PEP II Transverse Feedback System

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PEP II Transverse Feedback System
Ron Akre Anatoly Krasnykh Vojtech Pacak Uli
Wienands MAC December 13, 2004
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PEP II Transverse Feedback System
The PEP TFB system takes the vector sum of 2
BPMs, delays the signal by the remainder of 1
turn and delivers a kick to the beam the next
time around. Two stripline kickers, one for X
and one for Y, are used.
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PEP II Transverse Feedback SystemRun 4 Problems
Logged

• 23 Log Entries associated with problems
• (Some Entries have Multiple Problems)
• 12 Power Amp Problems
• 8 Receiver Setup / Timing
• 3 Filters - 2 Blown and 1 Broke
• 2 Problems with Digital Delays
• 2 Problems with BPM Attenuators

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PEP II TFB Receiver
Phase shifters were added to phase dX and dY
channels in HER. This will allow better
adjustment of phase and reduce sensitivities to
drift in reference system. Orbit offset
correction is now done by changing beam orbit to
minimize dX and dY
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PEP II TFB Digital Delays

• Lawrence Berkeley Laboratory

Principal Investigators John Byrd and Walter
Barry
Phase 1 February 2004 2 - 12 bit ADC to clock
data into FPGA at 238MHz Two tap filter with 1
turn delay plus variable delay 238MHz DAC with
differential output Programmable through JTAG
port. Phase 2 Record 16MS, 70mS, of data to
external memory Three trigger modes Grow/
Damp Measurements Fault File Data Software
trigger to capture data during running On board
EPICS control with Ethernet for programming
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PEP II TFB Digital Delays
New Digital Delays 2 tap filter and diagnostics
are being developed by LBNL
Jonah Weber LBNL
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PEP II TFB Digital Delays
Jonah Weber LBNL
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PEP II TFB Digital Delays
LBNL PEP TFB Digital Delay Board J. Weber, L.
Doolittle, M. Chin, M. Balagot
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PEP II TFB Power Amplifiers and Filters
Power Amplifiers The single largest reliability
concern this run. Each of the 8 amplifiers has 8
power transistors summed for the output. During
this run we have lost about 30 output power
transistors, almost half. There was also loss of
some of the supply current limiting resistors
for the output transistors. During the past down
time all the amplifiers have been tested and
repaired. The failure is thought to be due to
overdriving the amplifiers. More attention will
be given during this run to power levels into the
amplifiers output. Filters Previous failures have
been due to faulty connectors. New 7/16 DIN
connectors have been installed in LER Y- and
there has been no failures. The by-2 pattern
helps greatly in reducing the beam power reaching
the amplifier. During next run we need to
measure power coming back to the amplifiers.
Power spectrum of beam power from the kicker
going back to the amplifier. New kicker design
should lower these levels.
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PEP II TFB Kickers
Uli Wienands, Anatoly Krasnykh, Artem Kulikov,
Jay Langton, Many Others New kickers with moly
electrodes, redesigned coax to stripline
transition, and 7/16 DIN connectors have been
installed in LER.
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PEP II TFB Kickers
Studies of new kicker designs to improve match
and reduce beam induced power to amplifier
continue
A. Krasnykh
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PEP II TFB Kickers
New stripline kicker designs to improve match at
higher frequencies and reduce propagation delay
in beam induced RF pulse.
A. Krasnykh
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PEP II TFB Data Acquisition System
GAGE 82G PCI 8bit 2GHz 2 Channel Digitizer 16Mb
Memory External clock option 2 Cards 4 Channels
HER X and Y and LER X and Y Cards are used in a
PC running X windows
GAGE card is clocked at 238MHz bunch
frequency. Inputs are from vector sum out of
Analog Signal Processor for X and Y Programmable
triggers from HER fault, LER Fault, and 2
External Sources can be routed to HER, LER, or
both GAGE cards.
PEP TFB TRIGGER CHASSIS
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PEP II TFB Data Acquisition System
System for LER installed July 31 - last day of
run. Two data sets on faults collected during
high current running not normal operation.
Only last 700 turns of data before trip are
shown. Longitudinal Oscillation is present in
only a portion of the pulse train. It grows to a
level where the beam in dumped due to beam loss,
dI/dt abort.
V. Pacak
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Software Processing of Acquired Transverse Data
(LER)I) 3-D picture of sampled X-transverse
signal

