Download - NDCX beam experiments and plans Peter Seidl Lawrence Berkeley National Laboratory, HIFS-VNL
The Heavy Ion Fusion Virtual National Laboratory 1
NDCX beam experiments and plans Peter Seidl
Lawrence Berkeley National Laboratory, HIFS-VNL
11th Japan - US Workshop
December 18, 2008Berkeley, USA
…with A. Anders1, J.J. Barnard2, F.M. Bieniosek1, J. Calanog1,3, A.X. Chen1,3, R.H. Cohen2, J.E. Coleman1,3, M. Dorf4, E.P. Gilson4, D.P. Grote2, J.Y. Jung1, I. Kaganovich4, M. Leitner1, S.M. Lidia1, B.G. Logan1, S. Markadis1, P. Ni1, P.K. Roy1, K. Van den Bogert1,
J.L. Vay1, W.L. Waldron1, D.R. Welch5 1Lawrence Berkeley National Laboratory2Lawrence Livermore National laboratory
3University of California, Berkeley4Princeton Plasma Physics Laboratory
5Voss Scientific, Albuquerque
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Beam requirements
Method: bunching and transverse focusing
Beam diagnostics
Recent progress: longitudinal phase space measured
simultaneous transverse focusing and longitudinal compression
enhanced plasma density in the path of the beam
Next steps toward higher beam intensity & target experimentsgreater axial compression via a longer-duration velocity ramp
time-dependent focusing elements to correct chromatic aberrations
Outline
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Explore warm dense matter (high energy density) physics by heating targets uniformly with heavy ion beamsNear term: planar targets predicted to reach T ≈ 0.2 eV for two-phase studies. Assumptions for Hydra simulation: E = 350 keV, K+, Ibeam = 1 A (40X compression) tbeam = 2ns FWHM rbeam = 0.5 mm, E = 0.1 J/cm2 Etotal = 0.8 mJ, Qbeam = 2.3 nC
Later, for uniformity, experiments at the Bragg peak using Lithium ions
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Approach: High-intensity in a short pulse via beam bunching and transverse focusing
The time-dependent velocity ramp, v(t), that compresses the beam at a downstream distance L.
Velocity ramp:
€
v(t) =v(0)
(1 − v(0)t /L)Induction bunching module (IBM) voltage waveform:
€
V(t) =1
2mv2 (t) − φo , (eο = ion kinetic energy.)
2
2 Lp
L
kTLt
v M=
0
5
10
15
20
25
30
35
303 304 305 306 307
Energy (keV)
Intensity (Arb. units)
FWHM keV 0.30σE keV 0.13Tz eV 2.6 -02E
Measured energy spread is adequate for ~ns bunches.
Energy analyzer, unbunched beam
IBM voltage waveformModel vs experiment
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Neutralized Drift Compression Experiment (NDCX) with new steering dipoles, target chamber, more diagnostics and upgraded plasma sources
Injector
Target chamber, beam
diagnostics,FCAPS
Matching solenoids& dipoles
Focusing solenoid
IBM & FEPS
Beam diagnostics
New: steering dipoles, focusing solenoid (8T),
target chamber, more diagnostics, upgraded plasma sources
FEPS = ferro-electric plasma source
CAPS = cathodic-arc plasma sources
IBM = induction bunching module
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NDCX-1 has demonstrated simultaneous transverse focusing and longitudinal compression
diag. #1 diag. #2
Objectives: Preservation of low emittance, plasma column with np > nb,
(ni = 0.07 mm-mrad, nb-init ≈ 109 /cm3,
nbmax ≈ 1012 /cm3 now, later, ≈ 1013 /cm3)
Ei = 0.3 MeV K+ Ii = 25 mA
IBM
Matching solenoids& dipoles
K+ injector E = 280-350 keVI = 26-37 mA
FEPS
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Beam diagnostics - improved Fast Faraday Cup: lower noise and easier to modifyRequirements:Fast time response (~1 ns)Immunity from background neutralizing plasmaDesign:2 hole plates, closely spaced for fast response.Hole pitch (1 mm) & diameter (0.23, 0.46 mm) small
blocks most of the plasma
Front plate
bias platecollector
0V-150<V<-50
50<V<-150
plasma
K+ beamvb = 1.2 mm/ns
Hole plate front view
zoomed view
Metal enclosure for shielding. Easier alignment of front hole plate to middle
(bias) hole plate. Design enables variation of gaps between hole
plates, and hole plate transparency.
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Beam diagnostics in the target chamber: Fast faraday cup
Biased hole platecollector
4 Al plasma sources<Z> = 1.7
K+ beamvb = 1.2 mm/ns
window
front hole plateExample waveform
2.5GS/s
Backgroundzero’ed and
linear tiltremoved
Uncompressedhead
CompressedPeak
Ibeam = Icollector x (transparency)-1
= 35 mA x 44 = 1.5 A peak.
