Status of Heavy Ion Fusion Research

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Nov 16, 2013 (3 years and 8 months ago)

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The Heavy Ion Fusion Virtual National Laboratory

Status of Heavy Ion Fusion Research

Grant Logan

Director

Heavy Ion Fusion Virtual National Laboratory

(LBNL, LLNL and PPPL HIF groups)

Presented at

Fusion Power Associates Symposium

Washington, DC

November 19
-
21, 2003

The Heavy Ion Fusion Virtual National Laboratory

Outline


Motivation for heavy ion fusion research


Critical technical issues


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The Heavy Ion Fusion Virtual National Laboratory

Heavy ion fusion research motivation



World wide experience with high energy accelerators support inertial
fusion energy driver prospects for efficiency, pulse
-
rate, and durability.




Focusing magnets may survive target radiation and debris for many
years of operation.



Expected very good ion
-
target coupling efficiency (classical dE/dx)



Compatibility with indirect drive and thick liquid protected chambers.



These attributes are good for both fusion and high energy density
physics applications




Present heavy ion beam research emphasizes primary scientific issues:
intense ion beam transport physics, beam
-
wall interactions, focusing, and
beam
-
target plasma interactions.



Intense ion beam
-
wall interactions are a common area of accelerator
science important to heavy
-
ion fusion and high energy and nuclear
physics.

The Heavy Ion Fusion Virtual National Laboratory

Heavy ions can apply to a variety of targets, chambers,
and focusing schemes, but a key motivation is the
desirability of using thick liquid
-
protected fusion
chambers with much reduced materials development

Accelerator

Target

Focusing

Chamber

Induction

Linac

Indirect Drive,

Distributed
Radiator

Ballistic,
Neutralized

Thick
-
Liquid
-
Protected Wall

RF Linac +

Storage Ring

Indirect Drive,

Hybrid Target

Ballistic,

Vacuum

Thin
-
Liquid
-
Protected Wall

Induction

Recirculator

Indirect Drive,

Fast ignition

Pinch Modes

Solid Dry

Wall

High Gradient

Line Linacs

Direct Drive,

Aspherical

Granular
-
Solid
Flow Protected
Wall

Approaches emphasized in the U.S. program

(primary emphasis)

(secondary)

The Heavy Ion Fusion Virtual National Laboratory

Heavy ion beam requirements follow from the designs of
accelerators, chambers and targets
that work together


Beams at high current
and sufficient
brightness to focus


Long lasting, thick
-
liquid protected
chambers for 300 MJ fusion pulses
@ 5 Hz

High gain targets that can
be produced at low cost
and injected

A self
-
consistent
HIF power plant
study was
recently
published in
Fusion Science
and Technology,
44, p266
-
273
(Sept. 2003)

Beam brightness B
n

t

㸠㑸㄰
6

A
.
s/(m
2
rad
2
) at target


The Heavy Ion Fusion Virtual National Laboratory


The science of heavy
-
ion fusion is unique

To drive inertial fusion energy or high energy density
physics targets, heavy ion beams must be intense
enough that beam space
-
charge forces (without
plasma neutralization) dominate the ion particle
thermal pressure due to emittance. This
space
-
charge
-
dominated regime

and the associated
collective phenomena
distinguish much of heavy
-
ion
fusion beam science from that of higher energy
particle accelerators. The primary scientific
challenges are to
transport, compress and focus

heavy ion beams onto targets.


A few selected examples of the most important scientific issues follow.

The Heavy Ion Fusion Virtual National Laboratory

Office of Fusion Energy Sciences
-

Targets and Measures


Ten Year Measures for Inertial Fusion Energy and

High Energy Density Physics

Develop the fundamental understanding and
predictability of high energy density plasmas for Inertial
Fusion Energy (IFE).




Minimally Effective Outcome: Develop and apply physical theories and
mathematical techniques to model the physical processes in high
-
energy
density plasmas and intense beams for inertial fusion energy.




