Cecil, W5DXP wrote:
"How many joules are contained in that feedline?"

I`ll speculate that after one second, 200 joules are contained in the
forward wave on that line. Then, after two seconds, another 100 joules
has been reflected back toward the line feedpoint where it opposes
growth of power input to the line. Total joules on the line is 300.

Forward power minus the reflected power equals 100 watts being supplied
by the generator to the load with 200 watts forward power and 100 watts
reflrcted power in the line.

Best regards, Richard Harrison, KB5WZI