Transcript Operation and Upgrade of SPring

SSRF(Feb. 16, 2009)
Topics on Beam Dynamics
at SPring-8 Storage Ring
K. Soutome (JASRI/SPring-8)
on behalf of JASRI Accelerator Division
Topics
1) Sextupole Optimization for the Ring with LSS
2) Short Bunch Generation by Low-Alpha Operation
3) What we are discussing on Machine Upgrading
SX Optimization for LSS
8GeV Electron Storage Ring
Circumference: 1436m
Beam Current: 100mA
Lattice: Double-Bend with four 30m-LSSs
Natural Emittance: 6.6nmrad (Achromat)
3.4nmrad (Non-Achromat)
SX Optimization for LSS
Ring with 48-Cell Structure
[ (Normal Cell) * 9
+ (Matching Cell) + (Long Straight) + (Matching Cell) ] * 4
Cell Length: 30m
SX Optimization for LSS
4/48 of
Ring
1997/3 - 1999/7
Hybrid Optics with 6.9nmrad
40
2
y
30
x
1.5
20
1
10
0.5
0
0
x
0
20
40
60
80
Path Length [m]
100
Dispersion Function  [m]
Betatron Function  [m]
Missing-B
120
We started beam commissioning with this optics.
"24-Fold Symmetric"
SX Optimization for LSS
1999/9 - 2000/7
HHLV Optics with 6.3nmrad
40
2
x
30
1.5
20
1
10
0.5
0
0
x
0
20
40
60
80
Path Length [m]
100
Dispersion Function  [m]
y
Betatron Function  [m]
4/48 of
Ring
120
HHLV: High-Horizontal and Low-Vertical beta
"48-Fold Symmetric"
SX Optimization for LSS
2000/8 - 2002/11
2003/10 - 2005/9
Achromat Optics with 6.6nmrad
60
3
50
2.5
40
2
y
30
x
1.5
20
1
10
0.5
0
x
0
20
0
LSS
40
60
80
Path Length [m]
100
Dispersion Function  [m]
Betatron Function  [m]
4/48 of
Ring
120
"4-Fold Symmetric" strictly, but owing to matching condition
"36-Fold Symmetric" approximately (36=48-3*4)
SX Optimization for LSS
2002/11 - 2003/10
2005/9 Low-Emittance Optics with 3.4nmrad
60
3
50
2.5
40
2
y
30
x
1.5
20
1
10
0.5
0
x
0
20
0
LSS
40
60
80
Path Length [m]
100
Dispersion Function  [m]
Betatron Function  [m]
4/48 of
Ring
120
Emittance was reduced by dispersion leakage.
"4-Fold Symmetric" approximately
SX Optimization for LSS
Matching Condition
0.6
Matching Section
50
0.5
40
0.4
x
30
x y
0.3
20
0.2
10
0.1
0
0
0
30
SFL
60
s [m]
90
SFL
Only SFL-sextupoles are used in
matchign section.
Horizontal chromaticity is corrected to
keep high injection efficiency and long
Touschek beam lifetime.
H.Tanaka, et al., NIMA486(2002)521
[m]
[m]
60
(1) Betatron Phase Matching
Dyx=4p, Dyy=2p
For on-momentum electrons this
makes the matching section
transparent and the dynamic
aperture is kept large.
(2) Local Chromaticity Correction
For off-momentum electrons the
above condition does not hold
due to non-zero chromaticity, and
sextupoles (SFL) are weakly
excited to correct local
chromaticity in the horizontal
direction.
SX Optimization for LSS
Matching Condition + Counter-Sextupoles
(3) Counter-Sextupole
Non-linear kick by SFL can be
canceled by another sextupole
located np apart from SFL.
Dy = p
x
Kick
by SFL
s
beam
SFL
Counter-Kick
by SCT
SCT
We actually adopted triplet
scheme where three sextupoles
are used to take account of the
vertical direction too.
K.Soutome, et al., Proc. EPAC08, p.3149
SX Optimization for LSS
0.6
Matching Section
50
0.5
40
0.4
x

x
30

y
0.3
20
0.2
10
S1L
SFL
SCT
SCT
SFL
S1L
0
Triplet Scheme
[m]
[m]
60
0.1
0
0
20
40
60
80
s [m]
60

