• V.S. Kashikhin, N. Andreev, V. Kashikhin, M.J. Lamm, A.V. Makarov, G.V. Romanov, K. Yonehara, M. Yu, A.V. Zlobin
  Fermilab, Batavia

Helical Solenoids (HS) were proposed for a muon beam ionization cooling. There are substantial up to 30 MeV/m energy losses during passing the muon beam through an absorber. The main issue of such system is the energy recovery. A conventional RF cavity has diameter which is too large to be placed inside HS. In the paper presented results of dielectric filled RF cavity design. The proposed cavity has helical configuration. Presented Helical Cooling Channel module design which includes: high pressure vessel, RF cavity, and superconducting HS. Discussed parameters of this module sub-systems and shown results of muon beam tracking in combined magnetic and electric 3D fields.

• 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. Caspi, D.W. Cheng, D.R. Dietderich, H. Felice, P. Ferracin, R.R. Hafalia, J.M. Joseph, J. Lizarazo, G.L. Sabbi, X. Wang
  LBNL, Berkeley, California
• G. Ambrosio, R. Bossert, A.V. Zlobin
  Fermilab, Batavia
• M. Anerella, A.K. Ghosh, J. Schmalzle, P. Wanderer
  BNL, Upton, Long Island, New York

Advanced superconductors such as Nb₃Sn are being considered for future magnet upgrades of the Large Hadron Collider (LHC) at CERN. The US LHC Accelerator Research Program (LARP) has developed a large bore (120mm) Nb₃Sn IR quadrupole (HQ) capable of reaching 15 T at its conductor and a gradients of 199T/m at 4.4K and 219T/m at 1.9K. HQ is addressing coil alignment and accelerator field quality in a shell-based mechanical structure. In this paper we summarize the fabrication, assembly and initial test results of the 1 m long two-layer magnet.

• Y. Alexahin, E. Gianfelice-Wendt, V. Kashikhin, N.V. Mokhov, A.V. Zlobin
  Fermilab, Batavia
• V.Yu. Alexakhin
  JINR, Dubna, Moscow Region

Design of a muon collider interaction region (IR) presents a number of challenges arising from low beta* < 1 cm, correspondingly large beta-function values and beam sizes at IR magnets, as well as the necessity to protect superconducting magnets and collider detectors from muon decay products. As a consequence, the designs of the IR optics, magnets and machine-detector interface are strongly interlaced and iterative. A consistent solution for the 1.5 TeV c.o.m. muon collider IR is presented. It can provide an average luminosity of 10³⁴/cm²/s with an adequate protection of magnet and detector components.

• S.A. Kahn, G. Flanagan, R.P. Johnson, M.L. Neubauer
  Muons, Inc, Batavia
• V.S. Kashikhin, M.L. Lopes, K. Yonehara, M. Yu, A.V. Zlobin
  Fermilab, Batavia

A helical cooling channel (HCC) consisting of a pressurized gas absorber imbedded in a magnetic channel that provides solenoidal, helical dipole and helical quadrupole fields has shown considerable promise in providing six-dimensional cooling for muon beams. The energy lost by muons traversing the gas absorber needs to be replaced by inserting RF cavities into the HCC lattice. Replacing the substantial muon energy losses using RF cavities with reasonable gradients will require a significant fraction of the channel length be devoted to RF. However to provide the maximum phase space cooling and minimum muon losses, the HCC should have a short period and length. In this paper we examine an approach where each HCC cell has an RF cavity imbedded in the aperture with the magnetic coils are split allowing for half of the cell length to be available for the RF coupler and other services.