Status of the PROTO-SPHERA Proposal

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Status of the PROTO-SPHERA Proposal
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Franco Alladio, Alessandro Mancuso, Paolo
Micozzi, 1Stamos Papastergiou and 2François
RogierCR-ENEA, CP 65, 00044 Frascati (Roma),
Italy1Euratom-Enea ,2ONERA Toulouse, France

• Outline of the Talk
• PROTO-SPHERA purpose aims
• PROTO-PINCH Experiment results
• Frascati Panel question answer
• Multi-Pinch Experiment
• Conclusions

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Purpose
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PROTO-SPHERA (Spherical Plasma for Helicity
Relaxation Assessment)

Aims at producing a spherical torus (ST) with a
screw pinch (SP) replacing the centerpost
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Physics Design
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Ie, Ip 40, 50 kA pinch, ST
currents Ie, Ip 60, 240 kAA 1.6
aspect ratio A 1.3tpulse 80
ms1/100tR pulse duration tpulse 70 ms 1 tR

• PROTO-SPHERA aims at sustaining the plasma for
  more than tRm0a2/h (resistive time)

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Physics Engineering Design
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- ST diameter 0.7m- Toroidal plasma current
Ip240kA  - Aspect ratio A1.2, - Elongation
k2.35  - Pinch current Ie60 kA Complete
engineering design- Geometry of keycomponents
- Estimation of the safety margins of stresses
and temperatures
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Main Breakdown features
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• Screw pinch (SP) formed by a hot cathode
  breakdown
• Filling pressure pH10-310-2 mbar
• Cathode filaments heated to 2600 C
• Ve100 V applied on the anode
• Electrode arc current limited to Ie8.5 kA

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PROTO-PINCH Testbench
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• Test of PROTO-SPHERA Cathode Anode
• Arc breakdown in configuration similar to
  Proto-Spera

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PROTO-PINCH Results
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• Arc breakdown V 80-120 V
  
• Stable arc Ie1 kA
• Capability to fulfillPROTO-SPHERA requirements
• Arc Current, up to 60 kA
• Electron Emissivity (1 MA/m2)
• Arc Power handling capability up to 9.0 MW
  

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Cathode Extrapolation to PROTO-SPHERA
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• Cathode Emissivity
• Coil Material Pure W
• Wire Diameter 2 mm
• Total Coils Number 378
• Single Coil emission 167 A
• Tot126 module 3 X 167.5 A 63 KA
• Current Density 1 MA/m2

Conical Wire Terminal Clamp
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Anode Extrapolation to PROTO-SPHERA
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Anode Power Handling CapabilityPROTO-SPHERATeste
d 9 MWPROTO-SPHERAMax 6.0 MW
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Panel Questions Answers
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• Results of the PROTO-SPHERA Panel held in
  Frascati on March 2002
• Interesting Concept Exploration Experiment,
  adeguate size useful contribution to magnetic
  fusion programs.
• Is the physics basis for undertaking an
  experiment as proposed with PROTO-SPHERA
  adeguate? YES, BUT We recommend that a wider
  range of operation scenarios of m and pressure
  profiles be analysed... (equilibria stability,
  including n0)
• Are the PROTO-PINCH electrode experiments a
  sufficient technical basis for a reliable
  electrode operationin PROTO-SPHERA?
•   YES, BUT are not yet adequate for reliable
  
• multi-electrode
  operation...

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Equilibria Ip180 kA, Ie 60 kA, 0.22
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mm(e,h)h0.9 and e0.5
I2SP ? ya PST?I2ST ? y1.1 a3.0
Reference Equilibrium I2SP ? y2 PST?I2ST ?
y1.1
All Equilibria has been obtained with the same
coils set
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PROTO-SPHERA Stability Results
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n1
IST/Ie 5 and b15 Unstable
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Results STABLEN0mu Code n0
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PROTO-SPHERAn0 stable for any scenarios up to
R/a 1.2 k lt 4
Comparison of the instabilities growth rate for
free boundary codes Mode numbers n0,
m-15,15.
Ulart Magnetic Structure preventsRadial Pinch
Drift
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MULTI-PINCH Proposal
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START Dimension.Simplified PF coils system Fed
with 600 A, 120 V Does not need cooling.
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Multi-Pinch Cathode
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• Limited number of cathode coils (18 vs. 378)
• Coils will drive a total limited current (2.7 kA
  vs. 60 kA) simplifying the power supply
• Each coil will be capable of delivering the
  design current
• (150 A).

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Conclusions
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• Answers to the Questions raised by Panel
• ...We recommend that a wider range of operation
  scenarios of m and pressure profiles...
• An exhaustive range of scenarios with several m
  and pressure profiles, equilibria stability,
  has been investigated
• The PROTO-PINCH electrode experiments provide
  sufficient technical basis for designing the
  electrodes themselves in PROTO-SPHERA, but are
  not yet adequate for reliable multi-electrode
  operation
• The answer is the proposed MULTI-PINCH Experiment
• Depending on boundary conditions, we plan to
  start the MULTI-PINCH experiment next year