Ion Source and Injector Experiments at the HIF/VNL
description
Transcript of Ion Source and Injector Experiments at the HIF/VNL
The Heavy Ion Fusion Virtual National Laboratory
Ion Source and Injector Experiments at the HIF/VNL
J. W. Kwan, D. Baca, E. Henestroza, J. Kapica, F. M. Bieniosek, W.L. Waldron, J.-L. Vay, S. Yu, LBNL
G.A. Westenskow, D. P. Grote, E. Halaxa, LLNLI. Haber, Univ. of Maryland
L. Grisham, PPPL
HIF Symposium, Princeton, NJJune 7, 2004
The Heavy Ion Fusion Virtual National Laboratory
This talk is dedicated to the amazing Cicada
In the hope that the HIF symposium 2021, Princeton, NJ
will tell the story of heavy ion beams achieving fusion
The Heavy Ion Fusion Virtual National Laboratory
A summary of main experiments
Experiment Purpose Facility
Large diameter ion diode
Study large beam optics and benchmark simulation
STS-500
RF plasma source
Prepare source for Merging Beamlets
STS-100
Merging Beamlets
High average current density (J) injector
STS-500
Negative ions Check if Cl- is applicable for HIF
STS-100
Accel-decel injection
High line charge density () beam for solenoid focusing
NDCX
Al-Si source development
Long and short pulse length for special applications
STS-50
The Heavy Ion Fusion Virtual National Laboratory
Experiments on STS-500 to study beam optics
500 kV, 17 s pulse, 1.0 s rise time
The Heavy Ion Fusion Virtual National Laboratory
Experimental Apparatus
10-cm diameter K+ Al-Si source with Pierce electrode
For Beam Imaging, use:
Kapton
100 m Alumina scintillatorFaraday cup with electron suppressor using a honeycomb bottom
Slit scanners: 2 mils, 17.8 cm apart
The Heavy Ion Fusion Virtual National Laboratory
Warp simulations
Good agreement between experimental results and simulation predictions
Experimental results
150 kV48A heater
Emittance taken here
10 cm source, 21 cm diode gap,Space charge limited mode
2/3
2/351044.0
AVP
The Heavy Ion Fusion Virtual National Laboratory
The emission-limited under-dense beam did not show much aberration
The Heavy Ion Fusion Virtual National Laboratory
5.0 cm aperture
Aperturing the large beam7.5 cm aperture
aperture
Aperture Beam fraction
Norm. emittance
Brightness ratio
None 100% 0.60 17.5 cm 55% 0.152 8.65.0 cm 25% 0.048 39
Brightness comparison
The Heavy Ion Fusion Virtual National Laboratory
The apertured beam showed no aberrations
Optical image from the alumina scintillator taken with a gated camera
-100
-50
0
50
100
0 0.5 1
Normalized intensity
posi
tion
[mm
]
Integrated current density profile (compares to a slit cup measurement)
7.5 cm aperture
The Heavy Ion Fusion Virtual National Laboratory
Red--expt. data;black--simulation
Time-dependent adaptive-mesh simulation shows how to achieve a fast rise time
Current at Faraday cup
• The current pulse rises faster than the applied voltage pulse.
• Capacitive coupling softens the signal rise time.
• One dimensional theoretical model:
• Example: 50ns/350ns
Applied Diode Voltage
3/ 242 2 2( ) 4
9 27p p
qe qeJ JV t dt t
A m A m
The Heavy Ion Fusion Virtual National Laboratory
Merging high density beamlets is an innovative approach to build compact multi-beam HIF injector
x-z
y-z
• Achieve high current, and high average current density
• Minimize the injector and matching section size for a compact multi-beam HIF driver system
WARP-3D simulation to study emittance growth
39.9 m
0.5 m past column 1.9 m
4.1 m
91 beamlets (each semi-Gaussian, 0.006 A, 0.003 π-mm-mrad, 160k particles), 1.2-1.6 MeV, 1024x1024, 1 cm/step
After the beamlets are merged, the emittances settle down at about 1.0 pi-mm-mrad.
Emittance is optimized if the number of beamlets is large and the beamlets are slight converging, but only weakly dependent on the emittance of each beamlet.
