WIR SCHAFFEN WISSEN – HEUTE FÜR MORGEN

Boris Keil for the SLS 2.0 BPM Team :: GFA :: Paul Scherrer Institute

Development of the SLS 2.0 BPM System
IBIC 2023, Sep. 11, 2023, Saskatoon, Canada

ContentsIntroduction
Mechanics
Electronics
Test Results
Summary & Outlook

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Swiss Light Source Upgrade Project: SLS 2.0
SLS 1.0:• 3rd generation synchrotron
light source• User operation since 2001
• Last beam Sept. 30, 2023
SLS 2.0:• 1st beam 1/2025• New storage ring: >40x higher
hard X-ray brilliance• Replace ageing hardware (BPMelectronics from 2001, ...)
• Keep linac, booster
Page 3SLS 2.0
Parameter

Units

Circumference

m288

Beam Current

mA400

Injection ChargenC~0.15

Beam Energy

GeV

2.42.7Main RFMHz

499.637499.654

Harmonic No.

#Hor. Emittance

pm

5030

131-158

Vert. Emittance

pm

5-10

10Ring BPMs

#75136

Stainless Steel

Copper (NEG)

Ring Beam Pipe

SLS 1.0

SLS 2.0480

Page 4SLS 2.0: BPM Types & Beam Pipe
Decaying 500
MHz sine

Location
Linac & Transfer Lines
Booster
SLS 1.0 Ring
SLS 2.0 Ring

All: 4 diagonalelectrodes A,B,C,DX[mm] ~ kx * (A-B-C+D)/(A+B+C+D)

BPM Type

geometry factors kx/ky [mm]Resonant Stripline
ButtonButtonButtonvarious8.3/7.7
16.7/14.3
7.1/7.2
Same BPM electronics has >2x better
resolution at SLS 2.0 compared to SLS 1.0Dimensions [mm]Page 5SLS 2.0 BPM Requirements
σY~5µm nominal, may be
reduced/adjusted

Parameter

Goal% of σY

Position Noise (0.1 Hz - 1 kHz BW), 400 mA<50 nm RMS

1%

Position Noise (0.1 Hz - 0.5 MHz BW), 400 mA<1000 nm RMS

20%

Position Noise (0.5 MHz BW), 0.15nC, 1 Bunch<50 um RMS-<100 nm / hour

2%<400 nm / week

8%<1000 nm / year

20 %<250 nm / hour

5%<1000 nm / week

20%

<2500 nm / year

50%

<100 nm / 4 mA

2%Electronics Drift (400mA beam, constant)Overall Drift (Electronics + Cables + Mechanics)
Beam Current Dependence (Const. Fill. Patt.)

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Contents

Introduction
Mechanics
Electronics
Test Results
Summary & Outlook

Page 7

BPM Mechanics

Combined BPM + orbit corrector dipole magnet beam
pipe (taper 18→21 mm = synchrotron radiation
shielding). 0.5 mm steel + 5 µm Cu + 0.5 µm NEG)

Borosilicate glass (dark blue): Inner
conductor (red) with coaxial
asymmetry → HOM power
reduction & spectral spreading
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BPM Mechanics: Support

Water cooled copper
block reduces
position drift

Double steel plates, filled withsealed compound ofbalsawood & viscoelastic glue

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BPM Mechanics: Temperature Simulation
Beam-induced distributed heatup: (impedance + stray sync.
radiation): Tmax= 64°C .Worst
case, 400 mA, 3rd harmonic
cavity off → 9 ps bunch length(usually ~60 ps)
Top of BPM block
warmer than cooled
bottom (steel CTE~16ppm/°C)

Local BPM button heat up(HOMS ...): ~0.4W + perelectrode (worst case)

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BPM: Button Temperature
Simulation of button electrode temperature (rare worst case: 400 mA,
3HC off, 9 ps bunch length)
Inconel button (= standard for ourproduction company BC-Tech) + borosilicate
glass isolator: 52°C max. -> O.K.

Alternative: Molybdenum button.
Temperature only 11°C lower (button
temperature dominated by glass, not metal).

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BPM: Thermal Stress of Borosilicate GlassInconel button: Stress = 14 MPa (values < 50 MPauncritical) for worst case (400mA, 9ps bunch length)

Molybdenum button: 12 MPa (values < 50 MPauncritical) → not much better, but BC-Tech never used
it → schedule risk → keeping Inconel for SLS 2.0

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BPM Mechanics: Performance
Center of BPM block would move even if bottomside did not: Stainless steel CTE ~16 ppm/°C →distance of ~30 mm & dT ~ 10°C causes dY ~ 5 µm.

