Charged particle beam steering arrangement

A charged particle optical assembly for use in additive layer manufacture, arranged to form a product in a series of layers, each layer formed by irradiating a powder bed using a charged particle beam to fuse powder to form a desired layer shape, the assembly comprising:

• a charged particle source;
• a beam forming apparatus operable to form the beam of charged particles from the charged particles provided by the charged particle source that travels along a direction of propagation;
• and
• a beam steering apparatus;
• wherein the beam steering apparatus comprises a long-range deflector operable to deflect the charged particle beam over a first deflection range and a short-range deflector operable to deflect the charged particle beam over a second deflection range, wherein the first deflection range is larger than the second deflection range;
• wherein the long-range deflector is configured to be used repeatedly to set an array of base positions of the charged particle beam on the powder bed;
• and
• the short-range deflector is configured to be used to scan the charged particle beam around each of the array of different base positions set by the long-range deflector to trace a pattern on the powder bed to fuse the powder in a predetermined shape at each base position, such that wherein the predetermined shapes at the array of base positions combine to form the desired layer shape of fused powder,
• wherein the current of the charged particle beam is controlled and the scan speed of the short-range deflector is controlled to raise and maintain the temperature of the powder bed evenly within each predetermined shape.