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Overview of Beam Instrumentations for High-Power Operation of the Spallation
Neutron Source
Saeed Assadi for SNS B.I. Group
Beam Instrumentation Group Leaser
SNS/ORNL
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OUTLINE
Overview of Beam Instruments
SCL Laser Profile Monitor Project
Recent results
Challenge
Future plan
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The Spallation Neutron Source
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Liquid Hg Target
SNS Accelerator Complex
Front-End:Produce a 1-msec
long, chopped, H- beam
1 GeV LINAC
Accumulator Ring: Compress 1 msec long
pulse to 700 nsec
Ion Source2.5 MeV 1000 MeV87 MeV
CCLCCL SRF, =0.61SRF, =0.61 SRF, =0.81SRF, =0.81
186 MeV 387 MeV
DTLDTLRFQRFQ
RTBT
HEBT
InjectionExtraction
RF
945 ns
1 ms macro-pulse
Cur
rent
mini-pulse
Chopper system makes gaps
Accumulation 700 nsecPulse
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Interceptive Beam Instrumentation Systems
RING 2 Wire-deleted
RING 2 Wire-deleted
SCLSCL
RTBT5 WireScanners
1 Harp1 RTBT VideoTarget Video
RTBT5 WireScanners
1 Harp1 RTBT VideoTarget Video
HEBT5 Wire Scanners
2 BSM
HEBT5 Wire Scanners
2 BSM
IDump2 Wire 2 IDump Video
IDump2 Wire 2 IDump Video
Edump 1 WireEdump 1 Wire
LDump1 Wire LDump1 Wire
CCL/SCL Transition 1 Wire
CCL/SCL Transition 1 Wire
CCL 8 Wire , 4BSM,1 Faraday Cup
CCL 8 Wire , 4BSM,1 Faraday Cup
OperationalOperational
MEBT5 WiresD-box emittance D-box beam stop D-box aperture1 fast faraday cup1 faraday/beam stopD-box video
MEBT5 WiresD-box emittance D-box beam stop D-box aperture1 fast faraday cup1 faraday/beam stopD-box video
DTL5 Wire5 Faraday Cup
DTL5 Wire5 Faraday Cup
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Non-Interceptive Beam Instrumentation Systems
RING2 Electron Profile Scanner 5 Electron Det. 12 FBLM1 Beam in Gap Monitor1 Tune, 84 BLMs, 4 NDs2 Transverse feedback system
RING2 Electron Profile Scanner 5 Electron Det. 12 FBLM1 Beam in Gap Monitor1 Tune, 84 BLMs, 4 NDs2 Transverse feedback system
SCL32 Position 86 Loss 9 Laser Wire1 Laser Wire24 PMT Neutron
SCL32 Position 86 Loss 9 Laser Wire1 Laser Wire24 PMT Neutron
RTBT1 Movable Harp3 FBLM26 BPMs26 BLMs
RTBT1 Movable Harp3 FBLM26 BPMs26 BLMs
HEBT29 Position 1 Laser Beam in-gap1 Laser emittance sys48 BLMs, 4FBLM
HEBT29 Position 1 Laser Beam in-gap1 Laser emittance sys48 BLMs, 4FBLM
IDump1 Position1 Current2 BLM
IDump1 Position1 Current2 BLM
EDump 4 BLM, 1 BCM
EDump 4 BLM, 1 BCM
LDump2 Loss1 Wire ,1 BCM5 position
LDump2 Loss1 Wire ,1 BCM5 position
CCL/SCL Transition
2 Position1 Loss 1 Current
CCL/SCL Transition
2 Position1 Loss 1 Current
CCL8 Neutron, 2 Thermal48 Loss
CCL8 Neutron, 2 Thermal48 Loss
OperationalOperationalMEBT
2 Thermal Neutron3 PMT Neutron D-box Mode-lock laser2 Beam-Gap Monitor [ChuMPS]6 BPMs2 BCMs1 Mode-lock laser
MEBT2 Thermal Neutron3 PMT Neutron D-box Mode-lock laser2 Beam-Gap Monitor [ChuMPS]6 BPMs2 BCMs1 Mode-lock laser
DTL2 Beam-Gap Monitor [ChuMPS]3 Diff BCM Monitor6 Thermal and 12 PMT Neutron6 Current, 12 BLMs
DTL2 Beam-Gap Monitor [ChuMPS]3 Diff BCM Monitor6 Thermal and 12 PMT Neutron6 Current, 12 BLMs
Not OperatingNot Operating
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Quick History and Facts about SNS
The SNS is a short-pulse neutron source, driven by a 1.4 MW proton accelerator [ presently at .54 MW].
