Post on 16-Dec-2015
ICC2004 Madison, Wisconsin
Assoc iazione Eu ratom -ENEA sulla Fu si one
The Multi-Pinch Experiment
Outline
• PROTO-SPHERA purpose & aims
• Theoretical basis & analysis
• Multi-Pinch: a step towards PROTO-SPHERA
• Conclusions
Franco Alladio, Alessandro Mancuso, Paolo Micozzi, 1Stamos Papastergiou and 2François Rogier
CR-ENEA, CP 65, 00044 Frascati (Roma), Italy1Euratom-Enea ,2ONERA Toulouse, France
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ICC2004 Madison, Wisconsin
Assoc iazione Eu ratom -ENEA sulla Fu si one
PROTO-SPHERA
Ie, Ip = 40, 50 kA pinch, ST currents Ie, Ip = 60, 240 kA
A = 1.6 aspect ratio A ≤ 1.3pulse = 80 s~110 A pulse duration pulse ≥ 70 ms~1 R
Goals: sustain the plasma (Helicity Injection SPST) for more than R=0a2/
(resistive time) and compare E with START
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Aims at producing a spherical torus (ST) with a screw pinch (SP) replacing the
centerpost
ICC2004 Madison, Wisconsin
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PROTO-SPHERA & Spheromaks (TS-3)
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Two important requirements are different for the PROTO-SPHERA equilibriawith respect to Flux-Core-Spheromaks like TS-3:
1) Tokamak-like safety factor profile of ST: q0~0.94, q95~2.6 at the edge2) Strong jump of the surface averaged relaxation parameter <>=0<j•B/B2>
between SP and ST Helicity Injection (~35 m-1 inside SP, ~10 m-1 inside ST)
PROTO-SPHERA (Rsph=0.35 m) has been designed in order to beas far as possible from the pure Spheromak STRsph≤4.49 eigenvalue
ICC2004 Madison, Wisconsin
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Physics & Engineering Design
ST diameter = 0.7 m
Toroidal plasma current Ip= 240 kA
Aspect ratio A = 1.2Elongation = 2.35
Pinch current Ie= 60 kA
Engineering design complete
(geometry, stresses and temperatures)
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ICC2004 Madison, Wisconsin
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Main Breakdown features
Screw 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
Electrode arc current limited to Ie~8.5 kA
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Proto-Pinch
Testbench
(Ie~ 700 A)
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Theoretical analysis of the PROTO-SPHERA configuration
Ideal MHD Equilibria:
• formation phase fully analyzed
• equilibrium resilience checked by varing the functional forms of p() & f()
both on the SP and on the ST
Ideal MHD Stability:
• New free boundary code developed plasmas extending up to the
symmetry axis (R=0) with regular (|B|≠0) & singular (|B|=0) X-points
• Toroidal mode numbers n=0 (axisymmetric), 1, 2, 3 investigated
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All equilibria has been obtained with the same coils set
PROTO-SPHERA Equilibria: Ip=180 kA, Ie= 60 kA, = 0.22
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PROTO-SPHERA Stability Results
IST/Ie = 5 and 15%
Unstable
n=1,2,3 investigated for all equilibriaMain constraint IST/Ie
Stability obtained for:• = 21÷26% , IST/Ie= 0.5 - 1
• = 14÷15% , IST/Ie= 2-4
With T0=20<p>vol/< >vol
• T0=28÷29% , IST/Ie= 0.5 - 1
• T0=72÷84% , IST/Ie= 2-4
The dominant instabilities are:• up to IST/Ie≈3 Spherical Torus
instabilities• IST/Ie> 3 Screw Pinch kink instabilities
€
B 0T2
n=1
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Results for axisymmetric stability (n=0)
Instabilities growth rate for free boundary codes
(vacuum contribution fully included)Mode numbers
n=0, m=[-15,+15]
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Pinch Magnetic Structure prevents n=0
Vertical ULART Drift
PROTO-SPHERAn=0 stable for any
scenarios up to R/a = 1.2 < 4
Ulart Magnetic Structure prevents
Radial Pinch Drift
ICC2004 Madison, Wisconsin
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Theoretical work to be done
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Investigation about the resistive MHD instabilities,
in particular at the Screw Pinch / Spherical Torus interface
Evaluation of the Helicity Injection efficency
both from a macroscopic as well as a microscopic point of view
ICC2004 Madison, Wisconsin
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Possible evolution of thePROTO-SPHERA proposal
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PROTO-SPHERA can be viewed as a simplification of the
Chandrasekar-Kendall-Furth (CKF) configurations
(stable up to ~ 1)
Screw Pinch replaces in part
the surrounding discharge
Divertor PF coils replace
the secondary tori
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- Provisional simplified PF coils system with constant current (partially recoverable for PROTO-SPHERA)
- Fed with 0.6 kA, 120 V (no water cooling)
(1.9 kA, 350 V in PROTO-SPHERA)
Multi-Pinch Experiment
START vacuum vessel (already in Frascati)
Aims:Stable Screw Pinch plasma with the full dimension and mushroom shape,but reduced current Ie (2.7 Vs. 8.5 kA)
Phylosophy:Almost all parts should be reutilizedin PROTO-SPHERA
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Multi-Pinch Experiment (first phase)
Cathode plasma only is mushroom-shapedPower density on the “single”
anode ~ PROTO-SPHERA
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Multi-Pinch Experiment (second phase)
Anode & Cathode plasma mushroom-shaped
Definitive PROTO-SPHERAAnode
Possibility of arc anchoring needs of saddle coils?
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Definitive PROTO-SPHERA Cathode, but only partially filled
Multi-Pinch Cathode
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Multi-Pinch Cathode
•Multi-Pinch test is proposed with a limited number of cathode coils(18 Vs. 378)
•Coils will drive a total limited current (2.7 kA vs. 60 kA) inside the pinch, simplifying the power supply for the Multi-Pinch
•Each coil will be capable of delivering the design current (150 A)
Conical terminal & clamp
Wire Length = 400 mm
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Mo support
W wires
ICC2004 Madison, Wisconsin
Assoc iazione Eu ratom -ENEA sulla Fu si one
Conclusions•PROTO-SPHERA aims to explore the feasibility of a ST formed around a SP, with respect to the possibility to sustain it through Helicity Injection on resistive time scale
•An exhaustive range of PROTO-SPHERA scenarios has been investigated (resilience of the equilibria Vs. internal profile & ideal MHD stability boundaries)
•The Multi-Pinch experiment will investigate the feasibility of a stable mushroom-shaped Screw Pinch
•Multi-Pinch will be built inside the START vacuum vessel, PROTO-SPHERA can be obtained with a modular implementation of this experiment
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