andreas streun paul scherrer institut (psi) villigen, switzerland … · 2015-07-08 · portrait of...

Andreas Streun Paul Scherrer Institut (PSI) Villigen, Switzerland

Future Research Infrastructures: Challenges and Opportunities

Varenna, Italy, July 8-11, 2015

A. Streun, PSI Swiss Light Source: the next 20 years, Varenna, July 10, 2015 2

Outline

Portrait of the SLS; history and achievements

The new generation of light sources

The challenge to upgrade the SLS

A new type of lattice cell for lower emittance: longitudinal gradient bends and anti-bends

SLS-2 design: performance, challenges, highlights


Paul Scherrer Institut (PSI)

1960 Eidgenössisches Institut für Reaktorforschung (EIR)

1968 Schweizer Institut für Nuklearphysik (SIN)

1988 EIR + SIN = PSI research with photons, neutrons, muons

PSI Accelerators:

590 MeV proton cyloctron: 1.3 MW beam power spallation neutron source SINQ & muon source SmS

5.8 GeV / 1 Å free electron laser SwissFEL: operation 2017

2.4 GeV synchrotron light source SLS


The SLS

4 days

1 mA

90 keV

pulsed (3 Hz)

thermionic

electron gun

Synchrotron (“booster”)

100 MeV 2.4 [2.7] GeV

within 146 ms (~160’000 turns)

100 MeV

pulsed linac

2.4 GeV storage ring

ex = 5.0..6.8 nm, ey = 1..10 pm

400±1 mA beam current

top-up operation

shielding

walls

transfer lines

Current vs. time

Electron beam cross

section in comparison

to human hair


SLS: beam lines overview


SLS: history

1990 First ideas for a Swiss Light Source

1993 Conceptual Design Report

June 1997 Approval by Swiss Government

June 1999 Finalization of Building

Dec. 2000 First Stored Beam

June 2001 Design current 400 mA reached Top up operation started

July 2001 First experiments

Jan. 2005 Laser beam slicing “FEMTO”

May 2006 3 Tesla super bends

2010 ~completion: 18 beamlines


SLS achievements

Rich scientific output > 500 publications in refereed journals/year

four spin-off companies (e.g. DECTRIS)

Reliability 5000 hrs user beam time per year

97.3% availability (2005-2014 average)

Top-up operation since 2001 constant beam current 400-402 mA over many days

Photon beam stability < 1 mm rms (at frontends) fast orbit feedback system ( < 100 Hz )‏

undulator feed forward tables, beam based alignment, dynamic girder realignment , photon BPM integration etc...

Ultra-low vertical emittance: 0.9 ± 0.4 pm model based and model independent optics correction

high resolution beam size monitor developments

150 fs FWHM hard X-ray source FEMTO laser-modulator-radiator insertion and beam line


Storage rings in operation (•) and planned (•). The old (—) and the new (—) generation.

The storage ring generational change

Riccardo Bartolini (Oxford University) 4th low emittance rings workshop, Frascati , Sep. 17-19, 2014

Ho

rizo

nta

l em

itta

nce

no

rmal

ized

to

be

am e

ne

rgy

3

2

ncecircumfere

energyemittance


New storage rings and upgrade plans

Name Energy [GeV] Circumf. [m] Emittance* [pm] Status

PETRA-III 6.0 3.0

2304 4400 1000 85 (round beam)

operational

MAX-IV 3.0 528 328 200 2015

SIRIUS 3.0 518 280 2016

ESRF upgrade 6.0 844 147 2020

DIAMOND upgrade 3.0 562 275 started

APS upgrade 6.0 1104 65 study

SPRING 8 upgrade 6.0 1436 68 study

PEP-X 4.5 2200 29 10 study

ALS upgrade 2.0 200 100 study

ELETTRA upgrade 2.0 260 250 study

SLS now 2.4 288 5020** operational

SLS-2 2.4 (?) 288 100-200 ? 2024 ?

