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The Heavy Ion Fusion Virtual National Laboratory
Neutralized Transport Experiment (NTX)
P. K. Roy, S. S. Yu, S. Eylon, E. Henestroza, A. Anders, F. M. Bieniosek, W. G. Greenway, W. L. Waldron, D. B.
Shuman, D. L. Vanecek, B. G. Logan, LBNLD. R. Welch, D. V. Rose, C. Thoma, MRC
R. C. Davidson, P. C. Efthimion, I. Kaganovich, E. P. Gilson, A. B. Sefkow, PPPL
W. M. Sharp, LLNL
15th International Symposium on Heavy Ion Inertial FusionPPPL, Princeton University, New Jersey, USA
June 7-11, 2004
The Heavy Ion Fusion Virtual National Laboratory
Overview
● Requirements of NTX for Driver
● NTX system and diagnostics
● Keys to a small spot
● Experimental results of neutralization.
● Sensitivity study
● Achievements/conclusion
The Heavy Ion Fusion Virtual National Laboratory
NTX and HIF Driver
The Heavy Ion Fusion Virtual National Laboratory
The HIF Driver Requires Beam Neutralization in Chamber Transport to Hit mm-sized Spot on Target
How and what Neutralized Chamber Transport can do:●Electrons from external source are entrained by the beam and neutralize the space charge sufficiently that the pulse focuses on the target in a nearly ballistic manner for a small spot.
●Present generation of drivers requires total of ~40 kA divided between perhaps hundred beams, each beam of 2 mm focal spot radius. Plasma Plug
(externally injected plasma)
Low pressure chamber (~ 10-3
Torr).
Final focus magnet
Target
Volumetric plasma
Convergingion beam
Chamber Wall
Driver needs:
Buncher Finalfocus
Chambertransport TargetIon source
& injector Accelerator
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Distance (cm)R
MS
Rad
ius
(cm
)
Perfect Neutralization
Vacuum
MEVVA Source
The Heavy Ion Fusion Virtual National Laboratory
Neutralized Transport Experiment (NTX) Addresses Driver-Relevant Issues
Final Focus Chamber Transport
Final focusmagnet
Magnetic-transport section Neutralization drift sectionBeam source
Cathode arcPlasma plug
RF plasma source
Diagnostic box
Quadrupoles
2.4 m 1 m
Source chamber
A schematic of the NTX beam line setup
●Perveance is the key parameter for final focus and neutralization
●NTX covers range of perveance relevant to the driver (K≤10-3).
The Heavy Ion Fusion Virtual National Laboratory
NTX System Setup and diagnostics Located at LBNL
GatedCamera
The Heavy Ion Fusion Virtual National Laboratory
Keys to a Small Spot
●Low source emittance
●Optimal convergence angle
Source of emittance growth:●Geometric Aberration●Magnetic transport mismatch
●Efficient neutralization—plasma plug—volume plasma
r
The Heavy Ion Fusion Virtual National Laboratory
Low emittance Source
The Heavy Ion Fusion Virtual National Laboratory
Extraction of Uniform High Brightness Beam from NTX Injector
Increased SourceTemperature (~185W)Aperturing
Sm
oo
th s
ou
rce
surf
ace
Unapertured beam
Lower Temperature source(~160w)
Uneven source
The Heavy Ion Fusion Virtual National Laboratory
Aperturing for High-brightness and High Perveance beam Designed by EGN code
EGN simulation of NTX diode &beam aperture
NTX beam scraper system
The Heavy Ion Fusion Virtual National Laboratory
NTX Provides low emittance beam (300kV, 25 mA, 2-cm aperture).
Slit-integrated density profile and (x, x’) phase space of a high-brightness apertured beam (300kV, 25 mA, 2-cm aperture).
The Heavy Ion Fusion Virtual National Laboratory
Magnetic final focus
The Heavy Ion Fusion Virtual National Laboratory
Magnetic Final Focus Transport
Final Focus Chamber Transport
Final focusmagnet
Magnetic-transport section Neutralization drift sectionBeam source
Cathode arcPlasma plug
RF plasma source
Diagnostic box
Quadrupoles
2.4 m 1 m
Source chamber
A schematic of the NTX beam line setup
●Perveance is the key parameter for final focus and neutralization
●NTX covers range of perveance relevant to the driver (K≤10-3).
