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

Electrodes and PROTO-PINCH

Presented by A. Mancuso

PROTO-SPHERA Workshop - Frascati, 18-19/03/2002

Associazione Euratom-ENEA sulla Fusione

Outline

1)PROTO-SPHERA Requirements2)PROTO-PINCH Experiment3)Cathode, Anode & Diagnostics4)Extrapolation to PROTO-SPHERA



PROTO-SPHERA Requirements

Arc Current, up to 60 kA

Electron Emissivity ( 1 MA/m2)

Arc Power, up to 6.0-10 MW

Power Density Handling Capability (20-30 MW/m2)



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 Ie≤1 kA, with qPinch≥ 2.PROTO-SPHERA Workshop - Frascati, 18-19/03/2002


PROTO-PINCH has produced Hydrogen and Helium arcs in the form of screw pinch discharges.

Image of PROTO-PINCH Hydrogen plasma with Ie=600 A, B=1 kG.

Pinch Length : 75 cm Stabilizing Field : 1.5 kGSafety Factor qPinch≥2

Ie = 670 AEmax = 6.7 A/cm2

Vpinch = 80 –120 VVcathode = 14.5 V

PROTO-PINCH Discharges



Cathode Layout

Material Plates: MolybdenumColumns:TantalumInsulator : AluminaCoils : Pure WModule Power = 8.4 KWModule Current = 670 AModule Voltage = 14.5 VWire Number = 4Wire Length = 40.0 cmWire Surface = 4X25 cm2

Wire Temp = 2600 CWire Em = 6.7 Amp/cm2

Wire Weight = 4X22 Gr.



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.

Icath=550-590 A (rms.) at Vcath=14.5 V (rms.)

allows for Ie=600-670 A of plasma current Ie/Icath≈1.

Pcathode≈ 8.5 kW allows for Pe≈50-70 kW into the Pinch.

No damages after 400 shots at Ie= 600 A, t = 2-5 sec



HeliConical Coil

HeliConical Coil

Wires 1 out 4T = 2600 C

Ground

Conical Wire&Terminal

Clamp

Tantalum Column

AC Power14.5 V

D= 14 mm

d=2mm AluminaInsulator

Double HelicalZeroField

Molybdenum Plates

Ic=150A

Null FieldOptimize Temperature DistributionOptimize Weight Distibution Ie =167 A (each coil)DPFS= Ie/PFS

m2



Plasma Face SurfacePFS=1.5 10-4m2

HeliConical Coil Test Test Results :

Very Small Displacement after 2700 Sec at 2700 C



Structural Analysis

Max VonMisess Stress = 0.16 Kg/mm2

C = 0.85 Kg/mm2

Safety Factor = C Stress PROTO-SPHERA Workshop - Frascati, 18-19/03/2002


W - Bending Proof Strength vs Temperature

0.40

0.50

0.60

0.70

0.80

0.90

1.00

1.10

1.20

1.30

1.40

1.50

2300 2400 2500 2600 2700 2800 2900 3000 3100 3200

Temperature (° C)

(K

g/m

m2)

A

Max Stress 0.16 Kg/mm2

Anode

NoDamages after 1000 discharge

Material W 95% Cu5%.

Scheme : Puffed Hollow Anode

PWAnode = 2/3 (670 120) KW W ( module) Asurface 1 • 10-3 m2

Dpw = PW/ Asurface MW/m2

anode arc anchoringwithCathode DC heated (a) No Anode anchoring with AC cathode heating (b)

a b



Anode Extrapolation to PROTO-SPHERA

W Cu5%

Gas Puff Ie

TotSurf = 0.2 m2

Anode Power Handling Capability:PROTO-PINCH=670A • 120V 80 KW (2-5sec)

(ProtoSphera/ ProtoPinch)AnodeSurface 100

ProtoSpheraTested up to 100 * 80 KW = 8 MWProtoSpheraMax 6.0 – 10 MW ( < 1 sec)

OFHC CU

Gas Puff



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/m2

Molybdenum

Conical Wire Terminal & Clamp



VisibleSpectroscopy

Spectral lines of filling gas (H2/He ) and impurities

1 eV < Te 3.0 eV - No HeII (4686 Å)

EnlargedÅ

Å

Å

He

Very few impurities

OII & CIII at a count level

of the largest Helium line counts

H2 ZoomH2

ÅÅ ÅÅÅ

He zoomHe



Density Measurements

2mm microwave interferometer with 140 GHz oscillator :