SNS will be the world’s leading facility for neutron scattering research with peak neutron flux ~20–100x ILL, Grenoble
SNS construction project, a collaboration of six US DOE labs, was funded through DOE-BES at a cost of 1.4 B$
SNS will have 8x beam power of ISIS, the world’s leading pulsed source user facility,Stepping stone to other high power facilities, expected to achieve 1.4 MW in two years.
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Motivation to Add &/or Modify More Beam Instruments
Improve reliability
Improve user friendliness – i.e. automation, additional features –
Support, diagnose “unexpected” events – i.e. Spark detectors, LEBT and RFQ RGAs
Accelerator Physics requests – Laser emittance system.
Allow “parasitic” studies; IPM, electron profile monitor. Different types of BLMs.
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Continue: Motivation to Add &/or Modify More Beam Instruments
60 Hz Beam Accounting [Never was in the plan]
Low Energy Beam Loss Measurements , WGF4- A. Zhukov’s talk
Differential Current Measurements in DTL/CCL
High Power Operations.– e/p Instabilities, use of digital active transverse feedback system for the Ring. WG F- (wed) – Craig Deibele’s talk
Ring Electron Profile Monitor, BINP collaboration with SNS, initial results by W. Blokland in this talk.
Computation of Space-Charge Effects in Allison Scanner and Its Application to the Measurement of Emittance by Timofey Gorlov
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Laser Striping Experiment
SCL Laser ProfileMonitors, 9-stations
MEBT 3-D LaserProfile Monitor
1) MEBT Mode-lock laser initially in 1-D – 9/20042) SCL Nd:YAG 1064 nm Laser, 9-station – 9/20053) Laser Stripping test Nd:YAG, 3ed harmonic -- 8/20054) Working on making SCL Laser system turn-key -- to present
ORNL-SNS Laser Diagnostic Activities
4M 4H 1D
Laser Emittance
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What does the Laser do? Photo-neutralization
Requirements• High peak power• Small spot size• Transverse scan• Temporal stability• Detection
h H- H0 + e
Cross-section is well known therefore stripping efficiency calculation is a matter of algebraic manipulation
-H-
time
12nsIbeam
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Principle of Laser Wire, direct electron current measurement at SNS.
hH-
N
S
Faraday Cup
H0
e
H0
Photodetachment
• Detected electron number is proportional to the ion density
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Redundant Lasers are available for the SCL.
Q-switched Nd:YAG laser = 1.06 m frep = 30 Hz, Tw = 7 ns
Ep = 50 – 200 mJInjection seededTiming synchronized to SCL
Laser Room
• High pulse energy
• Small spot size
• Single wavelength
• Pointing stability
• Temporal stability
Requirements:
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SCL
1 2 3 4 5 321712 13 14 15
250 m 227 m 25 m160 m
LR Laser room
Laser wire station
Cryomodule number
Camera
Mirror
Power meter32
LR
Ring
Layout of the SCL Laser Wire System
CCLDTL
Target
MEBT
• 4 LW from 200 MeV
• 4 LW from 450 MeV
• 1 LW at 1 GeV
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Q-switched Nd:YAG laser1064 nm30 Hz7 nsUp to 1.5 JInjection seeded
SCL Laser Transport Line
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Schematic of Laser Wire Station Optics
Mirror
Lens
Photodiode
Beam Dump
Flip-Mirror
From LTL
V-scan
H-scan
Ion Beam
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Top-Level Software Controls all Stations and collects Data.
