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

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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

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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

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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

14

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

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• 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.

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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

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Thanks!

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