Overview and Challenges of the Vacuum
Systems of Diffraction Limited Storage Rings

www. wihlborgs.se

Marek Grabski, Max IV laboratory
67th ICFA Advanced Beam Dynamics Workshop on Future Light Sources: FLS 2023
27 August to 1 September 2023, Luzern, Switzerland

FLS 2023, August 2023, Luzerne, Switzerland
Marek Grabski

1

Contents• Introduction,• Vacuum system requirements for Diffraction
Limited Storage rings (DLS),• Design approaches,• Chosen vacuum system design aspects of DLS,
• DLS summary• Conclusion
FLS 2023, August 2023, Luzerne, Switzerland
Marek Grabski2Locations of Diffraction Limited Storage rings
APS-U
ALS-U

DIAMOND II
Soleil II
ESRF EBSMAX IVPETRA IVHEPSBESSY IIISLS 2.0

SPRING 8-II

ALBA II

HALF

ELETTRA 2.0

SPS IISIRIUS

Operation
FLS 2023, August 2023, Luzerne, Switzerland
Marek Grabski

Installation on goingcommissioning in <3 years

commissioning in >3 years
3Introduction
Reductionin beamemittance

Large numberof magnets(high field)

Reduce thecircumference/cost

Compact
lattice/magnets (smallmagnet aperture,
limited space
between magnets)

Small aperture
vacuumchambers

MAX IV 3 GeV: top view of a magnet block

MAX IV 3 GeV: sextupole magnet aperture

Sextupole

Ø25

Limitedspace forabsorbers

Limitedspace forpumps

impedance

ESRF-EBS: Top view of one cell (31 magnets per cell, 32 cells)

Magnet apertures Ø25mm
Status report of vacuum system of ESRF, C. Maccarrone, eeFACT September 2022

FLS 2023, August 2023, Luzerne, Switzerland
Marek Grabski

4Requirements and constraints of vacuum system• Vacuum related beam lifetime >5 Ah ---> average totalpressure ~1e-9 mbar at dose 100 Ah.
• beam stay clear area (size of vacuum chambers, absorbers),• allow photon beam extraction,• ensure stability of BPMs (thermal and mechanical),• must fit magnetic lattice (magnet apertures, distances
between the magnets),• beam impedance (material, shape, coating thickness,connecting flange type, shielding of bellows),• compatible with stability requirements (mechanical design,supports system, water cooling),• handle high power loads from synchrotron radiation from
dipoles and IDs,
• must not distort magnetic fields (material, support system),• Integration of RF, injection, diagnostics, ID systems• resistant to radiation (materials used),• Installation compatible with the infrastructure (tunnel size,availability of handling cranes, time plan),• serviceability,• Cost, energy consumption, standardization,
FLS 2023, August 2023, Luzerne, Switzerland
Marek Grabski

Lifetime related tor residual gas density (Pressure level)

Envelopes defining beam stay clear area

Photon beam
Electron beam

5

Design approach 1: NEG coating, distributed absorbers
NEG coated copper tubes,
with distributed absorbers
at MAXIV (similar at Sirius).

Photon beam

MAX IV 3One
GeV storage
ring: 20 cells, 7BA,achromat
C=528 m, 4.5 m straight sections (L)1 cell 26,4 m
Beam direction
U2, VC4 (2,4 m long)

At MAX IV magnets are embedded
in a closed magnet block.

Limited lumped pumping instandard cell:• MAX IV - 3 pumping ports
with ion pumps (75 l/s), 1
crotch absorber,• Sirius – 5 pumping ports
with ion pumps (20 l/s) andNEG cartridges (200 l/s), 3
crotch absorbers,
FLS 2023, August 2023, Luzerne, Switzerland
Marek Grabski

