energy analyzersenergy analyzers june 26, 2008june 26, 2008uspas.fnal.gov/materials/08umd/energy...
TRANSCRIPT
1
Energy AnalyzersEnergy AnalyzersJune 26, 2008June 26, 2008
USPAS - Summer 2008
Rami Kishek
2
PresentationsPresentations
Sources Carlos Maidana
Beam Monitors Matt Hodek
Imaging Tiago Silva
Tomography
Solenoid Jamie Blowers
Rotating Coil Ed Nissen
Longitudinal Dynamics
Energy Analyzer Yingjie Li
Tune Measurements Adam Lichtl
Resonances Finn O’Shea
Friday, 6/27, 9:30 AM - NOON ANNAPOLIS (Breakfast Room)10 min each, including questions (recommend 5 slides)
3
MotivationMotivation
Particle velocity affects its response to a given field
Lenses:– Chromatic effects, ability to focus
Bends:– Dispersion (different trajectories for different energy particles)
– Energy modulations ⇒ beam bunching
⇒ Coherent Synchrotron Radiation
Goal: Map the Energy Distribution – Longitudinal Phase-space
4
OutlineOutline
1. Measuring the Energy Distribution
2. High-Resolution Retarding Potential Energy Analyzer
3. Operation and Data-Processing
4. Space Charge Effects in EA
5. Outline of Experiment
5
Dipoles and DispersionDipoles and Dispersion
B
F = qvxB
Sector Magnet
Ro
α
l
2
o
vm qvBR
γ = R =αl
mcBq
γβ α=
l
E.g., for UMER:
βγ = 0.20mc2 = 511,000 eVq = -eleff = 3.85 cmα = 10° = 0.174 rad
B = 15.4 Gauss
Rigidity of UMER beam = [Bρ] = B*l/α = 340 G-cm/rad
6
Measuring the Energy Distribution Measuring the Energy Distribution –– part 1part 1
Bend radius depends on momentum
mc PRqB qB
γβ= =
Δx
Pr > Pb
oo
PR RPΔ
Δ =Can easily show:
x RΔ ≈ Δ
What about transverse displacement?
In sector dipole with uniform field:
Exploit dispersion! - “mass spectrometer”
Highest sensitivity for 180° angle (Δx = 2 ΔR)
Tradeoff between size and sensitivity
ScreenCollector
oo
x 2RP PΔ
=Δ
Tends to be large, but can handle high-energy beams, high resolution
7
Measuring the Energy Distribution Measuring the Energy Distribution –– part 2part 2
Want compact device ⇒ Retarding Potential Energy Analyzer
Parallel-Plate Design
Structure of a parallel-plate energy analyzerH. Suk, Ph.D. dissertation
Pinhole Collector
Beam
HV Retarding Mesh
For ions: ElectronSuppression
An “inverse gun”
8
Correlated and Uncorrelated Momentum SpreadCorrelated and Uncorrelated Momentum Spread
Typical beam
Correlated Longitudinal Velocity Spread
Laminar Beam (Ideal)
Energy spread (random)
9
Transverse expansion of beam causes apparently larger energy spread.
Monoenergetic electron Beam
5° angular spread
Grounding PlateHigh Voltage Plate
Collector
Energy Resolution Not Good (20 eV / 10 keV)
ParallelParallel--Plate EA ProblemPlate EA Problem
Credits: Yun Zou, SimIon simulation
10
Equipotential lines
Particle trajectories
Curved equipotential lines collimate beam, so particles with tilted trajectories can overcome the retarding potential.
Credits: Yun Zou, SimIon simulation
HighHigh--Resolution Energy Spread MeasurementsResolution Energy Spread Measurements
Monoenergetic electron Beam
5° angular spread
Collimating CylinderRetarding
Mesh
Collector
GroundedHousing
2nd Generation ~ 8 eV Resolution
11
High Voltage Input Pins
Steel Washer
Collector
Ground ShieldingHigh Voltage Cylinder
Insulating Material
Signal OutputElectron Beam
Retarding Mesh
-10130 V -9999.5 V
Equipotential lines
Particle Trajectories
Spatial resolution: ~1 mm, Time resolution: ~ few ns
Relative energy resolution: < 10-4
Credits: Cui Yupeng
33rdrd--Generation Device SchematicsGeneration Device Schematics
12
Resolution ComparisonResolution Comparison
Credits: Yun Zou and Yupeng Cui, SimIon simulation
Simulated energy spread measurement for monoenergetic beamwith initial divergence angle of 5°
13
References for Further StudyReferences for Further Study
• Y. Cui, Y. Zou, A. Valfells, M. Walter, I. Haber, R.A. Kishek, S. Bernal, M. Reiser, and P.G. O'Shea, "Design and Operation of a Retarding Field Energy Analyzer with Variable Focusing for Space-Charge Dominated Electron Beams," Review of Scientific Instruments 75(8), 2736 (2004).