Successful Outcome: With the help of experimentally validated
theoretical and computer models, determine the physics limits that
constrain the use of IFE drivers in future key integrated experiments
needed to resolve the scientific issues for inertial fusion energy and high
energy density physics.

The Heavy Ion Fusion Virtual National Laboratory

An important scientific question fundamental to future
application of heavy
-
ion beams to both high energy
density physics and inertial fusion energy:

Can accelerated bunches of heavy ions be compressed to
sufficient intensity to create the high energy density conditions for
warm dense matter and propagating fusion burn in the laboratory?


Some subsidiary science campaigns needed to address this top
-
level
question are:



Determine how well high beam brightness can be preserved under
transport and focusing of intense high current beams.



Understand how beam
-
plasma interactions affect transverse focusing.



Explore the shortest pulses achievable with longitudinal compression.



Measure how uniformly warm dense matter can be heated with
accelerated and tailored ion beams.

The Heavy Ion Fusion Virtual National Laboratory

Random acceleration
and focusing field errors

Aberrations,
emittance
growth,
instabilities
in plasma

Source &

injector

Accelerator

Final focus



Drift compression

Beam mismatches

Beam loss
-
halos, gas desorption,
neutralizing secondary electrons

D
p
z
-

momentum
spread increase
with drift
compression

Issues that can affect
beam emittance
e

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扲楧桴h敳猠B
n
=
I
b
/
e
n
2

STS

HCX

NTX

Current
experiments

Hitting targets allows ~10 x
lower brightness and ~10x
higher
D
瀯p 瑨慮a慴a楮橥捴楯n


How well can initially compact 6
-
D beam phase space
density (~I
b

t

/
e
nx
e

e


)
be preserved through
acceleration, compression, and focusing to the target?

PTSX

The Heavy Ion Fusion Virtual National Laboratory

Example of critical physics issue: beam loss in high intensity accelerators
-
a
current world research topic (GSI
-
SIS
-
18, LANL
-

PSR, SNS)


0 %

2


2%

10%


10%

Ion Beam

(core)

Electron

Fraction

(extreme case)



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.


Random focusing magnet errors

Gradient and displacement errors can
also create halos and beam loss.

Ion Halo

The Heavy Ion Fusion Virtual National Laboratory

Example of critical physics issue: drift compression of
bunch length by factors of 10 to 30

Perveance

Final Focus



Drift compression line

Induction acceleration is most
efficient at
t
pulse

~100 to 300 ns

Target capsule
implosion times
require beam drive
pulses ~ 10 ns

Bunch tail has a few percent higher
velocity than the head to allow
compression in a drift line

Physics issues that need more study and experiments:

1.
Balance beam focusing and space
-
charge forces during compression.

2.
Beam heating due to compression (conservation of longitudinal invariant)

3.
Chromatic focus aberrations due to velocity spread

The beam must be confined radially
and compressed longitudinally
against its space
-
charge forces


The Heavy Ion Fusion Virtual National Laboratory

Example of critical physics issue: plasma neutralization
of beam space charge in focusing chamber


Example:
simulations of time histories of a driver Xenon
beam radius at selected points over a 6 meter focal length

Without plasma in the chamber, the ion kinetic energy and linac voltage, length and
cost would have to increase by 2 to 3 x to recover the 2 mm focal spot for the target

With

by plasma

Target

No

by plasma

The Heavy Ion Fusion Virtual National Laboratory

Status of heavy ion fusion research


Past research (prior to FY01) validated fundamental beam dynamics
with low current (mA
-
scale) beams with correct energy/current ratios for
relevant space
-
charge regimes.


Research since FY01 has completed initial phase of experiments on
injection (STS), transport (HCX) and focusing (NTX) at higher currents
(25 to 250 mA) where non
-
ideal effects can be studied, such as gas and
electron effects, and neutralization of beam space charge with plasma.


More research is needed and planned (FY04
-
06 ) to complete high
current experiments, and to study longitudinal physics, including drift
compression.


An integrated beam experiment to study beam brightness evolution
from the source through acceleration, drift compression and focusing
to the target is the appropriate (proof
-
of
-
principle) next step.

