| | The Large Hadron Collider (LHC) will accelerate
beams of protons with a main RF system of sixteen
400 MHz superconducting cavities. The different
requirements at injection and collision together with the
heavy beam loading have imposed the use of a variable
power coupler with a coupling value varying by a factor
20. The power requirements are high; 250 kW cw forward
for several hours and pulses of 1.85 MW local peak
power. In order to withstand these levels, copper sealing
rings are used on the main ceramic. To avoid multipactor
occurring at high powers and beam intensities, a second
ceramic is used to provide a second DC polarization of
the antenna. Twenty-five couplers have already been fully
conditioned using a special dedicated FM+AM
conditioning process, with 16 installed in the cavities in
the LHC tunnel for first powering tests. | |