Adjustable permanent magnetic lens having thermal control device

An electromagnetic lens comprising a charged-particle lens and a sleeve insert inserted into the passage space along the longitudinal axis,

• wherein the charged particle lens is configured to modify a charged-particle beam of a charged particle optical system, the lens being provided with a passage space extending primarily along a longitudinal axis and allowing the passage of a charged-particle beam, said lens including a magnetic circuit assembly comprising:
• at least one permanent magnet;
• and
• a yoke body;
• said yoke body being composed of at least two yoke components, of which a first yoke component realizes an inner yoke shell, arranged surrounding the passage space, and a second yoke component realizes an outer yoke shell which is arranged surrounding the inner yoke shell, said yoke components being arranged circumferential around the longitudinal axis and comprise highly magnetic permeable material;
• said at least one permanent magnet being arranged between the at least two yoke components and circumferentially around the inner yoke shell, said at least one permanent magnet comprising a permanent magnetic material being magnetically oriented with its two magnetic poles towards respective yoke components;
• wherein in the magnetic circuit assembly, the at least one permanent magnet and the yoke body form a closed magnetic circuit but having at least two gaps formed between respective axial faces of different yoke components, configured to direct a magnetic flux density coming from said at least one permanent magnet through the yoke body and in said gaps induce a magnetic field, which is reaching inwards into the passage space,
• the charged particle lens being provided with a thermal control assembly including at least one thermal control element located in the yoke body, said thermal control assembly being configured to control and actively change the temperature of at least portions of components of the magnetic circuit assembly for controlling and/or modifying the magnetic flux in the magnetic circuit, using the at least one thermal control element for introducing heat and/or extracting heat from said components
• said sleeve insert surrounding a beam passage of radius smaller than the radius of the passage space of the charged-particle lens, extending along a longitudinal axis,
• said sleeve insert comprising a mounting body, which is at least partially electrically conductive, and at least one electrically conductive electrode element,
• said at least one electrically conductive electrode element being configured to be applied an electric potential so as to generate an electrostatic field within the beam passage,
• wherein the at least one electrically conductive electrode element are configured to form a particle-optical lens in conjunction with the magnetic field within the beam passage at at least one of the gaps of said charged-particle lens, wherein a focal length of said charged particle-optical lens is adjustable through modifying the electric potential applied to the at least one electrically conductive electrode element.