Simulated beam-induced BPM pickup center motion

ΔX [µm]ΔY [µm]Motion from 0 mA to 400mA beam current

-11.3

4.7

Motion @ Top-up (400...404mA)

< 0.1

<0.05

•
•

•

Assume worst case (400 mA, 9 ps bunch length, 3HC off)
Additional drift due to air & water:• Simulation: ΔY ~ 5 µm/°C water temperature change• SLS 1.0 water often ~0.03°C peak-peak (→150nm), but not always ...
• Being improved for SLS 2.0 (variable RPM for cooling machines, ...)
Beam, air & water cause common drift of all BPMs → less critical (X-ray angle ...)
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BPM Mechanics: Production Status••••All BPM electrodes produced>25% of BPM blocks produced
1/12 of beam pipe assembled
No vacuum problems so far
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BPM Button Electrode Sorting••

Transfer impedance of all button
electrodes measured pre-welding
Sorted by impedance: Reduce
contribution to position offset from~50 µm to ~1 µm

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Contents

Introduction
Mechanics
Electronics
Test Results
Summary & Outlook

Page 16

SLS2 BPM Electronics: "DBPM3" (PSI Design)

Generic 19'' backend (AMD/Xilinx
Zynq UltrasCSCale+MPSoC), also usedin SwissFEL (->IBIC'22 TUP12)SLS 2.0: 3 RF FrontEnd (RFFE) modules
per unit, integrated
ADC (JESD204B)
Redundant power
supply module
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DBPM3 SLS 2.0 RFFE Block Schematics
Internal beam/pilot combiner

Pilot SMA output (for RF cable
drift compensation via externalbeam/pilot combiner

2x2 crossbar switch

2 pilot tone generator PLLs
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SLS 2.0 BPM Position Drift Suppression
Mechanics → stable air & water & beam current (top-up).
RF cables (differential drift relevant):• Passive methods:• Equalize cable properties (measure & sort by TOF/attenuation)• Thermal cable bundle isolation• Cable trays below floor (lower temp. variation)• Active methods (so far):• Pilot tone
Electronics: Pilot tone, crossbar switch, active temp. regulation (DBPM3: 14 heatingzones per RFFE ...), choose low-drift components, ...
All: Optional feed-forward correction on temperature & humidity sensors
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Contents

Introduction
Mechanics
Electronics
Test Results
Summary & Outlook

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GUI: Settings for DBPM3 Test @ SLS 1.0 Ring

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Python GUI: DBPM3 DDC Filters

Programmable during
operation via EPICS ...

DDC Stage 0:
1.04 MSPS (=turn-by-turn),
0.5 MHz BW

DDC Stage 1:
20 kSPS, 3.3
kHz BW ("fastorbit feedbackdata").
bandwidth shown in GUI
not yet accurate, to be fixed(get accurate value fromfreq. response plots ...)DDC Stage 2:
20 SPS, 11 Hz
BW ("slowdata")
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DBPM3 Electronics Test @ SLS Storage Ring
Test Setup:• DBPM3 RFFE Rev. C (received mid August): First with pilot output• 400 mA SLS 1.0 ring BPMs beam signal• Sum signal of 4 buttons combined with DBPM pilot output• Then split to 4 RFFE channels (test electronics drift only → short cables)• Simulates centered beam
• 1 pilot , fpilot = fbeam + 0.531 MHz• ADC: 433 MSPS, 50% full scale (25% beam + 25% pilot)• 2x2 crossbar switches @ 130 kHz• kx/ky = 7.1mm/7.2mm (SLS 2.0 ring)• Water cooled 19'' rack

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DBPM3 Electronics: RMS Position Noise
Beam signal only:
20 nm (X) / 15 nm (Y)Pilot signal only:
27 nm (X) / 18 nm (Y)20 kSPS,3.3 kHzbandwidth

Beam minus Pilot:27 nm (X) / 20 nm (Y)Page 24

DBPM3 Electronics: 24 Hour Position Drift
20 SPS, 11 Hz bandwidth, 1 plot point per 30s recorded, no smoothing

Beam signal only:< 17.9 nm RMS

Pilot signal only:< 14.3 nm RMS

Beam minus Pilot:< 11.1 nm RMS

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DBPM3 Drift Test: SLS Hall Ambient Conditions

Test in SLS 1.0 building.
Expect similar/better
conditions in SLS 2.0(rack PID temp.
controller & coolingwater to be improved ...)

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Contents

Introduction
Mechanics
Electronics
Test Results
Summary & Outlook

Page 27

Summary & Outlook
BPM Status:• Mechanics: Production ongoing (>25% done).
• Electronics: Latest results promising, now long-term test with more units. Strategy:• 1st beam 1/2025: Upgrade only ring BPMs with present DBPM3 design ("gen. 1")• Series production soon, ~2 months left for minor changes• Q1/2026 = 2nd (shorter) dark time: Move DBPM3 gen. 1 from ring to linac/booster/TL(finally replacing old SLS1 systems there), install improved DBPM3 "gen. 2" in ring.
Outlook & To Do:• Test pilot-based drift compensation with long RF cables (20-36m)• Build "passive" beam-pilot combiner box, install near beam (copy from present RFFE)• Test 1 vs. 2 pilot tones, drift/noise dependence on pilot & ADC clock frequencies, ...
• Firmware/software upgrades (temperature regulation, ...)• Develop DBPM3 "gen. 2". Ideas: Newer ADC, generate pilot tone with fast DAC (DDS), ...
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Wir schaffen Wissen – heute für morgenThanks to:
F. Marcellini (Pickup/RF)
M. Roggli (RF Front-End)
M. Rizzi (RF/Electronics)
R. Ditter (Crate/Back-End)
J. Purtschert (Firmware/Software)
G. Marinkovic (SW/FW/HW)
X. Wang (Mechanics/Simulations)D. Stephan (Vacuum/Mechanics)...
and many others the SLS 2.0 project
team & support groups
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