*Emittance without with damping wigglers **without FEMTO insertion


The Multi-Bend Achromat (MBA)

Miniaturization small vacuum chambers [NEG coated]

high magnet gradients

more cells in given circumference


SLS upgrade constraints and challenges

Constraints get factor 20...50 lower emittance (100...250 pm)

keep circumference & footprint: hall & tunnel.

re-use injector: booster & linac.

keep beam lines: avoid shift of source points.

“dark period” for upgrade 6...9 months

Main challenge: small circumference (288 m)

Multi bend achromat: e (number of bends)─3 Damping wigglers (DW): e radiated power

Low emittance from MBA and/or DW requires space !

Scaling MAX IV to SLS size and energy gives e 1 nm

New lattice concept e 100...200 pm

ring ring + DW


Theoretical minium emittance (TME) cell dilemma

Conditions for minimum emittance (h = 1/r = eB/p curvature)

periodic/symmetric cell: b ’ = h’ = 0 at ends

over-focusing of bx phase advance m min =284.5°

2nd focus, useless overstrained optics,

huge chromaticity...

long cell

better have two relaxed cells of f/2

MBA concept...

x

xoJ

E3o

2min ])[(])GeV[(

1512

8.7]radpm[

fe =

24152

2minmin hLLoo == hb

0 1 2 3 4 5 6

0

2

4

6

8

10

12

14

16

Betafunctions [m]

-0.18

-0.16

-0.14

-0.12

-0.10

-0.08

-0.06

-0.04

-0.02

0.00

0.02

0.04

0.06

0.08

Dispersion [m]

bx by h

f, L, h


Deviations from TME conditions

Ellipse equations for emittance

Cell phase advance

Real cells: m < 180° F ~ 3...6 MBA: F > 10

Conventional cells = relaxed TME cells

minminmin

o

o

o

o

xo

xo dbFh

h

b

b

e

e===

1)()1( 222

45 = FFbd

)3(15

6

2tan

=

d

bm


how to do better ?

1. disentangle dispersion h and beta function bx release constraint: focusing is done with quads only.

use “anti-bend” (AB) out of phase with main bend

suppress dispersion (ho 0) in main bend center.

allow modest bxo for low cell phase advance.

2. optimize bending field for minimum emittance release constraint: bend field is homogeneous.

use “longitudinal gradient bend” (LGB)

highest field at bend center (ho = (e/p) Bo)

reduce field h(s) as dispersion h(s) grows

sub-TME cell (F < 1) at moderate phase advance


step 1: the anti-bend (AB)

General problem of dispersion matching:

– dispersion is a horizontal trajectory

– dispersion production in dipoles “defocusing”: h’’ > 0

Quadrupoles in conventional cell:

– over-focusing of beta function bx

– insufficient focusing of dispersion h

disentangle h and bx

use negative dipole: anti-bend

– kick Dh’ = , angle < 0

– out of phase with main dipole

– negligible effect on bx , by

bx by

dispersion: anti-bend off / on

relaxed TME cell, 5°, 2.4 GeV, Jx 2

Emittance: 500 pm / 200 pm


21)2(2

4

2

2 == I

I

xJIdskbbh4I

AB emittance contribution

– h is large and constant at AB

low field, long magnet

Cell emittance (2AB +main bend)

– main bend angle to be increased by 2| |

in total, still lower emittance

AB as combined function magnet – Increase of damping partition Jx

• vertical focusing in normal bend

• horizontal focusing in anti-bend.

– horizontal focusing required anyway at AB

AB = off-centered quadrupole half quadrupole

AB emittance effects

bx by

Disp. h LhdshI AB

L H

b

he

233

5 |||| =


21)2(2

4

2

2 == I

I

xJIdskbbh4I

Anti-bend negative momentum compaction a

Head-tail stability for negative chromaticity!