Sextupole

25mmCorrectorDipoleØ22(ID)Ø25Chamber ID 22mm

Magnet apertures Ø25mm

Min. clearance with the iron 0.5 mm, min. clearance with the coils 2 mm.
6

Design approach 1: NEG coating, distributed absorbers
NEG coated copper tubes, distributed absorbers at MAXIV (similar at Sirius): Chamber• Extruded OFS (oxygen-free silver bearing) copper tubes - high thermalbody
conductivity (stainless steel sections for fast correctors),
Ribs• Water cooling to dissipate synchrotron radiation power,• Absorber features (tapers) embedded in the vacuum chambers,
Cooling for• NEG coating to lower Photon Stimulated Desorption (PSD) and provide corrector
area
distributed pumping after activation (@ ~180 deg C),
Distributed
Cost effective, MAX IV 3 GeV ring vacuum system total cost:cooling
6,336,000 €; ~12,000 EUR/m (in 2014).
DistributedcoolingØ22DipoleFLS 2023, August 2023, Luzerne, Switzerland
Marek GrabskiNEGcoating

MAXIV standard
vacuum chamber

Water coolingchannelCoppersubstrate

Copper taper forphoton beaminterception

SpigotCF knife edge(stainless steel)

Welded bellows
with RF shielding7

Design approach 2: Lumped absorbers and pumps
Conventional: Stainless steel and aluminium vacuum chambers with antechambers,
lumped vacuum pumps and photon absorbers, NEG coating only in ID chambers (ESRF-EBS)ESRF-EBS: Top view of one cell: 4 girders (31 magnets per cell, 32 cells)

Status report of vacuum system of ESRF, C. Maccarrone, eeFACT September 2022

ESRF-EBS: Side view of one girder with magnets (4 girders per cell)
ESRF – EBS Design Report, September 2018

ESRF-EBS CuCrZr photon absorbers
In each cell:• 2 photon extraction ports.
• Lumped photon absorbers: 13units (made of CuCrZr alloy).
• 24 lumped pumps: IP 55-75 l/s(14), NEG cartridge 100 l/s (10),• NEG coating in ID straight
ESRF – EBS Design Report, September 2018sections only.
FLS 2023, August 2023, Luzerne, Switzerland
Marek Grabski

Status report of vacuum system of ESRF, C. Maccarrone, eeFACT September 2022

8

Design approach 2: Lumped absorbers and pumps
Conventional: Stainless steel and aluminium vacuum chambers with antechambers,
lumped vacuum pumps and photon absorbers, NEG coating only in ID chambers (ESRF-EBS)
Aluminum vacuum chambers

Stainless steel Vacuum chambers: 316 LN, 316 L

ESRF – EBS Design Report, September 2018

Courtesy: ESRF EBS Vacuum Chambers & RF fingersL.Goirand- MEDSI 2016 - 11-16 September

FLS 2023, August 2023, Luzerne, Switzerland
Marek Grabski

9Design approach: Vacuum performance of DLS in operation
Vacuum systems based on NEG coating
and distributed copper absorbers (MAXIV and Sirius) work well and conditionedfast.
• There are no operational issues
related to the NEG coating that limit
the operation or machine
performance in any way (no peel off,saturation not observed),• Neon venting technique was used for
vacuum interventions (MAX IV,Sirius), significantly reducing theintervention time.
Conventional vacuum system (as inESRF-EBS) works good as well.

FLS 2023, August 2023, Luzerne, Switzerland
Marek Grabski

10Design aspect: light extraction
MAX IV: 1 photon extraction
port per cell (1 copperphoton absorber)

Photon beam

MAX IV One
3 GeVachromat
storage ring: 20 cells, 7BA,
C=528 m, 4.5 m straight sections (L)1 cell 26,4 m
e- beam direction

Short straight section 1 (S1) – synchrotron light
extraction to the Front End and Beamline
BPM

VC2

Crotch absorber

BPM

Photon beam

e- beam direction

VACUUM SYSTEM DESIGN FOR THE SIRIUS
STORAGE RING, R.M. Seraphim, IPAC 2015

Sirius: absorbers have different design andare NEG coated, 2 photon ports per cell