The Heavy Ion Fusion Virtual National Laboratory

Past research (prior to FY01) validated fundamental
beam dynamics with low current (few mA scale) beams

Final
-
Focus Scaled Experiment

showed
ballistic focusing at 1/10 scale, and
neutralizing electrons from a hot filament
could reduce the focal spot size


Some examples:



Single
-
Beam Transport Experiment
(SBTE)

Verified simulations of transport over 86 electric
quadrupoles with negligible emittance growth.

Multiple
-
Beam Experiment with 4 beams

(MBE
-
4)

Studied 200
-
900 keV acceleration, >5 x current
amplification in drift compression, longitudinal
confinement, and multiple
-
beam transport

The Heavy Ion Fusion Virtual National Laboratory

Source
-
Injector Test Stand (STS


operating at LLNL)

Beamlet brightness
measurement meets
IFE requirement

Injector Brightness:

source brightness,
aberration control with
apertures, beamlet
merging effects


0


5


10


15


20

0.0

0.5

1.0

Z

Z (m)

0.5 m

Merging
-
beamlet simulation

(Recent paper submitted
for publication in Review
of Scientific Instruments.
Simulation published Jan
2003 Phys. Rev Special
Topics
-
Accelerators and
Beams)

The Heavy Ion Fusion Virtual National Laboratory

High Current Experiment (HXC
-

operating at LBNL)

ESQ injector

Marx

Matching and
diagnostics

10 ES quads

End Diagnostics



Low
e
n

~ 0.5
p


-
浲m
⡮敧汩e楢汥i杲潷瑨⁡猠
simulations predict)


Envelope parameters
within tolereances for
matched beam transport

1 MeV K+ on SS target, baked overnight & run at 220 C (1-8-03)
0
50
100
150
76
78
80
82
84
86
88
90
Angle of incidence (deg.)
Coefficient of electron emission
N_e/N_b
6.06/cos
New Gas
-
Electron Source Diagnostic
(GESD) shows secondary electrons per ion
lost follows theory (red curve)

Four magnetic quadrupoles
and additional diagnostics
have been recently added to
study gas and secondary
electron effects

Propagation of
longitudinal perturbation
launched at t = 0.

(Recently submitted for
publication in Physical
Review Special Topics
-
Accelerators and Beams)

The Heavy Ion Fusion Virtual National Laboratory

Neutralized Transport Experiment (NTX
-

operating at LBNL)

Focusing magnets

Pulsed arc

plasma source

Drift tube

Scintillating glass

Space charge
blow
-
up causes
large 1
-
2 cm
focal spots

without plasma.

Smaller 1 to 2 mm
focal spot sizes with
plasma are consistent
with WARP/LSP PIC
simulations.


(Submitted for publication
in Physical Review Special
Topics
-

Accelerator and
Beams)

400 kV Marx / injector

.
Envelope
simulation
of NTX
focusing
with and
without
plasma

The Heavy Ion Fusion Virtual National Laboratory

Small
-
scale experiments are available to study long
-
path transport physics such as slow emittance growth

The Paul Trap Simulator
Experiment at PPPL uses
oscillating electric quadrupole
fields to confine ion bunches
for 1000s of equivalent lattice
periods (many kilometers).

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.

The Heavy Ion Fusion Virtual National Laboratory

A key goal is an
integrated
,
detailed
, and
benchmarked
source
-
to
-
target beam simulation capability

ES / Darwin PIC and moment models
EM PIC
rad -
hydro
WARP: 3d, xy, rz, Hermes
LSP
EM PIC,

f, Vlasov
LSP BEST WARP-SLV
Track beam ions consistently along entire system

Study instabilities, halo, electrons, ..., via coupled detailed models

Systems code IBEAM for synthesis, planning

The Heavy Ion Fusion Virtual National Laboratory

Understanding how the beam distribution evolves passing
sequentially through each region requires an integrated experiment

