Andreas Streun Paul Scherrer Institut (PSI) Villigen, Switzerland … · 2015-07-08 · Portrait of...
Transcript of 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
A. Streun, PSI Swiss Light Source: the next 20 years, Varenna, July 10, 2015 3
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
A. Streun, PSI Swiss Light Source: the next 20 years, Varenna, July 10, 2015 4
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
A. Streun, PSI Swiss Light Source: the next 20 years, Varenna, July 10, 2015 5
SLS: beam lines overview
A. Streun, PSI Swiss Light Source: the next 20 years, Varenna, July 10, 2015 6
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
A. Streun, PSI Swiss Light Source: the next 20 years, Varenna, July 10, 2015 7
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
A. Streun, PSI Swiss Light Source: the next 20 years, Varenna, July 10, 2015 8
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
A. Streun, PSI Swiss Light Source: the next 20 years, Varenna, July 10, 2015 9
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
A. Streun, PSI Swiss Light Source: the next 20 years, Varenna, July 10, 2015 10
The Multi-Bend Achromat (MBA)
Miniaturization small vacuum chambers [NEG coated]
high magnet gradients
more cells in given circumference
A. Streun, PSI Swiss Light Source: the next 20 years, Varenna, July 10, 2015 11
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
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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
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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
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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
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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
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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 |||| =
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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
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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
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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
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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
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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
A. Streun, PSI Swiss Light Source: the next 20 years, Varenna, July 10, 2015 22
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
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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
A. Streun, PSI Swiss Light Source: the next 20 years, Varenna, July 10, 2015 24
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)
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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.
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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
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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
A. Streun, PSI Swiss Light Source: the next 20 years, Varenna, July 10, 2015 28
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
A. Streun, PSI Swiss Light Source: the next 20 years, Varenna, July 10, 2015 29
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.
A. Streun, PSI Swiss Light Source: the next 20 years, Varenna, July 10, 2015 30
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.
A. Streun, PSI Swiss Light Source: the next 20 years, Varenna, July 10, 2015 31
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