The
Ion Sources
Sources
The ISIS
ISIS Penning
Penning Ion
Ion Source
Source and
and the
the Volume
Volume
Ion
−
from
from Frankfurt
Frankfurt and
and DESY
DESY for
for H
H" Production
Production
#
@
J.
J. Peters
Peters@
J. W.
W. G.
G. Thomason*,
Thomason*, H.
H. Klein
Klein*,, J.
*
CLRC RAL, Didcot,
*CLRCRAL,
Didcot, Oxon,
Oxon, UK
UK
#
#IAP, Germany
@ IAP, Germany
@DESY, Germany
DESY, Germany
−
Abstract.
the Institut
Institut fur
für Angewandte
Angewandte
Abstract. HH~ ion
ion source
source development
development work
work atat Rutherford
Rutherford Appleton
Appleton Laboratory
Laboratory (RAL),
(RAL), the
Physik
(IAP)
in
Frankfurt
and
the
Deutsches
Elektronen-Synchrotron
(DESY)
will
be
described,
along
with future
future
Physik (IAP) in Frankfurt and the Deutsches Elektronen-Synchrotron (DESY) will be described, along with
avenues
ion source
will be
be presented
presented in
in the
the context
context
avenuesofofresearch.
research. The
The most
most recent
recent values
values of
of important
important parameters
parameters for
for each
each ion
source will
of
Source (ESS).
(ESS). A
A brief
brief progress
progress
of next
next generation
generation particle
particle accelerators,
accelerators, particularly
particularly the
the proposed
proposed European
European Spallation
Spallation Source
report
RAL ion
ion source
source measurements
measurements were
were taken,
taken, will
willbe
beincluded.
included.
reporton
onthe
the ISIS
ISIS RFQ
RFQ test
test stand,
stand, on
on which
which many
many of
of the
the RAL
INTRODUCTION
INTRODUCTION
r
AA key
key element
element in
in the
the design
design of
of the
the ESS
ESS is
is the
the ion
ion
source
for
producing
pulsed
currents
at
relatively
source for producing pulsed currents at relatively high
high
duty
duty cycles.
cycles. The
The minimum
minimum requirement
requirement for
for the
the ESS
ESS−
short
pulse
option
is
a
source
delivering
a
60
short pulse option is a source delivering a 60 mA
mA H
FT
ion
ion beam
beam inin 1.0
1.0ms
ms pulses
pulses atat aa repetition
repetition rate
rate of
of 50
50 Hz
Hz
(5%
(5% duty
duty cycle)
cycle) and
and with
with aa low
low normalised
normalised rms
rms
emittance
~
0.1
π
mm
mrad
(although
emittance ~ 0.1 71 mm mrad (although aa normalised
normalised
rms
rms emittance
emittance of
of0.2
0.2–- 0.3
0.3πnmm
mmmrad
mrad at
at the
the entrance
entrance
−
to
the
RFQ
would
be
acceptable).
If
H
ions
to the RFQ would be acceptable). If FT ions are
are also
also to
to
be
used
for
the
ESS
long
pulse
option
a
similar
source
be used for the ESS long pulse option a similar source
will
will be
be required,
required, but
but delivering
delivering 2.0
2.0 ms
ms pulses
pulses at
at aa
repetition
rate
of
50/3
Hz
(3.3%
duty
cycle).
repetition rate of 50/3 Hz (3.3% duty cycle). In
addition
addition to
to meeting
meeting these
these requirements
requirements these
these sources
sources
1
must
mustoperate
operate with
withhigh
high availability
availability and
and reliability
reliability1.
ICffliflni
a
FIGURE
cross section
section of
of the
the Frankfurt
Frankfurt H~
H−
FIGURE 1.
1. Schematic
Schematic cross
volume
volume source.
source.
As a result of these experiments,
experiments, the
the ion
ion source
source
3
shown in figure
1
has
been
chosen
for
further
study
figure
chosen for further study3..
The plasma chamber of the
the ion
ion source
source isis made
made of
of aa
water-cooled copper cylinder 7.0
7.0 cm in
in diameter
diameter and
and
10.0
is surrounded
surrounded by
by ten
ten CoSm
CoSm
10.0 cm in depth. It is
magnets in cusp field
field arrangement. Near the
the chamber
chamber
axis are mounted four
four tungsten filaments
filaments of
of 1.8
1.8 mm
mm
diameter. The front
front end of the
the chamber
chamber is
is enclosed
enclosed by
by
the plasma electrode. An electromagnet
electromagnet isis installed
installed in
in
the flange
of
the
plasma
electrode.