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Beam diagnostics in the target chamber: scintillator + CCD or streak camera, photodiode
Biased hole platescintillator
V≈-300 V
Al2O3
4 Al plasma sources<Z> = 1.7
K+ beamvb = 1.2 mm/ns
PI-MAX CCD camera
window
10mm
10ns gate
10-20 pixels/mm typ.
photodiode
Streak camera
Optical fiber
Al2O3 wafer with hole plate:
Hole plate to reduce beam flux: less damage prevent charge buildup.
Image intensified CCD camera using 2 < t <500 ns gate.
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Simultaneous longitudinal compression and transverse focusing, compared to simulation.
7.5 mr 13.5 mr
Net defocusing in gap due to energy change, Er
0
5
10
15
20
4.9 5 5.1 5.2 5.3 5.4
Time (us)
FWHM (mm) FWHM (x)FWHM (y)
Angle at entrance to bunching module
ExperimentLSP Calculation
(m)
(m)
z (m)
B (
T)
2.6 1.4 0.6 2.3
WARP Calculation
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Uncompressed
Preliminary analysis of latest measurements show a smaller focused spot: R(50%) = 1 mm.
6mm
10ns gate
400 ps slices
≈10 mJ/cm2
(compared to previous 4 mJ/cm2)
2 ns fwhm
Higher plasma density near the focal plane.
5 Tesla --> 8 Tesla final focusing solenoid.
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LSP simulation of drift compression
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With the new bunching module, the voltage amplitude and voltage ramp duration can be increased.
12 --> 20 induction cores --> higher Vt
Beam experiments in 2009.
etraps FEPS
FEPS = ferro-electric plasma source
New bunching module
-150
-100
-50
0
50
100
150
0 0.1 0.2 0.3 0.4 0.5 0.6
Time (us)
L=2.88 mL=1.44 m
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It is advantageous to lengthen the drift compression section by 1.44 m via extension of the ferro-electric plasma source
~2x longer drift compression section (L=2.88 m), Uses additional volt-seconds for a longer ramp and to limit Vpeak & chromatic effects
2.24 mFerroelectric plasma source
L = 2.88 m
New plasma source built
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Calculations support a longer IBM waveform with twice the drift compression length
Comparison of LSP, the envelope-slice model, and the simple analytic model.
(a) no final focusing solenoid.
(b) New IBM, the final focusing solenoid (Bmax = 8 Tesla) Ldrift =144 cm, present setup
(c) with twice the drift compression length (L=288 cm) as the present setup.
FF (T)t (ns)
initial kinetic energy (keV)
a(z=284) (mm)
a' (mrad)
Current at focus (Amps)
pulse width @ focus (ns)
E (J/cm2) envelope
E (J/cm2) LSP2
E (J/cm2) (Eq. 1)
a) 0 200 300 21.50 -23.803.08 1.69 0.06b) 8 282 300 9.55 -9.82 4.01 1.83 0.39 0.30 0.59c) 8 400 300 14.40 -13.703.23 3.22 0.82 0.69 0.94
etraps
IBMVelocity ramp
Drift compression in Ferro-electric plasma source
8 T solenoidFCAPS plasma
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1.0E+10
1.0E+11
1.0E+12
1.0E+13
1.0E+14
-5 0 5 10 15 20 25Z (cm)
Density (1/cm
3)
n(plasma), B=8T
n(plasma), B=0
n(beam), B=8 T, LSP
The improved cathodic arc plasma source (CAPS) injection has led to a higher plasma density near the target
Plasma density > 1013 / cm3 after modifications to CAPS: straight filters,2 --> 4 sources, increased Idischarge
Plasma density
beam density
Targetplane
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Recent simulations show how insufficient plasma density affects the beam intensity at the target
Schematic near the target chamber, showing regions where lower plasma density exists in the experiment.
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Warp simulation of plasma injection from Cathodic-Arc Plasma Sources
Warpt = 7.5 sBmax = 8 T
includes calculated Eddy fields (Ansys transient model).
Warp
Experiment
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Parametric variation of plasma density distributions and the effect on the beam fluence
Energy fluence (time integral of beam power over a 10 ns window) from idealized Warp simulations of unbunched beam, showing effects of gap and limited radius plasma.
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Possible changes to the plasma source configuration to improve intensity on target
(1) Reducing the gap between the FEPS and the FFS (12 cm 5 cm)
(2) compact plasma sources on the beam pipe wall, near the end of the solenoid
(3) Collective focusing, Reducing B 0.05 T, & only FEPS plasma (I. Kaganovich talk).
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We are studying time dependent lenses to compensate the chromatic aberrations
Ramped electric quadrupole or Einzel lens correction, close to the IBM.
Example:
V(t) = [100 kV](t/1s)1/2
4 periods, P = 6 cm, R = 2 cm300 kV K+
Modulates envelope by ≈20 mr in 1s.
V= 0 +V 0 +V 0 +V 0 +V 0
BeamR
P
Insulators
Electrodes
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Example of envelope model approach to time-dependent corrections to chromatic aberrations
Target plane = 572 cm
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The beam characteristics are now satisfactory for target diagnostic commissioning and first target experiments
Energy spread of initial beam is low (130 eV / 0.3 MeV = 4 x 10-4 ) --> good for sub ns bunches.
