status of the multi-pinch/proto-sphera load assembly

Assoc iazione Eu ratom -ENEA sulla Fu sione

The Joint Meeting of 4th IAEA Technical Meeting on Spherical Toriand 14th International Workshop on Spherical Torus Frascati, 7 to 10 October 2008

Outline of the Talk1) Introduction to PROTO-SPHERA

2) Engineering Design and Analysis of PROTO-SPHERA

3) Multi-Pinch Experiment

4) Timetable

5) Conclusions

Stamos Papastergiou, Franco Alladio, Alessandro Mancuso, Paolo Micozzi CR-ENEA, CP 65, 00044 Frascati (Roma), Italy

Status of the Multi-Pinch/Proto-Sphera Load Assembly



Engineering Design of PROTO-SPHERA



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



- 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.

Design Philosophy



Operationability, 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.

Design Aims



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

Operating conditions



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



•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

Protection Componenets



• 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.

Thermal and Heat transfer Behaviour



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.

Electromagnetic Forces and Stresses



ASME III-NB 3221 Stainles SteelASME III-NB 3221 Stainles 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

Predicted and Permitted Stresses



Provisional single anode Cathode

Aim: verification of the arc formation & stability ~ START Dimension

Pinch Current Ie=8.5 kA(same of ProtoSphera) - PF-Coils do not need cooling

Multi-Pinch Experiment

STARTVacuum Vessel

Multi-Pinch Experiment



START in Frascati

Arrival

Disassembling

May 2004

October 2004



Multi-Pinch Experiment: Phase I & Phase II



GAS

ELECTRICAL CONDUCTORS

Cu

W80%Cu

≤1000°C

ANODE PHASE - ASSEMBLY



GAS

Cu

WCu


WATER

ANODE PHASE 2 - ASSEMBLY



SECTION OF ANODE PHASE 2

WCu

GAS

WATER COOLED PROTECTION PLATES




Protection Plate Cu

W-Cu

SECTION OF

ANODE PHASE 2 SECTOR



W

Water

Cu


CATHODE - ASSEMBLY



CuW

Mo

WATER COOLED PROTECTION PLATES

15 V

CATHODE - CROSS SECTION



COIL PF2



MultiPinch Coils Delivery: 04/06/2007

EURATOM, ENEA & ASG Personnell



SECTION OF PF2



ASG – Test of PF2 Coil



MultiPinch Timetable

• Delivery of Load Assembly * September 2009

• I.a Construction & Delivery

Magnetic Diagnostics to ASG * April 2009

• II International Tender Action for Construction

• of Power Supplies * March 2009

• II.a Delivery of Power Supplies * June 2010

• III Site Preparation * June 2009

• IV Services (Vacuum, Electricity, Diagnostics) * June 2010

• V Commissioning * December 2010

• VI First Plasma * December 2010



• There 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

• The PF Coils have been delivered, while the Load Assembly is half way in construction using the START Vacuum Vessel

• First Plasma can be obtained in December 2010

• PROTO-SPHERA can be obtained by simply adding components to Multi-Pinch

CONCLUSIONS

status of the multi-pinch/proto-sphera load assembly

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