Overview of U'S' Heavy Ion Fusion Progress and Plans

1
Overview of U.S. Heavy Ion Fusion Progress and
Plans
B. Grant Logan Heavy-Ion Fusion Virtual National
Laboratory (HIF-VNL) LBNL, LLNL, PPPL 15th
International Symposium on Heavy Ion Inertial
Fusion June 7-11, 2004 Princeton Plasma Physics
Laboratory Princeton University, Princeton, New
Jersey USA
2
U. S. institutions participating in heavy ion
fusion research
3
U.S heavy ion research is pursuing beam science
common to both High Energy Density Physics (HEDP)
and Inertial Fusion Energy (IFE).

• Past experiments have validated theoretical
  models at low currents (few mA).
• We have made good progress at higher currents
  (25-180 mA) in the STS, HCX, and NTX experiments,
  and supporting theory and simulations (next few
  slides)
• Over the next 5-10 years, we plan to continue
  high brightness beam transport, and a new area in
  neutralized drift compression and focusing. Both
  address a scientific question central to both
  high energy density physics and IFE
• How can heavy ion beams be compressed to the high
  intensities required
• for creating high energy density matter and
  fusion ignition conditions?

Progress?
Plans?
?Understanding how beams can be compressed to
drive targets to 1eV for high energy density
physics, would be an important intermediate step
towards 250 eV targets for inertial fusion energy.
4

• Progress

5
Experiments with large beams (see talk J. Kwan
Tu.I-13)

• ? Study beam optics of large surface ionization
  source, bench- mark simulations (see Kwan
  Th.P-11, and Westenskow Th.P-12)
• ? Demonstrate the concept of merging beamlets for
  compact driver-scale injectors.

STS-100 Source test stand
STS-500 Injector test stand
6
Beamlets from Argon RF Plasma Source meet HIF
requirements
Single Beamlet

• Parameters Results Status
• Current density 100 mA/cm2 (5 mA) met goal
• Emittance Teff lt 2 eV met goal
• Charge states gt 90 in Ar met goal
• Energy spread lt a few beam suffers CX met goal?

RF Source
Multiple Beamlet
Image on Kapton
7
STS-500 is also investigating large-aperture
diode dynamics
(See talk by A. Friedman W.I-08 for details on
simulations)
10-cm diameter K Alumino-silicate source
Phase Space at End of Diode
Risetime
Theory
150 kV48A heater
Results on the right benefited from a new
computer technique (Adaptive Mesh Refinement),
that has moved the state-of-the-art. (See J-L
Vay, W.P-08)
8
Since 2002, HCX has explored transport to high
fill factors in ten electric quads, and
gas/electron cloud effects in four magnetic
quads.
The HCX with magnetic quad section (2003)
Gas, electron source diagnostic (GESD)
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In both 60 and 80 fill-factor cases measured,
no evidence of emittance growth, within
diagnostic sensitivity.
(See talk by L. Prost W.I-07)
80 fill factor
60 fill factor
en 0.40 p.mm.mrad
Beginning of Electrostatic Section
en 0.48 p.mm.mrad
en 0.40 p.mm.mrad
en 0.48 p.mm.mrad
End of Electrostatic Section
10
Rough surfaces mitigate electron emission, gas
desorption, and ion scattering (see Molvik,
Th.I-01)
Gas desorption
Electron emission
X2-3 reduction
X10 reduction
Surface roughened by glass-bead blasting
(inexpensive) Angle of incidence grazing ?
60o from 1/cos emission Sawtooth surface
(CERN-SPS) more effective, but more expensive.
11
The Neutralized Transport Experiment (see talk by
P. Roy Th.I-05)
12
Plasma neutralization of space charge for a high
perveance (6 x10-4) 25 mA, 300 keV K beam
reduces beam focal spot size by 10 x, consistent
with particle simulations
After magnetic focus, data and calculated beam
density profiles agree well, except for halo.
Simulations (D. Welch Th.I-06) predict 1.4 mm
rms spot radius for plug plasma case
13
Small-scale experiments will be available to
study long-path transport physics such as slow
emittance growth
Construction of the University of Maryland
Electron Ring experiment (UMER) is nearing
completion. UMER uses electrons to study HIF-beam
physics with relevant dimensionless space charge
intensity. (See R. Kishek, W.I-11)
The Paul Trap Simulator Experiment at PPPL uses
oscillating electric quadrupole fields to confine
ion bunches for 1000s of equivalent lattice
periods (See E. Gilson W.I-10)
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Noteworthy U.S. progress in beam theory,
simulation and modeling

