Progress and perspective for high frequency, high performance
superconducting ECR Ion Sources
Daniela LeitnerM L Galloway, T.J. Loew, C.M. Lyneis, D.S. Todd
CYCLOTRONS 2007, Giardini Naxos, Messina, Italy
• Introduction• 3rd Generation ECR ions source / VENUS project• Key parameters for the performance of an ECR• Recent results from VENUS• Perspectives on 4th generation ECR ion sources
2The requirements of next generation heavy ion facilities made the development of 3rd Generation sources (and maybe 4th Generation) ECR ion sources necessary
SC-ECRIS, RIKEN, Japan
Post Accelerator
Isotope Separator
Fragmentation Production Target
Fragmentation Separator
Driver Linac (400 MeV/nuc U, 900 MeV p)
RFQ’s
Experimental Areas
“Gas Catcher”
Nuclear Structure
In Flight Separation
IsotopeRecovery
E< 15 MeV/u E>50 MeV/u
Applied Physics
Astro Physics
E< 1 MeV/u
No Acceleration
VENUS, 270 eµA U33+ and 270 eµA U34+
SPIRAL 2, GANIL, France
SECRAL, Lanzhou, China
H. Zhao
MS ECRISGSI, Germany
SuSINSCL,USA
525 eµA U35+
50-100 eµA U41+
1mA Ar12+
VENUS has a dual mission: Major upgrade for the 88-Inch Cyclotron and prototype for next generation heavy ion facilities
Produce intense (very) high-charge-state heavy ion-beams for the 88-Inch Cyclotron q/A .2 to .5
Provide (very) high intensity high-charge state beams for the next generation heavy ion accelerators q/A .14
0
5
10
15
20
25
30
35
0 50 100 150 200 250
Ene
rgy
in M
eV/a
mu
Pa rticle Mass in amu
Evolution of the 88-Inch Cyclotron Performance for
Heavy Ions at 1pnA
VENUS
AECR-U 1995
ECR- 1989
PIG-1984
Experimental Areas
Post Accelerator
Driver LINAC FRIB (RIA)
Superconducting magnetsstate of the art cryostat
Beam transport with high transmission dipole magnet
28 GHz microwave technology
Design solutions developed in VENUS have been incorporated in the design of other 3rd generation ECR ion sources
Ta X-ray shield
VENUS is the first and currently only high field SC ECR ion source optimized for and operated at 28 GHz
Aluminum plasma chamber for high power operation with incorporated x-ray shield
Water cooling for high power
The demonstrated source performance show that the next generation accelerator performance requirements are possible
2300 e•A2860 e•AO6+
810 e•A850 e•AO7+
5 e•A
200 e•A
.5 e•A
28 e•A
36 e•A
860 e•A
∼ 400 e•A
VENUS28GHz or
28+18 GHz
Xe42+
8.5 e•AAr17+
510 e•AAr12+
U47+
U34+
12 e•AXe35+
O8+
SECRAL(18 GHz)
e•A
0
50
100
150
200
250
5 6 7 8 9 10 11
Ana
lyze
d C
urre
nt [e
µA]
Mass to Charge Ratio
3132
3334
35
36
37
38
39
29
28
2726
2524
23
O2+
O3+
4kW 28 GHz770 W 18 GHz
High Intensity Uranium Production
6kW 28 GHz770 W 18 GHz
Coupling of VENUS to the 88-Inch Cyclotron
Mission (since 2004) 5000 hours/year, 10/4 operation• Conduct basic research in low energy nuclear
physics and chemistry 60%– with a special emphasis on the training of the next
