Overview of Recent Progress in the Heavy Ion Fusion Science Virtual National Laboratory

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Overview of Recent Progress in the Heavy Ion
Fusion Science Virtual National Laboratory

• J. J. Barnard1 on behalf of the HIFS VNL
• B. G. Logan2, R.C. Davidson3, F.M. Bieniosek2,
  R. J. Briggs5, C. M. Celata2, R. H. Cohen1, J.
  E.Coleman2, C.S. Debonnel2, A. Friedman1, M.
  Kireeff Covo1, D. P. Grote1, P. C. Efthimion3,
  S. Eylon2, L. Grisham3, E. P. Gilson3 , E.
  Henestroza2 , I. D. Kaganovich3 , J. W. Kwan2,
  E. P. Lee2, M. Leitner2, S.M. Lund1, R. More2,
  A.W. Molvik1, G.E.Penn2, H. Qin3, P. K. Roy2, D.
  V. Rose4, P.A. Seidl2, A. Sefkow3, W.M. Sharp1,
  E. A. Startsev3, M. Tabak1, C. Thoma4, J-L Vay2,
  W. L. Waldron2, D.R. Welch4, G. Westenskow1,
  J.S. Wurtele2, and S. S. Yu2
• Workshop on Recent Progress in Induction
  Accelerators
• March 7-10, 2006
• KEK, Tsukuba, Japan
• 1. LLNL 2. LBNL 3. PPPL 4. Voss Scientific 5.
  SAIC
• Work performed under the auspices of the U.S.
  Department of Energy under University of
  California contract W-7405-ENG-48 at LLNL,
  University of California contract
  DE-AC03-76SF00098 at LBNL, and contract
  DEFG0295ER40919 at PPPL.

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The goal of the HIFS-VNL is to investigate the
beam science common to both High Energy Density
Physics (HEDP) and fusion

• The program concentrates on ion beam experiments,
  theory and simulations to address a top-level
  scientific question central to both HEDP and
  fusion
• How can heavy ion beams be compressed to the
• high intensities required for creating high
  energy
• density matter and fusion?
• Principal science thrust areas
• - High brightness beam transport
• - Focusing onto targets
• - Longitudinal beam compression
• - Advanced theory and simulation tools
• - Beam-target interaction and warm dense matter
  physics

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Outline of Presentation

• The HEDP/Warm Dense Matter mission for the HIFS
  VNL
• - Bragg peak heating
• Neutralized Focusing and Drift Compression
  Experiments
• Neutralized focusing
• Neutralized longitudinal beam compression
• Pulse Line Ion Accelerator (PLIA)
• Novel slow-wave accelerator for producing
  intense high-current ion beams.
• High Brightness Beam Transport
• Electron cloud
• Beam stability
• Multi-beamlet injector
• Future Warm Dense Matter and NDCX-II
• Other VNL talks R. Briggs - PLIA (Tuesday)
• G. Westenskow -
  Multibeamlet Injector (Wednesday)
• S. Lund - Space
  charge transport limits (Wednesday)
• H. Qin - Time dependent envelope equation
  (Thursday)

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The r - T regime accessible by beam-driven
experiments is similar to the interiors of giant
planets and low-mass stars
Figure adapted from Frontiers in HEDP the
X-Games of Contemporary Science
Accessible region using Intense beams
Region is part of Warm Dense Matter (WDM)
regime WDM lies at crossroads of
degenerate /classical and strongly coupled/
weakly coupled
Terrestial planet
See http//hifweb.lbl.gov/public/AcceleraorWDM/Tab
leOfContents.html for talks from 2006 Workshop
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Warm Dense Matter Science requires short intense
beam pulse ( ns). Strategy placing center of
foil at Bragg peak, maximizes uniformity
In simplest example, target is a foil of solid or
foam metal


fractional energy loss can be high and uniformity
also high if operate at Bragg peak (Larry
Grisham, PPPL)
Ion beam
Example Ne
Energy loss rate
DdE/dX ? DT
In example, Eentrance1.0 MeV/amu Epeak 0.6
MeV/amu Eexit 0.4 MeV/amu (DdE/dX)/(dE/dX)0.05
(MeV/mg cm2)
Enter foil
Exit foil
(dEdX figure from L.C Northcliffe and
R.F.Schilling, Nuclear Data Tables, A7, 233
(1970))
Energy/Ion mass
(MeV/amu)
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Various ion masses and energies have been
considered for Bragg-peak heating
Beam parameters needed to create a 10 eV
plasma in 10 solid aluminum foam, for various
ions (10 eV is equivalent to 1011 J/m3 in 10
solid aluminum)
As ion mass increases, so does ion energy and
accelerator cost
As ion mass increases, current increases,
increasing need for neutralization
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LSP-PIC simulations demonstrate the possibility
of large compression and focusing of charge
neutralized ion beams inside a plasma column
(Welch et al., 2004)
Snapshots of a beam ion bunch at different times
shown superimposed
Background plasma _at_ 10x beam density (not shown)

