Top-Up Experience at SPEAR3 Jeff Corbett Stanford Linear Accelerator Center (SLAC) National Accelerator Laboratory Presented at University of Melbourne 9 October, 2009
Jan 13, 2016
Top-Up Experience at SPEAR3
Jeff Corbett Stanford Linear Accelerator Center (SLAC)
National Accelerator Laboratory
Presented at University of Melbourne
9 October, 2009
• SPEAR 3 and the injector
• Top-up requirements
• Hardware systems and modifications
• Safety systems & injected beam tracking
• Interlocks & Diagnostics
---------------------------------------• Beam lifetime rate equation • PEP-X
Contents
3GeV Injector
BTS5W, 1.6nA
E
W
N S
3GeV10nm-rad 500 mA
Booster (White Circuit)
LINAC/RF Gun
10Hz
SPEAR3 Accelerator Complex
PXPD/XAS
SAXS/PX
XAFSNEXAFS
PX
PX
XAS/TXM
ARPES
EnvironmentXAS
CoherentSingle bunch/pulse
o Rebuild SPEAR into SPEAR3 (1999-2003)
o Operated at 100mA for ~6 years (beam line optics)
o Recently increased to 200mA
o Chamber components get hot at 500ma (450kW SR, impedance)
o 500mA program suspended because of
power load transient on beam line optics
o Instead worked to top-off mode (beam decay mode, fill-on-fill)
Top ‘off’ at SPEAR3
RF system and vacuum chamber rated for 500ma
o 13 exit ports taking SR (9 Insertion Device, 4 Dipole)
o 7 ID ports presently in ‘fill-on-fill’ open shutter mode
o 4 dipole beam lines open shutter injection by end of October 2009
o Last two ID shutters fill-on-fill by June 2010
o Trickle charge 2011
Present Status
SPEAR 3 100 vs. 500 mA Fill Scenarioslifetime = 14 h @ 500 mA = 60 h @ 100 mA
0
50
100
150
200
250
300
350
400
450
500
0 4 8 12 16 20 24
time (hrs)
curr
ent
(mA
)
100mA and 500mA Operation
=12ma
=180ma
100ma
500ma
~6.5 Amp-hr
delivery time = 8 hrtfill = ~6-7 min
delivery time = 2 hrtfill = ~1.5-2 min
0
50
100
150
200
250
300
350
400
450
500
0 6 12 18 24
time (hrs)
cu
rren
t (m
A)
delivery time = 0.5 hrtfill = ~17 sec
0
50
100
150
200
250
300
350
400
450
500
0 6 12 18 24
time (hrs)
cu
rren
t (m
A)
delivery time = 1 mintfill = ~0.5 sec(or 10ms single shot)
500mA Injection Scenarios
RFB132-102
B116-101
B117control roomB118power
suppliesSLM room
B132-101
B120
B131
B130
3 GeVBooster
120 MeV linac
B140
LTB
BTS
RF HVP
S
• Guno higher currento stablize emission rateo “laser-assisted” emission
• Linaco restore 2nd klystron
(higher energy, feedback)o phase-lock linac and booster rf
• Boostero improve capture with modified latticeo improve orbit and tune monitorso develop fast turn-on mode
• BTSo eliminate vacuum windows (done)o diagnostics
• SPEARo add shielding, interlockso improve kicker responseo transverse feedback
• Beamlineso add shielding, interlockso timing
Hardware Upgrades
• Vertical Lambertson septum (booster outside ring) - operates DC, skew quadrupole added
• Three magnet bump• ~15 mm amplitude, ~12mm separation• Injection across three cells (sextupoles)• Slotted stripline kickers (DELTA, low impedance)• Transverse field dependence in K2
SPEAR3 Injection Notes
Elevation viewPlan view
Injected beam
Stored beam
Se
ptu
m w
all
Se
ptu
m w
all
With windows: ~20% beam loss No windows: ~no loss
Hardware Upgrade: BTS Windows
Huang & Safranek
Injected beam profile measurements
Turn number
Movies…
Visible diagnostic beam line
• Synchrotron oscillations measured with turn-by-turn BPMs:
• Kickers set to dump injected beam each cycle• Injection energy stable• Injection time varies over hours
– RF cable temperature
• Develop method to measure timing with stored beam
Before correction After correction
Hardware upgrade: Injection Timing and Energy
Huang, Safranek & Sebek
V
H
mS
V
H
mS
Single shot
injection kicker transient = ~10 ms
(~0.1 ms with feedback)
• Kickers can interrupt data acquisitiono What is interruption sequence?
