\mathrm{MV}/\mathrm{m}$. In a first series of 27 industrially produced TTF cavities the average gradient at ${Q}_{0}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}5\ifmmode\times\else\texttimes\fi{}{10}^{9}$ was measured to be $20.1\ifmmode\pm\else\textpm\fi{}6.2\mathrm{MV}/\mathrm{m}$, excluding a few cavities suffering from serious fabrication or material defects. In the second production of 24 TTF cavities, additional quality control measures were introduced, in particular, an eddy-current scan to eliminate niobium sheets with foreign material inclusions and stringent prescriptions for carrying out the electron-beam welds. The average gradient of these cavities at ${Q}_{0}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}5\ifmmode\times\else\texttimes\fi{}{10}^{9}$ amounts to $25.0\ifmmode\pm\else\textpm\fi{}3.2\mathrm{MV}/\mathrm{m}$ with the exception of one cavity suffering from a weld defect. Hence only a moderate improvement in production and preparation techniques will be needed to meet the ambitious TESLA goal with an adequate safety margin. In this paper we present a detailed description of the design, fabrication, and preparation of the TESLA Test Facility cavities and their associated components and report on cavity performance in test cryostats and with electron beam in the TTF linac. The ongoing research and development towards higher gradients is briefly addressed.

A principal goal of the ongoing TESLA superconducting linac project is the production of affordable cryostats that still meet stringent requirements for alignment, vibration and heat leak. Each cryostat contains 8 superconducting RF cavities cooled to 1.8 K, a quadrupole magnet package cooled to 4.5 K, thermal shields cooled to 70 K and 4.5 K, active and passive magnetic shielding, cryogenic service pipes and all associated instrumentation. The axes of the 8 cavities must be aligned to the ideal beam axis to within ± 0.5 mm and those of the quadrupoles to within ± 0.1 mm. Additionally, the vertical mid plane of the quadrupole package must be aligned to the vertical direction to ± 0.1 mrad. These alignments must remain fixed after cool down and during operation. The cryostat must be designed so that there are no resonant vibration modes near the 10 Hz operating frequency of the accelerator. Although dynamic loads associated with the operation of the RF and the beam dominate the heat load, reasonable efforts to reduce the static heat leak into the cryostat are necessary.

The magnetic lattice of the TeV electron superconducting linear accelerator (TESLA) will consist of superconducting quadrupoles for beam focusing and superconducting correction dipoles for beam steering, incorporated in the cryostats containing the superconducting cavities. This report describes the design of these magnets, presenting details of the magnetic as well as the mechanical design. The measured characteristics of the TESLA Test Facility (TTF) quadrupoles and dipoles are compared to the results obtained from numerical computations.