Scaled Models: Space-Charge Dominated Electron Storage …...Electron Beam Dynamics Laser structure preserved through linac Direct Electron Beam Modulation at Cathode using a Ti:Sap
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1IREAPIREAP
Institute for Research in Institute for Research in Electronics & Applied PhysicsElectronics & Applied Physics
University of Maryland, College Park, MD
Scaled Models: Scaled Models: SpaceSpace--Charge Dominated Charge Dominated
Electron Storage RingsElectron Storage Rings
Research sponsored by US DOE & DoD ONR
Rami A. Kishek
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Institute for Research in
Electronics & Applied Physics
Research Focus:Interdisciplinary research in engineering and the physical sciences with emphasis on large and complex experiments. Faculty and students from Electrical & Computer Engineering, Physics and Materials Science.
Specialties:• Chaos and Nonlinear Dynamics• Nanoscience and Engineering•• Beam PhysicsBeam Physics• Microwaves and Electronics• Space & Fusion Plasmas• Materials Processing (using microwaves, plasmas, ion beams)
University of Maryland University of Maryland (near Washington, DC)
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The Charged Particle Beam Group
University of Maryland Electron Ring (UMER)University of Maryland Electron Ring (UMER) Team:Patrick O’Shea Martin ReiserRami KishekIrving Haber
Junior Scientists:Santiago BernalMark WalterBryan Quinn
Graduate:Gang Bai Kai TianC PapadopoulosDiktys StratakisCharles Tobin
Former:Yun ZouJonathan
NeumannYupeng CuiHui LiYijie HuoJohn Harris
Renee FeldmanDon FeldmanRalph FioritoHenry FreundTerry F. GodloveKevin Jensen
A. Shkvarunets Mike HollowayDave GillinghamDavid DemskeNathan Moody
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Maryland CPB Group: Projects Underway
• High-brightness, durable, photocathode development• Advanced diagnostic development• Self-consistent modeling and simulation• Scaled experimental studies of collisionality and
energy spread evolution for Heavy Ion Inertial Fusion• Multi-disciplinary studies of breakdown and
multipactoring in high-gradient metal and dielectric structures
•• UMER: The University of Maryland Electron RingUMER: The University of Maryland Electron Ring
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UMER: a testbed for space charge dynamics
1. Bright electron beams and space charge effects
2. The University of Maryland Electron Ring
3. Status update
4. Sample results and experiments
5. Conclusion
6IREAPIREAP Goal: 1Å with pulses of a few fs
Ultra short wavelengthLinac Coherent Light Source (Stanford)
InterstateInterstate--280280
Sand Hill RdSand Hill Rd
http://www-ssrl.slac.stanford.edu/lcls/
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Requirements of an FEL beam
1. Bright electron beamintense space charge at the source
2. In ERLs the injection energy is lost, so injection at lower energies preferable
space charge3. Coherence for short wavelengths requires small
emittance (εn < γλ/4π)e.g. for LCLS, turns out εn < 2 μm for λ = 1 nm
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Beam2a
k02a
external focusing
2
3Ka a
ε+
Space charge + emittance
Dimensionless Space Charge Intensity
2 2
space charge forceexternal focusing force
≡ =o
Kk a
χ
0 ≤ χ ≤ 1
Intensity Parameter:
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Intensity ScalingsEmittanceDominated
Space-chargeDominated
Intensity Parameter (χ)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
0.0 0.2 0.4 0.6 0.8 1.0
BetatronOscillations
Curve1ω χ
ω= −
0
0
2Pω χω
=
PlasmaOscillations
CurveλD >> a λD
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Realistic pulse shapes are not “clean”Rectangular Pulse
(thermionic) 100 ns
Parabolic Pulse (thermionic)
50 ns
Photoemission Drive Laser Pulse
2 ns
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SLAC linac tunnelSLAC linac tunnel FEL HallFEL Hall
LinacLinac--00L L =6 m=6 m
LinacLinac--11L L =9 m=9 m
LinacLinac--22L L =330 m=330 m
LinacLinac--33L L =550 m=550 m
BCBC--11L L =6 m=6 m
BCBC--22L L =22 m=22 m
DLDL--22L L =66 m =66 m
DLDL--11L L =12 m =12 m
undulatorundulatorL L =120 m=120 m
7 MeV7 MeVσσz z ≈≈ 0.83 mm0.83 mm
σσδδ ≈≈ 0.2 %0.2 %
150 MeV150 MeVσσz z ≈≈ 0.83 mm0.83 mmσσδδ ≈≈ 0.10 %0.10 %
250 MeV250 MeVσσz z ≈≈ 0.19 mm0.19 mm
σσδδ ≈≈ 1.8 %1.8 %
4.54 GeV4.54 GeVσσz z ≈≈ 0.022 mm0.022 mm
σσδδ ≈≈ 0.76 %0.76 %
14.35 GeV14.35 GeVσσz z ≈≈ 0.022 mm0.022 mm
σσδδ ≈≈ 0.02 %0.02 %
...existing linac...existing linac
newnew
rfrfgungun
2525--1a1a3030--8c8c
2121--1b1b2121--1d1d XX
LinacLinac--XXL L =0.6 m=0.6 m
2121--3b3b2424--6d6d
An X-Ray FEL is a complex Machine= Many possibilities for emittance growth!