AB impact on chromaticity

=

ABLGB

1dshdsh

Chha

small large

negative

< 0

side note: AB history

1980’s/90’s: proposed for isochronous rings and to increase damping - but

PAC 1989


step 2: the longitudinal gradient bend (LGB)

h(s) = B(s)/(p/e) b

bhahh 22 )'( =H

)()(')()('' ssshs hhh =

21

00 0

202)( sss

b

aabb

=

3

5 |''|)'',',,(min)'',',,( hhhhhhh sfdssfIL

H== functional with

Dispersion’s betatron amplitude

Orbit curvature

Longitudinal field variation h(s) to compensate H (s) variation

Beam dynamics in bending magnet

– Curvature is source of dispersion:

– Horizontal optics ~ like drift space:

– Assumptions: no transverse gradient (k = 0); rectangular geometry

Variational problem: find extremal of h(s) for

numerical optimization

=L

dssshI )(|)(| 3

5 He


Half bend in N slices: curvature hi , length Dsi

Knobs for minimizer: {hi}, b0, h0

Objective: I5

Constraints:

length: SDsi = L/2

angle: ShiDsi = F/2

[ field: hi < hmax ]

[ optics: b0 , h0 ]

Results:

hyperbolic field variation (for symmetric bend, dispersion suppressor bend is different)

Trend: h0 , b0 0 , h0 0

LGB numerical optimization

Results for half symmetric bend ( L = 0.8 m, F = 8°, 2.4 GeV )

homogeneous

optimized hyperbola fit

I5 contributions

I


Numerical optimization of field profile for fixed b0, h0

Emittance (F) vs. b0, h0 normalized to data for TME of hom. bend

LGB optimization with optics constraints

F = 1

F = 1

small (~0) dispersion at centre required, but tolerant to large beta function

F 0.3


Conventional cell vs. longitudinal-gradient bend/anti-bend cell

both: angle 6.7°, E = 2.4 GeV, L = 2.36 m, Dmx = 160°, Dmy = 90°, Jx 1

conventional: e = 990 pm (F = 3.4) LGB/AB: e = 200 pm (F = 0.69)

The LGB/AB cell

bx by bx by

dipole field quad field total |field|

} at R = 13 mm

longitudinal gradient bend

anti-bend

Disp. h Disp. h


SLS-2 lattice layout

TBA 7BA lattice: ½ + 5 + ½ cells of LGB/AB type

periodicy 3: 12 arcs and 3 different straight types:

6 4 m 6 2.9 m 3 7 m 3 5.1 m

split long straights: 3 11.5 m 6 5.1 m

beam pipe: 64 mm x 32 mm 20 mm

magnet aperture 26 mm


SLS-2 lattice db02l (one superperiod = 1/3 of ring)

optics and magnetic field (field at poletips for R = 13 mm)

Superbends in arcs 2/6/10 3 2.9 T 3 5.0 T


SLS-2 lattice parameters Name SLS*) db02l fa01f

status operating baseline fallback

Emittance at 2.4 GeV [pm] 5022 137 262

Lattice type TBA 7BA 5BA

Total absolute bending angle 360° 585° 488°

Working point Qx/y 20.42 / 8.74 38.38 / 11.28 28.29 / 10.17

Natural chromaticities Cx/y 67.0 / 19.8 67.5 / 36.0 64.1 / 39.9

Optics strain1) 7.9 5.6 8.9

Momentum compaction factor [104 ] 6.56 1.39 1.86

Dynamic acceptance [mm.mrad] 2) 46 10 17

Radiated Power [kW] 3) 205 228 271

rms energy spread [103 ] 0.86 1.05 1.15

damping times x/y/E [ms] 9.0 / 9.0 / 4.5 4.5 / 8.0 / 6.4 5.0 / 6.8 / 4.1

1) product of horiz. and vert. normalized chromaticities C/Q 2) max. horizontal betatron amplitude at stability limit for ideal lattice 3) assuming 400 mA stored current, bare lattice without IDs *) SLS lattice d2r55, before FEMTO installation (<2005)


Non-linear optimization

13 sextupole & 10 octupole families

step 1: perturbation theory: insufficient 1st & 2nd order sextupole terms

1st order octupole terms

up to 3rd order chromaticities

step 2: multi-objective genetic optimizer objectives: dynamic aperture at Dp/p = 0, 3%

contraints: tune fooprint within ½ integer box

Lattice acceptance results (ideal lattice)

horizontal acceptance 10 mm·mrad sufficient for off-axis multipole injection from existing booster synchrotron

Touschek lifetime 3.2 hrs 1 mA/bunch, 10 pm vertical emittance, 1.43 MV overvoltage further increase to 7-9 hrs by harmonic RF system.


