High-Quality Beams for Next-Generation Accelerators Rami A. Kishek

High-Quality Beams for Next-Generation
Accelerators
Rami A. Kishek
Institute for Research in Electronics & Applied Physics
University of Maryland, College Park, MD, USA
Outline:
1. Why Cold Beams?
2. What is Beam Quality?
3. Key Issues
4. Past Work
5. Future Prospects
Research sponsored by US DOE & DOD ONR
International Linear Collider (ILC)
Primary Goal: Higher Acceleration Energy (200-500 GeV)
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Old Paradigm: Livingston Plot
Energy
M. Stanley
Livingston
Historical Development
of Accelerators
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Year of commissioning
3
New Applications Demand Higher-Quality
Spallation Neutron Source
Energy Recovery Linacs
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X-Ray Free Electron Lasers
Heavy Ion Inertial Fusion
4
“Nanoscopes” Revolutionize Science
X-rays:
• Diffraction Imaging
• Scattering
• Protein Folding
1 cm
10 mm
Microwave
106 nanometers
=
~ 2.5 nm
10-4 m
0.1 mm
100 μm
10-5 m
0.01 mm
10 μm
Infrared
DNA, Proteins
10-3 m
Microworld
Neutrons:
• Plastics
• Medicine
• Magnets
• Manufacturing
• Environment
10-2 m
1,000 nanometers =
1 micrometer (μm)
Visible
10-6 m
0.1 μm
100 nm
Ultraviolet
Nanoworld
10-7 m
10-8 m
0.01 μm
10 nm
10-9 m
Soft x-ray
http://www.sns.gov/
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1 nanometer (nm)
10-10 m
0.1 nm
5
Why Brightness?
• Very short pulses ⇒ movies of reactions / processes
• More X-rays ⇒ ability to image single molecules
Bright secondary beams (X-rays / neutrons) require
high-quality primary beams (electrons / protons)
Typical requirements
1 nC, 1 ps, 1 μm emittance
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Measures of Beam Quality
1
mc
2
Phase space volume compactness
Emittance
εx,n =
Brightness
2I
Bn = 2
π ε x,nε y,n
Phase space density
Luminosity
N1
L=
N2 νrev
4πσ x σ yB
Reaction Rate at target
(composite measure)
Intensity
K
χ≡ 2 2
k 0R m
x
2
p
2
x
K≡
− xpx
2I
Io (βγ )
3
Dimensionless,
transport dynamics
K = Generalized perveance
space charge potential energy /
total kinetic energy
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Intensity Parameter Definition
external focusing
K
ε
Matched Beam
κ oR m =
+ 3
(Smooth Focusing)
Rm Rm
2
k 02a
Define intensity parameter
χ≡
K
space charge force
2 2 =
k 0R m
external force
Beam
Space charge + emittance
0 ≤ χ ≤1
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2a
K ε 2
+ 3
a a
Betatron tune depression:
ω
= 1− χ
ω0
Plasma frequency:
ωp
= 2χ
ω0
8
Plot frequencies vs. intensity parameter
χ≡
K
k 02Rm2
Plasma
kp
= 2χ
ko
1.5
Betatron
k
= 1− χ
ko
1
0.5
0
EmittanceDominated
Space-ChargeDominated
λD > Rm
λD < Rm
0
Rings
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M. Reiser, et al., PAC ’99.
0.5
χ
1
Sources
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Space Charge Effects – Cold Beams are Plasmas
χ = 0.21
EmittanceDominated
Space-Charge-Dominated
Halo
χ = 0.7 - 0.9
1 cm
Experiment
Z=17 cm
27 cm
35 cm
42 cm
50 cm
58 cm
66 cm
74 cm
Simulation
Bernal, Kishek, Haber, and Reiser, PRL, 82, 4002 (1999).
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Higher-order modes can result in nonlinear x-y coupling
χ = 0.98
SG
y
x
z
I. Hofmann, Phys. Rev. E, 57 (4), 4713 (1998).
Kishek, O’Shea, Reiser, Physical Review Letters, 85, 4514 (2000).
