LabVIEW CODE DEVELOPMENT AT SLAC Cappelletti CERN 22 Apr 2009 I Q CW 11424 GHz KLY KLY TWT H Y B Other experiment Delay 2 round trips Mode conversion H Y B STRUCTURE ID: 580695
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Slide1
KLYSTRONS OUTPUT CORRECTION: LabVIEW CODE DEVELOPMENT AT SLAC
Cappelletti
CERN, 22 Apr 2009Slide2
I
Q
CW @ 11.424 GHz
KLY.
KLY.
TWT
H Y B
Other experiment…
Delay (2 round trips) +
Mode conversion
H Y B
STRUCTURE
ATTENUATOR
PH. SHIFTER
ATTENUATOR
-
MODULATION
POWER SUPPLY
PULSE
COMPRESSION
FEEDBACK
SYSTEM OVERVIEW
50
M
W @ 1.5
m
s
p/2
AMP – PH DETECTION
AFG
LAPTOPSlide3
MODULATION ISSUES
User input and klystrons output are handled in terms of amplitude and phase, but practical concerns make Re-
Im
data a better choice.
Ideally, the objective is to get both a
flat top amplitude pulse to feed the compressor, and a constant phase
waveform.Slide4
REAL WORLD SIGNALS…
We always refer to
modulating
signals, but it has to be remarked that they are transmitted on a 11.4 GHz carrier
We perform a demodulation…
… through the analytical representation
s
a(t) = s(t) + j H{s(t)} = A(t)
ej(f(t))Where H{} denotes the Hilbert transform.
The main concern is flattening A(t), the phasebeing coerced to the arbitrary value of
p/4
A(t)Slide5
The basic idea is a simple point-by-point compensation.If the first input/output relation looks like
Then the input could be modified this way:
In more detail, the first step is to define an error vector intended to (iteratively) modify the input.
Error vector after 1 stepSlide6
THE CORRECTION ALGORITHM
FIND ERROR VECTOR
+
+
0
0
0
…
0
Current (ideal) input
Corresponding output
FIND ERROR VECTOR
+
+
(Initial) error vector
New input…
… and corresponding new output
…
…Slide7
The algorithm assumes a 1 to 1 correspondence between the acquired output and the ideal input: a time shift is needed and performed through a cross-correlation.
For the same reason, the output has to be properly
downsampled
(# of pts is different).
The error vector has to be opportunely (and manually!) rescaled, otherwise it won’t significantly affect the input, whose level is approximately 3 times higher.
CONVERGENCE: each iteration is triggered by a user’s command. In 3-4 steps the correction reaches its best…
OTHER ISSUES
t
=
argmax
{Rin,out}Slide8
… and the resulting pulse is already better looking.
PERFORMANCES
Example 1 (After 2 steps)
Example 2 (After 3 steps)Slide9
Basic and intermediate level training was complete.Allowed to operate ASTA’s RF power controls if supervised.
Choke seen from the
boroscope
ABOUT ASTA AND THE PETS