Minimum quench energies of Rutherford cables and single wires

IEEE Trans. Appl. Supercond.

Verweij

Scheuerlein

et al. 2008

Abstract-Keystoned superconducting Rutherford cables are widely used in accelerator magnets like in the LHC at CERN. An essential requirement in the cable design is its stability against local heat releases in the magnet windings originating from for example, strand movement or beam loss. Beam loss is the highest at the coil inner radius of the magnet, where also the magnetic field peaks. Also the local compaction of the cable is maximum here and hence the helium content minimum. When performing stability measurements on several superconducting Nb-Ti cables used in LHC dipole and quadrupole magnets, we observed that the stability against point-like heat disturbances is much worse very close to the cable edges as compared to the central part of the cable. The main reason is related to the geometry of the cable causing variation of many parameters across the cable width, like inter-strand electrical resistance, inter-strand heat conductivity, cooled strand surfaces and RRR. In this paper we show results of new stability experiments and thoroughly compare the data with results obtained with the numerical network model CUDI, which is updated for stability simulations.

mentioning

confidence: 99%

Difference in Stability Between Edge and Center in a Rutherford Cable

IEEE Trans. Appl. Supercond.

Verweij

Scheuerlein

et al. 2008

“…During the curing of the epoxy, pressure was applied in such a way that a final resistance between 1 and 2 is reached. A similar set-up of heaters was used by [8]- [10].…”

Section: Methodsmentioning

confidence: 99%

Stability of Nb-Ti Rutherford Cables Exhibiting Different Contact Resistances

IEEE Trans. Appl. Supercond.

Verweij

Kaugerts

et al. 2008

Abstract-Dipole magnets for the so-called SIS-300 heavy-ion synchrotron at GSI are designed to generate 6 T with a field sweep rate of 1 T/s. It is foreseen to wind the magnets with a 36 strands Nb-Ti Rutherford cable. An important issue in the cable design is sufficiently low AC loss and stability as well. In order to keep the AC loss at low level, the contact resistance between crossing strands R c is kept high by putting a stainless steel core in the cable. The contact resistance between adjacent strands R a is controlled by oxidation of the Sn-Ag coating of the strands, like in the LHC. In order to investigate the effect of R a on the stability of the cable, we prepared four samples with different R a by varying the heat treatment and applying a soldering technique, resulting in values between 1 to 9 m. The stability of each sample against transient point-like heat pulses was measured. The results of the stability experiments and a comparison with calculations using the network model CUDI are presented. It is concluded that variation of R a has a strong influence on cable stability and that optimization of R a is mandatory to properly design the cable for the SIS-300 magnets, or likewise for similar magnets that might be used at CERN for a possible LHC injector upgrade.

“…[19] divides the cable in five clusters of strands and is focused on describing the mqe of a cable against a heat deposition in a local strand section. The comparison of the calculations of mqe in [19] with measurements in [39] shows the ability of the model to describe the stability mechanisms well. More recent models, described in [40] and [41], also describe the full cable with clustered strands, so-called superstrands.…”

Section: Analytical Approachmentioning

confidence: 99%

“…However, the 8 µm Kapton heaters showed mechanical failure in too many occasions. Graphite paste heater Graphite paste heaters were used for wire stability measurement by [68] and for all cable stability measurements reported in [69,39,54,51,56]. The heat is produced with a current through the resistive paste.…”

Section: Strain Gagesmentioning

confidence: 99%

Stability of superconducting Rutherford cables for accelerator magnets

f c e e r g s o r a c l r a t o m a n e t Gerard Willering S t a b i l i t y o f S u p e r c o n d u c t i n g r C b l e R u t h e f o r d a s PrefaceThe work described in this thesis results from an extensive collaboration between the special chair for Industrial Application of Superconductors in the Low Temperature Division at the University of Twente and the Magnets, Superconductors and Cryostats group at CERN. The research has been carried out at CERN as well as at the University of Twente and it is funded by both institutes. Part of the cable samples were prepared by GSI in the frame of research collaboration on cable stability.I am very grateful to the members of these groups for giving me the opportunity to perform the research, for their interest and useful discussions.i ContentsPreface i Chapter 1 IntroductionAfter the discovery of superconductivity in the beginning of the 20 th century the understanding of the phenomenon has grown. Practical conductors are produced for various magnet applications. Although the number of superconducting materials is high, only a few can be used in high-field and high-current density applications. This thesis deals with cable stability, with the focus on application in accelerator magnets.In this chapter a brief overview of the existing and near future accelerators and their superconducting magnets is presented. The most recent superconducting accelerator, the lhc and the near future superconducting accelerator sis 300 are described.The phenomenon of superconductivity is shortly discussed and practical superconductors are introduced with an emphasis on strands and cables. Different types of cables are presented and the relevance of this thesis for in particular the Rutherford type of cable is discussed.The terms quench and recovery are introduced. The importance of research on stability is illustrated by the large number of training quenches in the lhc main dipole magnets. Superconducting accelerator magnetsIn High Energy Physics the interaction of elementary particles is being studied. Many particle accelerators have been constructed to accelerate particles and collide them at high energy. Synchrotron accelerators provide a circular track with RFcavities to accelerate bunches of particles each cycle.Synchrotron accelerators require dipole magnets to bend the particle beam and keep it in its circular track. Quadrupole magnets are used to focus and defocus the beam and higher-order magnets correct field distortions and chromaticity. The collision energy depends on the magnetic field in the aperture of the dipole B a (T) and the bending radius of the dipole magnets r d (km) following E ≈ 0.3B a r d (TeV). The limitation in the track circumference is strongly dictated by the amount of material and the costs involved. In normal conducting magnets iron is applied to enhance the electromagnetic field produced with copper windings. The magnetic field in iron saturates at about 2 T, therefore the needed amount of copper windings and the costs involved increase strongly for hig...