TRENDS IN BPM SYSTEM DESIGN The ATF Damping Ring BPM Upgrade Nathan Eddy Manfred Wendt Fermilab...

TRENDS IN BPM SYSTEM DESIGNThe ATF Damping Ring BPM Upgrade

Nathan EddyManfred Wendt

Fermilab

Low-ε-Ring Workshop 2011

Heraklion, Crete, Greece

October 5, 2011 – LER 2011 – N. Eddy & M. Wendt

Contents

• Part I (Manfred)– Introduction– BPM Pickup Design

“Button-style” BPM– Read-out Electronics

• Part II (Nathan)– The ATF DR BPM System


BPM Building Blocks

• BPM pickup– RF device, EM field detection,

center of charge– Symmetrically arranged electrodes,

(or resonant structure)

• Read-out electronics– Analog signal conditioning– Signal sampling (ADC)– Digital signal processing

Analog Signal

Conditioning

Digital Signal Processing

Data Acquisition

Trigger, Timing & RF

Control

Power Supply &

Misc.

BPM Pickup

positiondata

controlsystem(LAN & FB)

timing,RF & CLKsignals

feedback bus(if applicable)

– Data acquisition and control system interface

LAN & fast feedback

– Trigger, CLK & timing signals


Beam Structure

• tbeam repeats with– trev in circular accelerators

• Bunch intensities may vary– Bunch to bunch, within tbeam

– “Missing” bunches– Or chance with time, e.g.

slowly due to lifetime fast due to top-up injection

• Adapt BPM integration time– Single / multi-bunch– TBT, multiturn, narrowband,

etc. System BW:

• Operation conditions may change– Particle species (e-, e+)– RF gymnastics, bunch

patterns,…

𝑖bunch (𝑡)=𝑞bunch

𝜎 √2𝜋𝑒

− 𝑡2

2 𝜎2

tbunch

trev

time

bunched beam

tbeam

𝑡 bunch=𝑛𝑓 RF

Gaussian bunch:

∝𝟏 / (𝒕𝒓𝒆𝒗−𝒕𝒃𝒆𝒂𝒎 )


BPM Characteristics & Applications• Measurement / integration time• Position resolution

– Resolve an orbit difference (depends on the measurement time).

• Linearity and accuracy– Absolute error of the reported beam position– BPM offset (zero-order correction coefficient) – BPM tilt (roll) -> x-y coupling

• Dynamic range– Beam intensity independence (saturation / noise floor).

• Reproducibility and long term stability– Reference “golden” orbit

• Variety of applications beyond beam orbit measurements– Injection oscillations, betatron & synchrotron tunes, dispersion

& beam energy, x-y coupling, beam optics, magnet alignment and errors, non-linear field effects, etc.

– Machine commissioning (intensity).


BPM Offset & Tilt

BPM Read-out(electr. offset)

x

y

BPMoffset

quadoffset

beamposition

reportedbeam

position

• BPM – quad alignment– Mechanical & “electrical” offsets– E.g. BBA procedure

• Similar for BPM / quad tilt


Broadband PU: Image Current Model

• Broadband, e.g. “button” BPM pickup:– Difference and common mode signal components

• Laplace problem solved for circular and elliptical cross-section– Image current density

(cylindrical coordinates, ρ=r/R)

– Electrode beam position sensitivity

– Two symmetric arranged electrodes

• Example: – Sensitivity near center for ϕ = 300

-> 3.43 dB/mm (R = 10 mm)-> 2.58 dB/mm (R = 20 mm)

𝐽𝑤 (𝑅=1 ,𝜙𝑤 )=−𝐼𝑏𝑒𝑎𝑚2𝜋

1−𝜌2

1+𝜌2−2 𝜌 cos (𝜙𝑤−𝜑 )

𝑠 (𝜌 ,𝜑 )=𝜙+4∑𝑛=1

∞ 𝜌𝑛

𝑛cos (𝑛𝜑 )sin (𝑛𝜙2 )

hor= 𝑓 (𝑅−𝐿𝑅+𝐿 )∨¿ 𝑓 (20 log10(𝑅𝐿 ))

𝑉 elec (𝑥 , 𝑦 ,𝜔 )=𝑠 (𝒙 ,𝒚 )𝑍 (𝜔 ) 𝐼beam(𝜔)


