Measuring Debuncher Tunes

April 13, 1995

J. Morgan

The nominal tunes of the Debuncher are νx = 9.775 and νy = 9.790. Tunes
should be kept within .01 of these nominal values, although there are
numerous other locations in tune space that work just as well. The
approach to measuring the Debuncher tunes is similar to that used for
the Accumulator, however the beam intensity is at least 1,000 times
smaller so the signal is very noisy. In general, any location on the
tune diagram that is not very close to a resonance of order 5 or below
will work well. A tune diagram is attached that shows where the nominal
tunes are located with respect to the higher order resonance lines.
Difference resonances (the upward sloping diagonal resonance lines) do
not seem to be a problem in the Debuncher, however the sum resonances
(the downward sloping resonance lines) up to order 4 do cause beam loss.
Stacking can proceed normally during the tune measurements and
adjustments.

*Setting up the spectrum analyzers*

Any one of Spectrum Analyzers 2-5 can be used for this measurement, but
it\'s recommended that you use either SA 4 or SA 5. The spectrum
analyzers can either be used locally at AP-10 or remotely through the
use of the SA emulator located on the \"Sanalyzer Display\" page P42.
Unlike measuring tunes in the Accumulator, one does not need to measure
the frev (revolution frequency) of the Debuncher. DRF-1 and the momentum
cooling keep the frequency very close to 590,035 Hz. On the \"SANALYZER
DOWNLOAD\" page (P41), files 59 and 60 have been set up to download the
proper parameters for measuring the horizontal and vertical tunes
respectively (make sure that you are downloading to the correct
analyzer). The download does not set the trigger for the spectrum
analyzers, The trigger timing event (D:SA12T for example) should be set
up for .6 seconds after a \$90. This time was chosen because it is after
the bunch rotation process has been completed, but before the stochastic
cooling system has had a chance to cool the beam which reduces the size
of the signal. If you elect to manually load in the parameters, either
from AP-10 or by using the SA emulator, the following are the
appropriate values.

•Send an Instrument Preset

•Set the resolution bandwidth to 1 kHz

•Set the sweep time to 300 ms

•Set the Frequency span to 150 kHz

•Make the vertical scale 1 log scale of 1 db/div.

•Set the reference level to -65 db (hor. tune) or -69 db (ver. tune)

•Set the center frequency to 73.9184 MHz (hor. tune) or

74.7987 MHz (ver. tune)

•Set the spectrum analyzer trigger to .6 sec after and event \$90,

trigger externally

•Video average over 50 sweeps

•Enable marker to measure frequency

The proper Schottky detector will need to be selected before making the
measurement. At AP-10 use the MUX box to select the appropriate signal
(either the Debuncher horizontal or Debuncher vertical Schottky
detector). If you are using the emulator, interrupt on the port(s) at
the bottom of the page to select the desired input.

The lower sideband is used for the measurement of the horizontal
frequency and is found by the equation fs = (126 - νx) \* frev (use only
the fractional portion of the tune i.e. .775 instead of 9.775). The
revolution frequency of the Debuncher is very close to 590,035 Hz, as
mentioned above. Our target tune in the horizontal plane is 9.775, so we
can plug these values into the equation to get the nominal value for the
sideband on the spectrum analyzer (73.8871 MHz). This frequency should
be used as the center frequency on the spectrum analyzer, and will
locate the nominal tune value on the center of the display. The upper
sideband is used for the vertical measurement, and the appropriate
sideband frequency can be found by the equation fs = (126 + νy) \* frev
. Plugging in a revolution frequency of 590,035 Hz and a fractional tune
of .790 results in a center frequency of 74.8105 MHz.

*Adjusting the Debuncher tunes*

After the Schottky signal has averaged over the 50 sweeps the cumulative
trace can be displayed by hitting (interrupting on) the \"View\" button
(for the A trace), the \"shift\" button and the \"sweep time\" button.
To find the sideband frequency hit the hit the \"Nrm\" button, the
\"knob\" image and the \"Pk Src\" (peak search) button this will find
the peak and display the frequency. If the marker is not quite on the
center of the sideband, hit the \"Nrm\" button and the \"knob\" image
again. The console knob can then be used to move the marker and the
marker frequency can be read off the spectrum analyzer. The sideband is
not very clearly defined as it is in the Accumulator, but it normally is
strong enough to be recognizable. Hard copies of typical spectrum
analyzer displays have been included. The decimal part of the tune can
be calculated by using the appropriate formula:

νx = 126 -- (fs/frev) νy = (fs/frev) -- 126

Once the tunes have been measured they should be checked against the
nominals to determine if a tune change is in order. Even if the tunes
are not at their nominals, you can use a tune diagram to determine if
the beam is in a stable location away from any high order resonances.
Tune mults have been set up on P60 DEB10 subpages 9 and 10. Unlike the
Accumulator tune mults, the Debuncher tune mults have minimal affect on
the tunes in the other plane. As noted at the top of each page, a +1 Amp
change *to the D/A* of the top element of the mult (D:QS101) results in
a --.005 change when changing the horizontal mult and a --.030 change
when tuning the vertical mult. This is a bit confusing since the D/A\'s
are positive and the A/D\'s are negative. A larger absolute value of the
D/A and A/D results in a negative tune change. *For both mults a
clockwise knob rotation results in a negative tune change*. Repeat the
tune measurements after each tune change is made. If using the emulator,
interrupt on the \"Clr Wrt\" button on the A trace. If using P41 to
download the parameters, a fresh download will restart the video
averaging and you can iterate until finished.