• Simulation studies in support of experiments
• Injectors large-aperture aberrations short
  rise-time tests multi-beamlet merging
• HCX WARP studies of transport matching into
  magnetic quads analysis of optical-slit and
  other data
• NTX WARP and LSP studies of beam transport and
  focusing
• Studies of future experiments
• Neutralized Drift Compression Experiments
  studying compression in space and time
• simulation and analysis of HEDP-relevant beam
  experiments and modular driver approaches
• time-dependent 3D simulations of a model IBX
• scoping of scaled multi-beam experiment using
  electrons (with U. Md.)
• Fundamental beam science studies
• electron cloud effects, and roadmap for
  comprehensive electron/gas modeling
• quantitative assessment of effects of quadrupole
  magnet strength errors
• Harris and Weibel anisotropy modes, and
  two-stream instability
• drift compression and final focus (both
  non-neutral and neutralized), including solenoid
  focusing time-dependent focusing and chromatic
  aberration studies
• beam aperturing and effects of beamline
  transitions
• parametric limits to stable transport set by both
  envelope and kinetic effects
• Development of advanced simulation capabilities
• Mesh refinement capability in WARP (application
  to injector triode, rise time study)
• New Vlasov modeling methods for halo, including
  moving-mesh and non-split advance (with U.
  Strasbourg)

See talks by Kaganovich Tu.I-06 and W.P-14,
Davidson Tu.I-11, Startsev Tu.I-12, Friedman
W.I-08, E. Lee W.I-12, Vay W.P-08, W. Lee W.P-09,
Grote W.P-10, Rose W.P-15, Sharp W.P-19, Cohen
Th.I-03, Welch Th.I-6, Barnard Th.I-08, Qin
Th.I-08, Lund Th.P-20, and DuBois Th.P-24
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• Plans

16
We have an idea and several recent innovations
to help us meet the goal of reaching 1 eV in
targets within five years
Idea Ion beams entering a foil target
just above the Bragg peak energy where
d2E/dx2?0 can provide more uniform deposition
(Larry Grisham, PPPL).

• Recent innovations
• Neutralized drift compression? much shorter
  pulses and less expensive to test. Simulations
  show minimal impact of beam plasma instabilities.
• Solenoid/adiabatic plasma lens tolerate
  uncompensated velocity spreads with neutralized
  compression and focusing? higher focus intensity.
• Injectors incorporating deceleration after
  initial acceleration and/or higher current
  density ? shorter bunches needed for short pulse
  acceleration.

17
Strategy maximize uniformity and the efficient
use of beam energy by placing center of foil at
the Bragg peak in dE/dx
In simplest example, target is a foil of solid or
foam material


Perveance of beams at Bragg peak are high
?require neutralized compression and focusing.
Ion beam
Example He
Energy loss rate
DdE/dX ? DT
Deposition rate and uniformity best if driven at
Bragg peak (Larry Grisham, PPPL).
(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)
18
LSP-PIC simulations of proposed experiment
(NDCX-I ) show dramatically larger compressions
of tailored-velocity ion beams inside a plasma
column (Welch, Henestroza, Yu 3-11-04)
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
Existing 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 (see Welch Th.I-06, Rose W.P-15,
  Kaganovich W.P-14)