• Y. Zou, Y. Cui, V. Yun, A. Valfells, R.A. Kishek, S. Bernal, I. Haber, M. Reiser, P.G. O'Shea, and J.G. Wang, "Compact high-resolution retarding field energy analyzer for space-charge-dominated electron beams," Physical Review Special Topics - Accelerators & Beams 5, 072801 (2002).
• Cui Yupeng, Ph.D. thesis:
http://hdl.handle.net/1903/1889
14Credits: Zou, Cui, Stratakis and Tian
Energy Analyzer and LSE Test SetupEnergy Analyzer and LSE Test Setup
S1 S2
GunAperture
Energy Analyzer Screen
Bergoz coil
Electron Gun
First SecondSolenoid Solenoid
Third Solenoid
Energy Analyzer
Diagnostic Chamber
Linear and Rotation Feedthrough
15
Electrical SchematicsElectrical Schematics
16
Operation and DataOperation and Data--ProcessingProcessing
• Computer Automation:– C++ program
– fine steps on retarding potential (~ 0.1 eV)
– much faster acquisition
• Computerized Processing– MATLAB interface
17
Data Acquisition InterfaceData Acquisition Interface
Typical Signal
Credits: Yun Zou and Yupeng Cui, Experimental Measurement
18
Typical Collector Signals at Different Retarding VoltagesTypical Collector Signals at Different Retarding Voltages
(1) ΔV= 0 V(2) ΔV= 1 V(3) ΔV= 2 V(4) ΔV= 6 V(5) ΔV= 16 V(6) ΔV= 20 V
-300
-200
-100
0
100
-20 0 20 40 60 80 100 120 140
Ene
rgy
Ana
lyze
r Sig
nal(m
V)
Time(ns)
(1)
(2)
(3)(4)
(5)
(6)
Credits: Yun Zou and Yupeng Cui, Experimental Measurement
19
Measured Energy Spectrum at one point in time (60 ns)Measured Energy Spectrum at one point in time (60 ns)
Measured beam energy spectrum
Mean Beam Energy
Energy Spread
Credits: Yun Zou and Yupeng Cui, Experimental Measurement
20
Mean Energy as a function of Time along the PulseMean Energy as a function of Time along the Pulse
Beam Energy : 5 keV, Location: 25 cm from anode
4600
4700
4800
4900
5000
5100
5200
5300
5400
0 20 40 60 80 100
Bea
m E
nerg
y (e
V)
Time (ns)
Mean energy along the pulse
Zoom in
5066
5068
5070
5072
5074
5076
30 40 50 60 70 80 90 100
Bea
m E
nerg
y (e
V)
Time (ns)
Gun grid pulse
Measured mean energy
Beam head Beam tail
Credits: Yun Zou and Yupeng Cui, Experimental Measurement
21
Energy Spread as a function of timeEnergy Spread as a function of time
Beam Energy : 5 keV, Sampled position: 60 ns
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
5050 5060 5070 5080 5090
Rel
ativ
e P
artic
le D
ensi
ty
Retarding Voltage (V)
Beam current: 135 mAEnergy spread: 2.1 eV
Beam current: 13 mAEnergy spread: 1.7 eV
0
5
10
15
20
25
0 20 40 60 80 100
Ene
rgy
Spr
ead
(eV
)
Time (ns)
0
5
10
15
20
25
0 20 40 60 80 100
Bea
m E
nerg
y S
prea
d (e
V)
Time(ns)
Beam current: 135 mA Beam current: 13 mA
Energy spread along the pulse (time resolved)
Credits: Yun Zou and Yupeng Cui, Experimental Measurement
22
Longitudinal PhaseLongitudinal Phase--Space MappingSpace Mapping
Credits: Yun Zou and Yupeng Cui, Experimental Measurement
23
Space Charge Effects in the HighSpace Charge Effects in the High--Resolution AnalyzerResolution Analyzer
WARP Simulation (RZ):
Higher current density leads tocomplex space charge effects inside EA
Space charges causes faster beam expansion, affecting collected signal
(virtual cathode)
Returning particles affect incoming particles –time-dependence
Credits: Yupeng Cui and Rami Kishek
24
11--D model of virtual cathodeD model of virtual cathode
Credits: Yun Zou
Va
Vr
Xm dr
Region I Region II
J0 pJ0
(1-p)J0
Can derive limiting current to minimize sc effect2 3/ 2
lim 2
43 4
a
r
VJCd
⎛ ⎞= ⎜ ⎟⎝ ⎠
(Child-Langmuir Law)
25
ReferencesReferences
• Y. Zou, Y. Cui, I. Haber, M. Reiser, and P.G. O'Shea, "Longitudinal space-charge effects in a retarding field energy analyzer," Physical Review Special Topics - Accelerators & Beams 6, 112801 (2003).
26
Outline of ExperimentOutline of Experiment
1. Examine Collector Signal
2. Do coarse scan of retarding potential, manually
3. Run automated program to collect and then process EA data
– mean beam energy vs. time
– energy vs. time
– energy distribution at middle of beam pulse