Travelling-wave tube

A travelling-wave tube comprising:

• a helix joined by posts to a vacuum chamber, each post made of electrically insulating material being covered by an electrically conductive material, of electrical conductivity comprised between 1000 and 100000 S·m−1, only over a portion of the post extending from the end of the post joined to the helix to the end of the post joined to the vacuum chamber and corresponding to a height comprised between 10% and 50% of the post, wherein the helix has as electrical potential 2 kV with respect to ground, wherein the potential difference between the cathode and the helix is 4 kV;
• four collectors, wherein the four collectors have as respective electrical potentials, with respect to ground, from closest to the helix to furthest from the helix, 0 kV, −0.5 kV, −1 kV, and −1.5 kV;
• and
• a collector tip at an electrical potential of −2 kV with respect to ground.