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Five-year goal Integrated beam and target
experiments at nominal solid target temperatures
of 1 eV (NDCX-II)
Use existing NTX injector, but with1 A Helium
beam source instead of present 25 mA K, and
larger B.a solenoid
Goal 1 eV in targets
See talk by M. Leitner, F.I-06
Limited-shot and/or non- intercepting target
focus diagnostics
1
Existing 400 kV NTX Marx
Short acceleration and compression tilt section
to 700 keV (use existing ETA and DARHT Cores)
1.4 m long Neutralized Drift
Short Pulse accel-decel Injector
Solenoid and Z-Pinch focus
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• PARAMETERS AT TARGET
• 30 MeV Ne / 60 MeV Ar
• 20- 40 J BEAM ENERGY
• 1- 2 kA peak CURRENT
• 0.5 to 1 ns PULSE LENGTH

EXISTING BUILDING 58
600kV ACCEL-DECELINJECTOR
UNNEUTRALIZED DRIFT COMPRESSION to 20 ns
2-3 MV INDUCTION BUNCHER 200 ns
TARGET CHAMBER 1 to 10 eV warm dense matter
physics
High gradient short pulse ACCELERATOR 30 MV _at_
3MV/m
See talk by M. Leitner, F.I-06
PLASMA-NEUTRALIZED DRIFT COMPRESSION AND FOCUS
Ten-year goal
Conceptual NDCX-III High Energy Density User
Facility
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High-brightness transport science campaign

• Can high-current ion beams be transported at
  high fill factor over 100s to 1000s of magnetic
  quadrupoles?
• Recent theory / modeling ? predictions of the
  consequences from e--cloud buildup. Benign up to
  a few percent?
• Near term
• Compare experiments and model predictions in lt
  10 quadrupoles by forcing electron effects
  through variations of beam fill-factor, current,
  centroid steering. Test mitigation methods.
• Objectives
• Understanding established in lt 10 magnetic
  quadrupoles (2006). ? More extensive and
  sensitive experiments (2009).
• Connect with e--cloud high intensity
  accelerator community.

22
Chromatic focus aberrations with neutralized beam
drift compression with velocity tilts dv/v lt 10
may be tolerable with larger spot hybrid
targets, together with focusing using solenoids
and/or adiabatic plasma lens.
Hybrid target allows large 5 mm radius focal
spots (D. Callahan M.I-06). See also low cost
manufacturing methods for hohlraums with foam
x-ray converters (D. Goodin M.I-09).
23
Neutralized drift compression/focusing hybrid
targets may reduce costs 50 for both
conventional multiple-beam quadrupole and modular
solenoid driver options for IFE (See talk by
Meier F.I-05)
Multiple-beam quad linac driver
Modular solenoid linac driver
3000
?Robust Point Design
2500
24
Key areas for further research in neutralized
beam drift compression and focusing

• Injection/acceleration/bunching to high
  perveance (gt 10-2) with sufficiently low parallel
  and transverse emittances before plasma
  neutralization.
• Beam transitions at high line-charge densities
  from Brillouin flow into neutralizing plasma
  columns with tolerable emittance increases.
• Control of beam plasma instabilities over long
  regions of drift compression in background
  plasma, and controlled stripping.
• For IFE, extension of neutralized final focus to
  longer standoff distances.
• For IFE, validation of symmetry control in
  large-focal-spot hybrid targets.

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SUMMARY

• We have made good progress at higher currents
  (25-180 mA) in the STS, HCX, and NTX experiments,
  and supporting theory/ simulations
• Over the next 10 years we plan to continue high
  brightness beam transport, with a new area in
  neutralized drift compression and focusing. Both
  address a scientific question central to both
  high energy density physics and IFE
• How can heavy ion beams be compressed to the high
  intensities required
• for creating high energy density matter and
  fusion ignition conditions?