generation of nuclear scientists.• Support national security and other US space
programs in the area of radiation effects testing 40%• R&D directed toward Rare Exotic Beam accelerators
(GRETA/GRETINA, VENUS)
Beam line connection into the axial injection line
Solenoid Lens
Vertical 90°ROBIN Magnet
To Cyclotron Center
First Beam from VENUS extracted from the Cyclotron September 2006, Ar9+ at 200 MeV
Faraday Cupand Diagnostics
VENUS beam
Horizontal 90°BATMAN Magnet
VENUS
Beam developments with heavy ion beams show the potential of VENUS to boost the energy and intensity out of the 88-Inch Cyclotron
First commissioning experiments for high charge state heavy ionshave been promising
Uranium High Charge States
0
5
10
15
20
25
4 4.5 5 5.5 6 6.5 7 7.5 8
Ana
lyze
d C
urre
nt in
the
FC (e
µA)
Mass to Charge Ratio
3132333435
36
37
3839
414243
46
4748
4950N3+
O3+
C2+
N2+
3.5 kW 28 GHz 650 W 18 GHz
O2+
optimized on HCS
• 11x more beam extracted than with the AECR, uranium intensities make nuclear structure experiments feasible
• 160 x more Xe beam intensity was extracted at 10MeV/nuc
• 80 x more Kr beam intensity was extracted at 10 MeV/nuc
U47+
Xenon beam developments show big gains for high charge state ion beams, but smaller or no gains at lower charge states
1
10
100
1000
104
4 6 8 10 12 14 16 18Ext
ract
ed b
eam
from
the
Cyc
lotro
n [e
nA]
MeV/nuc
Xe28+
Xe42+
Xe43+Xe34+
Xe28+
VENUS
AECR
Beams not available with the AECR
Xe44+
Xe42+
Xe34+
Beam intensity is space charge limited in the injection line, and by the buncher gradientupgrade of the cyclotron center region and injection line will be necessary.
Neon like Xe has been extracted, pointing to plasma densities ∼1012/cm3
(ne τi ∼2·1011 sec/cm3)
88-Inch CyclotronK=140
ωe = = ωrfe•Bm
Key parameters for an ECR ion source performance
Plasma is resonantly heated with microwaves
e
Magnetic flux line
Bqvmr
rmBvq
⋅⋅
=
⋅⋅=⋅⋅ 2ω
f=28 GHz, B= 1T
rLamor=0.01…1 mm
Solenoids and Sextupole forma minimum-B field confinement structure
Plasma
e- heatingµ-wave
IONSgas
Charge exchange/neutral gas density σex
eV to MeVElectron temperature Te
109 - 1012 /cm3Plasma densities ne
~msIon confinement times τi
Key parameters
21276.217.1 10 cmIq p−− ⋅⋅
Optimization of the VENUS source for Ar12+ to demonstrate the ‘tuning’ of the plasma parameters
118+
3617+
27016+
51414+
86012+
VENUS(28GHz)
e•A
Ar
0
200
400
600
800
2 3 4 5 6 7 8 9
Ana
lyze
d C
urre
nt [e
µA]
Mass to Charge
O3+
O4+
10
O5+
O6+
15
9
8
7
1112
13
14
16
O2+
6
Motivation: 1mA Ar12+ for the SPIRAL II Project
Product of ne•τi increases with power
0
100
200
300
400
500
7 8 9 10 11 12 13 14 15 16 17
Ana
lyze
d C
urre
nt [e
µA]
Argon CS
1.6 kW
4.2 kW
7.6 kW
The argon CSD shifts from lower charge states to higher charge state for constant gas flow and same confinement fields as the power coupled to the plasma increases.
