System and method for producing superimposed static and time-varying magnetic fields

An apparatus for producing a magnetic field modulated at a fundamental frequency of at least 20 Hz for scanning an ion beam over a selected surface comprising:

• two magnetic poles defining a gap therebetween, the poles being formed with electrically insulating material for confining any high frequency induced eddy currents to limited values in local paths in the poles;
• an ac coil associated with the magnetic poles for producing a time-varying magnetic field in the gap;
• a magnetic structure including a yoke and two cores which are respectively coupled to the two poles, the magnetic structure being formed of solid material, with a high magnetic saturation level;
• and
• dc coils associated with the cores of the magnetic structure for producing a static magnetic field in the gap;
• an ac current source for energizing the ac coil with a time-varying oscillatory electric current to produce a magnetic field in the gap that alternates in direction with time at a fundamental frequency of the order of 20 Hz or greater together with substantially higher order harmonics;
• and
• a dc current source for energizing the dc coil 5 with a static electric current to produce the static magnetic field in the gap.

An apparatus for producing a magnetic field having static and high frequency time-varying components comprising:

• two magnetic poles defining a gap therebetween, the poles being formed from a plurality of laminations of high magnetic permeability material separated by electrically insulating layers, the laminations providing a low reluctance magnetically permeable path for the high frequency time-varying component of the produced magnetic field;
• an ac coil associated with the magnetic poles for producing a time-varying magnetic field in the gap;
• a magnetic structure including a yoke and two cores which are respectively coupled to the two poles, the magnetic structure being formed of solid material, with a high magnetic saturation level;
• and
• dc coils associated with the cores of the magnetic structure for producing a static magnetic field in the gap.

An apparatus for producing a magnetic field having static and high frequency time-varying components comprising:

• two magnetic poles defining a gap therebetween, the poles comprise different sets of laminations of high magnetic permeability material separated by electrically insulating material, the sets being disposed cross-wise to each other so that magnetic flux passing through any given lamination in one of the sets is distributed into a multiplicity of laminations in another of the sets;
• an ac coil associated with the magnetic poles for producing a time-varying magnetic field in the gap;
• a magnetic structure including a yoke and two cores which are respectively coupled to the two poles, the magnetic structure being formed of solid material, with a high magnetic saturation level;
• and
• dc coils associated with the cores of the magnetic structure for producing a static magnetic field in the gap.

An apparatus for producing a magnetic field having static and high frequency time-varying components comprising:

• two magnetic poles defining a gap therebetween, the poles being formed from high magnetic permeability ferrite material;
• a first pair of electrical conductors, each of the first pair of conductors being positioned at opposite sides of the gap, the first conductors being constructed and arranged to produce a first magnetic gradient field over a substantial portion of the region of the gap;
• an ac coil associated with the magnetic poles for producing a time-varying magnetic field in the gap;
• a magnetic structure including a yoke and two cores which are respectively coupled to the two poles, the magnetic structure being formed of solid material, with a high magnetic saturation level;
• and
• dc coils associated with the cores of the magnetic structure for producing a static magnetic field in the gap.

A method for scanning an ion beam over a selected surface comprising the steps of:

• providing a scanning magnet comprising
• two magnetic poles defining a gap therebetween, the poles being formed with electrically insulating material for confining any high frequency induced eddy currents to limited values in local paths in the poles,
• an ac coil associated with the magnetic poles for producing a time-varying magnetic field in the gap,
• a magnetic structure including a yoke and two cores which are respectively coupled to the two poles, the magnetic structure being formed of solid material, with a high magnetic saturation level, and
• dc coils associated with the cores of the magnetic structure for producing a static magnetic field in the gap;
• passing an ion beam into the gap along a first beam path;
• and
• generating in the ac and dc coils energizing waveforms to produce in the gap a substantially unipolar scanning magnetic field that varies in magnitude as a function of time to cause scanning of the ion beam over the selected surface.