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Superconducting Ion Source Development in Berkeley
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Transcript of Superconducting Ion Source Development in Berkeley
Superconducting Ion Source Development in Berkeley
Daniela Leitner, S. Caspi, P. Ferracin, C.M. Lyneis, S. Prestemon, G.L. Sabbi, D.S. Todd, F. Trillaud
HIAT 2009, Venice, Italy
• Motivation for developing superconducting ECR ion sources
• Key parameters for the performance of an ECR
• VENUS Source Project• Some results and status of the
VENUS ECR ion source • Future ECR ion source – Path to
56 GHz ECRIS
ECR ion sources have made remarkable improvements over the last few decades, but the demand for
increased intensities of highly charged heavy ions continues to grow
SC-ECRIS, RIKEN, Japan
P ost A cce le ra to r
Iso tope S eparato r
F ragm enta tion P roduction Targe t
F ragm enta tion S eparato r
D rive r L inac (400 M eV /nuc U , 900 M eV p)
R F Q ’s
E xperim en ta l A reas
“G as C a tcher”
N uclea r S tructu re
In F ligh t S epara tion
Iso topeR ecovery
E < 15 M eV /u E > 50 M eV /u
A pp lied P hys ics
A s tro P hys ics
E < 1 M eV /u
N o A cce le ra tion
VENUS, FRIBMSU, USA
SPIRAL 2, GANIL, France
525 eµA U35+ 1mA Ar12+270 eµA U33+ and 270 eµA U34+
Supermafios (Geller, 1974)15 eµA of O6+
VENUS (2007)2850 eµA of O6+
Factor 200
increase
The demonstrated VENUS source performance shows that these ion beam intensity requirements are possible
VENUS28GHz or 28+18 GHz
O6+ 2860 eμA
O7+ 850 eμA
O8+ 400 eμA
Ar12+ 860 eμA
Ar17+ 36 eμA
Xe35+ 28 eμA
Xe42+ .5 eμA
U34+ 200 eμA
U47+ 5 eμA
0
50
100
150
200
250
5 6 7 8 9 10 11
Ana
lyze
d C
urre
nt [
eµA
]
Mass to Charge Ratio
31
32
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
Required temperature of 2100 C in a 4 T B field
ECR (1983)0.4 T, 0.6 kW, 6.4 GHz
AECR-U (1996)1.7 T, 2.6 kW, 10 + 14 GHz
VENUS (2001)4.0 T, 14 kW, 18 + 28 GHz
Higher magnetic fields and higher frequencies are the key to higher performance
Minimum-B field ConfinementSolenoid Coils
Sextupole
e- heatingµ wave
gas
ions
qopt log ω3
ne ωrf2
e = = rf e•Bm
Resonant electron heating
Higher magnetic fields and higher frequencies are the key to higher performance
Normal conducting
Super conducting
10-2
10-1
100
101
102
103
104
10 12 14 16 1810-2
10-1
100
101
102
103
104
10 12 14 16 18
ECR 6 GHz
AECR 14 GHz
VENUS 28 GHz
VENUS 56 GHz predicted
Ana
lyze
d be
am c
urre
nt [
eµA
]
Argon Charge States
ECR (1983)0.4 T, 0.6 kW, 6.4 GHz
AECR-U (1996)1.7 T, 2.6 kW, 10 + 14 GHz
VENUS (2001)4.0 T, 14 kW, 18 + 28 GHz
ne $
Challenges
• Superconducting Magnet
• Cryogenic Technology
• X-rays from the Plasma
• Ion Beam Transport
Binj ~ 4 ∙ Becr
Bmin ~ 0.8 Becr
Bext ~ Brad
Brad ≥ 2 Becr
Becr
4T
.5-.8 T
2T
2T
1T
28 GHz
8T
1-1.6 T
4T
4T
2T
56 GHz Magnetic Design 28 GHz 56 GHz
Max solenoid field
on the coil 6 T 12 T
on axis 4 T 8 T
Max sextupole field
on the coil 7 T 15 T
on plasma wall 2.1 T 4.2 T
Superconductor NbTi Nb3Sn
Superconducting Magnets: ECR Design ‘Standard Model’
0
0.5
1
1.5
2
2.5
3
3.5
4
-60 -40 -20 0 20 40 60
B[T
esl
a],
sole
noid
s on
ly
Z (cm)
BECR
Bmin
Bext
Binj
Plasma
0