Power
Argon Charge States
Product of ne•τi increases with power
To keep the CSD peaked on Ar12+ more gas needs to be added to the plasma
CSD is shifted to higher charge states
100
200
300
400
500
600
700
800
900
1 2 3 4 5 6 7 8 9
Ana
lyze
d C
urre
nt [e
µA]
Total Power [kW]
pinj
=3.1 x 10-7 mbar
pinj
=3.35 x 10-7 mbar
pinj
=4.65 x 10-7 mbar
Axial bremstrahlung measurements indicate an increase in plasma density with power
101
102
103
104
105
106
0 200 400 600 800 1000
200030004000500060007000
coun
ts
Energy [keV]
(a)1
2
3
4
5
6
7
1 2 3 4 5 6 7 8C
ount
Inte
gral
[x10
7 ]28 GHz Power [W]
(b)
The energy spectra of electrons does not change with powerElectron temperature remains constant
Next Generation ECR Ion SourcesHigher magnetic fields and higher frequencies
I ∝ •rf2/M
I ∝ nion / τion
ne∝ •rf2
τion∝ Bmax/Bmin
Solenoid Coils
Sextupole
e- heatingµ-wavegas
ions
Minimum-B field Confinement
ωe = = ω rfe•Bm
28 GHz BECR= 1 Tesla
56 GHz BECR= 2 Tesla
To achieve optimum confinement fields superconducting magnets are necessary
Next Generation ECR Ion SourcesHigher magnetic fields and higher frequencies
I ∝ •rf2/M
I ∝ nion / τion
ne∝ •rf2
τion∝ Bmax/Bmin
28 GHz BECR= 1 Tesla
56 GHz BECR= 2 Tesla
To achieve optimum confinement fields superconducting magnets are necessary
10-2
10-1
100
101
102
103
10 11 12 13 14 15 16 17 18 19
anal
yzed
cur
rent
[eµA
]
Argon Charge State
AECR-U 14GHz
LBL-ECR 6.4 GHz
VENUS 28 GHz
AECR-U 14GHz
Argon beam intensities for the LBNL ECR, AECR and VENUS
0
0.5
1
1.5
2
2.5
3
3.5
-60 -30 0 30 60
Axi
al M
agne
tic F
ield
[T]
Ion Source Axis [cm]
ECR Design ‘Standard Model’
Binj ~ 4 • Becr
Bmin ~ 0.8 Becr
Bext ~ Brad
Brad • 2 Becr
28 GHz VENUS Tune
Main challenge for are the forces between the sextupole and solenoid magnet coils and the maximum field on the superconductor
Binj
Bext
Bmin0
1
2
3
-60 -30 0 30 60
Rad
ial M
agne
tic F
ield
[T]
Ion Source Axis [cm]
Brad
8T
1-1.6 T
4T
4T
56 GHz
Critical line and magnet load lines
86
42 2
46
810
1214
Field T
1
2
3
4
5
6
7
Cur
rent
den
sity
kA
mm-2
10
temper
atureK
Martin Wilson, Superconducting Magnets, Oxford University Press
Temperature Magnetic Field
Current density in the S
C w
ire
0
1000
2000
3000
4000
5000
0 5 10 15 20 25
Nb3Sn 4.2 K
NbTi 4.2 KNb
3Sn 1.8 K
Jc [A
/mm
]
B [T]
6T injection solenoid
3.6 T Hexapole
0
1000
2000
3000
4000
5000
0 5 10 15 20 25
NbTi 4.2 KNb
3Sn 4.2 K
Nb3Sn 1.8 K
Jc [A
/mm
]
B [T]
4 T Hexapole
6T injection solenoid
Preliminary Analyses of a 56 GHz source
Critical component in the traditional design is the maximum field at the sextupole coil.
Critical component in the inverted design is the maximum field at the injection solenoid coil
In both cases the clamping will be very challenging, since the forces increase a factor of 4