50
40

x
30
0.5
20
Dyy
10
0
0
0
10
S1L
20
SFL
30
s [m]
SCT
Betatron Phase Advance
1
x
40
Dy/2p
[m]
Dy
y
SX Optimization for LSS
Dynamic Aperture (Cal.)
with SCT
 = -1%
=0
 = +1%
 = -1%
=0
 = +1%
10
y [mm]
without SCT
8
6
4
0.8
0.6
Physical
Aperture
Limit
0.4
0.2
2
0
1
Survival Rate
12
Horizontal Aperture (Exp.)
with SCT
without SCT
-20
-10
0
x [mm]
10
0
-20 -15 -10
-5
0
5
x [mm ]
10
15
Exp.: Store the beam, fire a pair
of bump magnets and measure
beam current after the kick.
SX Optimization for LSS
Non-linear behavior of betatron tune has been improved.
x with SCT
y with SCT
x w/o SCT
0.4
y w/o SCT
0.3
0.40
0.30
0.20
Dp/p
0.1
0
-20 -15 -10 -5
0
x [mm]
cal.
Horizontal (with SCT)
Vertical (with SCT)
Horizontal (w/o SCT)
Vertical (w/o SCT)
0.10
-0.04 -0.03 -0.02 -0.01
0.2
0
0.01
0
0.01
0.02
0.03
0.50
5
10
15
Betatron Tune
Betatron Tune
0.5
Betatron Tune
0.50
0.40
Horizontal (meas.)
Vertical (meas.)
Horizontal (cal.)
Vertical (cal.)
0.30
0.20
0.10
-0.04 -0.03 -0.02 -0.01
Dp/p
0.02
0.03
SX Optimization for LSS
Non-linear dispersion has also been suppressed.
Dx = 0 + 12 + 23 + ... with  = Dp/p
Calculation
8
300
with SCT
w/o SCT
6
200
4
100
2 [m]
1 [m]
2
0
0
-100
-2
-200
-4
-300
-6
-8
0
200
400
600
800
s [m]
1000
1200
1400
-400
0
200
400
600
800
1000
1200
1400
s [m]
Perturbative Formula: H.Tanaka, et al., NIM A431(1999)396; NIM A440(2000)259
SX Optimization for LSS
Comparison with experiments
0.4
2
cal.
meas.
0.3
1
0
0.2
1 [m]
0 [m]
0.3
0.2
-1
0.1
-2
0.1
0
-3
0
200
400
600
800
s [m]
1000
1200
1400
0
200
400
600
800
s [m]
1000
1200
1400
SX Optimization for LSS
60
800
40
600
400
20
3 [m]
2 [m]
200
0
-20
0
-200
-40
-400
-60
-600
-80
0
200
400
600
800
1000
1200
1400
s [m]
40000
4 [m]
20000
0
-20000
-40000
-60000
200
400
600
800
s [m]
0
200
400
600
800
s [m]
60000
0
-800
1000
1200
1400
1000
1200
1400
SX Optimization for LSS
Injection Efficiency
(whit horizontal slit in transport line open)
Exp.
Cal.
95
100
90
Injection Efficiency [%]
Injection Efficiency [%]
with SCT
85
80
w/o SCT
75
70
65
60
0
0.5
1
1.5
Beam Position Dx [mm]
at the End of BT Line
2
95
with SCT
90
85
80
w/o SCT
75
70
65
-1 -0.5 0 0.5 1 1.5 2 2.5 3
Dx [mm]
SX Optimization for LSS
Momentum acceptance has been improved.
20
1mA/Bunch
with SCT, ID Gap Open
w/o SCT, ID Gap Open
with SCT, ID19 Gap=12mm
w/o SCT, ID19 Gap=12mm
Veff = V RF * U0/(U0+DU)
15
10
5
0
10
11 12 13 14 15
RF Voltage V RF [MV]
1mA/Bunch
25
Beam Lifetime [h]
Beam Lifetime [h]
25
16
20
U0=8.91MV
DU=0.39MV for ID19
15
10
5
0
9 10 11 12 13 14 15 16
