TWTA help

[kobulingam]

I am trying to learn how a TWT works and I can't seem to figure out how the RF signal induced by the bunched electrons is 90degrees lagging in phase.

I am reading the book PRINCIPLES OF TRAVELING WAVE TUBES by A.S. Gilmour, Jr.

I have attached the two pages that explain this (early on in the book).

Can someone explain the point (1) on the bottom of the second page?

Thanks

You can also use: http://img9.imageshack.us/img9/3192/helpzj.jpg

[marcusl]

You probably need to read the following page, too. The point is that as electrons in the beam bunch up, they influence the charge distribution in the helix, and since the electrons are moving, they effectively induce current into the helix. This current acts to increase the amplitude of the axial field which in turn reinforces the bunching (it's called secondary bunching), resulting in higher amplification.