The Heavy Ion Fusion Virtual National Laboratory
Good agreement between Experimental and Theoretical Beam profile at Entrance of Final Drift Section
Simulation
Experiment191keV
401keV
265 keV
283 keV
(1.5 mA beam, 5 mm initial radius, Ne ~ 1.2x1011/cm3, 20mm-20mr)
The Heavy Ion Fusion Virtual National Laboratory
Measured and Calculated Beam Profiles Agreed Well
265keV
283keV
Horizontal densityprofile
Vertical
Horizontal
Vertical
5mm diameter aperture, 265keV horizontal profile
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30000
40000
50000
60000
-30 -20 -10 0 10 20 30 40mm
Sli
t-in
teg
rate
d i
nte
ns
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Experimental Optical 040206021
Theoretical
5mm diameter aperture, 265keV vertical profile
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Experimental Optical 040206021
Theoretical
5mm diameter aperture, 283keV horizontal profile
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-30 -20 -10 0 10 20 30mm
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t-in
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Experim ental Optical 040206022
Theoretical
5mm diameter aperture, 283keV vertical profile
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-30 -20 -10 0 10 20 30mm
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t-in
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rate
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nte
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Experimental Optical 040206022
Theoretical
The Heavy Ion Fusion Virtual National Laboratory
Typical NTX Ion Beam is Focused to the Final Drift Section for Neutralization (24 mA Beam Current)
0
5
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30
230 250 270 290 310 330
Beam energy (keV)
Beam
cur
rent
(mA)
Data on040513&14
Experimental results and simulations of NTX beam profile and phase-space distribution at exit of channel
The Heavy Ion Fusion Virtual National Laboratory
Neutralized drift
The Heavy Ion Fusion Virtual National Laboratory
LSP predicted Neutralized Reduces Beam Spot
No neutralization 1.5 cm
Plasma Plug 1.4 mm Plasma Plug + Volume 1 mm
300 keV, 25 mA, 0.1 pi-mm-mrad, K+ beam
The Heavy Ion Fusion Virtual National Laboratory
Unexpected Partial Beam Neutralization in the Final Drift Section was controlled by a Radial Bias Mesh
6 inch pipe 3 inch pipeUnwanted neutralization for “vacuum”
propagation in small pipe
Mesh
Drift tubeInner wall
Ion beam
-35
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-25
-20
-15
-10
-5
0
5
-800 -400 0 400 800 1200 1600
Mesh voltage (V)
Cu
rre
nt
(mA
)
Electron current collected in the radial mesh
Radial mesh suppresses beam-Generated secondary electron
Final focusmagnet
Magnetic-transport section Neutralization drift sectionBeam source
Cathode arcPlasma plug
RF plasma source
Diagnostic box
Quadrupoles
2.4 m 1 m
Source chamber
Phase IIIPhase IIPhase I
The Heavy Ion Fusion Virtual National Laboratory
Electron Suppression provided beam for controlled Neutralization
Simulation
Experiment 6 inch pipe
Experiment 3 inch pipe
Mesh (+1kV)
260 – 300keV
The Heavy Ion Fusion Virtual National Laboratory
MEVVA Plasma Plug and RF Volume Plasma Source Neutralized Ion Beam for Small Spot Size
MEVVA plug
RFPlasma system
1 m
Cathode-arcPlasma sourceplasma plug
RF plasmasource
0.52 m
Diagnostic
a) b)
c)
Neutralization drift section
The Heavy Ion Fusion Virtual National Laboratory
High Density Plasma Obtained from MEVVA Plasma plug and RF Plasma (~1011 cm-3)
Argon Plasma3.7<t<4.0mSN>1011 cm-3
P<10-5 Torr
Neutral Pressure and RF Plasma DensityEach point on the IV characteristic for MEVVA plug.
The ion saturation current is used for plasma density.
Density~1011 cm-3
The Heavy Ion Fusion Virtual National Laboratory
Reduction of Spot Size Using Plasma Plug & Volume Plasma (24 mA beam, 20 mm initial radius)
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X(mm)
Mesh+250,31002060
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X(mm)
MEVVA30813016
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X(mm)
MEVVA & RF30813010
FWHM: 2.71 cm FWHM: 2.83 mm FWHM: 2.14 mm
Non-neutralized transport
Effect of plasma plugon spot size
Effect of plasma plug and volume plasma on spot size
The Heavy Ion Fusion Virtual National Laboratory
100% Current Transmission Through Neutralized Drift Section (24 mA Beam)
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15
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25
235 255 275 295
Beam energy (kV)
Be
am
cu
rre
nt
(mA
) At exit, no plasmaAt exit, with plasmaAt entrance
The Heavy Ion Fusion Virtual National Laboratory
*Image taken after pinhole sample has drifted 1 meter
Vertical Pinhole Scan
Full 2-D Pinhole Scan
7 mm
Pinhole scan at Entrance to Neutralization* and Neutralized beam (6 mA beam, Ne ~ 2x1011/cm3)
Neutralized beam
rms size ~ 1.0 mm
rms size ~ 1.4 mm
Plasma density ~ 2x1011/cm3
Movable Pinhole Measurements of 4-D Phase Space
The Heavy Ion Fusion Virtual National Laboratory
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0 0.5 1 1.5 2 2.5 3 3.5
FLU
ENC
E (a
.u.)
R(mm)
Beam profile at focal plane for three neutralization methods(6 mA beam, 10mm initial radius)
MEASUREMENT
SIMULATIONS
With plasma plugWith plasma plugand RF Plasma 100% neutralization
MEVVA ONLY
100% neutralized
MEVVA and RF
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FLU
ENC
E (a
.u.)
R(mm)
Fluence
MEVVA ONLY
100% neutralized
MEVVA and RF
The Heavy Ion Fusion Virtual National Laboratory
Sensitivity Study: Beam Spot Size Dependency on Convergence Angle
0
0.5
1
1.5
2
2.5
3
0 5 10 15 20 25
Convergence angle (mrad)S
pot r
adiu
s (m
m)
Non neutralized beam radius as a function of convergence angle calculated using WARP code
Measured neutralized beam radius as a function of convergence angle
at the end of final focus
The Heavy Ion Fusion Virtual National Laboratory
Sensitivity Study of Neutralization
0
1
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6
0 0.5 1 1.5 2 2.5
MEVVA discharge voltage (keV)
Be
am
ra
diu
s (
mm
)
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Axial distance (cm)
Be
am
ra
diu
s (
mm
)
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3.5
242 247 252 257 262Beam energy (keV)
Be
am
ra
diu
s (
mm
)
Head to tail variationVariation with beam energy
Beam envelope variation with axial position
Beam envelope variation with plasma discharge voltage
The Heavy Ion Fusion Virtual National Laboratory
Summary
●We have completed a detailed study of neutralized final transport.
● The experimental results are in good agreement with simulations.
● The NTX experiments have significantly increased our confidence for a variable driver final focused scenario.