Superconducting Magnet Package Research Articles

Design of an Emittance Compensation Superconducting Magnet Package for LCLS-II-HE's SRF Photo-Injector

An SRF photo-injector (low frequency, quarter-wave resonator plus emittance compensation magnet) is planned for LCLS-II-HE as it can provide a higher cathode gradient and better electron beam quality than other types of CW electron guns. The magnet package is located immediately downstream of the SRF cavity, and incorporates a solenoid doublet, bucking coils for reduction of the fringe field, normal/skew quadrupoles and horizontal/vertical dipoles. All the magnets are wound of NbTi wire and operate in liquid helium environment. The solenoid package is located inside the SRF gun cryomodule. Design considerations include space limitations, optimal emittance compensation, the magnetic field limits in the superconducting wire and quench protection. The solenoid coils must provide a peak excitation > 25 kgauss <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ·cm, a fringe field < 20 gauss at the wall of the SRF cavity, an integrated dipole field < 90 gauss·cm and an integrated quadrupole field < 10 gauss. A genetic algorithm was used to optimize the solenoid design. Correction dipoles and quadrupoles were designed using coil dominated Walstrom style coils.

Superconducting Magnet Performance for the LCLS-II Project

The new LCLS-II Superconducting Linear Accelerator Cryomodules are under construction at Fermilab. Installed inside each Super Conducting Radio Frequency (SCRF) Cryomodule is a superconducting magnet package to focus and steer an electron beam. The iron-dominated magnet package has conductively cooled racetrack-type coils with both quadrupole and dipole windings. For ease of installation, the magnet is splittable in the vertical plane. To confirm magnet specifications, we performed a quality acceptance in a liquid helium bath for quench testing, and we performed high-precision magnetic field measurements. The magnetic and mechanical center alignment was investigated using the vibrating wire technique. Several prototypes and all production units have been tested. This paper summarizes the magnetic measurements and quench test results of all tested units, including comparison of performance and repeatability between different units.

Serial testing of XFEL cryomodules: results of the cryogenic heat load measurements

The European X-ray Free Electron Laser (XFEL) is in operation at DESY. The superconducting XFEL linac will produce pulsed electron beam at an energy of 17.5 GeV. The linac consists of 768 superconducting niobium 1.3 GHz nine cell cavities and 96 superconducting magnet packages assembled in 96 cryomodules. Each cryomodule is 12 m long and includes a 2 K helium II bath circuit for the cavities, and 5/8 and 40/80 K thermal radiation shields. Before being installed in the XFEL linac tunnel all cryomodules were tested in the Accelerator Module Test Facility (AMTF.)In this paper methods and results of static and dynamic heat load measurements of all XFEL cryomodules are reported. A comparison with first integral heat load measurements in the XFEL linac is given.

Performance of Superconducting Magnet Prototypes for LCLS-II Linear Accelerator

The new LCLS-II Linear Superconducting Accelerator at SLAC needs superconducting magnet packages installed inside SCRF (superconducting radio frequency technology) cryomodules to focus and steer an electron beam. Two magnet prototypes were built and successfully tested at Fermilab. Magnets have an iron-dominated configuration, quadrupole and dipole NbTi superconducting coils, and splittable in the vertical plane configuration. Magnets inside the cryomodule are conductively cooled through pure Al heat sinks. Both magnets' performance was verified by magnetic measurements at room temperature, and during cold tests in liquid helium. Test results including magnetic measurements are discussed. Special attention was given to the magnet performance at low currents where the iron yoke and the superconductor hysteresis effects have large influence. Both magnet prototypes were accepted for the installation in FNAL and JLAB prototype cryomodules.

Performance of Conduction Cooled Splittable Superconducting Magnet Package for Linear Accelerators

New linear superconducting accelerators need superconducting magnet packages installed inside SCRF cryomodules to focus and steer electron or proton beams. A superconducting magnet package was designed and built as a collaborative effort of FNAL and KEK. The magnet package includes one quadrupole and two dipole windings. It has a splittable in the vertical plane configuration and features for conduction cooling. The magnet was successfully tested at room temperature, in a liquid He bath, and in a conduction cooling experiment. This paper describes the design and test results, including magnet cooling, training, and magnetic measurements by rotational coils. The effects of superconductor and iron yoke magnetization, hysteresis, and fringe fields are discussed.

