Richard Harrison wrote:

...
Terman says on the "Mechanism of Operation of the Traveling-Wave Tube"
at the bottom of page 678:
"The applied signal propagates around the helix and produces an electric
field at the center of the helix that is directed along the helix axis.
...
Best regards, Richard Harrison, KB5WZI


And, obeys basic rules, such as:

http://www.allaboutcircuits.com/vol_2/chpt_1/6.html

So, a summary of your point? Afraid I am a bit dense here today ...

Regards,
JS