Two stages of chirped pulse bunch compression
1 km
P.Emma SLAC
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Space Charge Raises Many Issues
• What is the ideal bunch shape? rectangular? ellipsoidal?
• How to model the source accurately?• How will perturbations evolve?
Can they be controlled?• What is the time scale for irreversible mixing in
beams? How soon do we have to perform emittance compensation?
• How to maintain a low emittance and prevent halo formation?
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UMERUMER:a testbed for space charge
physics in bright beams
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UMER Parameters
Energy 10 keVEnergy Spread 20 eVCurrent Range 0.6-100 mArms Emittance Range 0.2-3 μm
Circulation time 200 nsPulse length 5-100 nsZero-Current Tune 7.6Depressed Tune 1.5 – 6.5
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85 mA
Beams Circulated
Present UMER Operating PointsEmittanceDominated
Space-chargeDominated
Intensity Parameter (χ)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
0.0 0.2 0.4 0.6 0.8 1.0
BetatronOscillations
Curve1ω χ
ω= −
0
0
2Pω χω
=
PlasmaOscillations
Curve
0.6 mA
24 mA
7.2 mA
UMER Range
BeamSources
Relativistic E-Beams
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Extraction/diagnostic
section
10 kV Gun
Injection/matchingsection
UMER Schematic
Aug. 2004
The University of Maryland Electron Ring
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UMER Magnets & Lattice
72 Quads(~ 7.8 G/cm)
36 Dipoles(~ 15 G)
32 cm
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Commencement of Multi-Turn Operation
First Current Pulse indicating Multiple Turns
5/5/2005
(courtesy M. Walter)
6 Turns Oct. 2005
(Work in Progress)
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Example Results and Experiments
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Generating Perturbations with Lasers
Beam Current
Photoemission only (Cool cathode)
Thermionic only, 100ns pulse
Photoemission + Thermionic 5ns pulse
Drive Laser
Heated Photocathode
Electron Beam
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Drive Laser Setup
Nd:YAG Laser
KTP
BBO
Mirrors/filters
Telescope
Laser Mask
UV (355nm) LaserPhoton energy: 3.5 eVWork function: 2.7 eV
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Experiment: Propagation of Perturbed Beam
20 mA thermal-emission beam current
20 mA photo-emission beam current
Beginning
End
Y. Huo
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Experimental Study of Beam Energy SpreadEnergy Analyzer Design
Collimating Cylinder-10.13kV
Retarding Mesh
-9999.5 V
0 keV eam
3rd Generation: Res. < 1 eV
Collector
GroundedHousing
Y. Zou and Y . Cui
Measured Longitudinal Phase Space
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Aside: Anomalous Growth of Energy Spread
-5
-4.5
-4
-3.5
-3
-7.5 -7 -6.5 -6 -5.5 -5
5 keV4 keV
3 keV
⎛ ⎞⎜ ⎟⎝ ⎠
logo
ILI a
⎛ ⎞Δ⎜ ⎟⎜ ⎟Δ⎝ ⎠
log fo
EE
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Space charge converts densityperturbation to an energy perturbation
0 20 40 60 80 100 120
-0.05
-0.04
-0.03
-0.02
-0.01
0.00
Cur
rent
/A
time/nsInitial Current vs time
20 40 60 80 1004960
5000
5040
5080
5120
5160
mea
n en
ergy
(ev
)
time/ns
Experiment
Simulation (WARP)
Energy vs time2-m downstream
K. Tian
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ExperimentTime
Diagnostics
To Wigglers
RF Gun : 5 MeV
Magnetic Chicane
RF Tanks: 75 MeV
RF Tanks : InduceΔγ/γ for time diagnostics
Long Wavelength Diagnostics
Laser Pulse Shaping on sub ps time scale
1
2
THz Radiation Measurements
Electron Beam DynamicsLaser structure preserved through linac
Direct Electron Beam Modulation at Cathode using a Ti:Sap driver laser
J. Neumann
Production of Photoemission-Modulated Beams in a Thermionic Electron Gun, .J.G. Neumann, J.R. Harris, B. Quinn, and P.G. O'Shea, Review of Scientific Instruments, 76, 033303 (2005).
