LLRF
Requirement
and Parameters
at ESS
Rihua Zeng,
Anders J Johansson
LLRF workshop, Hamburg, 2011-1020
1
Picture from C. Carlile’s presentation at IPAC 2011
2
Neutrons in 2019 !
5 MW
2.5 GeV
2.9 ms
14 Hz
50 mA
352.2 MHz
704.4 MHz
< 1 W/m
beam power
protons (H+)
pulses
rep rate
pulse current
RF frequency
beam losses
No accumulator/compressor ring !
3
Picture from G. Trahern’s presentation at ICALEPCS11
Green field site
Picture from G. Trahern’s presentation at ICALEPCS11
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352.21MHz
Source
LEBT
RFQ
75keV
RF Source

MEBT
DTL
3MeV
1
704.42MHz
Spokes
50MeV
5
Low β
108MeV
28
High β
606MeV
64
spoke and elliptical cavities . (One klystron for one cavity.)
Many issues to be addressed

Stringent demands from ESS leads to tough challenges
2011-10-20
LLRF Workshop 2011, R. Zeng, A. J. Johansson
Target
2500MeV
120
More than 200 LLRF stations to be built by 2019 for RFQ, DTL,

HEBT
5
Pulse length:
2.86 ms
Rep rate:
14 Hz
Current:
50mA
An universal recipe for LLRF?
L
2011-10-20
LLRF Workshop 2011, R. Zeng, A. J. Johansson
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L
R
F
:
To do list
Frequency Generation
Phase Reference Distribution
Frequency Conversion
1. Generation of required
frequencies (RF, LO, IF, Clks)
2. Low phase noise
1. Phase stable and low temperature coefficient cable or fiber
2. Phase drift control
3. Distribution of the frequencies at each LLRF station
1. Down/up conversion
1. Selection of the IF and sampling rate
3. High isolation between channels
4. Low noise and phase drift control
Diagnostics
Cavity Field Control
1. Parameters calculation and
monitoring (Q value, cavity
detuning etc.)
2. Signals monitoring (power,
vacuum, temperature etc.)
3. Faults fast detection,
locating and analysis
4. Timing, logic, algorithm
communication checking
5. Cavity simulator
6. Interlock
1. Amplitude and phase setting
2. IQ detection
3. Feedback
4. Feed forward
5. Beam loading compensation
5. Klystron linearization
6. Fault avoidance, detection,
recovery and tolerance
8. Beam based feedback
Cavity Resonance
Control
1. Pre-detuning to compensate
synchronous phase operation
2. Normal conducting cavity
frequency control
3. Dynamic Lorentz force
compensation
4. Microphonics control
Control System Sever
1. High degree of automation to
enable easy operation, fast fault
detection and recovery
2. Fast communication and
high-speed data exchange
3. Powerful database to support
fast detection and recovery and
adaptive control
4. Interface to control system
5. Remote access/control
RF Control Hardware
Host CPU
1. Selection of FPGA/DSP, FLASH/SDRAM, fast and high resolution ADC, DAC
2. Boards with which interface to communication (VME, VXI, ATCA, PCI or Ethernet…?)
3. Hardware debug points
4. Hardware concerns: SNR (ADC nonlinearity, DC/DC convert noise, clock jitter, crosstalk) and
temperature independency
2011-10-20
LLRF Workshop 2011, R. Zeng, A. J. Johansson
General purpose CPU or
system on chip to implement
the control server
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To learn list
FLASH
SNS
JPARC
RF Stab 0.01%
0.5%
1%
IF freq.
250KHz
54 MHz
50
MHz
12 MHz
13 MHz 20 MHz 56
MHz
10 MHz
Sample 1 MHZ
Freq.
81 MHz
40
MHz
48 MHz
54 MHz 80 MHz 77.7
56 MHz
MHz
40 MHz
Sampl.
IQ
Other
IQ
Other
IQ
Other IQ
Crate
VME/ATC VXI
A
cPCI
VXI
VME
USB
Phase
Distr..
Coax
Opto
Opto
Opto
2011-10-20
Coax
Ferm.
LLRF Workshop 2011, R. Zeng, A. J. Johansson
CERN
LBNL
8
MYHHRA
PXI
…
To be listed list
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LLRF Workshop 2011, R. Zeng, A. J. Johansson
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Issues: multiple cavities control
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LLRF Workshop 2011, R. Zeng, A. J. Johansson
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Picture from S. Peggs’s presentation at IPAC 2011
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Issues: high effeciency
Predistorter
Input
I,Q
 Klystron Linearization
Compl
Complex
Multiplier
ex
Multipli
Del
Delay
ay
DAC
Up
Up
Converter
Conve
rter
Pre-amp
Delay
Linearize
Adapti
Table
on
Addressin
Addressing
g
Del
Delay
ay
Adaption
Adaptio
Algorithm
n
ADC
Down
Up
Converter
Conve
rter
 Minimize power overhead.
Is 20% enough?
2011-10-20
LLRF Workshop 2011, R. Zeng, A. J. Johansson
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Klystron
Output
RF
Issues: high availability
• Availability at ESS 95%
 Avoid failures that cause the whole system to fail
 Redundancy
 Automatically detect
 Fast recovery
2011-10-20
LLRF Workshop 2011, R. Zeng, A. J. Johansson
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Issues: others




2011-10-20
High intensity
Long pulse
High gradient
Spoke cavity
LLRF Workshop 2011, R. Zeng, A. J. Johansson
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Design guidelines
• Fault tolerant architecture and design
– Redundancy or adaption?
• Easy maintenance
– Generic design for all LLRF stations?
– Modular design?
– Auto-config and auto-calibration?
• Cost effective and long lived
– Multiple vendors?
– Software defined function by FPGA/DSP implementation
for future upgrades?
2011-10-20
LLRF Workshop 2011, R. Zeng, A. J. Johansson
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Main architecture of ESS LLRF
• FPGA based solution
• Separate analog mixers for down- and up-conversion
• I/Q-demodulation and modulation
• One master oscillator for the whole ESS
– Phase reference for RF
– Time reference for control, science
• Global phase reference distribution
• Coaxial phase reference line
• EPICS control system
2011-10-20
LLRF Workshop 2011, R. Zeng, A. J. Johansson
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Interesting possibilities:
• Co-design with Beam Instrumentation
– Simplify upkeep of installation
– Minimize cost of units for installation and inventory
• Open Hardware solution
– Multiple sources of hardware possible
2011-10-20
LLRF Workshop 2011, R. Zeng, A. J. Johansson
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What to do in the near future
• Simulation for more detailed parameters and requirement
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LLRF Workshop 2011, R. Zeng, A. J. Johansson
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• Build the prototype
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• More important, To ask more suggestions for the possible
solutions at ESS
Many thanks for your attention!
2011-10-20
LLRF Workshop 2011, R. Zeng, A. J. Johansson
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