4.1 m1.9 m
Configuration Phase
The Heavy Ion Fusion Virtual National Laboratory
Testing Plasma Source on STS-100
RF-driven 26 cm diam. multi-cusp source inside ceramic insulator
500s, 20kW, ~ 10 MHz Compact RF oscillator
The Heavy Ion Fusion Virtual National Laboratory
Characterization of the RF plasma source
18 kW of 13 MHz RF,multicusp Argon plasma source at optimum pressure of 2 mTorr
Multi-aperture extracts61 beamlets at 100 mA/cm2 using high gradient insulator
Einzel lens to focus beamlets and examine charge exchange loss
The Heavy Ion Fusion Virtual National Laboratory
RF plasma source beamlets results
020924
0
0.2
0.4
0.6
0.8
1
8 13 18RF power (kW)
Ar 3+
Ar 2+
Ar 1+
030117
0.00
1.00
2.00
3.00
4.00
5.00
6.00
0.00 5.00 10.00 15.00 20.00 25.00
RF drive (kW)
80kV70kV60kV50kV40kV
Achieve 100 mA/cm2
0.000
0.005
0.010
0.015
0.020
47 47.5 48 48.5 49 49.5 50 50.5Beam Energy (kV)
20ms
16ms
12ms
8ms
4ms
90% Ar+
< 0.5% low energy componentElectrostatic energy analyser
The Heavy Ion Fusion Virtual National Laboratory
Full Gradient test on STS-500 will begin this month
This experiment will confirm full current density, its uniformity, and voltage gradient across vacuum gap.
The Heavy Ion Fusion Virtual National Laboratory
Merging Beamlets test will begin in September
Apparatus is full scale in dimension, but1/4 scale in voltage,so 1/8 in current.
The experiment will study emittance growth physics, beam matching parameters, and beam halos.
Success in this experiment will establish the basis for building a (future) driver-scale injector.
The Heavy Ion Fusion Virtual National Laboratory
Negative ion beams is an innovative idea in response to the gas and electrons problem
Avoid the problem of electrons being trapped in positive ion beams
No charge exchange problem to cause energy dispersion
Low ion temperature for both negative and positive halogen ions
Can be efficiently converted to atomic neutrals by laser photo-detachment, if this can be of advantage to the final focusing at the fusion chamber.
The Heavy Ion Fusion Virtual National Laboratory
Negative ion sources for HIF Drivers
0.94
0.96
0.98
1
1.02
1.04
1.06
10 15 20 25 30 35
Source pressure (mTorr)
Ion
curr
ent (
mA
)
0
10
20
30
40
50
60
70
80
Elec
tron
curr
ent (
mA)
Cl-
electron
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 3 6 9 12 15 18
Extraction voltage (kV)
Ion
curr
ent (
mA)
012345678910
Elec
tron
curr
ent (
mA)
Cl-Cl+electron
We have already demonstrated 45 mA/cm2 of pure Cl- ions with relatively low co-extracted electrons (7:1) from a single aperture.
Current density scaled almost linearly with RF power (12.56 MHz).
Current density of Cl+ ~ 1.3 x Cl-.
A new experiment will run on STS-100 this summer to examine the negative ion production from a large source, measure emittance, and form an array of beamlets.
The Heavy Ion Fusion Virtual National Laboratory
At 3.3 mC/m, the HEDP is > 10x the present HCX experiment.
Longitudinal emittance can coupling to transverse emittance
Possible compression limit when the bunch’s forward kinetic energy becomes comparable to the beam potential.
30kV -350kV 0V
Solenoid
Ion Source
The accel-decel injector is an innovation to meet our HEDP challenge: build a low energy high current driver to hit target
• In an accel-decel injector, a long pulse is compressed when decelerates into a solenoid, the Super-High (line charge density) bunch is then accelerated without expansion.
= I/vThe situation is similar to loading passengers into a roller coaster train.
10A x 100ns= 0.3m x 3.3 C/m
The Heavy Ion Fusion Virtual National Laboratory
0
0.01
0.02
0 0.2 0.4 0.6 0.8 1 1.2
0
0.01
0.02
00.050.10.150.20.250.30.350.4
60 cm solenoid located 5 cm from ground plate(winding:7.7cm ID, 9.2 cm OD,1 Mega Amp-Turn)
Bz/100(Tesla)
30 kV 0 kV-220 kV -35 kV -55 kV
A proof-of-principle Super-High experiment
K+ Gun (using Al-Si source)
E.H.20.MAY.04
NDCX-1
The Heavy Ion Fusion Virtual National Laboratory
Conclusion
Several ion source/injector experiments at the HIF/VNL are aimed at:-- supporting on-going HIF needs, -- developing future HIF driver, -- innovative concepts (high J, high , fast rise,
negative ions) In response to funding difficulty, the injector test
facility at LLNL is scheduled to terminate in March 2004.
We hope STS-100 can be moved to LBNL to continue ion source development.
The Heavy Ion Fusion Virtual National Laboratory
What is unchanged is the constantly changing direction.
What is certain is the permanently uncertain state.
After Thought