8 T
Status of high field Nb3Sn Magnets
9 cm
National Labs, including LBNL10 T tested11 T under development
Quadrupole
National Labs, including LBNL13 TDipole
Commercial22 TSolenoid
Peak field
G. Sabbi et al., “Nb3Sn quadrupole magnets for the LHC IR”, ASC 2002, Houston (TX), August 2002.
Perspectives on 4th
Generation Sources
Other Challenges
Cold Mass
with Coils
Enclosed
Cold Mass
with Coils
EnclosedPlasma
HV Insulator
2mm TantalumX-ray Shield
Technical Solution VENUS Aluminum Plasma Chamber with 2mm Ta x-ray shield
Water Cooling Groovesat the plasma Flutes
A major challenge for high field SC ECR ion sources is the heat load from bremsstrahlung absorbed in the cryostat
A major challenge for high field SC ECR ion sources is the heat load from bremsstrahlung absorbed in the cryostat
1.5 - 2 mm Ta shielding effectively attenuates the low energy bremsstrahlung, but becomes transparent for x-rays above 400keV100
101
102
103
104
105
1
10
100
1000
104
105
-200 0 200 400 600 800 100012001400
1.5mm Ta xray xray
Cou
nts
Energy [keV]
Integral 3.5 106
Integral 3.5 105
Technical Solution VENUS Aluminum Plasma Chamber with 2mm Ta x-ray shield
HV Insulator
2mm TantalumX-ray Shield
Water Cooling Groovesat the plasma Flutes
with shield
without shield
Using scaled magnetic fields for 18 and 28 GHz (same ECR zone size), 28 GHz heating results in x-ray flux and energies
The scaling of the electron energy temperature with frequency has important consequences for 4th generation superconducting ECR ion source with frequencies of 37GHz, 56GHz. Several (10s of ) watts of cooling power must be reserved for the cryostat.
101
102
103
104
105
106
0 200 400 600 800 1000
28 GHz18 GHz
Cou
nts
Energy [keV]
(a)0
0.5
1
1.5
2
2.5
3
3.5
-60 -40 -20 0 20 40 60
B/B
EC
R
Z [cm]
BECR
28 GHz
BECR
18 GHz
1.5 kW power
0
0.05
0.1
0.15
0.2
0.25
21 22 23 24 25 26 27 28 29 30 31
28 GHz18 GHz
Nor
m. 1
rms-
emitt
ance
[πm
mm
rad]
Xenon Charge States
Beam transport is a challenge for high field SC ECR ion sources
Beam emittance grows with magnetic field at extraction (therefore with heating frequency)
Beam transport is a challenge for high field SC ECR ion sources
D.S.Todd et al., LBNL RSI submitted
D.S.Todd et al., LBNL RSI submitted
Experiment
Simulation
Experiment
Experiment
10 cm
Simulation of oxygen beam extraction and transport
O7+O7+
Summary• 3rd Generation sources fulfill their intensity promises • The performances are still increasing with power, but mA of high charge state ions have
been demonstratedFor example with VENUS– 2860 eµA of O6+
– 860 eµA of Ar12+, 270 eµA of Ar16+, 1 eµA of Ar18+
– 200 eµA of U 34+
However intensity needs and performance gains for next generation heavy ion accelerator might justify 4th generation ECR ion sources (>28 GHz)
• New magnetic materials (Nb3Sn) will be needed to fabricate a 56 GHz ECR magnet structure
– Further advances in technology will be necessary – Prototyping will be essential
• X-ray heating will be a major challenges for 4th generation ECR ion sources– Measurements of the axial bremsstrahlung on the VENUS ECR ion source show that the
electron temperature and x-ray flux increase with increasing frequencies
• Beam transport– Emittance grows with magnetic field, but not as strong as expected– Understanding of the beam formation at the ECR extraction will be key to optimize the beam
transport for high field ECR ion sources
30Operational Experience with 28 GHz since 2004
• Superconducting Magnets
• Conventional design has been optimized for operational reliability and ease of maintenance
• Performance is still increasing with power, the maximum total power coupled into VENUS so far has been 9 kW (1kW/liter), 12 kW available
• Source has been designed as an UHV device all metal seals (including 28 GHz components)
– fast recovery after source maintenance• Plasma chamber (Al+Ta), which allows for high power operation
• Robust and reliable magnet system • Magnets can be independently energized • No conditioning after warm up required• Magnetic fields can be explored over a wide range
• High intensity of the VENUS beams have reached the space charge limit of the current cyclotron injection beam line (~100eµA)
• Transmission of the cyclotron injection line increases with injection voltage
• Current beam line components do not have sufficient focusing strength for injection energies above 15 kV
• Center region of the cyclotron will require upgrade for high intensity operation
To take full advantage of the high current available from VENUS an upgrade of the cyclotron injection and center region is necessary
Beams from VENUS
Faraday Cup FCA1
Glaser GA1
Glaser GA2Buncher 2
Buncher 1
Chopper
88-Inch Cyclotron
Return YokeGlaser GA3
Inflector
Buncher 1
Buncher 2
Solenoid 1
InflectorCenter Region
Solenoid 2
Solenoid 3
What about performance?