Progress?
Plans?
?Understanding how beams can be compressed to
drive targets to 1eV for high energy density
physics, would be an important intermediate step
towards 250 eV targets for inertial fusion energy.
26

• Backup slides

27
Physics design of 119-beamlet merging experiment
on STS500 is complete (see talk by Friedman
W.I-08)
Current 0.07 Amps, Final energy 400 keV
Normalized emittance
28
Heavy ion fusion system studies show that driver
cost is very sensitive to fill factor
IBEAM results
Robust Point Design (2.8 B)
range being explored
W. Meier, LLNL
(fixed number of beams, initial pulse length, and
quadrupole field strength)
29
Example of critical physics issue beam loss in
high intensity accelerators -a current world
research topic (GSI-SIS-18, LANL- PSR, SNS)

• Gas desorption Gas desorbed by ions scraping
  the channel wall can limit average beam current.

• Electron cloud effects Ingress of wall-secondary
  electrons from beam loss and from channel gas
  ionization. WARP (below) and BEST simulations
  indicate incipient halo formation and
  electron-ion two-steam effects begin with
  electron fractions of a few percent.

Ion Halo
Ion Beam (core)
Electron Fraction (extreme case)
0
2 ? 2
10 ? 10

• Random focusing magnet errors Gradient and
  displacement errors can also create halos and
  beam loss.

30
Neutralized compression might lead to an improved
IFE driver with a modular development path
Example 6.7 MJ Ne1 at 200 MeV
Solenoid focusing (Lee) or adiabatic plasma
lens/ assisted pinch (Yu, Welch)
High l injector
Induction linac
Neutralized drift compression
Large spot Hybrid Target (Callahan)
31
HEDP has rich discovery potential
Fusion Effects of 3-D RT instabilities on burn
propagation (NIF)
Quark-gluon plasmas in heavy-ion nuclear
collisions (way off scale in this chart)
Fast igniter physics fast electron dissipation
enhancement via collective instabilities
Strongly-coupled plasmas Many ab-initio theories
of strongly coupled plasmas remain un-resolved by
existing laser data
32
In Warm Dense Matter regime large errors exist
even for most studied materials (slide courtesy
of R. Lee, LLNL)
Contours of differences in pressure
Aluminum
Copper

• EOS Differences gt 80 are common
• Measurements are essential for guidance
• Where there is data the models agree!!
• Data is along the Hugoniot - single shock
  r-T-P response curve

33
Uniform isochoric heating is desirable to enable
EOS measurements accurate enough to distinguish
different ab initio WDM theories
Variations in temperature or density less than a
few percent over diagnostic resolution volumes
needed to distinguish various theories
34
HEDP science would benefit from a variety of
facilities offering different tools, shots on
demand, and different convenient locations for
students
WDM regimes are presently accessed by heating a
solid (most useful) or by compressing/ shock
heating a gas. Volume and uniformity set limits
to accuracy of EOS measurements.
XFEL heating uniform but small volumes (10s of
millijoules). High range electrons can heat lt 1
mm spots but too small for diagnostics
MJ of soft-x-rays available on Z but limited
number of shots
Lasers absorb at critical density ltlt solid
density? large density/ pressure gradients
Fast heating of a solid with penetrating ions
?lower gradients? more accurate EOS

• Ion heated thin foils

• 100TW lasers ?10-50 mJ, ps ion bunches ?large
  energy spreads, non-uniform deposition
• GSI-SIS-100 plans 10-40 kJ of ions _at_100GeV,100
  ns? large volumes but limited T lt 1 eV