Its
transverse
flange
the plasma electrode. Its transverse
magnetic field
electron filter.
filter. An
An
field (Bff) acts as an electron
external oven for introducing
introducing caesium
caesium isis mounted
mounted on
on
the flange
flange of the plasma electrode.
electrode.
−
ItIt has
has been
been recognised
recognised that
that no existing H
FT ion
source
sourcecan
can immediately
immediately fulfil
fulfil the
the needs
needs of the
the ESS,
ESS, but
that
a
source
to
meet
the
minimum
requirements
could
that a source to meet the minimum
be
developed
from
present
technologies
within
be developed from present technologies within the
1, 2
time
the
time scale
scale of
of building
building the
the ESS
ESS1' . Two types, the
volume
volume source
source and
and the
the Penning
Penning source,
source, have been
confirmed
confirmed as
assuitable
suitable candidates
candidates for
for development.
development.
THE
THEFRANKFURT
FRANKFURT VOLUME
VOLUME SOURCE
SOURCE
The
The low
low electron
electron temperature
temperature and
and the
the high
high achievable
achievable
current
current densities
densities which
which characterise
characterise volume
volume sources
sources
make
make them
them one
one of
of the
the candidates
candidates for
for the
the ESS injector.
Several
Several source
source prototypes
prototypes have
have been
been used in
experiments atatIAP
IAP in
in Frankfurt
Frankfurt to
to test
test different
different source
source
experiments
geometries and
and methods
methods of
of plasma
plasma confinement,
confinement, and
and
geometries
tooptimise
optimise the
the cathode
cathode configuration.
configuration.
to
The electron
is extracted
extracted along
along with
with
electron beam which is
the H
behind the
the extractor
extractor at
at full
full
FT− ions is dumped behind
energy into a water-cooled
water-cooled cup.
cup. The
The extension
extension of
of the
the
filter magnet field
filter
field into the extraction
extraction gap
gap deflects
deflects the
the
electron beam out of the
the beam
beam axis
axis and
and an
an additional
additional
transverse magnetic field
field (Bss) is
is then
then used
used to
to steer
steer the
the
electron beam into the dumping tube.
tube.
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
293
Experiments have shown that, in operation with
caesium, the ion source is capable of producing 120
mA of IT beam, measured using a Faraday cup, at an
arc power of 47.5 kW (50 Hz, 1.2 ms). With caesium
the IT emission current is up to 4.5 times higher, and
the e/IT ratio is about 7 at 47.5 kW. The emittance of
the source has yet to be measured, but other beam
diagnostics have provided a plausible estimate that the
normalised rms emittance should be < 0.1 n mm mrad.
With the present filament configuration the ion
source has been run for 180 hours at an arc power of
40 kW, during which the diameter of the filaments was
reduced from 1.8 mm to 1.5 mm. Since the filaments
can be used down to a thickness of about 0.9 mm the
ion source lifetime could be expected to be about 15
days.
Caesium is injected on demand only, so there is
wear of the caesium layer, which has to be rebuilt
every 10 to 18 hours, requiring a reduction in the arc
power for about 15 minutes. A caesium injection
system will be developed that will allow caesium
injection at higher powers.
FIGURE 2. The DESY volume source with A12O3 antenna
cover.
An investigation of the production of an rf-driven
version of the Frankfurt volume source using an
external antenna based on the DESY design is planned
as part of a European initiative on negative ion
sources5, and may provide a source for ESS with
enhanced lifetimes.
The first phase of this study has shown that the
Frankfurt volume ion source has the potential to fulfil
the requirements for ESS, but further research and
development is required to improve the lifetime and
demonstrate the reliability of the source.
THE ISIS PENNING SOURCE
The ISIS ion source in operation at RAL is shown
in figure 3. It is a surface plasma ion source of the
Penning type, and routinely produces 35 mA of IT
ions (50 Hz, 200|is for uninterrupted periods of up to
50 days6'7. Caesium is used to enhance the production
of H~ ions by lowering the work function of the
cathode surface. In non-operational periods of ISIS the
source has delivered 55 mA for sustained periods in its
present form, which corresponds to a current density
of ~ 1 A cm"2, which is considerably higher than is
possible in volume sources. The e/IT ratio is ~ 1 and
so a relatively low electron current is extracted
simultaneously with the IT ion beam. The ISIS source
has slit extraction geometry, but the extracted beam is
immediately passed through a 90° sector magnet with
gradient n=l, which separates out any electrons and
produces an approximately round beam profile.
