Beam - GAPS

Intense Space Charge Effects of Relevance to
FEL Injectors
Rami A. Kishek
Institute for Research in Electronics & Applied Physics
University of Maryland, College Park, MD, USA
Coauthors:
B. Beaudoin, S. Bernal, M. Cornacchia, D. Feldman, R. Fiorito,
K. Fiuza, I. Haber, T. Koeth, P.G. O’Shea, C. Papadopoulos,
M. Reiser, D. Sutter, and J.C.T. Thangaraj
Acknowledgments:
A. Friedman, D. Grote, S.M. Lund, and J-L Vay,
for providing us with WARP
Research sponsored by US DOE & DOD ONR
1
Outline
1. Introduction: Transverse and Longitudinal Space Charge
2. University of Maryland Electron Ring (UMER)
3. Longitudinal Dynamics: Confinement, and Modulation Studies
4. Halo Studies
5. Future Directions
Invited Talk – D. Stratakis (Tuesday)
WG2 Talks
B. Beaudoin
T. Koeth
J.C.T. Thangaraj
2
Motivation : High Quality Beams
Quality of Injected beam impacts subsequent behavior
•
Halo
•
Longitudinal Modulation
•
Phase-Space Dilution
Cathode drive-laser
Einj
Injector
E-gun
Linac
180o Bend
Acc-Dec
Acc-Dec
E2
E0
E0
Cavity mirror
Edump
Undulator
180o Bend
E0 -Δfel
Cavity mirror
Δfel
E-beam dump
Relevance: X-ray FELs, High average power FELs and ERLs,
also proton and ion machines.
3
Graphic Credits: Adapted from Dinh Nguyen
Space Charge Physics
Transverse
external focusing
k 02a
2a
Beam
Longitudinal
Space charge force in
ellipsoidal bunch:
2
⎛c ⎞
2⎜ s ⎟ z ,
⎝ βc ⎠
K ε 2
+ 3
a a
qgλ o
c =
4πεo γ 5om
2
s
Space charge + emittance
χ=
1
βγIo ⎛ εn ⎞
1+
2I ⎜⎝ a ⎟⎠
2
At exit of LCLS Injector, χ > 0.9
4
Cause
Intense Beam at
Source – Space
Charge
Effect
Beam Halo
Radiation;
Structural Damage
Degraded
Performance
Modulations +
Bends
Emittance
Growth
Lower Brightness
at Undulator
5
UMER – A scaled experiment using low energy electrons
Energy
10 keV
Current
0.5-100 mA
rms Emittance 0.5 - 3 μm
100 ns
~ 5.75 m
3.7 m
5 ns
~ 30 cm
6
UMER Beams
Aperture Wheel inside gun:
can be rotated to select beam
σo = 66.0°
I
εn,rms
aave
[mA]
[μm]
[mm]
0.6
0.4
1.6
0.28
6.0
1.3
3.4
0.61
21
1.5
5.2
0.90
78
3.0
9.6
0.97
104
3.2
11.1
0.98
χ
7
UMER Layout
B
Velocity/energy
Perturbation
Induction Cell
ea
m
Density/current
Perturbation
Cathode Grid
Or Drive
Laser
Wall-Current
Monitor
8
Present Operational Status
5
Wall current
monitor
mA)
Medium-current
beam:
6 signal
mA (7(χ=0.61)
signal from RC10 wall-current monitor
σo ≅ 66.0°
σ/σo = 0.62
Steering solution: dated 080325
Steering solution: current
Wall current monitor signal (mV)
0
-5
-10
-15
-20
-25
up to 50 turns
-30
0
200
400
600
800
1000 1200
time(ns)
1 Turn = 6.6 λβo = 6 λp = 36 periods
1400
1600
Longitudinal
Edge Erosion
1800
2000
9
Chao Wu
Resonance Studies: Variation of Operating Point
Beam Current at RC10 - Restored Baseline
8.0
5th-Turn Current Ratios
7.0
ν0Y
6.0
5.0
5.0
8.0
First Turn
6.0
ν0X
7.0
8.0
23rd turn
6.0 mA, 10.00 keV
see Talk by Tim Koeth, WG2
ν0Y
7.0
6.0
5.0
B. Beaudoin, S. Bernal, T. Koeth
10th-Turn
ν0X
10
Longitudinal Dynamics: Focusing and Waves
11
E.g., Longitudinal Edge Erosion of UMER Beam
RC10 Wall Current Monitor
23rd turn
Eroding Beam Edges
6 mA
Turns
Injected Turn
B. Beaudoin, 2009
12
Application of Longitudinal Focusing