Profile Measurement LW Station Diagnostics
User specifies station, axis, scanning range/step/ave. number, controls timing, and data acquisition
User monitors laser beam position, lens focus, electron collector output raw signal
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0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Magnet Current (A)
LW Station 02
LW Station 15
LW Station 32
Falling edge cut
Rising edge cut
Normal profile
Effects of LW Magnet Current
0
2
4
6
8
10
12
14
0 2 4 6 8 10
Laser Wire Station #
Mag
net
Cur
rent
(A
)
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Vertical Beam Profile Measurement at LW32
12.912.411.911.410.910.49.99.48.98.47.97.4
Magnet Current
(A)
14 16 18 20 22 24 26 28 30
Vertical Position (mm)
Det
ecto
r O
utpu
t (10
0 m
V/d
iv)
One challenge that is solved Effects of LW Magnet Current
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Mini-pulse #1 #100 #200 #300
Advantage of Laser is to be able to scan the entire Macro-pulse.
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Beam Profile Measurements
0
0.1
0.2
0.3
0.4
0.5
0.6
10 15 20 25 30
Position (mm)
Sig
nal (
V)
0
0.1
0.2
0.3
10 15 20 25 30 35
Position (mm)
Sig
nal (
V)
0
0.1
0.2
0.3
0.4
10 15 20 25 30
Position (mm)
Sig
nal (
V)
0
0.1
0.2
0.3
0.4
0.5
10 15 20 25 30
Position (mm)S
igna
l (V
)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
15 20 25 30 35
Position (mm)
Sig
nal (
V)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
10 15 20 25 30
Position (mm)
Sig
nal (
V)
LW1
LW5
LW9
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Ion beamLaser beam
f
S
Ion beam
YdLaser beam
f
S
Laser beam shifts on the lens Laser beam shifts on the lens surfacesurface
Laser beam shifts + Ion beam Laser beam shifts + Ion beam shifts from waistshifts from waist
Realistic Laser Beam with respect to H-
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Ion beam
YdLaser beam
f
S
Measured profile as a function of lens position at LW14V
0
0.1
0.2
0.3
0.4
0.5
18 20 22 24 26 28 30
Position
Am
plitu
de (
V)
Yd=0 Yd=5mm Yd=10mm
Challenge! Experimental Measurements
Why do we get poor profiles in this case
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Current Laser Wire Box
14
11.5
12
11.5
12
13.5
4.5
4
2.75
2-3/8
2.5
2.5
2-3
/8
5.75
3.5
3.25
3.25 3.5 5
6.5
6.5
2.75
2.75
1
1
rear front
6.75
7.25
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Revised Laser Wire Box Design to Bring Larger Travel Range
14
11.5
12
11.5
12
13.5
4.5
4
2.75
2-3/8
2.5
2.5
2-3
/8
3.25
3.25 3.5 5
6.5
6.5
2.75
2.75
1
1
6.75
7.25
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SUMMARY of Laser Profile Monitor
Profiles have been measured at all 9 stations
Operational parameters have been investigated and optimized
Software platform has been improved
Issues of radiation and stability are looked into and solutions are provided
Future plan – Secure system reliability– Optimize/document operational procedure– Identify technical problems and work on solutions
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600750
MCP
Phosphor screen
Photo camera
Layout of the proposed EBP for SNS Accumulator Ring by BINP
Electron Gun
DeflectorQuadrupole
lens
Proton beam
Electron beam Transverse Profile Monitor
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Collaboration on Design and Construction of Electron Beam Profile MonitorBetween SNS-ORNL and BINP, Novosibirsk, Russia has started
Probe beam:
Energy=75keV,
Scan.-parallel,
3rd ,4th quads - ON
Proton beam:
Energy=1GeV
Np=1*1013
Transverse size r=1.5cm
Round uniform transverse distribution
-0,2
0
0,2
0,4
0,6
0,8
1
1,2
-3 -2 -1 0 1 2 3
Simulation
Blue line – theoretical profile,
Magenta + square – reconstructed profile
Alexander Starostenko
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Horizontal Profile after 500 turn, 8 Micro-Coulomb of charge in the Ring.
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Vertical Profile after 500 turn, 8 Micro-Coulomb of charge in the Ring ---- Another useful tool!