Theory, Design and Tests on a Prototype Module of a Compact ...

86 5. RADIOFREQUENCY MEASUREMENT
tank # cell type left [mm] right [mm]
1 AC +2.3 +7.6
CC +0.3 +7.2
2 AC +5.0 +6.2
CC +0.3 +7.2
3 AC +5.0 +6.8
CC +0.3 +7.2
4 AC out +6.0
CC +0.3 +7.2
Table 5.1. Tuners positions for the bead pulling of figure
5.14.
Since all the bead pulling measurement was made feeding the module
by the wave-guide, it was not possible to measure the first nearest
mode stop-b<strong>and</strong>. This stop-b<strong>and</strong> is related to a tilt-like behavior in the
response, since the nearest modes have a linear behavior from the first
cell to the last one <strong>and</strong> have a null in the central cavity; this means
that it is not possible to feed <strong>and</strong> to measure these modes from the
wave-guide at a recognizable level.
Last, in the table 5.1 the tuners positions for the figure 5.14 are
shown. Some comments on those values are necessary. For each tank,
two lines of tuners are available for each type of cell 13 . Here, the left
side is the one on the left when one looks the module from the first tank
to the fourth one. It is also possible to act on one side at a time. The
values shown represents the length of the part of the tuners that juts
out of the tank side wall; again, this is not important for our purposes,
since only relative displacement are relevant. In the table out means
that the tuner are completely out <strong>and</strong> the end side of the tuner does
not penetrate in the inner surface of the cavity. In the tuning process,
the tuners for each tank have been moved all at the same time, as each
tank should be one accelerating cavity <strong>and</strong> one coupling cavity <strong>and</strong>
this fact has simplified very much the procedure. Consider the bead
pulling measurement of figure 5.15. The only intervention was to push
the tuners of ACs on the right side of tank #1 inside of +0.3 mm,
because before the level of this tank was very low. Of course, the little
displacement does not change dramatically the situation, but it is in
the right direction since the level of tank #1 was increased. The π/2
frequency was increased to 2997.01 MHz <strong>and</strong> this was clear because
the resonant frequencies of ACs of tank #1 were increased. The Bump
stop-b<strong>and</strong> was decreased to SBB = +201 kHz <strong>and</strong> this was due to the
fact that the mean frequencies of ACs increased where the ones of the
CCs remained constant. In figure 5.16 is shown a bead pulling made
13 A lines of tuners is constituted by a number of tuners that move together.