IFMIF - A Challenging High-Intensity Accelerator
Robin Ferdinand
DSM/DAPNIA/SACM
CEA-Saclay
bldg. 124, 91191 Gif-sur-Yvette cedex, FRANCE
Abstract. The International Fusion Materials Irradiation Facility (IFMIF) employs an accelerator based D-Li intense
neutron source as defined in the 1995-96 Conceptual Design Activity (CDA) study under the direction of the IFA's
Executive Committee on Fusion Materials. Full performance operation (2 MW/m2 @ 500 cm3) allows to obtain
engineering data for potential DEMO materials under irradiation up to 100-200 dpa and a systematic search for high
performance materials. The linac design is reviewed and described.
INTRODUCTION
Materials required for the fusion reactor must be
able to survive irradiation in a high intensity neutron
field with an energy 14 MeV and annual damage doses
of the order of 20 dpa (displacements per atom).
Concepts for an irradiation test facility suitable for
identifying and validating such materials have been
explored through a number of studies over the period
of the last several decades. An accelerator-based
neutron source using the Deuteron-Lithium (D-Li)
stripping reaction has been selected as the basis of the
International Fusion Materials Irradiation Facility
(IFMIF) studies [l]-[3].
The main specifications for the IFMIF facility are
summarized in Table I. An intense flux of high energy
neutrons will be produced within sufficient irradiation
volume to enable realistic testing of candidate
materials and components up to about a full lifetime of
their anticipated use in DEMO and beyond.
Table 1: IFMIF top-level specifications
Neutron Flux
Operation Availability
D+ Beam Current
D+ Energy
D+ Beam Size
Li Jet Thickness
> 2 MW/m2 (@ 500 cm3)
70%
250 mA (CW, 2x125 mA)
32, 40 MeV
200 mm (width)x50 mm
(height)
19, 25 mm (resp. for 32,
40 MeV D+)
Li Jet Width
260mm
Li Jet Velocity
10-20 m/s
The technological approach adopted in the CDA
design of the IFMIF requires a relatively modest
extension of the current state of the art of the
technology for the radio frequency (RF) linear
accelerators and Li loops. In particular, the need to
achieve the necessary neutron fluences within
reasonable time and to maintain the required long term
uniformity and stability of the neutron flux imposes
high availability and reliability on the entire system
(80.7% for the total facility, 88.0% for the accelerator
facility). In order to assure the high availability and
reliability required for IFMIF, its key technology
elements like the 125 mA D+ linac and a continuously
operating liquid Li system require design and
fabrication of suitable prototypes for performing the
necessary endurance tests.
The basic approach is to provide two linacs
modules, each delivering 125 mA to a common target.
This paper describes the IFMIF linac modules.
COST AND STAGE APPROACH
The IFMIF CDA study was conducted during
1995-1996 [1]. In January 1999, IFMIF design focused
on potential for cost reduction. In addition, staged
deployment was to be examined as an option offering
a potential reduction of the annual expenditures during
construction. The total cost estimate was reduced to
61% of the CDA estimate, from 797.2 MICF to
487.8 MICF [4] (1 MICF - $1M US in January 1996).
The study of cost reduction and staged deployment
considered the following major items:
1) The potential for a future upgrade to four
accelerators with irradiation capability twice that of
the current user requirements, has been eliminated.
2) The building volume was reduced in accelerator
systems and lithium loop components.
In addition, the original CDA specifications were
critically reviewed with the objective of improving
component design and eliminating non-essential items.
For example, the energy dispersion cavity, the buncher
cavities in the High Energy Beam Transport (HEBT)
lines and the associated RF power source were
removed. The HEBT 90-deg beam turning lines were
eliminated. The transition energy between the RFQ
and the DTL was reduced from 8 MeV to 5 MeV.
The IFMIF deployment was assumed to proceed in
three stages, each addressing a specific materials
CP642, High Intensity and High Brightness Hadron Beams: 20th ICFA Advanced Beam Dynamics Workshop on
High Intensity and High Brightness Hadron Beams, edited by W. Chou, Y. Mori, D. Neuffer, and J.-F. Ostiguy
© 2002 American Institute of Physics 0-7354-0097-0/02/$ 19.00
102
development
developmentissue
issue as
as follows:
follows:
an RFQ.
RFQ. The
The RFQ
RFQ bunches
bunches the
the beam
beam and
and accelerates
accelerates
an
125
mA
to
5
MeV.
