Feedback on Nanosecond Timescales (FONT) - Review of Feedback Prototype Tests at ATF(KEK) Glenn Christian John Adams Institute, Oxford for FONT collaboration.

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 Christian John Adams Institute, Oxford for FONT collaboration.

Documents

digital feedback system

gev beam

ns bunch spacingdemonstrator

abd 240907font1

mev beam

ns train length

feedback prototype tests

ultrafast feedback