| 主权项 |
1. An insulation structure provided among a plurality of electrodes for extraction of an ion beam from a plasma generating section, the plurality of electrodes comprising a first electrode and a second electrode to which different potential from that of the first electrode is applied, the insulation structure comprising:
an insulation member comprising a first part connected to the first electrode and a second part connected to the second electrode and configured to support the first electrode to the second electrode, the first part having a first circular end surface on a side of the first electrode, the second part having a second circular end surface on a side of the second electrode, the insulation member having a cylindrical side surface that connects the first end surface to the second end surface, the cylindrical side surface having a recess formed thereon and positioned between the first end surface and the second end surface; a first protection member surrounding at least a part of the first part to protect the first part from contamination particles; and a second protection member surrounding at least a part of the second part to protect the second part from contamination particles, wherein at least one of the first part and the second part is made of a machinable ceramic or a porous ceramic; the first protection member is a first cover having a first cover end, the second protection member is a second cover having a second contact portion and a second stepped side wall, the second contact portion contacting the second part and sandwiched between the second part and the second electrode, the second stepped side wall extending from the second contact portion toward the first electrode to form a pathway of the contamination particles between the first cover and the second stepped side wall, the second stepped side wall comprises a thin wall portion, a thick wall portion, and a step of the stepped side wall formed between the thin wall portion and the thick wall portion, the thin wall portion surrounding the first cover end, the thick wall portion extending from an outer circumferential portion of the second contact portion to the thin wall portion and terminating at the step of the stepped side wall, an exit of the pathway is formed between the first cover end and the step, the exit opposed to the recess. |
