Patent ID: 11923166

Abstract:
In a cylindrical guard electrode (5) provided on the outer peripheral side of an electron generation part (31) of an emitter (3), a distal end section (5A) 5 positioned in the emission direction of an electron beam (L1) from the electron generation part (31) includes: a distal end inner-peripheral-side part (A1) having an inner-peripheral-side curved surface portion (a1) convex in the emission direction; a distal end outer-peripheral-side part (A2) having an outer-peripheral-side curved portion (a2) convex in the emission direction; and a 10 distal end middle part (A3) positioned between the distal end inner-peripheral-side (A1) and the distal end outer-peripheral-side part (A2). The distal end middle part (A3) has a flat surface portion (a3) between the inner-peripheral-surface portion (a1) and the outer-peripheral-side curved surface portion (a2) so as to extend in the direction therebetween.