• Data arranged into a matrix form
• dim 4760 x 1746
• 8-bit resolution, (-127 128)
• Sampling freq. fs 238 MHz

1746 acquired data, (every second
bucket), sampling fs 238MHz
4760 revolutions apparent sampling frequency
frev 136.31kHz
Shyam Prabhakars PhD thesis under John Fox was a
very helpful resource in this work.
V. Pacak
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Software Processing of Acquired Transverse Data
(LER) - 2
II) 2-D time domain display of X/Y transverse
motion Any bunch or any single revolution can be
selected
Turn-to-turn transverse position of the bunch
450
Bunch-to-bunch transverse position along single
revolution 4750
Time of 1 rev. 1746 x (1/238e6) 7.3 ?s
Total time (4760rev) x (1/136.3e3) 35 ms
V. Pacak
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Software Processing of Acquired Transverse Data
(LER) - 3
III) FFT of rms value of selected group of
bunches and range of revolutions

• Apparent sampling freq. frev 136.31 kHz
• Selected bunches 200600 (by-2 buckets
  400-1200)

First 3000 revolutions, stable beam, (note the
magnitude scale).
Last 1200 revolutions, synchrotron instability.
Weak (aliased) X-plane betatron oscillation, 66
kHz frev-fb-x, fb-x 70 kHz (LER)
Synchrotron oscillation and harmonic, 3.8 kHz
(LER)
V. Pacak
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Software Processing of Acquired Transverse Data
(LER) - 4

• Mode Evolution, X-transverse

• Shown for the last 1700 revolutions.
• Sampling freq. fs 238 MHz.
• Freq. spectrum is calculated for selected
  (complete) bunch
  trains. Single revolution at time.

FFT
Magnitude of freq. spectra plotted against bunch
(mode) number, for each selected revolution
number (time) Only every 50th mode plotted to
avoid busy picture
h-harmonic number 3492 (folded at ½ of
sampling freq.)
V. Pacak
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Software Processing of Acquired Transverse Data
(LER) - 5

• High Resolution FFT, Data filtering tells apart
  synchrotron and betatron oscillations.

Unfiltered data
Sampling freq. fs 238 MHz Max freq.
FNyq 119 MHz Plotted FFT done over last
765 revolutions ( 1.33e6 data points)
Freq. resolution increases with the number of
data. (here 178 Hz)
High-Pass Filter before FFT
Low-Pass Filter before FFT
V. Pacak
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PEP II TFB Concerns for Higher Current Running
Feedback Gain and Output Power We do not have a
factor of 2 margin. LER ran for several weeks
with only 1 power amplifier in vertical. LER was
often lost when HER beam was lost. Plan to do
growth rate measurements in both rings with new
acquisition system LBNL two tap filter will
greatly improve overhead in amplifiers If larger
power amplifiers are required, more rack space is
required Filters are currently working well no
failures with new connector Only 1 filter, LER
Y-, has 7/16DIN connector the rest use N
connectors Kickers New Moly electrodes will
handle much higher temperatures 7/16DIN
Feed-through connectors will replace SC, and
eliminate SC to N adapters. As the bunch length
shortens higher frequencies of beam induced power
will need to be directed to proper loads.
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PEP II TFB Highlights for Run 5
New Kicker Electrodes and larger, 7/16 DIN,
connectors will allow higher current running in
LER Measurement of both HER and LER kickers
will be done to verify the effects of change in
the coax to stripline transition. The knowledge
gained of the system components last run will
allow faster and better setup of the TFB with
fewer problems. Correct orbit offset with
beam Correctly tune up receiver chassis Added
phase shifters to HER receivers Replace HER BPM
Attenuators at BPMs The new data acquisition
system and analysis software will allow a better
understanding of how the system is operating and
to what levels the beam can be stabilized. New 2
Tap Filter / Delay will lower the forward power
levels in amplifiers