FLS 2023, August 2023, Luzerne, Switzerland
Marek Grabski

Crotch absorber

Radiation fan
interceptedby absorber

Challenges:• Lack of space through themagnets for the photon
beam chamber,• Photon beam high power
handling,

11Design aspect: BPM, bellows
BPM stability (with bellows)(MAXIV),Cooling

Taper

BPM (Beam Position Monitor)

BPMelectrodes

RF shields

To ensure thermal and dimensional stability of BPMs
(Beam Position Monitor) usuall approach (MAX IV):
• RF shielded bellows at chamber extremities toallow pipe expansion without affecting the BPM
position and temperature,• Taper to shield BPM stainless steel body fromradiation,• Copper chamber water cooled all-along.

Bellows
FLS 2023, August 2023, Luzerne, Switzerland
Marek Grabski

12Design aspect: BPM, bellows
Bellows integrated on the BPM block for possible
service (APS-U)

RF shielded bellow types (Sirius)

Final Design of the APS-Upgrade Storage Ring Vacuum System, J. Carter, NAPAC 2019

An Overview for the Sirius Vacuum System, T. Rocha, EIC 2021,

FLS 2023, August 2023, Luzerne, Switzerland
Marek Grabski

13Design aspect: connection flange
Gap-less flange assembly, modified
KEK MO-type used at Sirius

RF lipAPS-U, gap-lessflange

Final Design of the APS-Upgrade Storage Ring
Vacuum System, J. Carter, NAPAC 2019RF lipFLS 2023, August 2023, Luzerne, Switzerland
Marek Grabski

Gap of 0,1 mm flange, CF based(spigot type) used at MAX IV 3 GeV

Standard copper
CF copper gasket

Diamond-II Technical Design
Report (August 2022)

Gap-less flange assembly withcopper gasket (CF based) Diamond II,
based on APS-U design

Nominal gap between
chambers 0,1 mm

VACUUM SYSTEM DESIGN FOR THE SIRIUS STORAGE
RING, R.M. Seraphim, IPAC 2015

14

Design aspect: Installation (baking: Ex-Situ, in-situ)
Ex-situ installation and baking with an oven (MAX IV).
Strongback

Vacuum chambers
hanging

An Overview for the Sirius Vacuum System, T. Rocha, EIC 2021

Baking oven

FLS 2023, August 2023, Luzerne, Switzerland
Marek Grabski

Installation and In-situ baking with thin heater system(Sirius, ESRF-EBS).

Thin heater system at Sirius:• 0,4 mm thickness,• Max operating temperature 230 deg C.
Space needed inside magnets for longer
bellows to compensate thermal expansion

15

Design aspect: Serviceability
The more compact the lattice the more difficult is to do maintenance/exchange vacuum system components (limited access)Options for service/exchange:• Have one complete cell of vacuum chambers (spare achromat) assembled under vacuum with NEG activated (need to open all magnets),• Make use of in-situ baking system if available to bake/activate NEG (no need to open all the magnets),• If no in-situ baking system available need to bake/activate NEG outside the magnets with an oven (need to open all magnets),• Use of Neon venting (to avoid need of NEG reactivation and no need to open all the magnets) (confirmed at MAXIV, Sirius, CERN),

Strongback

Vacuumchambers

Gate ValveMAX IV: One spare vacuum cell insideaccelerator tunnel on a transport structure(~22 m long without straight section)

Neon venting is a procedure developed and used at CERN for interventions on
special vacuum chambers with NEG coating. Neon is a noble gas, it does not saturate
the NEG surface. Therefore there is no need of re-activation of the NEG film.
Transportstructure
FLS 2023, August 2023, Luzerne, Switzerland
Marek Grabski

At MAX IV Neon venting used in 2018 and 2020 for interventions. No limitationin storage ring performance was observed after ~10 A h beam dose.
16