• ?Ramped 220-390 keV K ion beam injected into a
  1.4-m -long plasma column
• Axial compression 120 X.
• Radial compression to 1/e focal spot radius lt 1
  mm.
• Beam intensity on target increases by 50,000 X.

cm
Initial bunch length
cm
3.9T solenoid focuses beam

• Velocity chirp amplifies beam power analogous to
  frequency chirp in CPA lasers.
• Solenoids and/or adiabatic plasma lens can focus
  compressed bunches in plasma.
• Instabilities may be controlled with npgtgtnb, and
  Bz field Welch, Rose (MRC) Kaganovich
  (PPPL).

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NDCX-I A series of experiments towards HEDP
(NDCX-II)
We have equipment in hand for all NDCX-1
experiments except NDCX-1c
Interchangeable
(First expts Neutralized focusing, NTX)
Interchangeable

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Neutralized Transport Experiment investigated
physics of neutralized focusing
Volumetric plasma from photoionization ("target
plasma"
F
D
F
D
Plasma plug neutralization
x and y envelopes (schematically depicted)
Non-neutralized
300 keV K ions at 25 mA
FWHM1.5 mm
FWHM6.6 mm
FWHM2.2 mm
2004
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Measurements on the Neutralized Transport
Experiment (NTX) demonstrate achievement of
smaller transverse spot size using volumetric
plasma
Plasma plug.
Plasma plug and volumetric plasma.
Neither plasma plug nor volumetric plasma.
FWHM 2.7 cm
FWHM 2.14 mm
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Neutralized drift compression experiment (NDCX)-
300 keV K ions at 25 mA
Tiltcore waveform
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50 Fold Beam compression achieved in neutralized
drift compression experiment
Phototube
Optical data
Corroborating data from Faraday cup
LSP simulation
Time (ns)
100
0
P.K. Roy et al, PRL, 95, 234801, 2 Dec. 2005
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Our first HEDP workshop (October, 2004) included
a new accelerator concept a Pulse Line Ion
Accelerator (PLIA) for potential applications to
HEDP and IFE

• Pulse Line Ion Accelerator is based on slow-wave
  structures (helices)
• Beam surfs on traveling pulse of Ez
• Ez (helix) gtgt Ez (space charge) ? Continuous
  purging of electrons!

December 2005, demonstrated energy extraction
from traveling wave
Solenoid provides transverse beam confinement
Dielectric-filled coax
Vz(z,t)
ttt
vacuum
Traveling wave?
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In a Pulse Line Ion Accelerator (PLIA), the
accelerating fields are those of a distributed
transmission line
NDCX-II Accelerator Cell
Solenoid cryostat
R.J. Briggs, et al. - LBNL Patent, Aug 2004
Helical winding
Output end
Input end
Compact transformer coupling (51 step-up)
Input
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NDCX-I A series of experiments towards HEDP
(NDCX-II)
We have equipment in hand for all NDCX-1
experiments except NDCX-1c
Interchangeable
(First expts Neutralized focusing, NTX)
Interchangeable

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High-brightness beam transport - electron
effects on intense ion beams
Electron cloud caused by
Synchrotron radiation Secondary emission from e-
accelerated by beam Beam halo scraping ? e-
emission Ionization of background
gas especially Expelled ions hitting vacuum
wall for HIF, Ionization of desorbed gas HEDP
e- motion in a quad
Goal Advance understanding of the physical
processes leading to the accumulation of
electrons in magnetic quadrupoles in the HCX
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The High Current Experiment (HCX) is exploring
beam transport limits
Focus of Gas/Electron Experiments
K Beam Parameters I 0.2 (- 0.5) Amp 1 (-
1.7) MeV, 4.5 ms
2 MV INJECTOR
MATCHING SECTION
ELECTROSTATIC QUADRUPOLES
MAGNETIC QUADRUPOLES
4 magnetic quadrupoles many diagnostics
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Comparison Clearing electrodes and e-suppressor
on/off
e-supp
200mA K

