1. Electrodes and PROTO-PINCH Presented by A. Mancuso PROTO-SPHERA Workshop - Frascati, 18-19/03/2002 Associazione Euratom-ENEA sulla Fusione

2. Outline 1)PROTO-SPHERA Requirements 2)PROTO-PINCH Experiment 3)Cathode, Anode & Diagnostics 4)Extrapolation to PROTO-SPHERA PROTO-SPHERA Workshop - Frascati, 18-19/03/2002 Associazione Euratom-ENEA sulla Fusione

3. PROTO-SPHERA Requirements Arc Current, up to 60 kA Electron Emissivity ( 1 MA/m 2 ) Arc Power, up to 6.0-10 MW Power Density Handling Capability (20-30 MW/m 2 ) PROTO-SPHERA Workshop - Frascati, 18-19/03/2002 Associazione Euratom-ENEA sulla Fusione

4. PROTO-PINCH Testbench Test of 1/100 of the PROTO-SPHERA Cathode& Anode Arc breakdown in configuration similar to ProtoSphera. Effects of the arc current I e 1 kA, with q Pinch 2. PROTO-SPHERA Workshop - Frascati, 18-19/03/2002 Associazione Euratom-ENEA sulla Fusione

5. PROTO-PINCH has produced Hydrogen and Helium arcs in the form of screw pinch discharges. Image of PROTO-PINCH Hydrogen plasma with I e =600 A, B=1 kG. Pinch Length : 75 cm Stabilizing Field : 1.5 kG Safety Factor q Pinch 2 I e = 670 A E max = 6.7 A/cm 2 V pinch = 80 –120 V V cathode = 14.5 V PROTO-PINCH Discharges PROTO-SPHERA Workshop - Frascati, 18-19/03/2002 Associazione Euratom-ENEA sulla Fusione

6. Cathode Layout Material Plates: Molybdenum Columns:Tantalum Insulator : Alumina Coils : Pure W Module Power = 8.4 KW Module Current = 670 A Module Voltage = 14.5 V Wire Number = 4 Wire Length = 40.0 cm Wire Surface = 4 X 25 cm 2 Wire Temp = 2600 C Wire Em = 6.7 Amp/cm 2 Wire Weight = 4 X 22 Gr. PROTO-SPHERA Workshop - Frascati, 18-19/03/2002 Associazione Euratom-ENEA sulla Fusione

7. Cathode Treatments & Results Filling Pressure 1 10 -3 – 1 10 -2 mbar AC current for heating the cathode, to spread the ion plasma current over the filaments. Time required for heating the cathode circa 15 s. I cath =550-590 A (rms.) at V cath =14.5 V (rms.) allows for I e =600-670 A of plasma current I e /I cath 1. P cathode 8.5 kW allows for P e 50-70 kW into the Pinch. No damages after 400 shots at I e = 600 A, t = 2-5 sec PROTO-SPHERA Workshop - Frascati, 18-19/03/2002 Associazione Euratom-ENEA sulla Fusione

8. HeliConical Coil Wires 1 out 4 T = 2600 C Ground Conical Wire&Terminal Clamp Tantalum Column AC Power 14.5 V D= 14 mm d=2mm Alumina Insulator Double Helical ZeroField Molybdenum Plates Ic=150A Null Field Optimize Temperature Distribution Optimize Weight Distibution I e =167 A (each coil) DP FS = I e /P FS m 2 Associazione Euratom-ENEA sulla Fusione PROTO-SPHERA Workshop - Frascati, 18-19/03/2002 Plasma Face Surface P FS =1.5 10 -4 m 2

9. HeliConical Coil Test Test Results : Very Small Displacement after 2700 Sec at 2700 C PROTO-SPHERA Workshop - Frascati, 18-19/03/2002 Associazione Euratom-ENEA sulla Fusione

10. Structural Analysis Max VonMisess Stress = 0.16 Kg/mm 2 C = 0.85 Kg/mm 2 Safety Factor = C Stress PROTO-SPHERA Workshop - Frascati, 18-19/03/2002 Associazione Euratom-ENEA sulla Fusione Max Stress 0.16 Kg/mm 2