• depends on current ripple, beam lifetime and charge/shot
• bunch train filling needs new booster RF system
o Gated data acquisition
o Tests with beam lines no complaints
o Lots of work to match kicker waveforms
Hardware upgrade: Injection Bump Closure
Huang & Safranek
downconverter schematic
Hardware Upgrade: PEP-II Bunch Current Monitor
bunch-by-bunch processor chassis
- visible APD (ASP)- x-ray APD (CLS)
downconverter chassis
A.S.Fisher
► S-band RF gun with thermionic cathode, alpha magnet, and chopper
► Most charge during the 2 μs RF pulse stopped at the chopper ► 5-6 S-band buckets pass into the linac, single booster bucket
► SPEAR3 single bunch injection, 10Hz presently ~50pC/shot
2.856 GHz (2s)
e- beam Tungstendispenser-cathode (1000 C)
1.5 cell RF gun
Hardware Upgrade: Thermionic Cathode as a Photo-Emitter
Nominal configuration
► high singe-bunch charge for top-off - reduce beam loading in linac - eliminate cathode back bombardment - eliminate chopper
2.856 GHz (~2s)
e- beam (~500ps) cold-cathode
UV or green laser
UV Green
1.5W heating
Sara Thorin/MAXLab, EPAC'08'Turning the thermionic gun into a photo injector has been very successful '
1.5 cell RF gun
Photo-emission cathode (cont’d)
Laser-driven configuration
Cu
S.Gierman
• Radiation Safety: the first hurdleo AP studies to demonstrate injected beam can not escape shielding
o Many clever scenarios (dreams and zebras)
o BL shielding sufficient? (higher average current, more bremsstrahlung)
o PPS/BCS interlock modifications
o Do users wear badges?
• Efficient injection into main ringo Injection time, charge/shot, repetition rate
The Injected Beam Safety Dilemma
Safety is complicated!
18
SPEAR3 DBA cell
Synchrotron Radiation Exit Ports
V4 MASK
V1, V2 MASKS
BPMs
H2 ABSORBER
TSPs
EDDY CURRENTBREAK
BM-2BM-2
QFCQFCBM-1BM-1
220 L/SION PUMP
150 L/S ION PUMP
TSP
V3 MASK
BELLOWS
BELLOWS
H1 ABSORBER H3 ABSORBER
TSP
BPM
BPM
BPM
ID BPM
ADDITIONAL BPM SET
220 L/S ION PUMP
84 mm
44.2 mm
34 mm
24 mm13 mm18.8 mm
ID BPM
BPM
Vacuum Chamber Construction
e- beam
photon beam
outside absorber
inside absorber
Photon Beam Exit Channel
A Closer Look…
22
Stored Beam
X-RaysInjected BeamX-Rays
Stored Beam
Injected Beam
NORMAL
X-RaysInjected BeamX-Rays
Stored Beam
Injected Beam
ACCIDENT
Stored Beam
X-RaysInjected BeamX-Rays
Injected Beam
Ratchet Wall
Fixed Mask
Top-Up with Safety Shutters Open
SAFE
23
X-Rays
Injected BeamX-Rays
Stored Beam
Injected BeamACCIDENT
•Bad steering, energy
Experimental
FloorStored Beam
Simulation is necessary!
Is this a real possibility?
•Bad magnet fields
Shield
Wall
QF QD BEND SDINSERTION DEVICE
A1 A2
Stored Beam on design orbit
Ratchet Wall
Fixed Mask I
Fixed Mask II
Comb Mask 9.1
CM
SPEAR3 Magnets BeamlineIncoming Beam
•No assumptions about initial steering
•All physical positions and angles possible
•Energy errors!