BPM Pickup Position Characteristics

Up

Down

Right(Out)

Left(In)

UR (Up-Right)Electrode A

DR (Down-Right)Electrode D

DL (Down-Left)Electrode C

UL (Up-Left)Electrode B

0.015 0.010 0.005 0.000 0.005 0.010 0.015

0.015

0.010

0.005

0.000

0.005

0.010

0.015

𝝓𝒉(𝒙 , 𝒚 )=(𝝓𝑼𝑹+𝝓𝑫𝑹) − (𝝓𝑼𝑳+𝝓𝑫𝑳 )𝝓𝑼𝑹+𝝓𝑫𝑹+𝝓𝑼𝑳+𝝓𝑫𝑳

=(𝐴+𝐷 ) − (𝐵+𝐶 )

𝛴

• Solve the Laplace equation numerically for one electrode (2D cross-section)

• Expansion of ϕUR by superposition using the symmetry of the pickup, e.g.:

𝜟𝜱=0⟹𝜱= 𝒇 (𝒙 ,𝒚 )

UR

AB

C D


BPM Pickup Scaling

• Rearrange horizontal and vertical potential arrays:

• Fit the 2D polynomials, e.g. of 7th order (or look-up table)

– The coefficients knn include the scaling of the pickup geometry knn‘s are the same for horizontal and vertical in case of

horizontal / vertical symmetry of the BPM pickup electrodes.– As of the symmetry, even terms are ~0.

limit the fit to odd terms, e.g. ϕ, ϕ3, ϕ5, ϕ7.– k00 is ~0, but reflects the monitor offset, i.e. found e.g. by BBA, and is

usually different in horizontal and vertical plane.– k01 is the “monitor constant”, slope at the origin

• BPM pickup scaling and non-linear field correction:– Iterate a few times:

𝑥=(𝑘00 𝑘01𝜙h ⋯ 𝑘07𝜙h

7

𝑘10 𝑦 𝑘11𝜙h 𝑦 ⋯ 𝑘17𝜙h7 𝑦

⋮ ⋮ ⋱ ⋮𝑘70 𝑦

7 𝑘71𝜙h 𝑦7 ⋯ 𝑘77𝜙h

7 𝑦7)

𝒙= 𝑓 (𝝓𝒉 , 𝑦 ) 𝒚= 𝑓 (𝝓𝒗 ,𝒙 )

𝑦=(𝑘00 𝑘01𝜙𝑣 ⋯ 𝑘07𝜙𝑣

7

𝑘10𝑥 𝑘11𝜙𝑣 𝑥 ⋯ 𝑘17𝜙𝑣7 𝑥

⋮ ⋮ ⋱ ⋮𝑘70 𝑦

7 𝑘71𝜙𝑣𝑥7 ⋯ 𝑘77𝜙𝑣

7 𝑥7)


Button BPM

𝑍 button (𝜔 )=𝑉 out (𝜔)𝐼 beam(𝜔)

=𝜙𝑅load (𝜔1𝜔2 )(𝜔1/𝜔2 )1+ (𝜔 /𝜔1 )2

• Commercial UHV RF button feedthroughs, made to specs– RF properties

(numerical simulation)– Environmental requirements

• Compact construction• Installation, tolerances, cabling• Other button load impedance,

than Rload = 50 Ω?

𝜔1=1

𝑅load𝐶button𝜔2=𝑣beam

2𝑟button

ϕ=𝑟button

4𝑅 pipe


Coupling Impedance

• Longitudinal coupling impedance

– Additional effects due to the annual button-ground gap

• TE11 gap waveguide resonance at:

• Try to minimize wake potential:– Reduce rbutton

– Minimize wgap

𝑍∥=1

𝐼 beam(𝜔) ∫02𝜋 𝑅

𝐸𝑧 (𝜔 )𝑑𝑧≈𝜙𝜔1𝜔2𝑍button(𝜔)

𝑍∥ 𝑔𝑎𝑝≈𝑍0𝜔 (𝑟 button+𝑤gap )3

8𝑐0𝑅𝑝𝑖𝑝𝑒2 {ln [32 (𝑟button+𝑤gap )/𝑤gap ]−2}

𝜆𝑇𝐸11=2𝜋𝑟button+(𝑟button+𝑤gap )

