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