THE DESY VOLUME SOURCE
The DESY rf-driven volume source was developed
from a design from Lawrence Berkeley National
Laboratory, but incorporating an antenna situated at
the wall of the source, completely covered by an
Al2Os ceramic4, as shown in figure 2. By removing the
antenna from the discharge chamber it is protected
from sputtering damage, and so antenna lifetime no
longer presents a limit to source performance. The
DESY source has now been run for more than 25,000
hours with no antenna failure. In normal operation,
without the addition of caesium, the source produces
48 mA of tT ions (10 Hz, 150|is) with a normalised
rms emittance of 0.2 n mm mrad.
A collar has been introduced into the source for
electron suppression, and considerable effort has gone
into the optimisation of its geometry, bias and
material. With this collar in place an tT current of 80
mA has been reached.
A dedicated ion source development rig (ISDR)
has been built at RAL that will allow further
development of the source to meet the duty cycle and
intensity requirements of the ESS8. The ISDR will
allow extraction at energies greater than the present 18
keV and emittance measurements to be made close to
the source.
294
ion
ionbeam
beam
ion
beam
extractor
extractor
extractor
introduced
IfIf this
proves
ineffective
introduced most
most efficiently.
efficiently. If
this proves
proves ineffective
ineffective aaa
introduced
most
efficiently.
this
scaling
approach
similar
to
that
previously
adopted
on
scaling
approach
similar
to
that
previously
adopted
on
scaling approach similar to that previously adopted
on
99
the
4X
and
8X
sources
at
Los
Alamos
9 may be
the
4X
and
8X
sources
at
Los
Alamos
the 4X and 8X sources at Los Alamos may be
adopted,
component
dimensions
has
adopted, where
where increasing
increasing component
component dimensions
dimensions has
has
adopted,
where
increasing
been
shown
to
offset
heating
effects.
been
shown
to
offset
heating
effects.
been shown to offset heating effects.
The
ion
source
results
at
RAL
have
The most
most recent
recent ion
ion source
source results
results at
at RAL
RAL have
have
The
most
recent
10
10
been
produced
on
the
ISIS
RFQ
test
stand
have
10 and
been
produced
on
the
ISIS
RFQ
test
stand
and
been produced on the ISIS RFQ test stand and have
demonstrated
rms
emittances
of
0.16
demonstrated normalised
normalised rms
rms emittances
emittances of
of εε8HHH=== 0.16
0.16
demonstrated
normalised
ππnmm
mrad
and
ε
=
0.24
π
mm
mrad
for
the
standard
mm
mrad
and
e
=
0.24
n
mm
mrad
for
the
standard
V
mm mrad and εVv= 0.24 π mm mrad for the standard
ISIS
pulse
of
200
µs
at
35
mA
ISIS source
source with
with aaa beam
beam pulse
pulse of
of 200
200 µs
|is at
at ≈≈~ 35
35mA
mA
ISIS
source
with
beam
(figure
4).
In
addition
the
solenoid
matching
system
(figure
4).
In
addition
the
solenoid
matching
system
(figure 4). In addition the solenoid matching system
has
excellent
matching
into
the
has been
been shown
shown to
to provide
provide excellent
excellent matching
matching into
intothe
has
been
shown
to
provide
RFQ,
allowing
transmission
factors
through
the
RFQ
RFQ,
allowing
transmission
factors
through
the
RFQ, allowing transmission factors through the RFQ
of,
an
input
current
of
36
mA.
of, typically,
typically, 91%
91% for
for an
an input
input current
current of
of 36
36 mA.
mA.
of,
typically,
91%
for
Further
and
development
of
the
Penning
Further research
research and
and development
development of
of the
the Penning
Penning
Further
research
source
is
needed
to
meet
the
ESS
specifications,
but
source
is
needed
to
meet
the
ESS
specifications,
source is needed to meet the ESS specifications, but
this
is
not
a
large
extrapolation
from
current
this
is
not
a
large
extrapolation
from
current
this is not a large extrapolation from current
performance
considered
feasible
in
the
performance and
and is
considered feasible
feasible in
in the
the
performance
and
isis considered
timescale
timescaleof
ofthe
the ESS.
ESS.
timescale
of
the
ESS.
aperture
apertureplate
plate
aperture
plate
discharge
dischargeregion
region
discharge
region
Penning
PenningBB
Bfield
field
Penning
field
anode
anode
anode
source
sourcebody
body
source
body
ceramic
ceramic
cathode
cathode
cathode
10
mm
10mm
10
mm
mica
mica
mica
flange
flange
flange
copper
copperdisc
disc
copper
disc
FIGURE
FIGURE3.3.