•No magnetic field
•Straight trajectories
Beamline Apertures Vacuum Chamber Radiation Masks
Safe Endpoint
Start Point
Field simulation region
SSRL Approach to Calculations
• Wide fringe fields
A.Terebilo
25
A1 Aperture
A2 Aperture
Fixed Mask
Stored Beam
Injected Beam
Ratchet Wall (2-ft Concrete)
Photon Beam Line
Forward Propagation Only
Chamber boundary
26
-3 -2.5 -2 -1.5 -1 -0.5 0-0.24
-0.22
-0.2
-0.18
-0.16
-0.14
-0.12
-0.1
-0.08
X [m]
X' [
rad]
Phase Space at Z = Fixed Mask
Phase Space at Z = Ratchet Wall
Fixed Mask Opening
Ratchet Wall Opening
Horizontal Position (m)
Hor
izon
tal A
ngle
(ra
d)
vacuum chamber acceptance fixed mask
10 bendo
spread in angles
(far fringe field)
Trajectories in Phase Space
27
-0.06 -0.04 -0.02 0 0.02 0.04 0.06 0.08 0.1-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
X [m]
X' [
rad]
Initial: A1 and BPM7
After BPM1
-0.08 -0.06 -0.04 -0.02 0 0.02 0.04 0.06 0.08 0.1 0.12-0.04
-0.03
-0.02
-0.01
0
0.01
0.02
0.03
0.04
0.05
X [m]
X' [
rad]
BPM1
After QFA2
Dipole Entrance
-0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2-0.04
-0.02
0
0.02
0.04
0.06
0.08
0.1
X [m]
X' [
rad]
Dipole Entrance
Dipole Exit
SD Exit
-3 -2.5 -2 -1.5 -1 -0.5 0-0.24
-0.22
-0.2
-0.18
-0.16
-0.14
-0.12
-0.1
-0.08Allowed Phase Space in BL coordinates
X [m]
X' [
rad]
Z = SD exit
Z = Fixed Mask
Z = Ratchet Wall
QF QD BEND SDInsertion Device HCOR
A1 A2
Stored Beam on design orbit
X-Rays to Beamline
Ratchet Wall
Fixed Mask I
BPM 7 BPM 1
Evolution of allowed phase space
28
-3 -2.5 -2 -1.5 -1 -0.5 0-0.24
-0.22
-0.2
-0.18
-0.16
-0.14
-0.12
-0.1
-0.08
X [m]
X' [
rad]
Phase Space at Z = Fixed Mask
Phase Space at Z = Ratchet Wall
Fixed Mask Opening
Ratchet Wall Opening
The Metric: Separation in Phase Space to Apertures
29
A1
QF QD BEND SD
ID A2BPM 7 BPM 1
Stored Beam on design orbit
Beamline Axis
Extreme Ray
4 6 8 10 12 14 16-1.4
-1.2
-1
-0.8
-0.6
-0.4
-0.2
0
Z [m]
BL
aper
ture
s an
d E
xtre
me
Ray
pos
ition
[m
]
Beamline apertures and the most severely mis-steered beam
BL4
BL5BL6
BL7
BL9
BL10BL11
mis-steered beam
Extreme Ray
All other Trajectories
The Extreme Ray
Position along beam line [m]
rise/run ~ -0.1 rad
ratchet wall
Off
set
[m
]
Separation at Fixed Mask
beam pipe w/apertures
30
Large SPEAR3 magnet field error
- and/or -
Large injected beam energy error
- AND -
“extensive intentional steering”
Condition for ‘Abnormal’ Scenario
special SLAC interpretation
4 6 8 10 12 14 16-1.2
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
Z[m] from ID center
BL
aper
ture
and
Ext
rem
e R
ay p
ositi
on [
m]
BL5BL6
BL7
BL9
BL10BL11
NominalB/B = -10%B/B = -50%B/B = -60%
Parameter To Pass Beyond Fixed Mask
To Pass Beyond Ratchet Wall
Target Value for Interlock Limit
EINJ/ESPEAR +59% +100% +10%
B/B -48% -60% -1% (-10%)
QF -100% Only with polarity reversed
-25%
QD +300% 55% (PS Limit)
HCOR 22 mrad 30 mrad 3mrad (2 x PS Limit)
Parameter Sensitivity
QF QD BEND SDInsertion Device HCOR
A1 A2 A3
Stored Beam on design orbit
X-Rays to Beamline
Ratchet Wall
PM
+60 / -43 mm +50 / -43 mm BL9: +112 / -101 mm
SPEAR Apertures
Beamline-Specific Aperture
Alignment of Apertures is Critical
33
FixedMask
ID sourceRingAperture
Experimental Floor
xxx
Mechanical Drawings & Tolerances
Documentation
Periodic checks
More documentation
Dose Calculations & Testing
Bauer & Liu
mis-steer and measure…
35
Passive Systems-Limiting apertures in transport line (BTS)
-Limiting apertures in SPEAR3 and beam lines
- Permanent magnets for dipole beam lines
Active Systems (Redundant Interlocks)
- Injection energy interlock - BTS dipole supply
- SPEAR3 magnet supplies
- Stored beam interlock
- Radiation detectors at each beam line
‘Hazard Mitigation’
Hardware Interlock Envelope
Software Alarm Envelope
A
B
* *
path 1
path 2
Software Monitor Envelope
Interlock Hierarchy
(reportable incident)
A Rastafarian Logic Table
Corbett & Schmerge
Accident Event Probability Analysis – Dipole Short
27333333 1010102
10102
102
10
SCIRadMon
DipoleShort
OrbitIntl’k
ConfigControlVolt
Intl’k
r=100m grain of sand: V=10-12 m3
How much sand?
