FONT4 Status Report Glenn Christian John Adams Institute, Oxford for FONT collaboration

Glenn Christian - LCABD 12/04/07 2 IP Feedback system - concept Last line of defence against 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 FONT – Feedback On Nanosecond Timescales

Glenn Christian - LCABD 12/04/07 3 FONT1,2,3 Analogue Feedback Tests NLCTA: , 170 ns train length, 87 ps bunch spacing –Achieved total latency of 67 (FONT1) & 54 ns (FONT2) ATF: , 56 ns train length, 2.8 ns bunch spacing –Latency 23 ns –BPM processor resolution of 3-5 microns

Glenn Christian - LCABD 12/04/07 4 FONT1,2,3: Summary 67 ns 54 ns 23 ns

Glenn Christian - LCABD 12/04/07 5 FONT4 motivation FONT1,2,3 – ultra-fast demonstration of feedback using analogue BPM processor originally driven by ‘warm’ bunch spacing FONT4 – demonstration of feedback on ILC-like bunches using digital processor –allows implementation of algorithms for luminosity recovery Now 3 bunch train at ATF produced from ~300 ns kicker pulse Later new extraction kicker - 20 ~150 ns (FONT5?)

Glenn Christian - LCABD 12/04/07 6 FONT4 system overview KICKERBPM 11BPM 13BPM 12 AMP Analog FE Witness BPMs Digital processor Feedback BPM Machine timing system Scopes ∑ ∆ BEAM clks, triggers LO DAQ I/O, digital DAQ

Glenn Christian - LCABD 12/04/07 7 FONT4 goals/challenges Stabilise third bunch at micron level –Require latency < bunch spacing –Nominal bunch spacing 154 ns but can be altered in 2.8 ns steps – must be able to work with this! –For this reason set latency target as 140 ns Max ADC sampling speed (14-bit device): 105 MHz –One sample per bunch – leads to rather complicated arrangement for sampling at the peak for each bunch –Need timing synchronised to machine (357 MHz machine clock, 2.16 MHz ring clock, and pre-beam trigger) –Want to sample as fast as possible (choose 357/4 MHz adjusted using 357/5 MHz between bunches)

Glenn Christian - LCABD 12/04/07 8 Digital Board 2 x Analog Input channels (single-ended) 2 x Analog Output channels (differential)4 x General-purpose digital outputs 3 x external clock/trigger inputs Xilinx Virtex4 FPGA Analog Devices ADC/DACs 40 MHz oscillator RS232 comms JTAG port PROM GP I/O Header

Glenn Christian - LCABD 12/04/07 9 FONT4 Latency Budget/Estimate Original Latency Budget Time of flight kicker to BPM (assuming 2m lever arm): 7 ns Signal propagation delay BPM to kicker: 15 ns Irreducible latency: 22 ns BPM analogue processor: 10 ns Digital processor: 68 ns –ADC/DAC: ~40 ns –FPGA I/O: 3 ns –FPGA processing (8 clock cycles): 25 ns Amplifier: 40 ns Electronics latency: ~118 ns Total latency: ~140 ns Digital board latency test Minimum latency ~6.5 clock cycles ~70 MHz

Glenn Christian - LCABD 12/04/07 10 FONT4 firmware features System clock frequency 357 MHz – locked to ATF and hence bunches Free-running design - 14-bit ADCs/DACs – 105 MSPS Use fact that harmonic number is 330 (ie 165 cycles of 357 per DR clock period) and pre-beam trigger to select correct ring- clock cycle then count in steps of 2.8 ns (357 MHz) to sample at bunch peak Use BRAM(ROM) to output the ADC and DAC enables, sample at 357/4 at the bunches and 357/5 during quiescence to adjust the enable bitstreams to ring clock period. BRAM also outputs clk_en strobes Baseline is 4 clock cycle latency MHz) from input to output buffer

Glenn Christian - LCABD 12/04/07 11 JTAG INPUTS OUTPUTS Clk_357 Clk_2.16 Clk_40 ILA Trigger VIO controls FPGA – Timing & Data Processing CTR1 RST CTR2== SYNC_DELAY RST BRAM ADDR Trigger processing ADC_clkDAC_clk & Difference Sum 1/Sum (LUT) X X GAIN +& AOUT DELAY ‘LOOP’ IDELAY

Glenn Christian - LCABD 12/04/07 12 New Amplifier Design New design for “universal” FONT amplifier –Designed to have flexibility to meet future requirements –Design for 10 us operation with 35 ns settling time at rep rate of 2 Hz –Output current up to +/- 30 A –Manufactured by TMD Technologies in UK – Two units delivered 1 December 2006

Glenn Christian - LCABD 12/04/07 13 Amplifier Tests at ATF (Dec 2006) Two amplifier variants tested on ATF extraction line, using special version of FONT4 firmware –Second variant 5 ns faster – both now same build standard ‘Feedback loop’ closed in terms of hardware, cables, timing etc but amplifier driven with top-hat signal, not position-feedback signal Variable amplitude, polarity flip, and delay of top-hat wrt nominal output time Measured kick linearity, kick as a function of electrode gap (kicker inductance), kick as a function of output delay (slack) – system latency

Glenn Christian - LCABD 12/04/07 14 Kick Linearity

Glenn Christian - LCABD 12/04/07 15 System Latency (BS = 154ns) Latency ~135ns

Glenn Christian - LCABD 12/04/07 16 System Latency (BS = 154ns) 20ns slack to 80% full kick

Glenn Christian - LCABD 12/04/07 17 Position Feedback Tests (Feb 2007) Ran with bunch spacing of 154 ns Firmware features: 8 left-shift gain settings (x1 – x128), delay loop, delay and feedback switches, output inversion, no saturation Took data at various positions and gain settings Checked functionality of gain and delay loop

Glenn Christian - LCABD 12/04/07 18 Feedback in action (154 ns BS, gain x16) Scopes Integrated Logic Analyser

Glenn Christian - LCABD 12/04/07 19 Current work Performance optimisation features still to include: –load ‘fixed’ gain curves into look-up tables BRAM(ROM) contents pre-computed and loaded using a partial reconfiguration technique –real-time charge normalisation Fast multiply-accumulate of gain-corrected difference and reciprocal- sum signals + delay register Fastest results utilise on-chip resources but require pipelining (eg DSP blocks – requires 3 levels of pipelining to run at 357 MHz – entire register budget) Delicate trade-off between speed and #pipelines (latency) and maybe #bits (resolution)

Glenn Christian - LCABD 12/04/07 20 Conclusions Demonstrated closed loop feedback at ATF with 3 bunches ~150ns spacing with digital feedback processor System latency ~135ns New amplifier manufactured by TMD Technologies and tested at ATF Further work to be done to optimise the performance of the system