11. Anode No Damages after 1000 discharge Material W 95% Cu5%. Scheme : Puffed Hollow Anode P WAnode = 2/3 (670 120) KW W ( module) A surface 1 10 -3 m 2 D pw = P W / A surface MW/m 2 anode arc anchoring with Cathode DC heated (a) No Anode anchoring with AC cathode heating (b) ab PROTO-SPHERA Workshop - Frascati, 18-19/03/2002 Associazione Euratom-ENEA sulla Fusione

12. Anode Extrapolation to PROTO-SPHERA W Cu5% Gas PuffIe TotSurf = 0.2 m 2 Anode Power Handling Capability: PROTO-PINCH=670A 120V 80 KW (2-5sec) (ProtoSphera/ ProtoPinch) AnodeSurface 100 ProtoSphera Tested up to 100 * 80 KW = 8 MW ProtoSphera Max 6.0 – 10 MW ( < 1 sec) OFHC CU Gas Puff PROTO-SPHERA Workshop - Frascati, 18-19/03/2002 Associazione Euratom-ENEA sulla Fusione

13. Cathode - Extrapolation to ProtoSphera 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/m 2 Molybdenum Conical Wire Terminal & Clamp PROTO-SPHERA Workshop - Frascati, 18-19/03/2002 Associazione Euratom-ENEA sulla Fusione

14. Visible Spectroscopy Spectral lines of filling gas (H 2 /He ) and impurities 1 eV < Te 3.0 eV - No HeII (4686 Å) Enlarged Å Å Å He Very few impurities OII & CIII at a count level of the largest Helium line counts H 2 Zoom H2H2 Å Å Å Å Å He zoom HeHe PROTO-SPHERA Workshop - Frascati, 18-19/03/2002 Associazione Euratom-ENEA sulla Fusione

15. Density Measurements 2mm microwave interferometer with 140 GHz oscillator : B = 1.25 kG : n e = 410 18 m -3 per fringe n e 6 10 19 m -3 Density measurable In Helium discharge up to I e = 200 A Line-averaged electron density increase linearly with current I e Helium ionization degree is about 16% at filling pressure of 4 10 -3 mbar & I e = 200 A fringes IeIe PROTO-SPHERA Workshop - Frascati, 18-19/03/2002 Associazione Euratom-ENEA sulla Fusione

16. MODELING of PROTO-PINCH PLASMA Ohmic input = electron flow convected flux T e Pinch 2 eV Good agreement with Spectroscopy 1<T e Pinch <3 eV Interferometry suggests plasma 50% ionized at I e =600 A p H2 =810 -3 mbar gives: n e Pinch 210 20 m -3 Estimated Ohmic input P 4kW - P tot pinch 50 kW electrode plasma sheaths P electrodes P tot pinch - P 46 kW solving power injected near the electrodes equation and electron flow near the sheets equation : T e electrodes 0.4 eV - n e electrodes 510 20 m -3 PROTO-SPHERA Workshop - Frascati, 18-19/03/2002 Associazione Euratom-ENEA sulla Fusione

17. EXTRAPOLATION to Screw Pinch of PROTO-SPHERA Assuming same plasma near the electrodes at I e =60 kA T e electrodes 0.4 eV, n e electrodes 510 20 m -3 Power into electrode sheaths P electrodes = 10046 kW = 4.6 MW In the main body of the discharge (far from electrode sheaths) Ohmic input = electron flow convected flux: T e Pinch = 36 eV Constant electron pressure : n e Pinch = 1.510 19 m -3 Ohmic input P = 5.4 MW OHMICP 5.4 MW + SHEATHSP electrodes 4.6 MW + Helicity InjectionP HI 0.6 MW = TOTAL POWERP Pinch 10.6 MW PROTO-SPHERA Workshop - Frascati, 18-19/03/2002 Associazione Euratom-ENEA sulla Fusione

18. Conclusions Associazione Euratom-ENEA sulla Fusione PROTO-SPHERA Workshop - Frascati, 18-19/03/2002 Arc breakdown in configuration similar to ProtoSphera : OK Stable arc I e 1 kA, with q Pinch 2 : OK Capability to fulfill ProtoSphera requirements : Arc Current, up to 60 kA : OK Electron Emissivity ( 1 MA/m 2 ) : OK Arc Power handling capability : OK Test of : 1/100 of the ProtoSphera Cathode & Anode : OK