More challenges... work just started

Collective effects large resistive wall impedance ( aperture3)

low momentum compaction factor |a|, and a < 0

close thresholds for turbulent bunch lengthening

head-tail stability for chromaticity 0

intrabeam scattering 15-30% emittance increase

Alignment tolerances common magnet yoke = girder

initial mechanical alignment will be insufficient

extensive use of beam based alignment methods

longer commissioning than 3rd gen. light source


Advanced options

A new on-axis injection scheme

cope with reduced aperture

(physical or dynamic)

interplay of radiation damping and

synchrotron oscillation forms attractive

channel in longitudinal phase space for

off-energy off-phase on-axis injection. Figu

re t

aken

fro

m R

. Het

tel,

JSR

21

(2

01

4)

p.8

43

Round beam scheme

Wish from users (round samples...)

Maximum brightness & coherence

Mitigation of intrabeam scattering blow-up

“Möbius accelerator”:

beam rotation on each turn to exchange

transverse planes

SLS SLS-2 SLS-2 RB


Longitudinal gradient superbend

Photon energy range

YBCO1) HTS2) tape in canted-cos-theta configuration on hyperbolic mandrel hyperbolic field profile

open for radiation fan

> 5T peak field

1) Yttrium-Barium-Copper-Oxide

2) High Temperature Superconductor

Dipole Flux [ph/mr^2/sec/0.1%bw]

0.00E+00

1.00E+13

2.00E+13

3.00E+13

4.00E+13

5.00E+13

0 20 40 60 80 100

1.4 T

2.95 T

5.7 T

Courtesy Ciro Calzolaio, PSI


Time schedule

Jan. 2014 Letter of Intent submitted to SERI (SERI = State secretariat for Education, Research and Innovation)

schedule and budget

• 2017-20 studies & prototypes 2 MCHF

• 2021-24 new storage ring 63 MCHF beamline upgrades 20 MCHF

Oct. 2014 positive evaluation by SERI: SLS-2 is on the “roadmap”.

Concept decisions fall 2015.

Conceptual design report end 2016.


Summary

The Swiss Light Source is successfully in operation since 15 years...

...but progress in storage ring design enforces an upgrade.

Upgrade of the Swiss Light Source SLS has to cope with a rather compact lattice footprint...

... but the new LGB/AB cell provides five times lower emittance than a conventional lattice cell:

Anti bends (AB) disentangle horizontal beta and dispersion functions.

Longitudinal gradient bends (LGB) provide minimum emittance by adjusting the field to the dispersion.

The baseline design for SLS-2 is a 12 7BA lattice providing 30-35 times lower emittance.

The design is challenged by non-linear optics optimization, beam instabilities and correction of lattice imperfections.

A conceptual design report is scheduled for end 2016.


Acknowledgements

Beam Dynamics: Michael Ehrlichman, Ángela Saá Hernández, Masamitsu Aiba, Michael Böge

Instabilities and impedances: Haisheng Xu, Eirini Koukovini-Platia (CERN), Lukas Stingelin, Micha Dehler, Paolo Craievich

Magnets: Ciro Calzolaio, Stephane Sanphilippo, Vjeran Vrankovic, Alexander Anghel

Vacuum system: Andreas Müller, Lothar Schulz

General concept and project organisation: Albin Wrulich, Lenny Rivkin, Terry Garvey, Uwe Barth

andreas streun paul scherrer institut (psi) villigen, switzerland … · 2015-07-08 · portrait of...

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