see Talk by Brian Beaudoin, WG2
Low-current beam 0.6 mA (χ = 0.28; σ/σo = 0.85)
Focusing Shuts off
Brian Beaudoin
Magnet Pulsers Shut off
400 turns; 2,640 λβo; 1,960 λp ; 14,400 lattice periods13
Longitudinal End Expansion – Effect on Beam
WARP simulation
prediction
Beam Current
R. Kishek
14
Z
WARP Modeling of Beam End Erosion and Re-bunching
Detector measures only peak-to-peak current
Experiment
WARP
Simulation
see Talk by Tim Koeth, WG2
Measurement of DC current
Irv Haber, Brian Beaudoin
15
Deliberate Modulation of Beam Density on UMER
BeamAtCurrent
z = 0.64m
At z=5.11m (RC6)
1.2
1.2
Laser induced perturbation
1
0.8
Normalized Current
0.6
0.4
100 ns
0.2
0
-0.2
-7
-1.5 10
0.8
0.6
0.4
0.2
0
-7
-1.0 10
-8
-5.0 10
0.0 10
0
5.0 10
-8
-7
1.0 10
-0.2
-7
-1.5 10
-1.0 10
-7
-5.0 10
Time (s)
-8
0.0
5.0 10
-8
1.0 10
-7
Time (s)
5200
5150
Energy (eV)
Normalized Current
1
Peturbation splits into
fast and slow
space-charge waves
Beam
Energy
5100
5050
5000
0
4950
20
WARP-RZ
Experiment
1-D Theory
40
60
Time (ns)
80
100
16
Multi-turn Transport of Space Charge Waves
17
Deliberate Modulation of Beam Energy on UMER
Apply induction pulse in the middle of the beam bunch
Compact induction module
2.59 cm
Modulator
Gap Potential
4.55 cm
e- bunch
Ez
9.65 cm
Beam pipe
Ceramic gap
18
Observation of Solitons on the UMER Beam
talk by J. Charles Tobin, WG2
2.5ns
19
Beam Halo Studies
Beam Image from
Phosphor screen
Color-coded to
enhance halo
Halo Particles
20
Halo Studies
Investment in Halo Diagnostics
– Fast imaging (~ 3 ns resolution)
– Tomographic Phase Space Mapping
– Optical Masking of Beam Core using Digital Micromirror Array
Simulation Studies using WARP
– Halo Origin, Collimation, and Regeneration
see Ph.D. thesis
Christos Papadopoulos
21
Tomographic Phase Space Mapping
Invited talk by Diktys Stratakis, Tuesday 11:30 AM
Lens
Experiment
Screen
RC3
y
x
y’
RC6
RC9
Projected / Slice, using Quadrupoles / Solenoids
with Space Charge
22
Simulations: Can identify halo particles
X-Y
R-R’
X’-Y’
Z=0m
Z = 100 m
Papadopoulos, et al.,
to be published
Particles in red: have been in the halo
23
Ideal “Surgical” Aperturing
Z=0m
X’-Y’
Eliminate all particles
that will ever be in halo
X-Y
R-R’
Z = 100 m
Papadopoulos, et al.,
to be published
Phase Mixing: New particles re-form halo
(unless mismatch stabilized)
24
WARP Simulation of Halo from Source
R’
Halo Particles
< 2007
23 mA
d = 0.5 mm
2008
d = 0.1 mm
23 mA
R
d
Grid
K
Haber, et al.,
NIM-A 606, 64 (2009).
25
Future Directions and Plans
• Extend Longitudinal Focusing to Higher-Current Beams
– Higher rep-rate modulator completed
• Continue Modulation Studies
• Halo experiments
• UMER Space Charge Mini-Workshop – Oct 15, 2009
http://www.umer.umd.edu/events_folder/Workshop09/
26
Conclusion
• UMER a unique platform for studies of beam dynamics relevant
to FEL injectors
• Propagated low-energy, high-current beams for long distances
• Studies of longitudinal focusing and modulation ongoing
• Have a wealth of diagnostics for halo studies.
Invited Talk – D. Stratakis (Tuesday)
WG2 Talks
B. Beaudoin
T. Koeth
J.C.T. Thangaraj
27