Experience from the Spallation Neutron Source Commissioning
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Transcript of Experience from the Spallation Neutron Source Commissioning
Experience from the Spallation Neutron Source Commissioning
Dong-o JeonAccelerator Physics GroupOak Ridge National Laboratory
May 9, 2007
OAK RIDGE NATIONAL LABORATORY
Diagnostics on Diagnostics-plate used for commissioning DTL Tank 1
Bunch Shape Monitor
(BSM)
Bunch Shape Monitor installed 50 inches downstream of DTL1
OAK RIDGE NATIONAL LABORATORY
DTL diagnostics devices
Wire-scanners
Beam Position Phase Monitors
Energy Degrader / Faraday Cup
Beam Loss Monitors
Beam Current Monitors
OAK RIDGE NATIONAL LABORATORY
CCL diagnostics devices
Wire-scanners
Bunch Shape Monitors (Z-profile)
Beam Position Phase Monitors
Beam Loss Monitors, Neutron Detectors
Beam Current Monitor
OAK RIDGE NATIONAL LABORATORY
SCL diagnostics devices
Laser Profile Monitors
Beam Position Phase Monitors
Beam Loss Monitor, Neutron Detectors
Beam Current Monitor
Bunch Shape Monitor will be installed.
OAK RIDGE NATIONAL LABORATORY
Emittance scanner is most valuable
Provides direct information about beam quality.
Can perform transverse matching.
Essential for physics studies, providing decisive information of interesting mechanisms.
Wire-scanners and Laser Profile Monitors Provide information about beam profile.
Limited compared with emittance scanner
Can perform transverse matching.
Laser Profile Monitors commissioned, almost ready…
OAK RIDGE NATIONAL LABORATORY
Transverse matching by minimizing rms emittance @ 38mA, nominal optics
design before afterQH12: -25.96 T/m -26.12 T/m -28.31 T/mQH14: -18.50 T/m -17.31 T/m -16.86 T/m
After MatchingBefore Matching
• RMS with 1% threshold: 0.31 0% threshold: 0.39• Gaussian fit to core: 0.19
• RMS with 1% threshold: 0.42 mm mrad 0% threshold: 0.50• Gaussian fit to core: 0.23
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Round Beam Optics improves X beam quality (Emittance Measurement)
Round Beam Optics reduces halo and rms emittance in X significantly
Nominal OpticsX= 0.349 mm-mrad (1% threshold) 0.454 mm-mrad (0% threshold)
Round Beam OpticsX= 0.231 mm-mrad (1% threshold) 0.289 mm-mrad (0% threshold)
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Tail is significantly reduced in X plane for Round Beam Optics
Round Beam Optics reduces beam tail visibly
Rare measurement data with no tail!
Tail is the source of beam loss
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Redundant diagnostics matters emittance data and wire-scanner
X beam size from emittance data is ~1.5 times bigger than that from wire scanner data.
Y beam size from emittance is consistent with that from wire scanner data.
Beam profile fromEmittance data
Beam profile from Wire scanner
OAK RIDGE NATIONAL LABORATORY
Comparison of beam profile from emittance data and wire-scanner
OAK RIDGE NATIONAL LABORATORY
Comparison of beam profile from emittance data and wire-scanner
OAK RIDGE NATIONAL LABORATORY
Comparison of Measured Beam Profiles with Model
• Fit of starting twiss to beam profiles using online model delivers matched beam in DTL
-3
-2
-1
0
1
2
3
4
0 2 4 6 8 10
s (m)
siz
e (
mm
) horizontal model
vertical model
Horizontal wire
Vertical wire
OAK RIDGE NATIONAL LABORATORY
Laser Profile Monitor This is a new way of diagnosing the transverse profile of
an H- beam.
R&D, implementation, and commissioning at the same time!!
LW04 Hor. 30 steps at 0.5mm each. analysis: average. time: 10:58
LW04, vertical, quads at nominal setting
Courtesy of S. Assadi et al
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Beam Phase Monitors and Energy Degrade/Faraday Cup
Beam Phase Monitors can provide information about tank rf amplitude, phase (A, ) and incoming beam energy deviation E
ED/FC generally can not determine E
ED/FC gives information of longitudinal beam profile.
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Acceptance Scan for DTL
Acceptance of DTL Tank 1
Results depend on incoming beam energy E
Acceptance Scan technique generally can not determine E
OAK RIDGE NATIONAL LABORATORY
DTL tanks rf set-point by Acceptance Scan with Absorber/Collector
Measurements consistent with simulations
Used to establish proper amplitude and phase setpoints
Measured bunch width consistent with MEBT design
FWHM = 28.8 deg
Simulated DTL1 Acceptance
Cur
rent
[mA
]
Tank 1 RF Phase [deg]
Bea
m P
rofil
e [a
.u.]
OAK RIDGE NATIONAL LABORATORY
Beam bunch length at the entrance of DTL tanks obtained from Acceptance Scans
Z beam size @ DTL 1 entrance is consistent with model 28.8 deg vs. 26.7 deg FWHM.
Z beam size remains consistent with the model beam distribution we used.
OAK RIDGE NATIONAL LABORATORY
Only DTL Tank 1 shows variations enough to detect the incoming beam energy deviation E
Data noisy!
