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September 26-29, 2005 Knoxville. Tennessee USA
Assoc iazione Eu ratom -ENEA sulla Fu si one
Progress and Plan of the PROTO-SPHERA Program
Outline of the Talk1) Introduction to PROTO-SPHERA
2) The PROTO-PINCH Experiment: results
3) Engineering Design and Analysis of PROTO-SPHERA
4) Multi-Pinch Experiment
5) Conclusions
Stamos Papastergiou, Franco Alladio, Alessandro Mancuso, Paolo Micozzi, CR-ENEA, CP 65, 00044 Frascati (Roma), Italy
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September 26-29, 2005 Knoxville. Tennessee USA
Assoc iazione Eu ratom -ENEA sulla Fu si one
Aims at producing a Spherical Torus (ST) with a Screw Pinch (SP) replacing the centerpost
2
Introduction to PROTO-SPHERA (Spherical Plasma for Helicity Relaxation Assessment)
Ip: toroidal current
Bt: toroidal field
Bp: poloidal field
Je: pinch current
September 26-29, 2005 Knoxville. Tennessee USA
Assoc iazione Eu ratom -ENEA sulla Fu si one 3
Engineering Design of
PROTO-SPHERA
September 26-29, 2005 Knoxville. Tennessee USA
Assoc iazione Eu ratom -ENEA sulla Fu si one
Physics Design
Ie, Ip = 40, 50 kA pinch, ST currents Ie, Ip = 60, 240 kA
A=R/a = 1.6 aspect ratio A ≤ 1.3pulse = 80 s~1/100R pulse duration pulse ≥ 70 ms ~ 1 R
•PROTO-SPHERA aims at sustaining the plasma for more than R=0a
2/ (resistive time) to verify the stability of the configuration
4
Tokyo University - Japan
September 26-29, 2005 Knoxville. Tennessee USA
Assoc iazione Eu ratom -ENEA sulla Fu si one
Main Breakdown featuresScrew pinch (SP)
formed by a hot cathode breakdown
Filling pressure pH~10-3÷10-2
mbar
Cathode filaments heated to 2600 °C
Ve~100 V applied on the
anode
Initial electrode arc current limited to Ie~8.5 kA
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September 26-29, 2005 Knoxville. Tennessee USA
Assoc iazione Eu ratom -ENEA sulla Fu si one
•Test of PROTO-SPHERA Cathode & Anode
•Arc breakdown in configuration similar to PROTO-SPHERA
PROTO-PINCH Experiment - Results
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September 26-29, 2005 Knoxville. Tennessee USA
Assoc iazione Eu ratom -ENEA sulla Fu si one
Anode
NoDamages after 1000 discharges
Material W 95% Cu5%.
Scheme : Puffed Hollow Anode
PWAnode = 2/3 (670 120) kW » 56 kW (module)
Asurface= 1.8 10-3 m2
Dpw = PW/ Asurface» 30 MW/m2
anode arc anchoring with Cathode DC heated (a)
No Anode anchoring with AC cathode heating (b)
a b
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September 26-29, 2005 Knoxville. Tennessee USA
Assoc iazione Eu ratom -ENEA sulla Fu si one
Cathode Emissivity Coil Material : Pure W Wire Diameter = 2 mm Total Coils Number = 378 Single Coil emission = 167 A Tot126 module 3 X 167 A 63 kA Current Density 1 MA/m2
Conical Wire Terminal & Clamp
Cathode – Extrapolation to PROTO-SPHERA
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W
Mo
September 26-29, 2005 Knoxville. Tennessee USA
Assoc iazione Eu ratom -ENEA sulla Fu si one
Gas Puff Ie
TotSurf = 0.2 m2W Cu5%
OFHC Hardened CU
Gas Puff
Anode Power Handling Capability:PROTO-SPHERATested = 9 MWPROTO-SPHERAMax = 6 MW
Anode Extrapolation to PROTO-SPHERA
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September 26-29, 2005 Knoxville. Tennessee USA
Assoc iazione Eu ratom -ENEA sulla Fu si one
Engineering Design and Analysis of
PROTO-SPHERA
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September 26-29, 2005 Knoxville. Tennessee USA
Assoc iazione Eu ratom -ENEA sulla Fu si one
Design Philosophy
- Simplicity, symmetry, conservatism.
- Viewing capability and good access to electrodes.
- All connections to PF coils from top and bottom flanges,
external to Machine.
- Bellows in coil feedthroughts for adjustment.
- Operation and disruption (but no fault) conditions considered.
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September 26-29, 2005 Knoxville. Tennessee USA
Assoc iazione Eu ratom -ENEA sulla Fu si one
Design AimsOperationability, Reliability, Repairability of Machine.
Reliability of electrodes and avoidance of arc anchoring.
Minimise Technological Risks: provide appropriate elecrical
insulation, avoid local coil overheating ( >100°C ) due to hot
anode and cathode ( 12MJ, 2750°C ), minimise electromagnetic stresses.
