overview of the llrf activities at slac r. akre*, z. geng, b. hong, d. brown, s. condamoor, k. kim,...
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Overview of the LLRF Activities at SLAC
R. Akre*, Z. Geng, B. Hong, D. Brown, S. Condamoor, K. Kim, R. Larsen, J. Olsen, Vojtech Pacak, R. Ragle, D. Van Winkle, C. Xu
SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, U.S.A.
October 1st, 2013
Overview of the LLRF Activities at SLAC—LLRF 2013Page 1
Overview of the LLRF Activities at SLAC—LLRF 2013Page 2
SLAC Facilities Overview
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Outline
• PAD/PAC based LLRF System at SLAC
System Architecture
Phase and Amplitude Detector (PAD) and Controller (PAC)
Projects Adopting the Pizza Box based LLRF System
• MicroTCA Development for LLRF
System Architecture
Highlights of the Technology
Results from a Prototype
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LCLS
• LCLS required upgrades of LLRF system:
• PAC--Fast phase and amplitude control => FPGA + DAC + I/Q Modulator + Solid-
state Amplifiers
• PAD--Precise phase and amplitude measurement => Down Converter + I/Q
Sampling + Digital Demodulation
• Fast data acquisition and pulse-to-pulse control at 120 Hz => EPICS + Fast
Private Network
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Architecture of the LLRF System for LCLS
• Measurement and control are done locally for each RF station. A new 1KW Solid-State Amp drives Klystron.
• Data process and feedback algorithm are performed in the central VME controller
• Ethernet was used for communications – good for 120 Hz operation, but almost at the limits
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Phase and Amplitude Detector and Controller--PAD and PAC
4 Chan - 130MSPS, 16 bit ADCs LTC2208 In PAD
One of the DownMix Channels
First PAC built in 2006
Phase and Amplitude measurement result
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Projects with PAD/PAC Based LLRF System
LCLS—LINAC Coherent Light Source
• 13 Fast Control RF stations (Injector, L1S, L1X, etc.)
• Phase Amplitude Control for LLRF Reference and Laser Drive System ASTA—Accelerator Structure Test Area for photocathode QE and beam
emittance study
• Reference System for LLRF and Laser.
• Feedback control for Gun RF signals with one Klystron Station XTCAV—X-Band Transvers Deflector for Femtosecond Electron/X-ray
Pulse Length Measurements
• The X-Band Frequency Generator and the Fast Feedback System
• A New Modulator Klystron Support Unit (MKSUII) replaces the >25 year legacy unit XTA—X-Band Test Area for Compact Photo-injector with X-Band
Structures.
• Customized X-Band Frequency Generator is implemented in the existing NLCTA
Test Hall. PADs/PACs are used for several RF stations.
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Motivations
• Limits of PAD/PAC based LLRF System A feedback control loop has to follow the chain of PAD-VME-PAC connected with
Ethernet, the real-time performance is limited. It is not possible to do intra-pulse
control (pulse width ~ 3 µs) Computation power of the Coldfire MCU used in PAD/PAC chassis is quite limited.
One more Channel Access client connected to the EPICS software in the Coldfire
MCU can significantly degrade its real-time performance One PAD chassis (2U or 3U) only contains 4 ADC channels. Channel density is low
to efficiently use the rack space Custom designed chassis is difficult to maintain
• New requirements to LLRF System Capability for intra-pulse feedback More ADC channels Fast waveform acquisition at 120 Hz More complicated data processing
Overview of the LLRF Activities at SLAC—LLRF 2013Page 9
LLRF Frequency Reference
Consists of 14 Chassis located in a temperature controlled enclosure
Generate S-band Ref/LO, X-band Ref/LO, ADC clock and Gun laser clock signals with required stabilities
Recent Phase Noise Measurements of the Frequency Reference System
476MHz : 22fSrms 10Hz to 10MHz 2856MHz : 21fSrms 10Hz to 10MHz
2830.5MHz : 21fSrms 10Hz to 1MHz 119MHz : 51fSrms 10Hz to 10MHz
476MHz = 22fSrms
2856MHz = 21fSrms
2830.5MHz = 21fSrms
25.5MHz = 165fSrms
119MHz = 51fSrms
102MHz = 65fSrms
476MHz Master Oscillator and the 60W Amplifier upgrades improved the MDL.
With the LO and Clock, a phase measurement resolution of 0.005 degree RMS within 1.2 MHz bandwidth can be achieved.
