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

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

2IREAPIREAP

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)

3IREAPIREAP

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

4IREAPIREAP

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

5IREAPIREAP

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/

7IREAPIREAP

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

8IREAPIREAP

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:

9IREAPIREAP

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

10IREAPIREAP

Realistic pulse shapes are not “clean”Rectangular Pulse

(thermionic) 100 ns

Parabolic Pulse (thermionic)

50 ns

Photoemission Drive Laser Pulse

2 ns

11IREAPIREAP

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

12IREAPIREAP

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?

13IREAPIREAP

UMERUMER:a testbed for space charge

physics in bright beams

14IREAPIREAP

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

15IREAPIREAP

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

16IREAPIREAP 3.7 m

Extraction/diagnostic

section

10 kV Gun

Injection/matchingsection

UMER Schematic

Aug. 2004

The University of Maryland Electron Ring

17IREAPIREAP

UMER Magnets & Lattice

72 Quads(~ 7.8 G/cm)

36 Dipoles(~ 15 G)

32 cm

18IREAPIREAP

Commencement of Multi-Turn Operation

First Current Pulse indicating Multiple Turns

5/5/2005

(courtesy M. Walter)

6 Turns Oct. 2005

(Work in Progress)

19IREAPIREAP

Example Results and Experiments

20IREAPIREAP

Generating Perturbations with Lasers

Beam Current

Photoemission only (Cool cathode)

Thermionic only, 100ns pulse

Photoemission + Thermionic 5ns pulse

Drive Laser

Heated Photocathode

Electron Beam

21IREAPIREAP

Drive Laser Setup

Nd:YAG Laser

KTP

BBO

Mirrors/filters

Telescope

Laser Mask

UV (355nm) LaserPhoton energy: 3.5 eVWork function: 2.7 eV

22IREAPIREAP

Experiment: Propagation of Perturbed Beam

20 mA thermal-emission beam current

20 mA photo-emission beam current

Beginning

End

Y. Huo

23IREAPIREAP

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

24IREAPIREAP

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

25IREAPIREAP

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

26IREAPIREAP

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).

27IREAPIREAP

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

28IREAPIREAP

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

30IREAPIREAP

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/

31IREAPIREAP

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