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September 26-29, 2005 Knoxville. Tennessee USA
Assoc iazione Eu ratom -ENEA sulla Fu si one
Operating conditions
Temperature 20°C
Vacuum < 1•10-7 mbar (predicted outgassing rate: ~3•10-5 mbar•l/s)
Baking
80-90°C
Adequate for water removal, coil protection; compatible to Viton O-rings
Possibility of N2 1 mbar contact gas
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September 26-29, 2005 Knoxville. Tennessee USA
Assoc iazione Eu ratom -ENEA sulla Fu si one
Spherical Torus (ST) diameter 0.7 mLongitudinal Screw Pinch current 60 kAToroidal ST current 120÷240 kAPlasma pulse duration 1 sMinimum time between two pulses 5 min.Maximum heat loads on first wall componenets in divertor region 2 MW/m2 , for 1 msMaximum current density on the plasma-electrode interface 1 MA/m2
Machine Parameters
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September 26-29, 2005 Knoxville. Tennessee USA
Assoc iazione Eu ratom -ENEA sulla Fu si one
Protection Componenets•Thermal and Heat Transfer Behaviour
Philosophy: collect the heat ( via radiation ) from the electrodes to black resilient componenet and then conduct or radiate it away in a controlled way. Hot spots are thus avoided.
Danger: the hot cathode (less the anode) radiates at 2750°C with ~3.5MW/m2 and even a 10mm thick coil casing cannot sustain this power density for more than 0.5s without exceeding 100°C
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September 26-29, 2005 Knoxville. Tennessee USA
Assoc iazione Eu ratom -ENEA sulla Fu si one Thermal and Heat transfer Behaviour
• Solution:
1. Use of Cu componenets to collect or reflect the heat away from coils. Conservative (but symmetrical) design for the anode. Thermal mass of these components results in operational temperature < 100°C. Water cooled! Optimum design; i.e. one circuit/component, D~10-15mm, v~2m/s, duty cycle 5min.
2. Use of thermocouples in no water cooled componenets to avoid >100°C with frequent pulses; every 5min.
3. Use of 10mm divertor AISI 304LN plates. 2 MW/m2 for 1 s gives T~120°C, th~320MPa
4. Use of optical diagnostics to view the electrodes which are relatively easily accessible.
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September 26-29, 2005 Knoxville. Tennessee USA
Assoc iazione Eu ratom -ENEA sulla Fu si one
Electromagnetic Forces and Stresses
B=50T/s B=500G t≤1 ms
Subdivision of Cu and 304LN plates to achieve ≤100 MPa of eddy current stresses.
Unaccounted skin effects (t ~1ms) significant. Conservative prediction of eddy current effects.
Electromagnetic forces in the coils (~x10 weight) require to be sustained.
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September 26-29, 2005 Knoxville. Tennessee USA
Assoc iazione Eu ratom -ENEA sulla Fu si one Predicted and Permitted StressesASME III-NB 3221ASME III-NB 3221
Stainles SteelStainles Steel
Allowable Sm for 304LN 100°C : 200MPa [304L Sm~150MPa]
Predicted e-m stresses : 320MPa
Thermal (divertor) local stresses : 320 MPa (2 MW/m2 ,1s)
Criterion 1 : 100 <200x1.5
Criterion 2 : 100320 <200x3
CopperCopper
Minimum required allowable at 100°C> 70 MPa (100MPa<70x1.5)
Thus y >115 Mpa and u > 230 MPa at 20°C i.e. Cu hardenned
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September 26-29, 2005 Knoxville. Tennessee USA
Assoc iazione Eu ratom -ENEA sulla Fu si one 19
Provisional single anode Cathode
~ START DimensionSimplified PF coils system fed with 600 A, 120 V
Does not need cooling
Aim: verification of the arc formation & stability
Multi-Pinch Experiment
STARTVacuum Vessel
September 26-29, 2005 Knoxville. Tennessee USA
Assoc iazione Eu ratom -ENEA sulla Fu si one 20
START in Frascati
Arrival
Disassembling
May 2004
October 2004
September 26-29, 2005 Knoxville. Tennessee USA
Assoc iazione Eu ratom -ENEA sulla Fu si one 21
Multi-Pinch Experiment: Phase I & Phase II
September 26-29, 2005 Knoxville. Tennessee USA
Assoc iazione Eu ratom -ENEA sulla Fu si one
CONCLUSIONSThere is high degree of confidence that the design, construction and reliable operation of PROTO-SPHERA are feasible
The Multi-Pinch experiment is being constructed to prove the formation and stability of the PROTO-SPHERA initial arc
PROTO-SPHERA can be obtained simply adding components to Multi-Pinch
Adequate technological basis, particularly in relation to electrodes, for extrapolation to a bigger device is expected
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