3.Schematic
Schematicof
ofthe
theISIS
ISISion
ionsource.
source.
FIGURE
Schematic
of
the
ISIS
ion
source.
horizontal
horizontalemittance
emittance54−216
54-216µs
\LS
horizontal
emittance
54−216
µs
100
100
100
εε
==0.16
0.16ππmm
mmmrad
mrad
ACKNOWLEDGMENTS
ACKNOWLEDGMENTS
ACKNOWLEDGMENTS
rms
rms
x′ (mrad)
x′ (mrad)
50
50
50
The
like
to
thank
K.
Volk
and
R.
The authors
authors would
would like
like to
to thank
thank K.
K. Volk
Volk and
and R.
R.
The
authors
would
Sidlow
contributions
to
ion
source
Sidlow for
for invaluable
invaluable contributions
contributions to
to ion
ion source
source
Sidlow
for
invaluable
development at
at IAP
IAP and
and RAL,
RAL, respectively,
respectively, and
and A.
A. P.
P.
development
and
RAL,
respectively,
and
A.
P.
development
at
IAP
Letchford
and
C.
P.
Bailey
for
data
from
the
Letchford
and
C.
P.
Bailey
for
data
from
the
ISIS
RFQ
Letchford and C. P. Bailey for data from the ISIS RFQ
teststand.
stand.
test
test
stand.
00
-50
−50
−50
-100
−100
−100
−6
−6
−2
−2
−4
−4
2 00 0
(mm)
xxx(mm)
(mm)
REFERENCES
REFERENCES
2
22
44
66
Ferdinand, R.,
R., Klein,
Klein, H.
H. and
and Thomason,
Thomason, J.
J. W.
1.1. Ferdinand,
J.
W. G.,
G., ESS
ESS
Workshop on
on Sources,
Sources, 28
28 November
November 2001,
2001, Saclay,
Saclay, ESS
ESS
Workshop
2001,
Saclay,
ESS
report,(April
(April2002)
2002)
report,
verticalemittance
emittance54−216
54-216µs
^s
vertical
vertical
emittance
54−216
µs
100
100
100
εrms
0.24ππmm
mmmrad
mrad
ε ==0.24
Schroder,L.,
L.,Leung
LeungK-N.,
K-N.,and
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Relevant to
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Pulsed
Workshop
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to
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66
High Performance
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4.Ion
Ionsource
sourceemittances
emittancesfrom
from the
theISIS
ISISRFQ
RFQ test
test
FIGURE
Ion
source
emittances
from
the
ISIS
RFQ
test
FIGURE
stand.
stand.
stand.
Thomason, J.J. W.
W. G.
G. and
and Sidlow,
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EPAC 2000,
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R.,
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2000,
THP4A07,(2000).
(2000).
THP4A07,
Thesource
sourceisisisvery
verycompact,
compact,and
andthe
theprimary
primaryproblem
problem
The
source
very
compact,
and
the
primary
problem
The
to
solve
is
that
of
stabilisation
of
the
cathode
and
solve isis that
that of
of stabilisation
stabilisation of
of the
the cathode
cathode and
and
toto solve
anode
temperatures
at
the
higher
power
levels
required
anodetemperatures
temperaturesatatthe
thehigher
higher power
power levels
levels required
required
anode
forthe
shortand
andlong
longpulse
pulseoptions
options by
bymeans
means of
of
for
theESS
ESSshort
short
and
long
pulse
options
by
means
of
for
controlled
cooling.
The
thermal
properties
of
the
controlled
cooling.
The
thermal
properties
of
the
controlled cooling. The thermal properties of the
standard ISIS
ISIS source
source will
will be
be modelled
modelled and
and this
this
standard
ISIS
source
will
be
modelled
and
this
standard
simulationwill
willthen
thenbe
beextended
extendedto
tolonger
longerduty
dutycycles
cycles
simulation
will
then
be
extended
to
longer
duty
cycles
simulation
in order
order toto
to establish
establish how
how additional
additional cooling
cooling can
can be
be
order
establish
how
additional
cooling
can
be
inin
8. Thomason,
Thomason,J.J.W.
W.G.,
G.,etetal.,
al,RSI
RSI73(2),
73(2),(2002).
(2002).
8.
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(2002).
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H.V.,
V.,etetal.,
al.,RSI
RSI65(1),
65(1),(1994).
(1994).
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(2000).
295