0.5
1
1.5
2
0 1 2 3 4 5 6 7
B[T
esla
], se
xtup
ole
only
R (cm)
Superconducting Magnet Structure 56 GHz: two options
Solenoid-in-SextupoleGeometry (SECRAL)
Sextupole-in-SolenoidGeometry (VENUS)
• Minimizes the influence of the solenoid on the sextupole field
• Significantly higher field required for the sextupole magnet surface due to the larger radius of the coils
• Strong forces on the solenoid coils
• Minimizes the peak fields in the sextupole coils
• Strong influence (forces) of the solenoid field on the sextupole ends
Superconducting Magnet 56 GHz: Magnetic Analyses
Critical line and magnet load lines: NbSn3
0
1000
2000
3000
4000
5000
8 10 12 14 16 18 20 22
J SC [A
/mm
2 ]
B [T]
4.2 K
5.7 K
6.7 K
Cur
rent
Den
sity
thr
ough
the
su
perc
ondu
ctor
Magnetic Field on the conductor
NbSn3
Superconducting Magnet Structure: Magnetic AnalysesC
urre
nt D
ensi
ty t
hrou
gh t
he
supe
rcon
duct
or
Magnetic Field on the conductor
•Magnetic field and current density requirements exceed the capability of NbSn3
Goal: Achieve 4.2T on the plasma chamber wall radially and 8 T and 4 T on axis
0
1000
2000
3000
4000
5000
8 10 12 14 16 18 20 22
J SC [A
/mm
2 ]
B [T]
4.2 K
5.7 K
6.7 K
Injection Solenoid
Sextupole
Extraction Solenoid
This geometry can be ruled out as candidate for a 56 GHz ECR ion source
Solenoid-in-Sextupole
Superconducting Magnet Structure: Magnetic AnalysesC
urre
nt D
ensi
ty t
hrou
gh t
he
supe
rcon
duct
or
Magnetic Field on the conductor
• 2.5 Kelvin temperature margin
for the Sextupole• Operates at 86% of current
limits
Goal: Achieve 4.2T on the plasma chamber wall radially and 8 T and 4 T on axis
This geometry is challenging but feasible with current NbSn3 technology
Sextupole-in-Solenoid
0
1000
2000
3000
4000
5000
8 10 12 14 16 18 20 22
J SC [A
/mm
2 ]
B [T]
4.2 K
5.7 K
6.7 K
Injection Solenoid
Sextupole
Sextupole-in-Solenoid: Clamping Structure
There are two limits to the maximum achievable field
with this design
To control these forces• In the end region each layer is subdivided in two blocks of conductors
separated by end-spacers. • The number of turns per block and the relative axial position of the end
spacers were optimized to reduce the peak field in the end region. • The coils are lengthen to reduce the peak field• Shell type support structure
Maximum peak field on the coil (15.1 T, 862 A/mm2 )
Maximum force on the end point (up to 175 MPa)
Sextupole-in-Solenoid: Sextupole Magnet
• 4-layer coils using cables (675 conductors/coil)• The same cable design is currently used by the
LARP program to develop high field
quadrupoles for future LHC luminosity
upgrades (peak fields 15 T)
Cable properties
Strand Dia 0.8 mm
Fill factor ~ 33%
No strands 35
Cable ~ 15.2x1.5 mm • The cable design requires high 8.2kA current
leads, the 56 GHz cryostat will most likely
require He filling during operation.
A practice coil winding for the LARP quadrupole (HQ)
Sextupole-in-Solenoid: Clamping Structure
• A shell-based structure using bladders and keys provides a mechanism for controlled room temperature pre-stress.
• Pre-stress is then amplified by the contraction of an aluminum shell during cool-down.