2

𝑑button

𝑤gap


Read-out Electronics

ADC 900

CIC FIR

ΣMEMORY

NCO

I-Channel

Q-Channel same as I

NB

WB

raw

AB

C

D

BPF Att BPF LPF

CoordinateTransform

ation

A-Electrode Analog Signal Conditioning

B, C, D Analog same as A

Ctrl LO

CLK & Timing

A Data

• Typical BPM read-out scheme– Pipeline ADC & FPGA

14-16 bit, 100-300 MSPS, >70 dB S/N

– Separate analog signal processing for the channels

– Analog down-converter if undersampling is not applicable.


Some Remarks

• Analog down-converter / signal conditioning– Defines the TD waveform / frequency band to be digitized.– May need to be located close to the BPM pickup

(e.g. pickup input frequencies in the microwave range)– Analog down-conversion vs. undersampling!?

CLK jitter requirements– Linearity / dynamic range extension (attenuator / gain switching)– Needs calibration & gain correction system

• Digital signal processing– FPGA vs. CPU processing?!– I-Q is only required if ADC CLK is not phase locked to fRF

– Down-conversion to base-band, low frequency but not DC Crawling phase

– Coordinate transformation √I2+Q2 vs. rotation to I’?!

• Key elements: Dynamic range (linearity) & statistics (sample-rate)!• Practical considerations, e.g. cabling, VME, xTCA, pizza-box, etc.

tjitter

Aerror

signal


Typical Performance

BSP-100 module(APS ANL)

Libera Brilliance(@APS ANL)

courtesy G. Decker


BPM Resolution vs. Beam Current

----: Bergoz system resolution: libera slow acquisition mode: Libera turn by turn mode: Libera turn by turn mode (decimated)

courtesy C. Milardi

• Observed at DAϕNE (INFN-LNF)– Libera and Bergoz BPM read-out electronics– Each point is averaged over 100 orbits


Automatic Gain Correction

• Use calibration tone(s)– 714+ε MHz, 714-ε MHz– Reflected and/or thru BPM

calibration signal– Inside analog pass-band– Separate DDC in NB mode– Error & correction signals:

• Advice:– Two calibration tones need

separate DDCs, or a“ping-pong” calibration tone workaround

𝑋Err=𝐴CAL+𝐵CAL+𝐶CAL+𝐷CAL

4 𝑋CAL

𝑋Corr=𝑋 raw 𝑋 Err 𝑋 : 𝐴 ,𝐵 ,𝐶 ,𝐷


Libera Crossbar Switch CAL Scheme

Schematics of crossbar switch based BPM electronics from Istrumentation Technologies.Pat. No.: US2004/0222778 A1


The ATF Damping Ring

Machine and Beam Parameters

beam energy E = 1.28 GeV

beam intensity, single bunch ≈ ~1.6 nC ≡ 1010 e- (≡ Ibunch ≈ 3.46 mA)

beam intensity, multibunch (20) ≈ ~22.4 nC ≡ 20 x0.7 1010 e- (≡ Ibeam ≈ 48.5 mA)

accelerating frequency fRF = 714 MHz

revolution frequency frev = fRF / 330 = 2.1636 MHz (≡ trev = 462.18 nsec)

bunch spacing tbunch = tRF / 2 = 2.8011 nsec

batch spacing tbatch = trev / 3 = 154.06 nsec

horizontal betatron tune ≈ 15.204 (≡ fh ≈ 441 kHz)

vertical betatron tune ≈ 8.462 (≡ fv ≈ 1000 kHz)

synchrotron tune ≈ 0.0045 (≡ fs ≈ 9.7 kHz)

repetition frequency frep = 1.56 /3.12 Hz (≡ trep = 640 / 320 msec)

beam time tbeam = ~460 / ~240 msec

1 2 19 20 1 2111 112 129 130 221 222 239 240

trev

tbunch


BPM Hardware Overview

BPF LPF

714

2.16

INJ

Down Mix

Cal (~ 714)

Timing(VME)

LO (729)CLK (64.9)

TRG

Digital Receiver

(VME)

