Cryosystem for a Proton‐radiography Achromat

Performing proton radiography on thick objects using conventional linear quadrupole lenses (four quadrupoles of equal strength and alternating sign) with the beam energy available (800 MeV) at the Los Alamos Neutron Science Center (LANSCE) results in significant chromatic aberrations — on the order of a few millimeters when a resolution of < 0.5 mm is desirable. We consider the use of a second‐order achromat with octupole correctors to eliminate second‐order terms and minimize the third‐order effects. A strawman achromat is constructed from five magnetic cells. The pool‐boiling superconducting magnets in each 5.27‐m long cell consist of a dipole (12° bend angle), a pair of multipole packages (quadrupole, sextupole and octupole), one immediately upstream and downstream of the dipole, and an octupole package. High‐temperature superconducting leads will be used with the higher current magnets (dipoles and quadrupoles). This paper describes a conceptual cryosystem for cooling the superconducting magnets of th...