Simultaneous axial compression (≈50x) to 1.5 A and 2.5 nsBeam diagnostics enhanced plasma density in the path of the beamPIC simulations of plasma and beam dynamics
Next steps: greater axial compression via a longer velocity ramp while keeping ∆v/v
fixed.Additional plasma sources, approaches to overcome incomplete
neutralization.time-dependent focusing elements to correct considerable chromatic
aberrations
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backup slides
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Example field modifications under consideration to increase plasma transport to the beam path near the target
An additional coil near target might increase plasma density just upstream of the target plane.
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Minimum spot size @ same time as peak compression
6
7
8
9
10
11
12
13
14
4.90 5.00 5.10 5.20 5.30 5.40
time ( )s
( )fwhm mm( )fwhm y( )fwhm x
2X reduction in the spot size (4X increase in beam intensity) brings the peak beam density to the range nb
≈1011-1012 cm-3.
Beam Current - FFC
-0.20
0.20.40.60.8
11.21.41.61.8
22.2
4.870 4.970 5.070 5.170 5.270 5.370
Time ( )s
( )Current A
4.920 s
: 4FWHM ns
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Alignment: Beam centroid corrections are required to minimize aberrations in IBM gap & for beam position control at the target plane
Alignment survey: mechanical structure aligned within 1 mm. Manufacturing imperfections (coil w.r.t support structure) not included.
Observe < 5 mm, <10 mrad offsets at exit of 4 solenoid matching section without steering dipole correction.
We can correct the centroid empirically with steering dipoles at the exit of the solenoid matching section.
3 dipole pairs between solenoids
Imax ~ 200 ABmax ~ 0.5 kG
Beam
Y dipole(inside)
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All
Errors:
Solenoids: Dispacements +tiltsSolenoids: tilts only
Solenoids: displacements only.
Initial conditions only (ion source)
Average centroid orbit
Next step: Minimization of the centroid betatron amplitude. Requires knowledge of the absolute offsets.
Ensemble of 10,000 random error combinations to estimate sensitivity, Lund, Po-24
Beam centroid measured without dipoles will be used to solve for beamline offsets
Beam distribution J(x,y) at exit of 4 solenoid matching section.We plan more measurements
to verify this method
1 2 3 4
5 6 7 8
9 10
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Increasing velocity tilt increases the peak current. Chromatic effects --> larger spot radius.
Transversely, spot radius determinedby emittance + chromatic aberrations
Higher momentumtrajectory
Lower momentumtrajectory Envelope
(average)
Minimum Spot radius
Tilt imposed
z
VDriftCompression
Length of beam prior to compression
Length of beam after compression
vtilt
Velocityspread beforecompression
Longitudinally, phase space undergoes rotation during drift compression; <(v/v)2>1/2 limits final bunch length
r0
€
Ε =4eφIτ
πεfΔF1 (η) tan −1 F2 (η)r0
2Δ
2fε
⎛
⎝ ⎜
⎞
⎠ ⎟ ∝
~
eφIτ
εfΔ
= v/v, e = beam energy, f = final solenoid focal length
Energy deposition (J/cm2):
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45 degree view -- zoomed field lines only
Plasma sources
target
Solenoid coilB lines
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0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
4690 4710 4730 4750 4770 4790 4810 4830 4850
Delay (ns)
Radius (mm)
Compression Ratio (a.u.)
80%
50%
Uncompressed
+ 2.55mm
+ 1.71mm
Uncompressed radii
Optical Analysis
10ns gate
6mm
10ns gate
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0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
4700 4725 4750 4775 4800 4825
Delay (ns)
Radius (mm)
10ns gate
2ns gate80%
50%
80%
50%
Spot size variations with camera gate
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0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
1.60
4700 4720 4740 4760 4780 4800 4820 4840 4860
Delay (ns)
Energy (mJ)
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
18.0
20.0
Fluence (mJ/cm^2)
Slice Energy (mJ)50% Fluence80% Fluence
10ns Gate
Totals (over 20ns)
1.70 mJ
22.1 mJ/cm2
14.1 mJ/cm2
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2ns Gate
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
4758 4763 4768 4773 4778
Delay (ns)
Energy (mJ)
0.00
0.50
1.00
1.50
2.00
2.50
Fluence (mJ/cm^2)
Slice Energy50% Fluence80% Fluence
Totals (over 20ns)
1.12 mJ
10.46 mJ/cm2
6.23 mJ/cm2
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Fluence (mJ/cm^2)
0
2
4
6
8
10
12
0 5 10 15 20 25
Position (mm)
0
0.4
0.8
1.2
1.6
2
2.4
10ns gate
2ns gate
Beam fluence from lineout
10mm 10mm
10ns gate 2ns gate
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Beam Steering Jitter
-50.0
-40.0
-30.0
-20.0
-10.0
0.0
10.0
20.0
30.0
40.0
4675 4725 4775 4825 4875
Delay (ns)
Fractional Deviation (%)
(X-<X>)/(50% Radius)
(Y-<Y>)/(50% Radius)
0.75mm 1.0mm 2.5mm
50% radius