VME µPMotorola

5500Q

Ibeamposition

4 buttonBPMpickup

IF (15)

beam

VME BUS

LAN

PLL

4ATT

4

CAN

CTRL

-100 0 100 200 300 400 500 600 700 800 900

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

-1

0

1

2

3

4

5

15MHZ BPF time rsponse

Time [ns]

Vo

lts

Vo

lts


Analog Signal Processing

• 4-ch. Analog downmixer– IN: 714, LO: 729.1, IF: 15.1 MHz– CAN-bus controlled gain,

attenuator & cal system– Gain switchable, low-noise, high

IP3 input gain stage– Image rejection (SSB) mixer– ~30 dB gain, ultralinear IF stage

15.145 MHz

BPFATT LNA BPF LNA LPF

SSB Mixer

LO

0°

90°

LNALPFDirectional

CouplerIN

714MHzCF: 714MHzBW: 10MHz G: 14/-2 dB

NF: 1dB0 - 28 dB

4 dB steps1.6 dB loss

729.145 MHz

CF: 15.1 MHzBW: 4MHz

G: 18 dB BW: 40 MHz

OUT

BW: 800 MHz G: 15 dBNF: 1dB

Cal Tone Signal


8-Ch,14-bit, 125 MS/s VME Digitizer

BLOCK DIAGRAM

FPGAAlteraCyclone III

VMEDrivers

4x32MDDR2SDRAM

JTAG

EPCS4Interface

VME bus

Oscillator

Oscillator

CLK IN

CLK OUT

GATE

TRIGGER

TCLK

SYNC IN

SYNC OUT

Generic Digitizer

External Control

Clock Driver (PLL & DIV)

ADC

ADC

AC passive

8 Analog Inputs 4 Channels per Chip

• 125 MSPS, 500 MHz BW• 4-ch serial ADC chips• 8-ch, AC passive (or DC active)• PLL/VCO CLK distribution• SNR > 72 dB (@50 MHz)• Ch-Ch xTalk > 80 dB


ATF FPGA Block Diagram

ADC Input14 Bits

71.4 MHz

NB Filter1.4kHz output

16 Bits/ch

32 ch/

NB Gate

WB Gate(s)

DDR RAM

NB DataTBT DataRaw Data

Σ50Hz

VMENB Data

VMERaw Data

TBT Filter

VMETBT Data

8 ch/

Trigger DAQ SMCh delays (clocks)

Gates in Turns

WB Gate(s)

NB Gate

32 Registers

VMENB Sums

VMEIRQ

reset latch

reset

latch

8 ch/


ATF Narrowband Signal Processing

• Process 8 ADC channels in parallel up to FIR filter• Digitally Downconvert each channel into I,Q then filter I,Q independently• CIC Filters operating in parallel at 71.4MHz

Decimate by 17KSPS to 4.2KSPS output rate

• 1 Serial FIR Filter processes all 32 CIC Filter outputs 80 tap FIR (400 Hz BW, 500 Hz Stop, -100 db stopband) -> 1KHz effective BW Decimate by 3 to 1.4 KSPS output rate -> ability to easily filter 50Hz

• Calculate Magnitude from I,Q at 1.4KHz Both Magnitude and I,Q are written to RAM Also able to write I,Q output from CIC to RAM upon request

ADC Input14 Bits69 MHz

X

NCO (sin, cos)24 Bits Phase

(~1 Hz)

I

Q16 Bits

CIC5 StagesR=17001

DDC24 Bits

4.2 KSPS

FIR (80 taps)LPF 500HzDecimate 3

BitShift

SelectSignificant

Bits

20 Bits4.2 KSPS

16 Bits1.4 KSPS

I

Q

- Denotes Peak Detectors to optimize scaling

CalculateMagnitude


ATF Standard Operation Data

• Trigger before beam injection (injection rep rate is ~1.5 Hz)– Beam in machine for ~1e6 turns (~450 msec)– Bunch RF is 714MHz with h=330, ADC clock 71.4MHz -> 33 ADC samples/turn– Gates specified in turns (need to account for filter delay/decimation for NB)– Data in digitizer boards is overwritten on each trigger– Note for WB readback (diagnostic and some TBT data) it will be necessary to use