The
5
MeV
RFQ
beam
injected
125 mA to 5 MeV. The 5 MeV RFQ beam isisinjected
directly
into
a
Room
Temperature
(RT),
rampeddirectly into a Room Temperature (RT), rampedgradient DTL
DTL of
of the
the conventional
conventional Alvarez
Alvarez type
type with
with
gradient
post
couplers,
where
it
is
accelerated
to
32
or
40
MeV.
post couplers, where it is accelerated to 32 or 40 MeV.
A high-energy
high-energy beam
beam transport
transport from
from the
the accelerator
accelerator toto
A
the
lithium
target
must
perform
a
variety
of functions,
functions,
the lithium target must perform a variety of
complicated
by
the
presence
of
strong
space-charge
complicated by the presence of strong space-charge
forces within
within the
the beam.
beam. Very
Very low
low beam
beam losses
losses along
along
forces
the
accelerator
and
transport
lines
is
a
prerequisite
to
the accelerator and transport lines is a prerequisite to
perform
maintenance
without
requiring
remote
perform maintenance without requiring remote
manipulators (no
(no halo
halo development).
development).
manipulators
1st
One
of
1st Stage:
Stage:
One accelerator
accelerator with
with aa maximum
maximum of
50
mA
operation,
to
be
used
for
material
selection
of
50 mA operation, to be used for material selection of
the
theITER
ITERbreeding
breedingblanket
blanket test
test modules,
modules, fusion-fission
fusion-fission
data
correlation
and
generic
damage
data correlation and generic damage studies.
studies.
2nd
2ndStage:
Stage: One
One 2 accelerator
accelerator 3 for
for 125
125 mA
mA
2 @ 500 cm 3), to be used to
operation
(i.e.
1
MW/m
operation (i.e. 1 MW/m @ 500 cm ), to be used to
demonstrate
demonstratematerials
materialsperformance
performance of
of aa reference
reference alloy
alloy
for
DEMO-relevant
fluences.
for DEMO-relevant fluences.
3rd
Two
3rdStage:
Stage:
Two 2 accelerators
accelerators for
for 250mA
250 mA
2 @ 500 cm33), used to obtain
operation
(i.e.
2
MW/m
operation (i.e. 2 MW/m @ 500 cm ), used to obtain
engineering
engineering data
data for
for potential
potential DEMO
DEMO materials
materials under
under
irradiation
up
to
100-200
dpa
and
a
systematic
irradiation up to 100-200 dpa and a systematic search
search
for
forhigh
highperformance
performance materials
materials for
for fusion
fusion reactors.
reactors.
In
the
2nd
stage,
more
RF
stations
are
In the 2nd stage, more RF stations are added
added to
to the
the
accelerator
to
increase
the
current
from
50
to
125
mA.
accelerator to increase the current from 50 to 125 mA.
InIn the
the 3rd
3rd stage,
stage, the
the second
second 125
125 mA
mA accelerator is
installed
installedtotobring
bringthe
thetotal
total beam
beam on
on target
target to
to 250
250 mA.
mA.
Sources
Sources
The IFMIF
IFMIF ion
ion injector
injector must
must deliver
deliver sufficient
sufficient
The
current to
to the
the RFQ
RFQ to
to achieve
achieve aa 125mA
125mA RFQ
RFQ output
output
current
current. This
This implies
implies that
that the
the ion
ion source
source will
will have
have toto
current.
produce an
an estimated
estimated 155mA
155mA DD++ of
of which
which 140
140mA
produce
mA
will be transported
transported through
through the
the LEBT.
LEBT.The
Theinjector
injectorhas
has
to provide excellent
excellent beam
beam quality
quality (transverse
(transverse
In addition
addition to
to high
high performance,
performance, the
the ion
ion
emittance). In
also have
have to
to provide
provide high
high operational
operational
injector will also
availability. There
There are
are two
two possibilities
possibilities for
for the
the IFMIF
IFMIF
availability.
ion source.
source. The
The first
first one
one isis the
theECR
ECRsource
source
deuterium ion
operated successfully
successfully atat Chalk
Chalk River,
River, Los
Los
of the type operated
and at
at Saclay
Saclay for
for the
the IFMIF
IFMIF program.
program. The
The
Alamos, and
second one is
is the
the RF
RF or
or filament
filament driven
driven volume
volume ion
ion
at LBL
LBL and
and under
under development
development for
for
source initiated at
IFMIF at the Institute
Institute for
for Applied
Applied Physics
Physics (IAP)
(IAP)of
ofthe
the
University of
of Frankfurt
Frankfurt and
and JAERI.