• The method was developed at Superconducting magnet group at LBNL and successfully applied to high field magnets.• 2D cross section structure
analyses has been conducted on the two critical regions
• Stress values are close to the maximum acceptable values
• Needs full 3D analyses
Quench protection
• Energy stored in the VENUS magnet is 800kJ
• VENUS coils do not require active quench protection
• Leads need protection for adequate cooling
• Energy stored in the 56 GHz Magnet 5.5MJ
• Active Quench protection with heaters at the coils (75% coverage, results in peak temperatures in the coil of 280K)
• Lead protection (Lesson from the VENUS quench failure)
LN
LHe
HTC leads
Passive Quench Protection
Sol 1 Sol 3 Sol 2
Sol 1 Sol 3 Sol 2
Sextupole Coil
Burned Lead
Spliced sextupole lead wire
Other Challenges
• Superconducting Magnet
• Cryogenic Technology
• X-rays from the Plasma
• Ion Beam Transport
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 400keV
100
101
102
103
104
105
1
10
100
1000
104
105
-200 0 200 400 600 800 1000 1200 1400
1.5mm Ta xray xray
Co
un
ts
Energy [keV]
Integral 3.5 106
Integral 3.5 105
HV Insulator
2mm TantalumX-ray Shield
Water Cooling Groovesat the plasma Flutes
with shield
without shield
The high energy tail of the x-ray spectrum increases substantially at the higher microwave frequency(10s of ) watts of cooling power must be reserved for the cryostat.
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
rm
s-e
mitt
ance
[m
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
Todd et al., Rev. Sci. Inst. 79 02A316
Todd et al., Rev. Sci. Inst. 79 02A316
Experiment
Simulation
Experiment
10 cm
Simulation of oxygen beam extraction and transport
O7+O7+
Summary
• The requirements of the next generation heavy ion accelerator continue to drive ECR ion source development
• Higher magnetic fields and higher frequencies are the key to higher performance
• 200eµA of U33+ and U34+ have been produced, high temperature oven development is key for long term production
• 56 GHz ECR ion source magnet structures are feasible with current NbSn3 technology
• Development should start now to be ready for operation in 5-10 years
• Understanding of the plasma physics and the beam transport is important for the design of the next generation superconducting ECR ion sources
e = = rf e•Bm
Key parameters for an ECR ion source performance
Plasma is resonantly heated with microwaves
e
Magnetic flux line
Bq
vmr
rmBvq
2
f=28 GHz, B= 1T
rLamor=0.01…1 mm
Solenoids and Sextupole forma minimum-B field confinement structure
Plasma
e- heatingµ-wave
IONS
gas
Key parameters
Ion confinement times i ~ms
Plasma densities ne 109 - 1012 /cm3
Electron temperature Te eV to MeV
Charge exchange/neutral gas density ex
21276.217.1 10 cmIq p
Superconducting Magnets: ECR Design ‘Standard Model’
28 GHz VENUS Tune
0
0.5
1
1.5
2
2.5
3
3.5
4
-60 -40 -20 0 20 40 60
B[T
esl
a],
sole
noid
s on
ly
Z (cm)
BECR
Bmin
Bext
Binj
Plasma
0
0.5
1
1.5
2
0 1 2 3 4 5 6 7
B[T
esla
], se
xtup
ole
only
R (cm)
Binj ~ 4 ∙ Becr
Bmin ~ 0.8 Becr
Bext ~ Brad
Brad ≥ 2 Becr
Binj ~ 4 ∙ Becr
Bmin ~ 0.8 Becr
Bext ~ Brad
Brad ≥ 2 Becr
4T
.5-.8 T
2T
2T
28 GHz
8T
1-1.6 T
4T
4T
56 GHz
BECR28 GHz BECR= 1 Tesla
56 GHz BECR= 2 Tesla
Magnetic Design 28 GHz 56 GHz
Max solenoid field
on the coil 6 T 12 T
on axis 4 T 8 T
Max sextupole field
on the coil 7 T 15 T
on plasma wall 2.1 T 4.2 T
Superconductor NbTi Nb3Sn
Superconducting Magnets: ECR Design ‘Standard Model’
The high energy tail of the x-ray spectrum increases substantially at the higher microwave frequency
100
101
102
103
104
105
1
10
100
1000
104
105
-200 0 200 400 600 800 1000 1200 1400
1.5mm Ta xray xray
Co
un
ts
Energy [keV]
Integral 3.5 106
Integral 3.5 105
with shield
without shield
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
Cou
nts
Energy [keV]
28 GHz
18 GHz