ε
4ε
rms
oscillation scale length ~ plasma wavelength
(mm-mr)
100
(a)
x
ε
y
50
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0
5s
(m ) 10
15
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New Paradigm: Quality Counts
beta*gamma
COST
V
V==electrons
electrons
1.E+06
ILC
O
O==protons
protons
Q
Q==heavy
heavyions
ions
XFEL
1.E+03
LHC
LCLS
Livingston Axis
15 MeV
Cornell ERL
Fermi
Booster
1.E+00
11, 6 MeV
SNS
UMER
HIF
1.E-03
Reiser Axis
0.0
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0.5
Intensity Parameter
1.0
COMPLEXITY 12
The University of Maryland Electron Ring (UMER)
Use 10 keV electrons to
inexpensively model
space charge effects in
other accelerators
3.7 m
Energy
Energy Spread
Current Range
10 keV
20 eV
0.6-100 mA
rmsIREAP
Emittance (n) 0.2-3 μm
Circulation time
Pulse length
Zero-Current Tune
200 ns
5-100 ns
7.6
Depressed Tune
1.5 – 6.5 13
UMER Magnets & Lattice
72 Quads
(~ 7.8 G/cm)
32 cm
36 Dipoles
(~ 15 G)
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UMER Multi-Turn: “Low-Current” Results
(Work in Progress)
Typical
BPM signals
for low current
060525 test2 : Beam Current Per Turn from BPM 2
8.
-4
6.
4.
1 mV/div
up to
125 turns
2.
500 ns/div
0.
0
50
100
time along pulse [ns]
Zero-current
Tune=7.3
Beam
Current
Estimated
Emittance*
Intensity
Parameter, χ
Tune Shift
Injected
690 μA
0.28 μm
0.21
0.80
After 25 turns
300 μA
0.23 μm
0.12
0.45
*rms, normalized
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S. Bernal, Proc. Advanced Accelerators Concepts Wkshp 2006.
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Multi-Turn: More Intense Space Charge
p
Beam Current (mA)
20
(Work in Progress)
15
up to
60 turns
10
05
0
500
Zero-current
Tune=7.3
1000
Time [ns]
1500
Injected
Beam
Current
18.6 mA
Estimated
Emittance *
1.2 μm
Intensity
Parameter, χ
0.70
After 9 turns
3.6 mA
0.5-1.25 μm
0.48-0.25
Tune Shift
3.3
2.0-0.9
*rms, normalized
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M. Walter, Proc. Advanced Accelerators Concepts Wkshp 2006.
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Next – the “Maryland Recipe”
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Step 1: Simulate
Two sets of coils at 45 deg
Quadrupoles with Electronically Adjustable Skewness
Exp. data
0.93o
Skew angle:
1.86o
2.79o
3.72o
4.66o
5.60o
χ = 0.98
Experiment
Simulation
Q1 is electronically rotated 3.720
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Step 2: Measure (6-D Phase-Space Mapping)
Longitudinal Phase-Space
Imagers:
– Fluorescent Screen Imagers
– Optical Transition Radiation
(OTR) Imagers
Y. Cui, et al, Rev
Sci Inst, 2004
E
Beam pickups:
– Capacitive Beam Position Monitors
– Bergoz Current Monitors
10-4 energy resolution
t
Phase-Space Mappers:
– Slit-slit (⊥)
– Pepper-pot (⊥)
– Retarding Potential Energy
Analyzers (//)
– Tomography (⊥)
High-Fidelity Tomography
RC3
y
x
y’
RC6
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D. Stratakis, R. Kishek, et al., to appear19
Step 3: Perturb (real beams are not perfect)
5200
Initial density modulation splits into slow and
fast wave, transforming to energy modulation
Energy (eV)
5150
At z = 0.64m
1.2
Laser induced perturbation
Normalized Current
0.8
0.6
0.4
0
0.2
100 ns
0
-0.2
-7
-1.5 10
-7
-1.0 10
Time
-8
-5.0 10
5100
5050
5000
4950
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WARP-RZ
Experiment
1-D Theory
40
60
80
100
Time (ns)
OTR Time-Resolved Images
0
0.0 10
-8
5.0 10
With perturbation
-7
1.0 10
Time (s)
At z=5.11m (RC6)
1.2
Peturbation splits into
fast and slow
space-charge waves
1
Normalized Current
Beam Current (normalized)
1
K. Tian, PRSTAB, 2006.
C. Tobin
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0.8
0.6
Without perturbation
0.4
0.2
0
-0.2
-7
-1.5 10
-1.0 10
-7
-5.0 10
-8
Time (s)
0.0
5.0 10
-8
1.0 10
-7
R. Fiorito
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New: Capability to produce pure energy modulations
20 ns
Converts to Current modulation
over 2 turns (RC7)
Beam Current (normalized)
9-ns energy pulse applied in
RC4 using induction module
Time
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200 ns
Time
B. Beaudoin
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Step 4: Control
• Linear Control
– Hui Li, Ph.D. 2004 (steering, matching, skew correction)
– Gang Bai
– Dr. Mark Walter
• Nonlinear Control
– Chao Wu, w/ Prof. Eyad Abed (ISR) –
Model Predictive Control
• Can we reverse perturbations?