JAERI. Ion
Ion source
source
availability may be
be one
one of
of the
the limiting
limiting operational
operational
considerations for
for the
the IFMIF
IFMIF accelerators.
accelerators. Therefore,
Therefore,
the ion source
source design
design will
will emphasize
emphasize preventive
preventive
maintenance,
maintenance, rapid
rapid change
change out
out of
of failed
failed parts
partsand
andrapid
rapid
restoration of
of service.
service.
ACCELERATOR DESCRIPTION
DESCRIPTION
ACCELERATOR
The IFMIF
IFMIF facility
facility requires
requires generation,
generation, by a linear
The
accelerator (LINAC),
(LINAC), of
of 250
250 mA
mA continuous
continuous current of
accelerator
deuterons atat aa nominal
nominal energy
energy of
of 40 MeV, with
deuterons
provision for
for operation
operation at
at ~32
~32 MeV.
MeV. The basic
provision
approach
is
to
provide
two
linacs
modules, each
each
approach is to provide two linacs modules,
delivering
125
mA
to
a
common
target.
This
approach
delivering 125 mA to a common target. This approach
hasavailability
availability and
and operational
operational flexibility
flexibility advantages.
advantages.
has
quasi-continuous operation
operation is
is mandatory.
mandatory. Annealing
Annealing
AAquasi-continuous
times of
of point
point defects
defects would
would introduce
introduce unacceptable
unacceptable
times
uncertainties. Consequently
Consequently RAM
RAM is
is aa major
major concern
concern
uncertainties.
in
the
facility
and
accelerator
design.
in the facility and accelerator design.
Acceleration of
of high
high current
current cw
cw D
D++ beams
beams
Acceleration
(125mA)
mA) has
has not
not yet
yet been
been demonstrated,
demonstrated, although
although
(125
recent experiments
experiments with
with the
the 100
100 mA
mA cw
cw proton
proton beams
beams
recent
at
the
LEDA
in
Los
Alamos
[5]
represent
a
significant
at the LEDA in Los Alamos [5] represent a significant
steptowards
towardsthis
thisgoal.
goal.
step
cw 155-mA
155-mA deuteron
deuteron beam
beam is
is extracted
extracted from
from the
the
AAcw
ion
source
at
95
keV.
A
low
energy
beam
transport
ion source at 95 keV. A low energy beam transport
(LEBT) guides
guides the
the deuteron
deuteron beam
beam from
from the
the source
source to
to
(LEBT)
Recently the
the ion
ion sources
sources showed
showed significant
significant
progress. The CEA-Saclay
ECR
source
CEA-Saclay ECR source was
was able
able to
to
demonstrate 95
kV,
114
mA
with
99.8%
availability
95 kV, 114mA with 99.8% availability
over
over 160
160 hours
hours (about
(about 11 spark
spark per
per day).
day). The
The ECR
ECR
source
source has
has no
no intrinsic
intrinsic lifetime
lifetime limitations,
limitations, and
and isis
power
power efficient
efficient (RF
(RF window
window isis located
located behind
behind aabend
bend
and
and was
was never
never changed
changed since
since 1996).
1996). The
The source
source
worked
worked also
also in
in pulse
pulse deuteron
deuteron mode
mode (2ms/s)
(2ms/s) inin order
order
to
minimize
the
neutron
production
(d,D
to minimize the neutron production (d,D reaction)
reaction) inin
+
the
gives
the LEBT.
LEBT. A
A coherent
coherent set
set of
of measurements
measurements
givesaaDD+
++
current
current of
of 130
130 mA
mA (@100
(@100 kV)
kV) with
with aa DD fraction
fraction over
over
96%,
96%, LEBT
LEBT transparency
transparency of
of 75
75 %
%and
andrms
rmsbeam
beamnoise
noise
of
% (mainly
kHz lines
of 1.2
1.2%
(mainly 19
19kHz
lines coming
coming from
from the
the
magnetron
power
supply).
Up
to
mA
magnetron power supply). Up to 170
170mA
(267
(267 mA/cm²)
mA/cm2) were
were extracted.
extracted.
IAP
Frankfurt
Source
IAP Frankfurt Source reached
reached also
also IFMIF
IFMIF design
design
current.
The
volume
source
produced
200
mA
protons
current. The volume source produced
200
mA
protons
+
(corresponding
(corresponding to
to 140
140 mA
mA DD+)) inin cw
cwmode
modeasaswell
wellasas
in
pulsed
mode
(1
msec
pulse
length,
50
Hz
repetition
in pulsed mode (1 msec pulse length, 50 Hz repetition
103
rate) with excellent beam quality and low noise.
assumes the use of tetrode or diacrode technology with
an output power level of 1.0 MW and a frequency of
175 MHz. The same relatively low frequency in both
the RFQ and DTL is a conservative approach for
delivering the high current deuteron beam with low
beam loss in the accelerator. This will facilitate the
achievement of hands-on maintainability without
remote manipulators. It also provides operational
simplification.