“snapshot” which insures synchronization & stores all data in snapshot buffer

Trigger

Beam

NB Gate

WB Gate(s)

Reset

Latch

IRQ ReadoutReadoutIRQ

CAL


ATF TBT Study Data

• Trigger before beam injection (injection rep rate is ~1.5 Hz)– Beam in machine for ~1e6 turns (~450 msec)– Bunch RF is 714MHz with h=330, ADC clock 71.4MHz -> 33 ADC samples/turn– Gates specified in turns (need to account for filter delay/decimation for NB)– Data in digitizer boards is overwritten on each trigger– Note for TBT readback it is necessary to use “snapshot” which insures

synchronization & stores all data in snapshot buffer

Trigger

Beam

No NB Gate

WB Gate

Reset

Latch

ReadoutIRQ


ATF Software Components

VMEECAN-2

PMC (1x)

VMETimingK-TGF

(1x)

VMEDigitizer

(12x)

CLK (64.9)

TRG(Gate)

A

B

C

D

714

2.16

INJ(BIS)

729

CAN

ClassADC

Interrupt

I/Q Data

Configure

ClassKTGF

Bucket Delay

Turn Data

Sample Count

ClassCALBox

Control

Status

ClassATFBPM

ClassATFBPM

CAL

Control

Status

Sample

Control

Interrupt

Control

Pos/ Int Data

EPICSIOC

Control

Status

Flash

WB / NB

Single/Multi-turn

Diag. Mode

Bucket Delay

Turn Delay

Diagnostic

Flash

Orbit

Multi-turn

VME Hardware Motorola 5500 µP Software (VxWorks)

Ethernet


TBT Inj.: Dispersion Measurement

Dispersion, horizontal Dispersion, vertical

• Use TBT data to fit the dispersion functions– Use nominal Dx to find the amplitude and

phase start values, which best fit x_TBT.– Subtract the synchrotron oscillation from x_TBT,

to find the actual dispersion function.


Dispersion Measurement (RF)

• Dispersion measurement using a frequency shift– Perform closed orbit measurements with Δf = -10 kHz

Reference orbit: average 50 data setsRF shifted orbit: average 15 data sets

Particle are now on the dispersion orbit ~ D dp/p, with dp/p ~ df/f

<Dx> <Dy>*

*note: in <Dy> the green line justconnects the measurement points


Dispersion Analysis (cont.)

• Compare RF and TBT inj. dispersion measurements– Good agreement in the horizontal plane

BPMs 73 and 85 where disconnected– Still fair agreement in the vertical plane,

having only little dispersion perturbation.

ΔDx ΔDy


TBT Phase Analysis

• Beam phase motion (synchrotron oscillation) results in an error on each button magnitude

• Observed on the intensity (button sum) and varies bpm to bpm

• In the ideal case where each channel is sampled at the same phase, this would not affect the position

• Simulated beam signals with expected synchrotron oscillation (200 turn period)

• We are looking into ways to minimize this effect – cable trims, fit correction


Narrowband Results (preliminary)

• 250 Orbit measurements recorded over an 8 hour shift

• Resolution estimated with split signal BPM and by SVD technique– 0.650 μm with split signal– 1.25 μm (6 SVD modes)– 0.660 μm (20 SVD modes)

• Measurements where performed in low gain– Expect ~3 improvement

• Need more investigations!


Summary & Final Remarks

• Trend to digital signal processing, plus some analog electronics with integrated calibration / drift correction scheme.– Complex processing / math in the digital domain.– Very flexible by FPGA re-programming, however labor intensive!

• ATF BPM system has been implemented using this scheme– Custom analog downmix module

Tailored to machine parameters Integrated gain control and calibration

– Custom digitizer ADC locked to machine RF Can customize signal processing to specific needs

– CO, TBT, FFT, etc– EPICs software interface

• ATF Installation complete at the end of 2010– Initial commissioning successful– Beam studies to continue – BBA, Tilt -> low emmittance operation!

TRENDS IN BPM SYSTEM DESIGN The ATF Damping Ring BPM Upgrade Nathan Eddy Manfred Wendt Fermilab...

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Transcript of TRENDS IN BPM SYSTEM DESIGN The ATF Damping Ring BPM Upgrade Nathan Eddy Manfred Wendt Fermilab...