• A.V. Zlobin, V. Kashikhin, N.V. Mokhov, I. Novitski
  Fermilab, Batavia

Magnetic and mechanical designs of a superconducting quadrupole magnet with 120-mm aperture suitable for interaction regions of hadron colliders are presented. The magnet is based on a two-layer shell-type coil and a cold iron yoke. Special spacers made of a low-Z material are implemented in the coil midplanes to reduce the level of radiation heat deposition in the coil. The quadrupole mechanical structure is based on a thick aluminum collar supported by the iron yoke and stainless steel skin. Magnet parameters including maximum field gradient, field quality and temperature margin for NbTi or Nb₃Sn coils at the operating temperatures of 1.9 K and 4.5 K are reported. The level and distribution of radiation heat deposition in the coil and other magnet components are discussed.

• A.V. Zlobin, Y. Alexahin, V. Kashikhin, N.V. Mokhov
  Fermilab, Batavia

Conceptual designs of superconducting magnets (dipoles and quadrupoles) for a muon collider with a 1.5 TeV c.o.m. energy and an average luminosity of 10³⁴ cm^-2s^-1 are presented. All magnets are based on the Nb₃Sn superconductor and designed to provide an adequate operation field/field gradient in the aperture with the critical current margin required for reliable machine operation. In contrary to proton machines, the dipole magnets should have open midplanes, and, for some of them, the required good field quality region needs to have a vertical aspect ratio of 2:1 that imposes additional challenges for the magnet design. Magnet cross-sections were optimized to achieve the best possible field quality in the magnet aperture occupied with beams. The magnets and corresponding protective measures are designed to handle about 0.5 kW/m of dynamic heat loads from the muon beam decays. Magnet parameters are reported and compared with the requirements.

• A.V. Zlobin, E.Z. Barzi, V.S. Kashikhin, M.J. Lamm, V. Lombardo, M.L. Lopes, M. Yu
  Fermilab, Batavia
• G. Flanagan, R.P. Johnson, S.A. Kahn, M. Turenne
  Muons, Inc, Batavia

The Helical Cooling Channel (HCC) is a technique proposed for six-dimensional (6D) cooling of muon beams. The HCC for muon collider and some other applications is usually divided into several sections each with progressively stronger fields, smaller aperture, and shorter helix period to achieve the optimal muon cooling rate. Novel magnet design concepts based on simple coils arranged in a helical solenoid configuration have been developed to provide HCC magnet systems with the desired parameters. The level of magnetic field in the HCC high-field sections suggests using a hybrid coil structure with High Temperature Superconductors (HTS) in the innermost coil layers and Nb₃Sn superconductor in the outer coil layers. The development of the concepts and engineering designs of hybrid helical solenoids based on advanced superconductor technologies, with special emphasis on the use of HTS for high fields at low temperature is the key step towards a practical HCC. This paper describes the conceptual designs and parameters of a short HTS model of a hybrid helical solenoid, and discusses the structural materials choices, fabrication techniques, and first test results.

• S.A. Kahn, G. Flanagan, R.P. Johnson, M. Turenne
  Muons, Inc, Batavia
• F. Hunte, J. Schwartz
  North Carolina State University, Raleigh, North Carolina

YBCO superconductors originally developed for high temperature operation carry significant critical current even in the presence of extremely high magnetic field when operated at low temperature. The final stage of phase space cooling for a muon collider uses a solenoid magnet with fields approaching 50 T. As part of an R&D effort we present measurements of mechanical and electromechanical properties of the YBCO conductor. We examine the critical current verses magnet field angle at 4.2 K in a magnetic field. Quench properties of the conductor such as minimum quench energy threshold and quench propagation velocity will be measured to establish safe operational conductions for the muon cooling magnets. In this paper we describe a conceptual picture for a high field solenoid to be used for muon phase space cooling that incorporates these low temperature properties of YBCO.

• M. Turenne, R.P. Johnson
  Muons, Inc, Batavia
• F. Hunte, J. Schwartz
  North Carolina State University, Raleigh, North Carolina
• H. Song
  NHMFL, Tallahassee, Florida

High field accelerator magnets are needed for high energy physics applications. Superconducting materials able to reach these fields with low losses are required, and YBCO Roebel cable is being developed to address this issue. Characterization of commercially available Roebel cables for high field low temperature superconducting magnets is needed. YBCO Roebel cable with low AC losses is being developed and has limited commercial availability. Its behavior is not fully understood, however, especially in liquid helium and at high magnetic fields. YBCO Roebel cable will be acquired from a commercial vendor and characterized at cryogenic temperatures, in varying magnetic fields, and different strain configurations. A comprehensive behavior analysis will be performed, including operational and fatigue limits. Characterization of YBCO Roebel cable at low temperatures will be performed, including determination of the current flow path in steady-state and during quench using magneto-optical imaging, investigation of the effects of strand insulation, and examination of the mechanical and quench behavior at 4.2 K, 77 K, and varying magnetic fields.

• M.A. Green, A.J. DeMello, D. Li, F. Trillaud, S.P. Virostek, M.S. Zisman
  LBNL, Berkeley, California
• X.L. Guo, S.Y. Li, H. Pan, L. Wang, H. Wu, S.X. Zheng
  ICST, Harbin

Tests of the spectrometer solenoids have taught us some important lessons. The spectrometer magnet lessons learned fall into two broad categories that involve the two stages of the coolers that are used to cool the magnets. On the first spectrometer magnet, the problems were centered on the connection of the cooler 2nd-stage to the magnet cold mass. On the second spectrometer magnet, the problems were centered on the cooler 1st-stage temperature and the connections between leads, the cold mass support intercept, and the shields to the cooler first-stage. If the cooler 1st-stage temperature is too high, the refrigerator will not produce full 2nd stage cooling. If the 1st-stage temperature is too high, the temperature of the top of the HTS leads. As a result, more heat goes into the 4 K cold mass and the temperature margin of the top of the HTS leads is too small, which are in a magnetic field. The parameters that affect the magnet cooling are compared for the MICE coupling magnet and the spectrometer magnet.