RF heat load compensation with electrical heater for XFEL accelerator - measurements at CMTB, AMTF and FLASH

A superconducting linac will provide electron bunches of 17.5 GeV beam energy for the operation of the European X-ray Free Electron Laser (XFEL) at DESY. 800 superconducting niobium 1.3 GHz nine cell cavities and 100 superconducting magnet packages will be cooled in a liquid helium II cooling bath at 2.0K temperature. Liquid helium II bath cooling at 2.0K is established by means of a 4 stages cold compressor system. For the stable operation of cold compressors sudden load changes should be avoided. Electrical heaters in the helium II bath will compensate dynamic heat load changes caused by the radio frequency (RF) operation of the cavities in the XFEL linac. The complementary load operation of electrical heaters is studied at the existing facilities at DESY. Measurements performed at Cryo Module Test Bench (CMTB), Accelerator Module Test Facility (AMTF) and FLASH accelerator are reported.

Compact Superconducting Magnet for Linear Accelerators

New Linear Accelerators based on superconducting radiofrequency (SCRF) cavities need compact and efficient superconducting magnet packages to focus and steer electron or proton beams. These magnets should be combined with SCRF cryomodules and installed inside or between them. A recent activity in this area was directed by FNAL-KEK collaboration to splittable conduction cooled magnets. Several magnet prototypes were built and successfully tested. These magnets were designed for high energy beams used in ILC, and Project-X. Nevertheless, there is an interest to explore splittable conduction cooled magnets for new accelerators: FNAL ASTA and PIP-II, KEK STF, SLAC LCLS II. The paper describes a conceptual design of splittable conduction cooled superconducting magnet which could be mounted inside SCRF cryomodule. The magnet package combines the quadrupole magnet and dipole correctors. The presented magnetic design confirms the specified magnet package parameters.

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.

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.

Rotating coil field measurement of superconducting magnet for BEPCII interaction region

Two multifunction superconducting magnets in the interaction region (IR) for Beijing electron positron collider upgrade project (BEPCII) have been measured in BESIII detector hall in 2007. Each superconducting magnet package contains multiple concentric layers with several function magnets called as a vertical focusing quadrupole (SCQ), a horizontal corrector (HDC/SCB), a vertical corrector (VDC), a skew quadrupole (SKQ) and three anti-solenoids (AS1, AS2 and AS3) to compensate the experimental detector solenoid field. All these function magnets SCQs, SCB/HDCs, VDCs and SKQs have been measured using two rotating coils. Their integral fields, their high order harmonics contents and the local fields along the beam line are obtained in detail with the rotating coil probe system. Comparing the results to the stretched wire, the differences for the integral fields are less than 0.2%. As a result, the method presented in this paper can be used as an absolute field measurement in our lab.

Harmonic Coil Design, Fabrication and Commissioning for European XFEL Linear Accelerator Superconducting Magnets Field Measurements

A harmonic coil assembly for the European XFEL superconducting magnet measurements was designed and fabricated in IHEP. Bare coil without protection tube was selected in order to save space and cover a larger measurement radius. The coil assembly can be moved along the anticryostat pipe and can be fixed at any position by rubber brakes touching on the inner surface of the pipe, which is a part of the magnet measurement dewar. The magnetic field can be measured by rotating the coil inside the anticryostat pipe at a selected position. The superconducting magnet package consists of a quadrupole, a horizontal and a vertical dipole. The harmonic coil includes a main coil for the quadrupole and for the dipole field measurement when the single coil mode is used to measure the main field component. Two bucking coils are available to compensate the quadrupole and dipole field respectively when the two-coil mode is used to measure the high order field harmonics. A skew coil with only 2 turns and open angle of 90 degrees can be used to cancel effects due to the angular differences between the main coil plane and the bucking coil plane. The harmonic coil was tested on quadrupoles for Korea Pohang Accelerator Laboratory (PAL), a high bucking ratio of 182 was reached. The coil was shipped and used in DESY to measure the XFEL superconducting magnets. The measurement precision and reproducibility were excellent and the driving and brake system worked well.

Superconducting magnet package for the TESLA Test Facility

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.