• Beam ions

• Electrons from ions hitting surface

• Secondary electrons

Comparison suggests semi-quantitative agreement.
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Non-neutralized space charge physics is also
being explored in HIFS-VNL New theoretical
explanation of an unanswered question

• Limit s0 gt 85 degrees/period (large emittance
  growth and particle loss)
• Explanation Higher order resonances between
  particle orbit and matched beam envelope external
  to the beam core (but near the edge) allow
  near-edge particles to rapidly increase in
  oscillation amplitude
• Core-particle criterion based on this effect
  reproduces the observed stability boundary
• PIC simulations confirm core-particle calculations

Empirical limit (Tiefenback, 1986)
Min
Stability boundary derived from core-particle
model
Space-Charge Strength
Max
Applied Focus Strength
Details will be presented in this workshop and
in S. Lund and S. Chawla, Nuc. Instr. Meth. A
(2006), in press.
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Merging beamlet injector experiments on STS-500
validated the concept of this compact, high
current source

• Monolithic solid sources suffer from poor scaling
  vs. size at high currents
• This new concept circumvents the problem via use
  of many small, low-current sources

Simulation
Experiment
From a full-gradient (parallel-beamlet) experiment
y (m)
-0.05 x (m) 0.05
-0.05 x (m) 0.05

• From scaled merging experiment
• Obtained emittances comparable to simulation
• Effects of dirty physics (electrons, charge
  exchange) were minimal
• Scales to 0.5 A, 1.6 MeV, 1 ?-mm-mrad, 13 mA/cm2

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Future goal a user facility for ion beam driven
HEDP will have unique characteristics
Precise control of energy deposition
Uniformity of energy deposition Large sample
sizes compared to diagnostic resolution
volumes Ability to heat variety of targets
(insulators and conductors) Relatively long
times allow equilibrium conditions A benign
environment for diagnostics High shot rates
(10/hour to 1/second) (simple targets and high
accelerator rep rates
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The experiments in the NDC sequence lead to a
user facility (IB-HEDPX)
Existing machine, 1 year goal
3 - 5 year goal
10 year goal
IB-HEDPX
NDCX neutralized drift compression
experiment IB-HEDPX integrated beam-high energy
density physics experiment
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NDCX-II Plan Pulse Line Ion Accelerator- a
unique, more capable accelerator for ion-driven
HEDP is being evaluated
Neutralized Compression
Final Focus
Solenoid Focusing
Helix Acceleration
Short Pulse Injector
1 eV target heating gt0.1 mC of Na _at_ 24 MeV
heating _at_ Bragg peak dE/dx NDCX-1C 5M hardware
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Hydra simulations confirm temperature uniformity
of targets at 0.1 and 0.01 times solid density of
aluminum (20 MeV Ne ions at 330 A)
0
Dz 48 m
r 1 mm
0.7
1.0
Axis of symmetry
1.2
2.0
t(ns)
2.2
Dz 480 m
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New theoretical EOS work meshes very well with
the experimental capabilities we will be creating
R. Lee plot of contours of fractional pressure
difference for two common EOS
R. More Large uncertainties in WDM region arise
in the two phase (liquid-vapor) region Accurate
results in two-phase regime essential for WDM
R. More has recently developed new high-quality
EOS for Sn. Interesting behavior in the T1.0
eV regime.
P (J/cm3)
Critical point unknown for many metals, such as Sn
r (g/cm3)
T (eV)
EOS tools for this temperature and density range
are just now being developed.
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Conclusions

• There have been many scientific advances by the
  HIFS VNL during the past two years
• - Demonstration of compression and focusing
  of ultra-short ion pulses in
• neutralizing plasma background.
• - New computational, theoretical and
  experimental results in high brightness beam
  research, including electron cloud effects
• - New accelerator concept Pulse Line Ion
  Accelerator.
• - Completion of a multibeamlet injector for
  heavy ion fusion drivers
• - Development of a concept and path to Warm
  Dense Matter investigations
• Heavy ion research is of fundamental importance
  to both HEDP in the near term
• and to fusion in the longer term.
• Experiments heavily leverage existing equipment
  and are modest in cost.
• Theory and modeling play a key role in guiding
  and interpreting experiments.