B = 1.25 kG : ne = 4•1018m-3 per fringe ne 61019 m-3

Density measurableIn Helium discharge up to Ie = 200 ALine-averaged electron density increase linearly with current Ie Helium ionization degree is about 16% at filling pressure of 4 10-3 mbar & Ie= 200 A

fringes

Ie



MODELING of PROTO-PINCH PLASMA

Ohmic input = electron flow convected flux TePinch 2 eV

Good agreement with Spectroscopy 1<TePinch<3 eV

Interferometry suggests plasma 50% ionized at Ie=600 A pH2=8•10-3 mbar gives: ne

Pinch 2•1020 m-3

Estimated Ohmic input P 4kW - Ptotpinch 50kW

electrode plasma sheaths Pelectrodes Ptotpinch - P 46 kW

solvingpower injected near the electrodes equation and electron flow near the sheets equation :Te

electrodes 0.4 eV - neelectrodes 5•1020 m-3



EXTRAPOLATION to Screw Pinch of PROTO-SPHERA Assuming same plasma near the electrodes at Ie=60 kATe

electrodes 0.4 eV, neelectrodes 5•1020 m-3

Power into electrode sheaths Pelectrodes= 100•46 kW = 4.6 MW In the main body of the discharge (far from electrode sheaths) Ohmic input = electron flow convected flux:

TePinch = 36 eV

Constant electron pressure : nePinch = 1.5•1019 m-3

Ohmic input P = 5.4 MW

OHMIC P 5.4 MW +

SHEATHS Pelectrodes 4.6 MW +

Helicity Injection PHI 0.6 MW =

TOTAL POWER PPinch 10.6 MWPROTO-SPHERA Workshop - Frascati, 18-19/03/2002


ConclusionsAssociazione Euratom-ENEA sulla Fusione


Arc breakdown in configuration similar to ProtoSphera : OK

Stable arc Ie≤1 kA, with qPinch≥ 2 : OK

Capability to fulfill ProtoSphera requirements :

Arc Current, up to 60 kA : OK

Electron Emissivity ( 1 MA/m2) : OK

Arc Power handling capability : OK

Test of : 1/100 of the ProtoSphera Cathode & Anode : OK

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.



W Impurities (Spectroscopy )

H

noise = 5 • 10-3

W = Hnoise = 125nH2 = 2 • 1020 1/m3

SHm3/sec; SHXBHXBH•m3/secSWm3/sec; SWXBW XBW

•m3/secnWS =( W/ HXBH/XBW) nH2 •1/m3

Zeff = ( nH2 (ZH2)2 + nW (ZW)2 )/(nH2 + nW )



W Impurities ( Pressure )

nH2 = 2 • 1020 1/m3

PH2 = 8 • 10-3 mbar

Facrcy= 5/100PW2700C = 1 10-5 mbarnW = (PW2700C /PH2) nH2 •1/m3

nWp/ nWS = 1/m31/m3



MODELING of PROTO-PINCH PLASMA



Ie=600 A ; < Pinch > = 0.1 m, ; B = 1 kG, qPinch2 ; Lc= 1.33 • LPinch m LnZeff=2 ; <Jpinch>= 1.9 • 104 A/m2 ; 2 102 lnTe

3/2/Zeff

PPinch=< Pinch >2 1.33 Lpinch/ neglecting radiation loss the convected flux :

Ppinch= 5/2<JPinch>Te< Pinch >2 equating the terms ->Te=2.45 eV in good agreement with spectroscopy 1<Te<3assuming plasma is 50% ionized and PH2=8 • 10-3 mbar -> ne2•10201/m3

PPinchkW , Ppinch= 50 kW -> Power in Plasma Sheats Pel

Pinch kWks• m/s; Sel=2•10-2 m2

Power injected in Plasma sheats

PelPinch = 1.6 10-19 Sel ks nel Tel

3/2 Watt

under condition constant electron pressure (plasma body – electrodes )

flow near the sheats -> 2 nel•Tel =ne•Te= 5.31020 eV/m3 Tel = 0.49 eV

4.6•104=1.610-19 2•10-2 ks nel Tel3/2 nel = 5.4 1020 1/m3

EXTRAPOLATION to Screw Pinch of PROTO-SPHERA



Sel=2 m2; Lpinch = 2m ; Lc= 2 • LPinch m; < Pinch > = 0.04 m LnZeff=2 ; Ie=60 103A; <Jpinch>= 1.2 • 107 A/m2 ; 2 102 lnTe

3/2/Zeff

Assuming plasma parameters near electrodes the same as PROTO-PINCHTel = 0.49 eV, nel = 5.4 1020 1/m3

PPinch=< Pinch >2 2 Lpinch/ 5.4 MW

neglecting radiation loss the convected flux :

Ppinch= 5/2<JPinch>Te< Pinch >2 equating the terms -> Te36 eV2 nel•Tel =ne•Te= 5.3 1020 eV/m3 -> ne = 1.5 1019 1/m3

Therefore the Power injected into the plasma sheets is : Pel

Pinch = 1.6 10-19 Sel ks nel Tel3/2 Watt = 4.6 MW

Emissivity vs Temperature (1)Associazione Euratom-ENEA sulla Fusione


Documents

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