JAERI is testing in parallel three candidate ion
sources on the same test stand (same beam extraction
system and instrumentation).
RFQs
The RFQs accelerate the beams from 95 keV to
5 MeV. They are four vanes structures to ensure steady
operations (based on LEDA [5] already achieved
performances and IPHI developments) and minimum
power consumption compared to coaxial RFQs. To
achieve this in a stable, tuneable cavity, the RFQ will
be composed in three segments resonantly coupled
(damping of field errors [6]). The transmission is about
97.9%. lAP-Frankfurt evaluates the 4-rod type RFQ.
In both cases, the RFQs lengths are about 12.5m long,
requiring 3 RF systems each.
IFMIF needs 12x2 1 MW RF station. Since at the
time of the design no such source was existing,
development and testing of a RF system was identified
as the highest impact development item. As a
consequence, a follow up of the progress in the world
was organised. THALES diacrode TH628 tube is a
candidate tube for IFMIF. This diacrode has delivered
1 MW cw @ 200 MHz. Monitoring of a long test
(lOOOh, 1MW cw) is on-going with success.
DTLs
High power beam diagnostics
The IFMIF DTL design is based upon conventional
Alvarez technology with post couplers for field
stabilization. The 5 MeV RFQ output energy allows
the use of conventional electromagnetic quadrupoles
which may help restricting the halo development. They
preserve the beam quality but at the expense of lower
shunt impedance (bigger tubes). A FD focussing
scheme is chosen. The phase advance per meter is
conserved between RFQ output and DTL input. The
DTLs consist in 5 tanks for a total length of 28.9m.
They require the use of 9 RF tubes. A 4-cell hot model
prototype is being built to test the cw, high current
DTLs technological feasibility of quadrupole magnet
design and fabrication, vacuum problems, cooling,
mechanical aspects, etc. Two drift tubes incorporating
two conventional quadrupole magnets have been
designed by AES [7] and CEA-Saclay and built. They
are of two different types. Tests will be done soon at
CERN. IAP is exploring the less common IH DTL
type of structure.
IFMIF beam power is about 15 kW after the
source, 625 kW after the RFQ and 5 MW in the HEBT
after the DTL. Any interceptive diagnostics would
immediately melt. New types of diagnostics mostly
based on light analyses are developed [8]. As an
example, the profile and position measurement based
on Doppler effect emitted light can be mentioned.
ACKNOWLEDGMENTS
Thanks to many participants in many countries:
Bob Jameson from USA, Horst Klein and his IAPFrankfurt team, Masayoshi Sugimoto and his JAERI
Japan team, AES team in US and CEA-Saclay team.
REFERENCES
1. IFMIF CD A final report, ENEA Frascati Report,
RT/ERG/FUS/96/11 (1996) edited by M. Martone.
2 FZK Report, FZKA 6199 (1999) edited by A. Moslang.
3 A. Moslang et. al., "Suitability and feasibility of the
International Fusion Materials Irradiation Facility
(IFMIF) for fusion materials studies", Fusion Energy
1998 (Proc. of 17th Int. Conf. Yokohama, 1998) p. 1203,
IAEA, Vienna (1999)
4 JAERI-Tech 2000-014 (2000) compiled by M. Ida
5 H.V. Smith, and J. D. Schneider, "Status report on the
low-energy demonstration accelerator (LEDA)",
proceedings of Linac 2000, Monterey, USA, p581
6 L. Young, "Segmented Resonant Coupled RFQ",
proceeding PAC 1993, Washington, D.C..
7 Advanced Energy Systems, Inc., "Conceptual design
development of the 5 MeV drift tube for the IPHI drift
tube linac - Phase I final report", April 23, 1999.
8 R. Ferdinand, "High current ECR source for protons and
deuterons at Saclay", this conference.
Linac sections were matched and multi-particle
simulations were done from the first RFQ input to the
linac exit. The input distribution is a 4D water-bag.
Without errors, there is no emittance growth and no
losses in the DTL. In order to evaluate the beam losses
arising from the beam dynamics in high space charge
conditions in a real linac, typical errors on linac
element have been defined and simulated (the
machining errors are different between the RFQ and
the DTL). As a result, the minimum ratio between the
bore radius and the 10~6 level is about 1.25.
RF system
The RF power system for the IFMIF accelerator
104