Horz V1 H1H2V2

Pbars in Recycler Ring

StriplineKickers

Split PlatePickups

A-B

A-B

VerticalDigitalDamper

Vert

Recycler Transverse Damper System

Similar for Horizontal

LPF

LPF

V1 Digital Damper• Boards used for MI Damper

systems• Standalone board with on board

cpu (Sharc) & ethernet – communicates with ACNET via OAC

• Four boards are operational– 2 for MI dampers, 1 for Recycler

Damper, 1 being used for Booster damper studies

– A 5th board exists but was never made operational

– At present, the Booster board can be considered spare hardware – work is needed to actually make it into a spare for any of the operational systems

• Operational since fall 2005 with no major hardware/system issues

Implemented in one FPGA based damper board developed by B. Foster & A. Seminov

V1 Damper Block Diagram

ADCInput

ADCInput

212MHz

X

X

InputGain

+ - X

OutputGain

DACOutput

DACOutputDelay

DelayDelay

Delay

1 Turn Invert 212MHz

Peak DetectorsReadback by ACNET

Peak Detector & RMSReadback by ACNET

Notch Filter

Box

Box

4 SampleBoxcarFilter

• System Bandwidth is determined by analog LPF on inputs• Programmable delay is limited to 212MHz clock rate (1/4 RF bucket)

V1 Damper Amplitude and Phase Response

• Phase has been inverted so that 0° is damping• The analog 30MHz LPF causes phase shift as it rolls off the gain• The system goes unstable at ~37Mhz once the Beam Density reaches about 2.5

V2 Digital Damper• Developed as next generation

replacement for the “Foster” Board• VME format to take advantage of

standard controls software– Interface implemented in FPGA– Remove Sharc processor

• Same basic design with updated FPGA and Digital to Analog Converters

– Applied lessons learned on V1 design to take better advantage of FPGA features

• 15 boards have been assembled – Used for Recycler RF Adaptive

Correction– Used for Recylcer ACBEAM intensity

Monitor– Used for MI Anti-proton Damper– Plan to replace MI Proton Dampers– 8 spares available

V2 Recycler Damper• Faster DACs and next generation

FPGA allow us to double the system bandwidth and increase performance

• Standard Controls ACNET interface implemented in VME processor

• Use extra channels for Testing & Diagnostics

• Network analyzer can be hooked up to spare channels for transfer function measurements– Can make both open loop

measurements without changing cables on operational system

– Can also make closed loop measurements

Use 2 VME boards -1 per plane

V2 Damper Block Diagram

ADCInput

ADCInput

212MHz

X

X

InputGain

+ - X

OutputGain

DACOutput

DACOutputDelay

DelayDelay

Delay

1 Turn Invert 636MHz

Peak DetectorsReadback by ACNET

Peak Detector & RMSReadback by ACNET

Notch Filter

FIR

FIR

8 TapFIR

Filter

• System Bandwidth is controlled by FIR filter with constant phase the analog anti-alias filter is upped to 70MHz• Programmable delay possible at 636MHz clock rate (1/12 RF bucket)• This allows increased system bandwidth to improve performance

V2 Damper Amplitude and Phase Response

• Phase has been inverted so that 0° is damping• The analog 70MHz Filter does not affect the phase until about 60MHz• System gain is controlled with programmable FIR filter• The system goes unstable >70MHz once the Beam Density is > 4

Brief V2 History• First issue was with analog input circuit to the ADC

– Modified circuit to improve signal termination– 1st modification was susceptible to a failure due to poor solder joint which

caused 7.5MHz resonance– Has been fixed

• Remaining issues have all been caused by timing issues within the FPGA design– Fixed logic which handles ADC/DAC data– Found and eliminated temerature dependence in FPGA PLL clocks – was

causing delay shifts in design– Latest issue appears due to rare (1 second/50 hours) timing glitch within

the digital filter logic • Only present in Horz board whose FPGA runs hotter due to crate

– Horizontal VME slots and poor air flow• This is a product of the most recent design – not observed before 12/07

– Note that marginal timing issues are sensitive to temperature & power

Installation on 3/18/08

• While preparing to switch that morning, Vertical board spontaneously performed a firmware reload from flash memory– Made decision to abort the switch– Never observed before– FPGA lost design – power glitch?– Glitch on VME_SysReset*?– Has not happened again…

• Horizontal Board had PLL losing lock that afternoon– Clock input was swapped and moved to Z crate– Removed from MI60 and put in teststand – fine since…

Installed on 4/23/08

• Found blown fuse on Reset Card– VME_SysReset* on backplane was 2V

• Updated Design to be less sensitive to glitches on VME_SysReset*– Require signal to be low for >200ns

• No further spontaneous resets observed for 3+ weeks of monitoring

• Made request to install

Initial Results Good

• Attempted to induce instability with 80e10– Density reached ~3.5– No instability

• Measured closed loop response during test– Looked good 0.7

0.8

0.9

1.0

1.1

0.44 0.46 0.48 0.50 0.52 0.54 0.56

f/frot

amplitude

-10

0

10

20

30

degrees

RR damper closed loop measurements

10/100/200/400 frot

amplitude

phase

Clock PLL Event on 5/1/08

• Vertical Damper Turned Off when it’s RF PLL lost lock– Got an immediate vertical

instability– The Vertical Damper in the

test crate also turned off

• Jim & I were both at MI60 at the time looking into scope and network analyzer issues

The Suspects

• Power– Hard to imagine this just hitting 1 of 2 boards in 2

different crates– The crates are on completely separate circuits

• Temperature– Known temperature issues with FPGA and PLL– Found Fan on Operational Vertical board was

stopped but Test Vertical was fine

• Noise/Problem with Clock– Could not see how only 2 of 4 boards would lose lock

Temperature

• Installed Temperature monitors and new fanpacks

• Did not see any Events or temperature correlation

Started Looking at Noise

• On 5/5 saw 4 glitches in 1 hour while poking around at MI60

• All recent glitches (last few months) occurred when someone was at MI60

• Discovered Cell phone activity at 800-900Mhz was coupling into clock circuit and causing PLL to lose lock

• Able to reproduce reliably in teststand• Looking at circuit on NA showed high impedance

from 700Mhz to 1GHz

Clock Improvements

• Implemented filters and shielding to eliminate high frequency noise from the clock input circuit

• No longer see PLL glitches from cell phone or 1Watt RF antenna

• Also implemented state machine to provide best recovery scenario should the PLL briefly lose lock in the future

Summary

• Have identified cause for PLL to lose lock– Last few “glitches” now completely understood– Have a very plausible root cause for the timing issues

which have plagued the system for the last 6 months

• The VME Dampers are now back in operation