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Architecture of MicroTCA based LLRF System
• RF Support Chassis is for down conversion, up conversion and klystron high voltage conditioning
• AMC board contains ADC, DAC and FPGA for RF detection and actuation
• CPU and EVR locate in the same crate as the ADC board
• Interconnections are via PCI Express
12
MicroTCA Crate and FPGA AMC Board
12
ADLINK AMC-1000 CPU
Vadatech MCH UTC002
Struck SIS8300 AMC (Virtex 5 FPGA ; 4 lane PCI Express; 10 Channels 125 MS/s 16-bit ADC; Two 250 MS/s 16-bit DACs; Twin SFP Card Cages) Overview of the LLRF Activities at SLAC—LLRF 2013
Page 12
FPGA Firmware Design
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Fast real-time functions for the RF station control:
• I/Q demodulation• Intra-pulse phase
amplitude control• RF pulse
generation• I/Q modulator
calibration
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Control Algorithm
Pulse-Pulse Feedback
• Implemented in software as a real-time
thread
• Use vector summation of multiple signal
as an input for the feedback loop
• Pulse-Pulse Feedback corrects slow
drift
Intra-Pulse Feedback
• Implemented in FPGA
• Correction only works for the same
pulse
• The feedback algorithm compares RF
pulse and Intra-Pulse I/Q set points
table and accumulates the error for the
given window. The result is applied to
feed-forward value for another later
window when the beam is accelerated
• Intra-Pulse Feedback takes care fast
random jitter
Software Architecture
Computation Nodes
Software Architecture in CPU
Overview of the LLRF Activities at SLAC—LLRF 2013Page 15
• Pulse-to-pulse feedback and real-time data acquisition is done with EPICS software in MicroTCA CPU
• Up to 6 AMC ADC boards are controlled by the same CPU
• Integration with Timing system (EVR) and provide Beam Synchronous Acquisition (BSA)
• Support function for Intra-Pulse Feedback: Loop Phase/Gain Compensation and Loop Phase/Gain Correction
Prototype Installed at LCLS Linac (LI28-2)
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SSSB
RF Support Chassis
6-slot MTCA Crate
MKSUII (Interlock)
Summary
• PAD/PAC systems work robustly and will be continuously
supported and maintained for LCLS and other projects
• MicroTCA system has been proved to be a powerful and
compact solution, providing improved control capabilities
and performance
• Future development for Linac upgrades or new projects
could be built/enforced with the experience of MicroTCA.
Overview of the LLRF Activities at SLAC—LLRF 2013Page 17
Note and References
Note: Ron Akre passed away on April 2nd, 2012.
References:
[1] P. Emma, “LCLS-II Conceptual Design Review,” SLAC, April 8, 2011, Chapter 6, Accelerator
[2] Z. Geng, “LCLS-II Injector LLRF System-MicroTCA Based Design”, SLAC, June, 4, 2012, SLAC AIP Report
[3] Z. Geng, “LCLS-II Low Level RF Controls”, FAC Presentation, SLAC, February 27-28, 2013
[4] Z. Geng, “LCLS-II Injector LLRF Final Design Report”, SLAC, January, 23, 2013
[5] R. Akre, “Linac Coherent Light Source (LCLS) Low Level RF System”, SLAC, September, 19, 2006, LCLS
LLRF Review
[6] C.G. Limborg-Deprey*, C. Adolphsen, et al. “COMMISSIONING OF THE X-BAND TEST AREA AT SLAC”,
MOPB029, Proceedings of LINAC2012, Tel-Aviv, Israel
[7] E. Jongewaard et al., “RF GUN PHOTOCATHODE RESEARCH AT SLAC”, IPAC2012, New Orleans,
Louisiana, USA
[8] R. Akre et al., “Commissioning the Linac Coherent Light Source Injector”, Phys. Rev. ST Accel. Beams 11,
030703 (2008)
[9] Y. Ding et al., “Femtosecond Electron and X-ray Beam Temporal Diagnostics Using an X-band Transverse
Deflector at LCLS”, Phys. Rev. ST Accel. Beams 14, 120701 (2011)
[10] P. Krejcik et al., “Engineering design of the new LCLS X-Band Transverse Deflecting Cavity”, IBIC 2013,
Sept. 16th, 2013, Oxford, UK
Overview of the LLRF Activities at SLAC—LLRF 2013Page 18
Thanks!
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