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Beam Control System Software
Quadrupoles ControlCentral Control Platform
Dipoles Control
BPMs Control
Steering Module
Skew Correction Module
Matching Module
Tomography Module
network
network
Hui Li
network
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3.8nC
Low Energy (10 kV) Optical Transition Radiation ImagesIdeal for exploring the fast time structure of low energy beams in injector
8.5 nC
1.6 nC
0.12 nC Fiorito & Feldman
29IREAPIREAP0. 2. 4.
10^-9
0.0
0.5
1.0
1.5
2.0
10^-4
Current at iz = 12
time (s)0. 1. 2. 3. 4.
10^-9
0.
1.
2.
10^-4
Current at iz = 6
time (s)
0. 1. 2. 3. 4.10^-9
0.
1.
2.
3.
10^-4
Current at iz = 12
time (s)0. 1. 2. 3. 4.
10^-9
0.
1.
2.
10^-4
Current at iz = 12
time (s)0 001 All i
-35V
-25V
-30V
-20V
(~ 0.6 mm from the cathode)
WARP Simulations Irving Haber
Current vs. time for different grid voltages
Self-Consistent Gun Simulations
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Conclusion
• Brighter electron beams can result in smaller, less expensive FELs
• UMER is a unique, well-diagnosed and flexible testbed for experimenting with space charge-dominated beam dynamics at reasonable time scales
• UMER can produce benchmarks for space-charge codes
• Collaborations welcome!
Website: http://www.ireap.umd.edu/umer
Publications: http://www.umer.umd.edu/
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Virtual Cathode Movie
Scaled Models: �Space-Charge Dominated Electron Storage RingsThe Charged Particle Beam GroupMaryland CPB Group: Projects UnderwayUMER: a testbed for space charge dynamics Ultra short wavelength�Linac Coherent Light Source (Stanford)Requirements of an FEL beamDimensionless Space Charge IntensityRealistic pulse shapes are not “clean”Space Charge Raises Many IssuesUMER:�a testbed for space charge �physics in bright beamsUMER ParametersUMER SchematicUMER Magnets & LatticeCommencement of Multi-Turn OperationExample Results and ExperimentsGenerating Perturbations with LasersDrive Laser SetupExperiment: Propagation of Perturbed BeamExperimental Study of Beam Energy Spread� Energy Analyzer DesignAside: Anomalous Growth of Energy SpreadSpace charge converts density perturbation to an energy perturbation8.5 nC Self-Consistent Gun SimulationsConclusionVirtual Cathode MovieScaled Models: �Space-Charge Dominated Electron Storage RingsThe Charged Particle Beam GroupMaryland CPB Group: Projects UnderwayUMER: a testbed for space charge dynamics Ultra short wavelength�Linac Coherent Light Source (Stanford)Requirements of an FEL beamDimensionless Space Charge IntensityRealistic pulse shapes are not “clean”Space Charge Raises Many IssuesUMER:�a testbed for space charge �physics in bright beamsUMER ParametersUMER SchematicUMER Magnets & LatticeCommencement of Multi-Turn OperationExample Results and ExperimentsGenerating Perturbations with LasersDrive Laser SetupExperiment: Propagation of Perturbed BeamExperimental Study of Beam Energy Spread� Energy Analyzer DesignAside: Anomalous Growth of Energy SpreadSpace charge converts density perturbation to an energy perturbation8.5 nC Self-Consistent Gun SimulationsConclusionVirtual Cathode Movie
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