E [MeV]
Acceptance Scan generally can not determine E
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Multiparticle Phase Scan for DTL
Schematic drawing
Multiparticle model
Single-particle model
Why Multiparticle Phase Scan?
When beam bunch is long,
Single particle tracking is not
accurate enough.
OAK RIDGE NATIONAL LABORATORY
Multiparticle Phase Scan vs Acceptance Scan
For low energy DTL tanks, beam bunch length is relatively long and it is important to do multiparticle tracking to accurately simulate the phase scan.
Agreement between measurement and simulation is excellent.
Agreement between multiparticle phase scan and acceptance scan is excellent.
DTL 1 Multiparticle Phase Scan DTL 1 Acceptance Scan
(A, )=(0.179, -125.5) (A, )=(0.176, -124.6)
E=-0.0265MeV, -1.06%
OAK RIDGE NATIONAL LABORATORY
Multiparticle Phase Scan vs Acceptance Scan
Agreement between measurement and simulation is excellent.
Agreement between multiparticle phase scan and acceptance scan is excellent.
DTL 2 Multiparticle Phase Scan DTL 2 Acceptance Scan
(A, )=(0.483, 166.5) E=-0.314% (A, )=(0.484, 168.0)
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Multiparticle Phase Scan vs Acceptance ScanDTL 3 Multiparticle Phase Scan DTL 3 Acceptance Scan
(A, )=(0.490, 105.0) E=0.254% (A, )=(0.494, 104.7)
Set-points from the phase scan and acceptance scan are consistent with each other within ±2% and ±2º.
OAK RIDGE NATIONAL LABORATORY
Phase Scan Acceptance Scan
DTL 1 (0.179, -125.5) (0.176, -124.6)
DTL 2 (0.483, 166.5) (0.484, 168.0)
DTL 3 (0.490, 105.0) (0.494, 104.7)
DTL 4 (0.599, 181.6) (0.585, 180.0)
DTL 5 (0.576, 116.6) (0.547, 112.0)
Multiparticle Phase Scan vs Acceptance Scan Summary
Set-points from the phase scan and acceptance scan are consistent with each other within ±2% and ±2º, except Tank 5.
Noisy Acceptance Scan data for DTL Tank 5 is an issue
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Longitudinal beam profile
Bunch Shape Monitors (INR)
Mode locked Laser Profile monitor
Energy Degrader/Faraday Cup
OAK RIDGE NATIONAL LABORATORY
Bunch Shape Monitor (BSM) Measurements
020
4060
8010
30
50
70
0
1
2
3
4
5
6
7
8
Phase, deg 402.5 MHz
Time, us
• INR Collaborators produced Bunch Shape Monitor (Feschenko, Jeon, Blokland et al.)
• Early BSM measurements indicated poor phase stability• Tracked to MEBT Rebuncher RF System
OAK RIDGE NATIONAL LABORATORY
Longitudinal Emittance at DTL1 Input Estimated Using the BSM
-0.10
-0.08
-0.06
-0.04
-0.02
0.00
0.02
0.04
0.06
0.08
0.10
-0.50 -0.40 -0.30 -0.20 -0.10 0.00 0.10 0.20 0.30 0.40 0.50
Phase, rad
En
erg
y D
evia
tio
n,
MeV
Tank 1 Entrance
Tank 1 Exit
BSM
Parameter list: 0.13 pi MeV-deg (RMS) for 38 mA
Estimated longitudinal emittance: 0.14 pi MeV-deg for 15 mA
-0.10
-0.08
-0.06
-0.04
-0.02
0.00
0.02
0.04
0.06
0.08
0.10
-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5
Phase, rad
En
erg
y d
evia
tio
n,
MeV
E=0.94EoE=0.94EoE=0.97EoE=0.97EoE=1.00EoE=1.00EoE=1.03EoE=1.03EoE=1.06EoE=1.06EoE=1.09EoE=1.09EoE=1.12EoE=1.12EoE=1.15EoE=1.15EoEquivalent Ellipse
Feschenko, Jeon et al. (INR)
OAK RIDGE NATIONAL LABORATORY
Now have mode-locked laser diagnostics for 3-dimensional profile measurement in MEBT (only longitudinal has been commissioned)
Longitudinal laser bunch profile monitor in MEBT
Longitudinal bunch profile (blue dots) and Gaussian fit (red line).
Courtesy of A. Aleksandrov et al
measurement
simulation
rebuncher phase
bun
ch s
ize
OAK RIDGE NATIONAL LABORATORY
Longitudinal beam profile from Acceptance Scan
Comparable quality to Mode-locked Laser Profile Monitor measurement
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Beam Loss Monitors
500 sec, peak = 0.004
Loss units in Rads/pulse
From loss studies calibrations, the peak loss (next to the linac dump window) ~ 2 W/m at 1 Hz
Linac dump window
SCL/HEBT transition
OAK RIDGE NATIONAL LABORATORY
Conclusions
Emittance scanners are very valuable for commissioning and future beam physics studies. SNS used to have once and gone!
Redundant diagnostics devices can play an important role … cross checking, backup.
Preplanning and testing of diagnostics are crucial … otherwise one might end up using the commissioning period in commissioning diagnostics devices.
LINAC4 … Uniquely positioned to carry out many valuable physics studies.