Effective RF Voltage Veff [MV]
SX Optimization for LSS
Application: Independent Tuning of LSS Optics
It is planned to modify optics in one of four LSS's.
DA Before Modification
60
12
0.6
50
0.5
40
0.4
x 
30
y
x
0.3
20
0.2
10
0.1
y [mm]
10
8
6
2
0
-20
S1L
SFL
60
SCT SCT
SFL
90
S1L
s [m ]
0
x [mm]
10
8
 = -1%
=0
 = +1%
 = -1%
=0
 = +1%
10
y [mm]
30
-10
DA After Modification
0
0
w/o SCT
with SCT
12
0
 = -1%
=0
 = +1%
4
[m]
[m]
Matching Section
 = -1%
=0
 = +1%
w/o SCT
with SCT
6
4
2
After modification of LSS optics,
enough DA is obtained by SCT.
0
-20
-10
0
x [mm]
10
SX Optimization for LSS
Summary of First Topic
For local modification of optics (30m-LSS in the
SPring-8 case), keeping symmetry is important, and
we adopted the following:
[1] Betatron Phase Matching
for on-momentum electrons to make transparent
[2] Local Chromaticity Correction
for off-momentum electrons to keep [1]
[3] Counter-Sextupoles
for cancellation of non-linear kicks due to [2]
Low-Alpha Operation
DL/L = -a
 = Dp/p
a = a0 + a1 + a22 + a33 + ...
Perturbative Formula:
H.Tanaka, et al., NIM A431(1999)396; NIM A440(2000)259
Bunch length scales as a1/2 at low bunch current.
Main Knob to Control a
a0 : Quadrupoles in the arc
Betatron tune must be adjusted with other quadrupoles.
a1 : Sextupoles in the arc
Chromaticity must be adjusted with other sextupoles.
a2 : Octupoles in the arc
(NB: No octupoles in SPring-8)
This term is important in extremely low alpha regime.
Low-Alpha Operation
Ring/4
User-Time
70
60
3
60
50
2.5
50
2
40
40
1.5
20
1
10
0.5
0
-10
x
0
50
100 150 200 250 300 350
s [m]
a0 = 1.68 e -4
3
x
-0.5
1/11
e = 3.4nmrad
Tune: (40.15, 18.35)
2.5
y
2
30
1.5
20
1
10
0.5
0
0
3.5
-10
x
0
50
100 150 200 250 300 350
s [m]
a0 = 1.58 e -5
e = 24.8nmrad
Tune: (39.15, 14.35)
Gradual Change, Tune Fixed
1/29
a0 = 5.8 e -6
0
-0.5
 [m]
30
y
 [m]
x
 [m]
3.5
70
 [m]
Ring/4
Low-Alpha Optics
Low-Alpha Operation
25
10
RMS Bunch Length [ps]
RMS Bunch Length [ps]
Bunch Current: 0.01mA
Exp.
Cal.
Nominal Optics
for User-Time
Low-a Optics
for Test Experiment
1
Short Beam Lifetime
0.1
-6
10
Vrf = 16MV
20
User-Time
15
10
5
a 0 = 1.6810-4
Low-Alpha
a 0 = 1.5810-5
0
-5
10
-4
a
10
-3
10
0.0001 0.001
0.01
0.1
1
10
Bunch Current [mA]
0
Measurement: Streak Camera, Hamamatsu C5680
Time-scale was calibrated with a beam and error was estimated to be
2.5ps by measuring bunch length as a function of synchrotron frequency.
Low-Alpha Operation
a=a0 + a1
Suppression of a1 by Sextupoles
for Stable Operation
a0
Stable
 << |a0 / a1|
-a0/a1

