The electron beam is reduced in size to tens of microns in diameter by strong focusing magnets
at each straight section where powerful arrays of permanent magnets called insertion devices are installed.
On Tuesday, March 27 2007, structural supports to a quadrupole magnet, one of an inner triplet of three focusing magnets
, failed a high-pressure test in the tunnel of the LHC accelerator under construction at CERN.
Figure 5a shows other details essential to TWT operation, including the beam focusing magnets and the internal attenuator.
The first limitation is especially applicable to coupled-cavity TWTs because the relatively large outer diameter of the circuit will cause the focusing magnets to be father from the electron beam than would be the case for a helix or helix-derived circuit.
The slow-wave circuit and the beam focusing magnets are to the left of the region illustrated; the curved lines represent electron trajectories into the collector.
If the operators reverse the polarity of all the bending and focusing magnets
, protons will go through the system in the direction intended for antiprotons.