The magnetic field in accelerator magnets decays when the current is kept constant during the particles injection phase, and returns quickly (snaps back) to the original values as soon as ramping is restarted. Here we show results of measurements of the decay of the field errors in 10 m long LHC model dipole magnets. In accordance with previous findings, precycles and stops at intermediate current levels influence the decay. We discuss a possible mechanism causing the decay and snap-back, based on the internal field change in the cable.

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Field errors decay and "snap-back" in LHC model dipoles

The new heavy ion synchrotron facility proposed by GSI will have two superconducting magnet rings in the same tunnel, with rigidities of 200T-m and 100T.m. Fast ramp times are needed, which can cause significant problems for the magnets, particularly in the areas of s c loss and field distortion. This paper discusses the 200T.m ring, which will use Cos0 magnets based on the RHIC dipole design. We discuss the reasons for choosing Rutherford cable with a resistive core and report loss measurements carried out on cable samples. These measurements are compared with theoretical calculations using measured values of inter-strand resistance. Reasonably good agreement is found, but there are indications of non-uniformity in the adjacent resistance R,. Using these measured parameters, losses and temperature rise are calculated for a RHIC dipole in the operating cycle of the accelerator. A novel insulation scheme designed to promote efficient cooling is described.

/pdf/cored-rutherford-cables-for-the-gsi-fast-ramping-synchrotron-3safy7oong.pdf

Cored rutherford cables for the gsi fast ramping synchrotron.

Several superconducting dipole magnets were manufactured in industry or at CERN as model magnets for the future Large hadron Collider (LHC) particle accelerator. Results of the measurements of the field quality is given for current variations in the range of those expected for the accelerator operation. We present measurements of the field errors resulting from persistent currents in the superconducting filaments, eddy currents flowing in and between the strands of the superconducting cable, and current differences between the strands of the cable. >

/pdf/dynamic-magnetic-measurements-of-superconducting-magnets-for-5cw6e8jj2c.pdf

Dynamic magnetic measurements of superconducting magnets for the LHC

Superconducting magnets have enabled the construction of some very large accelerators to explore the structure of matter at the highest energies. Small superconducting accelerators are used in medicine and industry. We review the special demands which accelerators make on superconductor technology, describe the magnets for large and small accelerators and mention some exciting prospects for the future.

/pdf/superconducting-magnets-for-accelerators-a-review-2iovfis1in.pdf

Superconducting magnets for accelerators: a review

The field quality of 10 m long LHC dipole models has been measured with short rotating coils to explore its dependence on time and position. Multipoles exhibit longitudinal periodic variation, with period equal to the twist pitch length. This periodicity is shown here to have at least two components with very different time constants. The amplitude of the component with the shorter time constant, in the range of 100 to 300 s, depends on position and time. Larger amplitudes are measured at early times after a ramp and close to regions with incomplete cable transposition with respect to the non-uniform external field change. As the multipoles periodicity is due to current imbalance in the cables, we attribute the short time scale variations to the presence of space and time decaying boundary induced coupling currents (BICC's) in the cable. An estimate of their value is given.

/pdf/experimental-evidence-of-boundary-induced-coupling-currents-23ecv0d6dk.pdf

Experimental evidence of boundary induced coupling currents in LHC prototypes

http://inspirehep.net/record/316761/files/sscl-414.pdf

Peter Schmueser

Papers

Observation of a periodic pattern in the persistent current fields of the superconducting HERA magnets

Reference magnets for the superconducting HERA proton ring