Abstract
Accelerators magnets must have minimal magnetic field imperfections to reduce particle-beam instabilities. In the case of coils made of high-temperature superconducting (HTS) tapes, the magnetization due to persistent currents adds an undesired field contribution, potentially degrading the magnetic field quality. In this paper we study the use of superconducting screens based on HTS tapes for reducing the magnetic field imperfections in accelerator magnets. The screens exploit the magnetization by persistent currents to cancel out the magnetic field error. The screens are aligned with the main field component, such that only the undesired field components are compensated. The screens are self-regulating, and do not require any externally applied source of energy. Measurements in liquid nitrogen at show for dipole-field configurations a significant reduction of the magnetic field error up to a factor of four. The residual error is explained via numerical simulations accounting for the geometric defects in the HTS screens, achieving satisfactory agreement with experimental results. Simulations show that if screens are increased in width and thickness, and operated at , field errors may be eliminated almost entirely for the typical excitation cycles of accelerator magnets.
Highlights
Future circular accelerators for high-energy particle physics are expected to rely on increasingly higher magnetic fields for steering and focusing the particle beams [1]
In this paper we study the use of superconducting screens based on high-temperature superconducting (HTS) tapes for reducing the magnetic field imperfections in accelerator magnets
This paper presents the proof of concept for HALO (HarmonicsAbsorbing Layered Object), a technology for field-error cancellation based on ReBCO tapes composing passive and selfregulating HTS screens
Summary
Future circular accelerators for high-energy particle physics are expected to rely on increasingly higher magnetic fields for steering and focusing the particle beams [1]. High-temperature superconducting (HTS) tapes based on rare-earth cuprate compounds (ReBCO) have an estimated upper critical field of 140 T [2], and a critical temperature of 93 K. HTS magnets are expected to be operated at fields around 20 T [3] and with enthalpy margins one order of magnitude above traditional low temperature superconducting (LTS) materials, such as Nb-Ti or Nb3Sn [4]. HTS magnets based on ReBCO tapes are a promising technology for high-field magnets in particle accelerators [3]. The field quality is determined by magnet design features such as coil geometry and mechanical tolerances, and influenced by material properties such as saturation and hysteresis of the iron yoke. Time-transient effects such as mechanical deformation due to Lorentz forces, and magnetization due to eddy currents and screening currents in normal conducting and superconducting materials are expected to have detrimental effects
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