1027 * 10-12 = 1015 m3 = 106 km3
1. Load operational lattice - software check of PS readbacks
2. Inject to <20 mA (orbit interlock)
3. Start orbit feedback (few microns)
4. Inject to 50 mA – top-off permit
5. Open beam line injection stoppers
6. Fill 500 mA maximum (FOFB runs continuous)
7. Fill-on-fill or trickle charge
SPEAR3 Operating Sequence
Thank you for hosting the Australian Synchrotron TopUp Workshop…
/0)( teNtN
CoulombungBremstrhalTouschek 1111
Classically, for short times t,
Electron Beam Lifetime - Analytic Calculations
where ~100
1
50
1
20
11
/NvNNN scatter
CoulGasBremsGasTousbunchbunch
iiscatteri
vPNvPNvM
N
M
NvNNN )( ,
More technically, use a rate equation
Touschek
bremsstrahlung
Coulomb
(units)
CoulGasBremsGasTousbunchbunch
iiscatteri
vPNvPNvM
N
M
NvNNN )( ,
Big rate equation from before…
The gas pressure has two terms: static and dynamic
NPPP DGBGGas ,,
CoulDGBGBremsDGBGTousbunch
vNPPNvNPPNvM
NN
)( ,,,,
2
)()( ,,,,22
CoulBGBremsBGCoulDGBremsDGbunch
Tous vPvPNvPvPM
vNN
Then
Collecting terms
or bNaNN 2
where a=a(Mbunch,VRF, yscraper)
b=b(VRF, yscraper)
NOTE: keep it simple – no coupling, dynamic aperture or bunch lengthening
first-order, non-linear rate equation
Touschek
bremsstrahlung
Coulomb
b
ae
eNtN
bt
bt
)1(1)( 0
bNaNN 2
Finally integrating the rate equation
yields tbaeNtN )(0)( ~
What's the point of all this?
a. want to know the relative Toushek, bremsstrahlung & Coulomb contributions b. plan for top-off shot/charge, fill pattern, duty cycle c. plan for future coupling (high brightness operation) d. ID collimators e. shielding, etc
Excellent, tractable student projectDelves deep into particle beam and accelerator physics, NN application
Very low emittance with on-axis injection: bunch replacement
• Assume ~30-40 pm natural emittance (15-20 pm/plane, fully coupled), very small dynamic aperture
• Lifetime (not yet calculated) < 1 h
• Injection options:
1. Accumulator ring used to replace all bunches in ring
2. Bunch train replacement (~20 bunches per train, trains separated by gaps (~10-20 ns, 5-10 buckets) to accommodate rise- and fall-times of injection kicker
• ~0.5 nC/bunch (68 A/bunch x 20)
• 116-140 trains (~160-190 mA total)
• inject every 1-10 sec, depending on desired current stability
R. Hettel
single-bunch injection limit
multi-bunch injection limit
PEP-X:
h = 3492 nb = 3400 Trev = 7.336 ms t(0) = 1800 sec
itot = 1.5 A qtot = 11010 nC ibavg = 0.441 mA qbavg = 3.235 nC
R. Hettel