Double frequency heating (steep + gentle) and single frequency heating (gentle gradient) can achieve similar performance at different power levels
See also PA56, PA32
Xe35+
0
5
10
15
20
25
30
3000 4000 5000 6000 7000 8000 9000
Bmin= .67T
Bmin= .45TXe35
+ Ana
lyze
d C
urre
nt [e
µA]
Total Microwave Power [W]
single frequency
double frequencies
0
0.5
1
1.5
2
2.5
3
3.5
-60 -40 -20 0 20 40 60
B[T
]
Z [cm]
BECR
28 GHz
BECR
18 GHz
Single Frequency
Double Frequency
Similar performance if the count rate for low energy x-rays is similar
See also PA56, PA32
0
0.5
1
1.5
2
2.5
3
3.5
-60 -40 -20 0 20 40 60
B[T
]
Z [cm]
BECR
28 GHz
BECR
18 GHz
Single Frequency
Double Frequency101
102
103
104
105
0 200 400 600 800 1000
4.4kG middle field6.4 kG middle field
coun
tsEnergy [keV]
Double frequency heating (steep + gentle) and single frequency heating (gentle gradient) can achieve similar performance at different power levels
9kW powersteep gradient
6 kW powershallow gradient
To achieve the similar performance in the two configurations the electron density below 200keV needs to be similar
The gradient of the magnetic field at the resonance zone strongly influences the heating efficiency and hot electron tail
101
102
103
104
105
0 200 400 600 800 1000
4.4kG middle field6.4 kG middle field
coun
tsEnergy [keV]
Axial Bremstrahlung spectra from VENUSfor the two field configuration
The bremsstrahlung spectrum with a shallow magnetic field gradient at the resonance contains much higher x-ray energies.
Magnetic field configuration for optimized single and double frequency heating.
steepgradient
Double freq.
shallowgradient
single freq.
0
0.5
1
1.5
2
2.5
3
3.5
-60 -40 -20 0 20 40 60
B[T
]
Z [cm]
BECR
28 GHz
BECR
18 GHz
Single Frequency
Double Frequency
The gradient of the magnetic field at the resonance zone strongly influences the heating efficiency and hot electron tail
0
1
2
3
4
5
6
7
0 1 2 3 4 5 6 7 8
Bmin = .64T Bmin = .45T
Hea
ting
[W]
Microwave Power [kW]
Consequently, the gradient of the magnetic field at the resonance zone strongly affects the heat load into the cryostat
0
0.5
1
1.5
2
2.5
3
3.5
-60 -40 -20 0 20 40 60
B[T
]
Z [cm]
BECR
28 GHz
BECR
18 GHz
Single Frequency
Double Frequency
Progress and perspective for high frequency, high performance
superconducting ECR Ion Sources
Daniela LeitnerM L Galloway, T.J. Loew, C.M. Lyneis, D.S. Todd
CYCLOTRONS 2007, Giardini Naxos, Messina, Italy
• Introduction• 3rd Generation ECR ions source / VENUS project• Key parameters for the performance of an ECR• Recent results from VENUS• Perspectives on 4th generation ECR ion sources
Perspectives on 4th
Generation Sources
1996 First R&D funds received
1997 Prototype magnet constructed
Sep. 2001 World Most Powerful ECR Plasma Confinement Structure! 4T Injection, 3T Extraction, 2.4 T Sextupole,
June 2002 First Plasma at 18 GHz
26/5/04 First 28 GHz Plasma
Superconducting ECR ion source developments are lengthy and costly projects. Development needs to start early
Product of ne•τi increases with power
• constant gas flow rates• constant confinement field
• Dependence of Ar12+ and Ar14+ on power
0
100
200
300
400
500
1 2 3 4 5 6 7 8
Ar12+
Ar14+Ana
lyze
d C
urre
nt [e
µA]
Total Power [kW]
The ionization rate for Ar12+
into higher charge states increases with power
To keep the CSD peaked on 12+ more gas has to be added
