1. Feedback systems and Low Level RF
Alessandro Drago
X SuperB General Meeting
SLAC
6-9 October 2009

2. Main topics
Tests of 500 W power amplifiers for transverse bunch-by-bunch feedback systems
Low Level RF collaboration proposal from CNRS Grenoble team

3. AR 500 W power amplifiers
On the rear panel analog i/o, RS232, GPIB and USB
Flat screen
power
Gain knob
Menu keys
key

4. Very compact, heavy but still portable

5. TFB power amplifiers
For transverse and longitudinal bunch-by-bunch feedback system in general (DAFNE, PEPII, other circular accelerators) 250 W power amplifiers are used, typically one for each kicker port
In DAFNE, due to the need of more power on the horizontal e+ feedback system for the presence of a very fast instability (of the order of 5 microsec. grow rate) two ways are under study:
double the horizontal e+ feedback system
double the horizontal final stage amplifier power
To do b) two new 500W amplifiers have been bought; the laboratory tests are just finished and they are presented in the following talk

6. Case a) double feedback systems
Implemented in
november 2008
Presented in April’09
MiniMAC

7. Case b) analysis Note to the following measurements
The nominal gain of the amplifier is 57 dB
On the amplifier output, in cascade, there are 3 stage of 20dB attenuators, the first working up to 1500W, the second up to 100W, the third 20 W
All the measurements in the following slides are done by this setup, so the effective nominal gain -3 dB and, if we consider also the cables, -3.3 dB

8. Network analyzer HP 8753B
Magnitude (dB)
Phase (degree)

9. Network analyzer HP 8753B
Magnitude (dB)
Phase (degree)

10. RF signal generator HP 8664A
Spectrum Analyzer Tektronix RSA3303A
Amplifier Research AR 500A250AM1

11. In input: 0dBm sinusoid at 100MHz

12. we can observe a spurious signal at 200MHz, -21 dB

13. Pulse response Oscilloscope LeCroy WaveSurfer 64Xs
Pulse/Function generator HP 8116A

14. Pulse (8ns) response: input to amplifier
Trigger

15. Pulse (8ns) response: output from amplifier
Trigger

16. Input Pulse(2ns) to AR amplifier

17. Output Pulse(2ns) from AR amplifier

18. Results on 500W amplifiers
Very compact: about the same size that the 250W model, only the weight is higher
It asks 2500 Watts from the mains at 220V
Roughly the cost is ~linear with power: ~25keuro+VAT, for a 250 W amplifier, ~50keuro+VAT, for a 500 W model
Good technical performances within specs
Perfect response to the pulse
Good flatness versus magnitude (< 3dB)
Good linearity in phase - apart for freq > 240Mhz

19. Critical Aspects on 500W amplifiers
First harmonic at -21 dB, it is a trouble or not? As the first also the other harmonics with f<250 MHz are in the output signal
Gain knob must be adjusted to the right value that is different for each individual amplifier: it can be set from 0% to 100% but it is not easy to choose the value that gives the maximum gain without reproduce distortion or saturation in the output
In fact the presented tests are done with gain values from 50% to 70% in base to the chosen input signal

20. Conclusion on power strategy
250W amplifier gives 54 dBm that is 115V output for 0dBm input signal
500W amplifier gives 57 dBm that is 160V output for 0dBm input signal, this means a 1.4 factor
The amplifier cost is linear with the power but of course the bunch to be deflected obeys to the Lorentz law and this means to the applied voltage
As consequence using 500W amplifier has the advantage to be very compact but it does not optimize cost versus effect
Installing more feedback system is more effective solution if the space (for kickers) is not a problem and if the cost of the feedback processing unit is not expensive

21. How much space ?
In PEPII, the installation of 6 bunch-by-bunch feedback systems asks for >10 racks, for power amplifiers, electronics and instrumentation. There is also some other space for the operators with computers and desks.
In DAFNE, there is a similar situation with 13 racks for seven bunch-by-bunch feedback systems – the space for the operators is in the main control room.
In both cases the power amplifiers are not very far (<20m) from the kickers to avoid power reductions on long cables

22. Low Level RF collaboration with LPSC -Grenoble

23. LPSC Electronics Group
Who are we :
LPSC : Laboratory of Subatomic Physics and Cosmology. IN2P3/CNRS laboratory in Grenoble/France (ex. ISN)
Electronics Technical Group of 21 people devoted to the conception and installation of electronics systems for the physics experiments of the LPSC.
Activities of the electronics group :
Systems Electronics
Microelectronics (ASIC and data conversion)
Integration and tests
PCB CAD team
Possible manpower for SuperB (TDR phase)
 1 engineer FTE
O. Bourrion, C. Vescovi, D. Tourres 23

24. Previous work
The electronics group is involved in most of the LPSC projects.
Some examples :
Astro/Cosmo :
AMS : RICH front-end electronics
CREAM : CHERCAM sub-detector + HVPSU
Planck : Control electronics for the Sorption Cooler (JPL/NASA) and Dilution Cooler (Air Liquide-DTA)
LHC experiments
ATLAS : pre-sampler calorimeter
Alice : EmCal, Jet trigger and super-modules Integration and Tests
Electronics for Accelerators
CNAO : LLRF
GENEPI/GUINEVERE : Control/Command of the neutron generator 24

25. CNAO Synchrotron for hadrontherapy installed in Pavia (Italia)
Development of a purely digital LLRF control system
Wideband (300kHz-4MHz) single cavity
Cavity (amplitude and tuning) and Beam (oscillations and position) controls
Design at LPSC, tests at CERN/PSB in cooperation with CERN LEAR team
More Info on EPAC08 papers : 25

31. The END