NTX
-
focusing

HCX
-

transport

STS
-

injection


The beam is collisionless, with a “long memory”



Its distribution function
---

and its focusablity
---

integrate the


effects of applied and space
-
charge forces along the entire system

NOW

NEXT

A source
-
to
-
target
integrated beam experiment
(IBX) which sends a high
current beam through
injection, acceleration, drift
compression, and final
focus





Combine these
elements and add
acceleration and
drift compression

The Heavy Ion Fusion Virtual National Laboratory

Ion accelerators provide a complementary tool to
lasers for High Energy Density Physics


Intense accelerator beam physics is itself part of the broad field of high
energy density physics.



Accelerator
-
produced ion beams can be tailored in velocity spread and at
energies near the Bragg peak to provide a tool to control and improve
deposition uniformity in thin foil targets. How much uniformity is possible
and how much it improves equation
-
of
-
state measurement accuracy
needs further exploration. Future accelerators could drive large volume
targets.



Ion
-
driven high energy density physics benefits from the same
accelerator and beam
-
plasma physics base needed for inertial fusion.



Laser

produced ion beams such as L’Oasis @ LBNL may also allow near
-
term studies of collective effects of intense ion beams in regimes relevant
to heavy
-
ion fusion.



There are excellent opportunities for collaboration in ion
-
driven high
energy density physics at GSI.

The Heavy Ion Fusion Virtual National Laboratory

Two ion dE/dx regimes are available to obtain uniform ion energy
deposition in 1 to few eV warm
-
dense matter targets


Linacs with ~
1 J

of ions @
~0.3 MeV/u

would work best
at heating thin foils near the
Bragg peak where dE/dx~ 0.





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⡇物獨慭Ⱐ偐偌⤮

Key
-
physics
issue: can < 300 ps ion pulses
to avoid hydro
-
motion be
produced?

z

dE/dx

Heavy ion beams of
>300 MeV/u

at GSI must heat thick
targets with ions well above the Bragg peak


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required
@ <300 ns

to achieve



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~3
m
m

~3 mm

The Heavy Ion Fusion Virtual National Laboratory

Key scientific issue for ion accelerator
-
driven HEDP: limits of beam
compression, focusing and neutralization to achieve short (sub
-
nanosecond) ion pulses with tailored velocity distributions.

z=900 cm

z=940 cm

z=100 cm

z=500 cm

z=980 cm

Recent HIF
-
VNL simulations of neutralized drift compression of heavy
-
ions in IBX are encouraging: a 200 ns initial ion pulse compresses to
~300 ps with little emittance growth and collective effects in plasma.

Areas to explore to enable ion
-
driven HED physics:


Beam
-
plasma effects in
neutralized drift compression.


Limits and control of
incoherent momentum spread.


Alternative focusing methods
for high current beams, such as
plasma lens.


Foil heating (dE/dx
measurements for low range
ions < 10
-
3

g/cm
2
) and diagnostic
development.

(LSP simulations
by Welch, Rose,
Olson and Yu

June 2003)

Ion driven fast ignition possibility ?

The Heavy Ion Fusion Virtual National Laboratory

Conclusions


Space
-
charge
-
dominated beam regimes and associated collective
phenomena

distinguishes much of heavy
-
ion fusion beam science from
that of higher energy particle accelerators, and poses the primary
scientific challenges:
transport, compress and focus

heavy
-
ion beams
onto targets.




High current experiments in injection (STS), transport (HCX) and
focusing (NTX) are underway at higher currents ( 25 to 250 mA) where
non
-
ideal effects can be studied, such as gas and electron effects, and
neutralization of beam space charge by background plasma.



An integrated beam experiment to study beam brightness evolution from
the source through acceleration, drift compression and focusing to the
target is the appropriate (proof
-
of
-
principle) next step.



Accelerator
-
produced ion beams can be tailored in velocity spread and at
energies near the Bragg peak to provide a tool to control and improve
deposition uniformity in thin foil targets. How much uniformity is possible
and how much it improves equation of state measurement accuracy need
further exploration.