Feedback on Nanosecond Timescales (FONT) - Review of Feedback Prototype Tests at ATF(KEK) Glenn...

Feedback on Nanosecond Timescales (FONT)

- Review of Feedback Prototype Tests at ATF(KEK)

Glenn Christian

John Adams Institute, Oxford

for FONT collaboration

Glenn Christian - LC-ABD 24/09/07 2

ILC IP Feedback system - concept

• Fast beam-based feedback system essential for the ILC interaction point to compensate for relative beam misalignment.

• Measure vertical position of outgoing beam and hence beam-beam kick angle

• Use fast amplifier and kicker to correct vertical position of beam incoming to IR

• Delay loop necessary to maintain the correction for subsequent bunches in the train

Last line of defence against relative beam misalignment


Previous Feedback Prototypes

• Originally FONT technology demonstrator for ultra-fast feedback, driven by challenge of ‘warm’ machine (192 x 1.4 ns) – very low latency system (analogue only)

• FONT@NLCTA – 2001-4, 65 MeV beam, 170 ns train length, 87 ps bunch spacing– FONT1 – latency 67 ns– FONT2 – latency 54 ns

• FONT3@ATF - 2004-5, 1.3 GeV beam, 56 ns train length, 2.8 ns bunch spacing– take advantage of ~ GeV beam (1 micron @ 1GeV -> 1 nm @ 1TeV)– latency aim: 20 ns (observe two and a bit periods), 23 ns achieved


FONT1,2,3: Summary67 ns

54 ns

23 ns


Current/Future Feedback Prototypes

• ‘Cold’-machine bunch parameters allow digital signal processing techniques:– support implementation of algorithms for greater luminosity recovery– easier inter-connectivity of processors – angle feedback?– integration of other systems – upstream feedbacks, feed-forward, lumi-

monitor etc.• FONT4@ATF 2005-present, 1-bunch/3-train mode, ~140ns -

~154 ns bunch spacing– demonstrator for digital feedback system with ILC-like bunch spacing– Latency target: < bunch spacing (~140 ns)

• Later,– ATF2 – aim to stabilise third bunch @ micron level– (FONT5 ?) 20 – 60 bunches @ 150 – 300 ns spacing (future extraction

scheme)


FONT4 system overview

KICKERBPM 11BPM 13 BPM 12

AMPAnalog FE Analog FE Analog FE

Witness BPMs

Digital processor

Feedback BPM

Machinetimingsystem

Scopes

∑

∆

BEAM

clks, triggers

LO

DAQ

I/O, digital DAQ


Analogue BPM processor

Resolution c. 3-5 umLatency c. 10 ns

old new

Output pulse width c. 5 ns

Tested @ ATF November 2006


Digital Board

2 x Analog Input channels (single-ended)

2 x Analog Output channels (differential or single-ended)

4 x General-purpose digital outputs

3 x external clock/trigger inputs

Xilinx Virtex4 FPGA

Analog Devices ADC/DACs (14-bit)

40 MHz oscillator

RS232 serial port

JTAG port PROM

GP I/O Header


Kicker Drive Amplifier

• New design for “universal” FONT amplifier– Designed to have flexibility to

meet future requirements – Design for 10 us operation with

40 ns settling time to 90%, rep rate up to 10 Hz

– Output current up to +/- 30 A (kicker shorted), +/- 15 A (50-ohm termination)

– Manufactured by TMD Technologies

– Two units delivered 1 December 2006

• Tested at ATF Dec 2006


FONT4 installation at ATF (May 2007)

BPM processor boardAmplifier FEATHERKicker


Recent tests at ATF (May 2007)

• Objectives:– Demonstrate closed-loop feedback with full version of firmware– Demonstrate acceptable latency– Optimise feedback gain

• Two versions of firmware:– Without charge normalisation

• Gain set in software and given as a virtual-input to FPGA in real-time• 5 clock cycles @357 MHz (expected latency ~140 ns)

– With real-time charge normalisation• Used a partial reconfiguration technique to recompute LUTs to optimise gain

setting• 8 clock cycles @357 MHz (expected latency ~148 ns)

– Evaluate the effect of normalisation


Latency without charge normalisation (154ns bunch spacing)

~15 ns slack to 90% of full kick

Latency ~140 ns


Feedback results – no real-time charge normalisation(average over 11 pulses)


Feedback results with charge normalisation (average over 11 pulses)


Further Development - FONT4

• FONT4 so far concerned with solving technical challenges in getting the closed-loop feedback working. Now, concentrate on quality measurements

• Reduce the processor resolution – FOM for system, system resolution– Limited by phase jitter in LO (~ 5 degrees) – Reduce the sensitivity to the LO jitter by balancing the signal levels and better

matching of input lengths to the analogue processor – tune the difference signal to zero in the working region of the system

• Understand statistical nature of the jitter – correlations?– Requires an integrated, online DAQ system to acquire large data sets and

analyse the data in real-time – Step towards making the feedback system ‘turn-key’ at ATF2


Further Developments – ATF2

• Goals/Plans for ATF2:– Resolution 1 micron or less

• Need to investigate methods to further improve processor resolution

– Defining BPM and kicker locations in beamline and simulate feedback performance

• Position and angle feedback in both planes (x,x’,y,y’)?

– For position feedback only, could use existing FONT4 processor, but for angle feedback latency increased by physical distance between BPMs, as well as extra clock cycles needed in the processing

• New digital board design – two channel, faster ADCs, Virtex-5 FPGA with RocketIO (fast digital interconnects)

– Feed-forward and constant-energy extraction (Kalinin)• Same kickers as feedback• Hardware tests at ATF


Summary

• Completed FONT3 analogue feedback – achieved latency 23 ns

• Developed FONT4 digital feedback system– New hardware developed and tested at ATF – analogue and digital

processors, amplifier – Demonstrated closed loop feedback at ATF with 3 bunches ~150ns

spacing with digital feedback processor – Optimised gain with and without real-time charge normalisation in the

system– System latency ~140ns (~148ns with real-time Q-normalisation)

• Ongoing programme to further develop system and prepare to employ system at ATF2

Feedback on Nanosecond Timescales (FONT) - Review of Feedback Prototype Tests at ATF(KEK) Glenn...

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