35
Two ion dE/dx regimes to obtain isochoric ion
energy deposition in 1-to-few eV warm-dense
matter targets
HIF linacs with 0.5-1 J of ions _at_ 0.3 MeV/u
would work best heating thin foils near the Bragg
peak where dE/dx 0 ? 3 uniformity possible
(Grisham, PPPL). Key-issue can lt 300 ps ion
pulses to avoid hydro-motion be produced?
dE/dx
z
3 mm
3 mm
Heavy-ion beams of gt300 MeV/u at GSI must heat
thick targets with ions well above the Bragg
peak? kJ energies required _at_ lt300 ns to achieve ?
15 uniformity.
36
1-D hydro calculations of aluminum foam target
examples driven by Ten-yr goal machine
parameters. (Slide courtesy of D. Callahan and M.
Tabak, LLNL)
Ne1 ions, 30 J total beam energy, 30 MeV kinetic
energy, 20 - 40 MeV energy spread, 1 mm radius at
best focus, 3.8 TW/cm2 center of beam, 0.5 ns
pulse duration
37
Example parameters Ne1 beam
Ne Z10, A20.17, Emin4.4 MeV, Ecenter11.7
MeV, Emax19 MeV Dzmin 40 m
(Eq. of state, Z Zeldovich and Raizer model
from R.J. Harrach and F. J. Rogers, J. Appl.
Phys. 52, 5592, (1981).)
38
First experiments (FY06) to assess physics
limits of neutralized ion beam compression to
short pulses (NDCX-I, before upgrade to NDCX-II)
First neutralized drift experiment using existing
equipment
Existing LBNL 400 kV injector, focusing magnets
and induction core
Neutralized DriftCompression Experiment using
PPPL large plasma source soon- 2004
2nd step Accel-Decel Bunching Solenoid
Transport Experiments using existing solenoids
and pulsers
1.4 m drift section
39
Ten-year plan to address the compelling question
How can heavy ion beams be compressed to the
high intensities required for creating high
energy density matter and fusion ignition
conditions?
40
Ion-driven targets for IFE and HEDP require
common beam physics high brightness injection
and acceleration with precision waveforms,
electron cloud control, longitudinal bunch
compression, beam neutralization in chamber
Ion-driven IFE
Ion-driven HEDP
Energy 7 MJ, 4 GeV No. of beams 120 Pulse rate
5 Hz Pulse width 8 ns Peak power/beam 5
TW Focal spot radius 2 mm _at_ 6 meters focal
length Peak deposition 1012 J/m3 (per beam,
into foam radiators)
Energy 0.2-2 J, 1-2 MeV No. of beams 1 Pulse
rate 100s per day Pulse width 0.3 ns Peak
power/beam 7 GW Focal spot radius 0.5-1 mm _at_
10 cm focal length Peak deposition 1011 J/m3 (for
1 Mbar, 1 eV, WDM)
A key new requirement for HEDP is sub-ns pulses
(needs neutralized drift compression as well as
chamber neutralization).
41
Isochoric heating with laser produced fast proton
beams for HEDP can complement accelerator driven
HEDP. Laser methods needs better understanding
and control of ion beam distribution and improved
resolution EOS diagnostics together with modeling

Simulations of isochoric heating of a 50 micron
copper cube by a 2x1011 proton pulse
(from Prav Patel LLNL)
42
A US-DOE and German Government agreement
supports cooperation in dense plasma physics

• Beam loss/vacuum issues and accelerator
  activation
• Petawatt laser for ion-driven HEDP diagnostics
• beam physics basis for high intensity ion drivers
• space charge effect on resonances
• models of beam halo generation
• longitudinal instabilities
• compression schemes for short pulses

GSI and HIF-VNL have agreed to the technical
content of a new proposed annex on gas desorption
and electron cloud effects in accelerators. Techn
ical Coordinators Arthur Molvik LLNL Hartmut
Reich-Sprenger GSI
New 600 M Euro SIS-100 Upgrade (approved)
Simulation of a cylindrical target driven by GSI
heavy ion beam
Implementing Agreement between the Department of
Energy of the United States of America and the
Federal Ministry of Education and Research of the
Federal Republic of Germany on Collaboration in
the Field of Dense Plasma Physics (2001)
Unilac and SIS-18 storage ring (present)