0
D.Robin, et al., Phys.Rev. E48 (1993) 2149
After setting sextupoles we can check this by observing dfsy / dfRF = 0.
RUN2
RUN1
f
s


400
200
x
y
0.2
0.1
0
50
0
100 150 200 250 300
Df [Hz]
rf
800
0.4
600
0.3

s
0.3
f [Hz]
600
f
s
400

200
0
-50
x
0.2
y
0.1
0
50
0
100 150 200 250 300
Df [Hz]
rf
0.5
s
800
0.4
600
0.3


400
200
0
-100 -50
x
0.2
y
0.1
0
0
50 100 150 200 250 300
Df [Hz]
rf
Betatron Tune
0.4
RUN3
1000
Betatron Tune
800
0
-50
0.5
s
Betatron Tune
f [Hz]
f
1000
s
0.5
f [Hz]
1000
Low-Alpha Operation
Suppression of a2 by Octupoles (Simulation)
2
a = a + a  + a  + ...
0
4 10
-5
up to a
-5
up to a
3 10
2 10
up to a
-5
1 10
a()
1
2
-5
3 10
1
2
a > 0 for small 
4
a < 0 for large 
0
-1 10
-5
-2 10
-5
-3 10
-5
-4 10
-5
Stable
-0.04
-0.02
0
with Octupoles
-5
4 10
0.02
-5
2 10
with Octupoles

calculation
for temporary set
of octupoles,
not optimized
-5
1 10
a()
-5
0
-5
up to a
-2 10
-5
up to a
-3 10
-5
up to a
-4 10
-5
-1 10
-0.04
0.04
-0.02
3
2
2
1
1
 [%]
 [%]

-1
-2
-2
-20
-10
0
10
20
 - s [deg]
30
40
4
0
0.02
0.04
0
-1
-3
-30
2

3
0
1
-3
-30
-20
-10
Alternative: operation with a0 < 0
0
10
 - s [deg]
20
30
40
Low-Alpha Operation
Summary of Second Topic
We lowered a0 down to 1/29 of nominal optics.
The shortest bunch length achieved was 2ps(rms) but lifetime
was short in this optics.
100
Vrf = 16MV
RMS Bunch Length [ps]
We carried out test experiments in the
25m-long undulator beamline under the
following condition:
Bunch Length: rms 4.2ps (FWHM 10ps)
Bunch Current: 0.01mA
Photon Intensity: 1/1000 of
Nominal User-Time
Filling: Several-Bunch Filling
Data analysis is in progress...
a 0 = 1.6810-4
10
a 0 = 1.5810-5
a 0 = 5.810-6
a 0 = 1.310-6
1
(plan)
0.1
0.0001 0.001
0.01
0.1
1
Bunch Current [mA]
10
Ongoing Discussion on Machine Upgrading
Discussion among "young" researchers (in accelerator group,
beamline group, ... including KS) is ongoing at SPring-8 ...
What I present here is not official and not fixed at all; just for showing
what "young" guys are discussing.
Figure of Merit = Brilliance
* 6GeV operation with damping wigglers in LSS; higher beam current;
optimized undulators for 6GeV
* Multi-bend lattice with sub-nmrad emittance; from 2B/cell to 3B/cell,
4B/cell, 10B/2cells
10-Bend: K.Tsumaki and N.Kumagai, EPAC'06, p.3362; NIMA 565 (2008) 394
* ERL with multi-turn circulation scheme
T.Nakamura, PRST-AB 11 (2008) 032803
* ...
Ongoing Discussion on Machine Upgrading
Example: QB Lattice with e = 0.29nmrad (eeff = 0.33nmrad) at 8GeV
0.2
x
30
4
20
0.1
10
0.05
0
0
0
5
10
15
s[m]
20
25
30
y[mm]
0.15
[m]
[m]
5
x
y
5
+2.0%
+1.0%
0%
-1.0%
-2.0%
Unit QB-CELL
w/o ERROR
3
2
1
0
-20
4
y[mm]
40
RING with
44 QB-CELLs and
4 FODO-STRAIGHTs
w/o ERROR
3
+2.0%
+1.0%
0%
-1.0%
-2.0%
2
1
-10
0
x[m m]
10
20
0
-20
-10
0
x[m m]
10
ISSUES: Emittance is calculated to be small, but ...
strong quadrupoles, large chromaticity and small dispersion and
hence strong sextupoles, narrow dynamic aperture, narrow
momentum acceptance, short beam lifetime, no magnet-free LSS
(difficult), small bore diameter, narrow chamber, limited space for
BPMs and correctors, high sensitivity against errors, long dark time,
cost, ...
20