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Step 5: Join Forces
• Usually expertise in accelerator physics tied to
particular machine
• Can learn much by interacting across boundaries
Ongoing collaborations:
• LBNL / LLNL / Princeton – Heavy Ion Fusion
• Ingo Hofmann – Ion Linacs / Rings
• Dave Dowell – SLAC FEL
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Chaos in Beams and Galaxies
X'
X
Court Bohn Henry Kandrup
(1953-2007)
(1954-2003)
X'
X
C. L. Bohn, in The Physics of High Brightness Beams, (WS, Singapore: 2000), p. 358.
R.A. Kishek, et al., PAC 2001, 151-153 (2001).
H.E. Kandrup, et al., Annals of the New York Academy of Sciences 1045, 12–33 (2005).
R.A. Kishek, et al., ibid., 45-54 (2005).
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Synergistic Research Directions for Cornell
• Space Charge Issues and Beam Quality, Halo
– ERL Injector and Linac
– ILC Damping Rings
• Portable items
– Some diagnostics (e.g. tomography)
– Use of controlled perturbations as a tool?
– Theoretical/Computational research
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Beam-Induced Multipactor – “Electron Cloud”
e-
+
Stray electrons, attracted by beam potential and accelerated to hit other
side of beam pipe, generate more secondaries.
Eventually a cloud develops that will break up trailing beam bunches
Limits on beam current
Can also develop in long bunch with slow fall time
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Electron Clouds
Of interest to a wide class of machines
–
–
–
–
ILC damping rings (positron)
Spallation Neutron Source Ring
LHC Upgrade
Heavy Ion Accelerators (e.g. GSI)
Specific items of interest:
– Theoretical modeling
– Low-energy electron diagnostics
(e.g. energy analyzer)
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Conclusion
• Intensity Parameter characterizes space charge forces in beam
• Intense beams exhibit plasma-like behavior / can carry waves
• Cornell ERL is extremely intense at the front end
• Beam in ILC damping rings has significant space charge
• Can benefit significantly from UMER experience
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I like to thank my colleagues …
University of Maryland Electron Ring (UMER) Team:
Patrick O’Shea
Martin Reiser
Rami Kishek
Irving Haber Brian
Beaudoin
Junior Scientists:
Santiago Bernal
Mark Walter
BryanQuinn
Bryan
Quinn
Brian Beaudoin
Graduate:
Gang Bai
Kai Tian
Donald
Dave
C Papadopoulos
Feldman
Sutter
Diktys Stratakis
Charles Tobin
Former:
Yun Zou
Jonathan
Neumann
Diktys
Stratakis
Yupeng
Cui
Hui Li
Yijie Huo
Santiago John
Martin
Harris
Renee Feldman
Don Feldman
Ralph Fiorito
Irving
Charles
Kai Tian
Henry FreundGang Bai
Haber
Tobin
Bernal
Terry F. Godlove
A. Shkvarunets
Mike Holloway
Kevin Jensen
Dave Gillingham
Mark
Christos
Patrick David
RamiDemske
Renee
Walter
Papadopoulos O’Shea
Kishek
Feldman
Nathan Moody
Terry
http://www.umer.umd.edu/
Godlove
Webmaster
Reiser
Ralph
Fiorito
Extras
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High Resolution Energy Analyzer
Retarding Mesh
Collimating Cylinder
Compact
10-4 energy resolution
1 mm spatial resolution
few ns time resolution
Y. Cui, et al, Rev
Sci Inst, 2004
E
Collector
Grounded Housing
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Generating Perturbations with Lasers
Beam Current
Electron Beam
Thermionic only, 100ns pulse
Heated
Photocathode
Drive
Laser
Photoemission +
Thermionic 5ns pulse
Photoemission only
(Cool cathode)
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