DLS summary
Chosen Diffraction Limited Storage rings in operation, installation and design:
FacilityNew/
Circumference [m]; Energy [GeV]; Magnet bore [mm];Retrofitted; (# of cells - Lattice) current [A]; chamber aperturecommissioningemittance
[mm]
year
[pm.rad]Vacuum systemdesign approach

Vacuum chambermaterial% of chambers # of lumped
Baking/
NEG coated pumps per cell activation(lengthwise)
methodALS-U, USA

Retro;
2026

196;(12 cell - 9BA)

2; 0,5;
7024;
13-20

Hybrid*St. steel, copper,

60

3-4

In-situAPS-U, USA

Retro;
2024

1104;(40 cell - 7BA)

6; 0,2;
60

26;
22Hybrid*

St. steel, copper,Aluminum40

9+4 NEG strips

In-situDiamond II, UK

Retro;
2027

560;(24 cell - MH6BA)

3,5; 0,3;
161

24;
20

Hybrid*St. steel, copper,Aluminum>90

8Ex-situ

ESRF EBS,FranceRetro;
2020

843;(32 cell - H7BA)

6; 0,2;133~28;13-20

Conventional (lumpedpumps and absorbers

St. steel, Aluminum,(only IDchambers instraights)

24In-situ

HEPS, China

New;
2024

1360;
(48 cell - H7BA)

6; 0,2;3424;
22

Hybrid*St. steel, CrCrZr, andInconel

70

14In-situMAX IV,SwedenNew;
2016

528;
(20 cell - 7BA)

3; 0,5;
300

25;
22

Distributed absorbers, Copper, (St. steel for
NEG coatingports and flanges)>95(fully)

3Ex-situ

SLS 2.0,
Switzerland

Retro;
2024

288;(12 cell - 7BA)

2.7; 0,4;
159

22;
18

Distributed absorbers, Copper, (St. steel for
NEG coatingBPMs)>95(fully)

14

Ex-situ

Soleil II, France

Retro;
2028

354;(20 cell - 12 x 7BA +8 x 4BA)

2,75; 0,5;
80

16;
12

Distributed absorbers, CuCrZr (full chambers),
NEG coating
copper>95(fully)

4 / 7 (1 perdipole)Ex-situ

Not in the table: Sirius, Alba II, Elettra 2.0, Petra IV, BESSY III, Spring-8 II, HALF, SPS II.
FLS 2023, August 2023, Luzerne, Switzerland
Marek Grabski* Hybrid: Distributed absorbers and NEG coating,also lumped pumping and lumped absorbers.
17

Conclusion
Vacuum systems based on NEG coating and distributed copper absorbers (MAX IV and Sirius) work very welland condition fast. Conventional vacuum systems perform good as well.
Challenges:
Choice of good solution depends on many factors:• Small chamber sizes, in antechamber down to 5 mm,• accelerator layout (arc and straight section lengths),• Tight tolerances - difficult to manufacture,• space inside and between magnets,• Ceramic chambers with high tolerances for injection• number and location of photon ports,
chambers,• Positioning of small, flexible chambers inside magnet• synchrotron radiation power to be dissipated,
apertures (spacers between poles).
• manufacturing capabilities,• surface treatment (etching before NEG coating, NEG
coating, copper coating),• knowledge and previous experience at the facility,• tunnel size and access (openable roof),• available facilities (crane),• Time constraints on the installation,

FLS 2023, August 2023, Luzerne, Switzerland
Marek Grabski

New technologies:• Broader use of CuCrZr alloy,• Use of Neon venting,• Chamber size down to ~6-7 mm in IDs or antechamber(NEG coating difficult and limited by chamber length),• Raytracing and extensive use of software: Synrad
software (used to generate and export synchrotron
radiation power maps for Finite Elements Analyses),• Software for vacuum simulations: Molfow+,• Reverse coating technique (CERN).
18

Thank you foryour attention
Special thanks to Eshraq Al-Dmour and MAX IV Vacuum Team.
Contact: marek.grabski@maxiv.lu.se
FLS 2023, August 2023, Luzerne, Switzerland
Marek Grabski

19