19. Answers to Panel Questions Are the PROTO-PINCH electrode experiments a sufficient technical basis for a reliable electrode operation in PROTO-SPHERA ? : YES How likely in the proposed experiment to advance the present state of science and tecnology...? : Anode & Cathode load, both in energy and power are relevant for, ITER and fusion reactor, divertor and plasma facing components. Associazione Euratom-ENEA sulla Fusione PROTO-SPHERA Workshop - Frascati, 18-19/03/2002

20. W Impurities (Spectroscopy ) H noise = 5 10 -3 W = H noise = 125 n H2 = 2 10 20 1/m 3 S H m 3 /sec; S H XB H XB H m 3 /sec S W m 3 /sec; S W XB W XB W m 3 /sec n WS =( W/ H XBH /XB W ) nH2 1/m 3 Zeff = ( nH 2 (ZH 2 ) 2 + nW (ZW) 2 )/(nH 2 + nW ) Associazione Euratom-ENEA sulla Fusione PROTO-SPHERA Workshop - Frascati, 18-19/03/2002

21. W Impurities ( Pressure ) n H2 = 2 10 20 1/m 3 P H2 = 8 10 -3 mbar Fac rcy = 5/100 P W2700 C = 1 10 -5 mbar n W = (P W2700 C /P H2 ) nH 2 1/m 3 n Wp / n WS = 1/m 3 1/m 3 Associazione Euratom-ENEA sulla Fusione PROTO-SPHERA Workshop - Frascati, 18-19/03/2002

22. MODELING of PROTO-PINCH PLASMA Associazione Euratom-ENEA sulla Fusione PROTO-SPHERA Workshop - Frascati, 18-19/03/2002 I e =600 A ; = 0.1 m, ; B = 1 kG, q Pinch 2 ; L c = 1.33 L Pinch m Ln Z eff =2 ; = 1.9 10 4 A/m 2 ; 2 10 2 ln T e 3/2 /Z eff P Pinch = 2 1.33 L pinch / neglecting radiation loss the convected flux : P pinch = 5/2 T e 2 equating the terms ->T e =2.45 eV in good agreement with spectroscopy 1 n e 210 20 1/m 3 P Pinch kW, P pinch = 50 kW -> Power in Plasma Sheats P el Pinch kW ks m/s; S el =210 -2 m 2 Power injected in Plasma sheats P el Pinch = 1.6 10 -19 S el k s n el T el 3/2 Watt under condition constant electron pressure (plasma body – electrodes ) flow near the sheats -> 2 n elT el =n eT e = 5.310 20 eV/ m 3 T el = 0.49 eV 4.610 4 =1.610 -19 210 -2 k s n el T el 3/2 n el = 5.4 10 20 1/m 3

23. EXTRAPOLATION to Screw Pinch of PROTO-SPHERA Associazione Euratom-ENEA sulla Fusione PROTO-SPHERA Workshop - Frascati, 18-19/03/2002 S el =2 m 2 ; L pinch = 2m ; L c = 2 L Pinch m; = 0.04 m Ln Z eff =2 ; I e =60 10 3 A; = 1.2 10 7 A/m 2 ; 2 10 2 ln T e 3/2 /Z eff Assuming plasma parameters near electrodes the same as PROTO-PINCH T el = 0.49 eV, n el = 5.4 10 20 1/m 3 P Pinch = 2 2 L pinch / 5.4 MW neglecting radiation loss the convected flux : P pinch = 5/2 T e 2 equating the terms -> T e 36 eV 2 n elT el =n eT e = 5.3 10 20 eV/m 3 -> n e = 1.5 10 19 1/m 3 Therefore the Power injected into the plasma sheets is : P el Pinch = 1.6 10 -19 S el k s n el T el 3/2 Watt = 4.6 MW

24. Emissivity vs Temperature (1) Associazione Euratom-ENEA sulla Fusione PROTO-SPHERA Workshop - Frascati, 18-19/03/2002