Patent ID: 7005953

Claim:
A magnet system comprising: a magnet arrangement for generating a magnetic field in a working volume; a pulse tube cooler having a magnetic regenerator material; and a shielding of magnetic material, said shielding structured and disposed to reduce a stray field of said magnet arrangement at said location of said magnetic regenerator material, wherein ⅓ |{tilde over (m)} REG R|+|m Mag Δx|< ⅙ |m Reg R|, with m Mag being a dipole moment of the magnetic material of said shielding, Δx a vibration amplitude of said magnetic material of said shielding, m Reg an amplitude of dipole fluctuations of said magnetic regenerator material in one cycle without said magnetic shielding, {tilde over (m)} Reg an amplitude of dipole fluctuations of said magnetic regenerator material in one cycle with said magnetic shielding, and R an average separation of said magnetic regenerator material from the working volume.