INTRODUCTION

TOROIDAL SUPPORT STRUCTURE MODIFICATIONS

Thermo-mechanical analyses and design of components for fusion devices

1 Consorzio RFX, EURATOM-ENEA, Corso Stati Uniti 4, I-35127 Padova, Italy

N.Patel1, M.DallaPalma1, P.Sonato1

nisarg.patel@igi.cnr.it

MotivationFull exploitation of RFX-mod sought upgrade of machine,� To improve passive MHD control by bringing passive copper shell as near as

possible to plasma (Reduced plasma-shell distance)� To minimize braking torque on plasma through the elimination of vacuum vessel

(Improve wall lock mode scenario)

Major mechanical modifications foreseen� Remove vacuum vessel and make Toroidal Support Structure (TSS) as new

vacuum bounday

� Design support of passive Cu-shell� Design support of FW tiles� Assembly and sensor cable routing

RFX ----> RFX-mod ----> RFX-mod2

1992

to

1999

2004

to

till now

Concept and

planning

phase

Major Radius, R(m) 2

Minor Radius, a(m) 0.5

R a

Supporting ring

TSS

Saddle coils

Vacuum vessel

Cu shellFW tiles

Requirements� Maintain UHV vacuum level

(10-8 mbar)

� Modifications in view of present TSS structure� To Provide vacuum sealing on toroidal and poloidal cuts� To provide electrical insulation at 3 cuts

� Attach vacuum ports on TSS� To close all holes and openings

Poloidal joint

�Vacuum sealing

�Electrically insulated

�Mechanical continuity

Internal toroidal joint

�Vacuum sealing

�Electrically insulated

External toroidal joint

�Vacuum sealing

�electrically continuity due to the

geometrical complexity

Welded configuration

Resistive plate weld configuration

Braze-weld configuration

Types of openings:I. Ports openings (151)

II. Support openings (24x2)

III. Poloidal bolt openings (24x2)

IV. Assembly centering holes (4)

Summary of modifications

Sr. TSS Qty. Modification

1 Int. eq. ports 7 To be closed

2 Ext. eq. ports 22 To be integrated

3 Vertical Ports 122 To be integrated

TSS support To be closed from inner

CeramicWeld plate

PASSIVE COPPER SHELL AND SUPPORT STRUCTURE

Euratom-ENEA

Association

Main constraints� Varying thickness of sealing surface

(Max. 47 mm to Min. 20 mm)

� Non-flat sealing surface (Ports at outer toroidal cut)

� Sealing surfaces crosses/intersecting each other

� Only 5 mm gap (Sealing + Insulation)

� No feasibility of flange connection

(Only connection options are, Clamping rings at

toroidal cuts and Bolted connection at poloidal cuts)

� Assembly sequence will be changed

� Considered at external

toroidal cut as most suitable

solution to accommodate

ports

� Weld at inner surface (No

trapped air)

� Minimum machining required

to prepare weld leaps

Weld lip

SS plate

� Resistive plate full weld:

� 200 mm long resistive metal plate

(Nichrome, Constantan) can be

welded to top and bottom TSS

� A plate made of electrical

insulating material (G10, ceramic)

between top and bottom TSS

�Braze-weld solution: need gap of around

50 mm to accommodate the joint

�welding solution:

�The equatorial sealing will be closed with

a cylindrical plate, which will be welded to

the resistive plate and to the poloidal cut

at the TSS

�Brazing solution:

�Cylindrical sealing plate will be brazed to

ceramic plate at both side which will be

welded to other cylindrical plate

�Mechanical stiffness:

�Toroidal continuity at poloidal joints will be

provided by bolted junctions electrically

insulated with G10/ceramic spacers and

bushes

4

TSS support

openings 48

To be closed from inner

side

5

Poloidal bolt

openings 48

To be closed from inner

side

6

Assembly

centering holes 4 To be closed

7 Poloidal cut 2 Braze-weld

8 Ext. toroidal cut 1 Full welded

9 Int. toroidal cut 1 Resistive weld plate

TSS Analysis

A. Max.= 298 MPA

C. Max.= 99 MPaB. Max.= 298 MPA

D E

B C

D

E

A. Max. = 0.4 mm

C. Max. = 0.4 mmB. max. total = 0.4 mm

D. Max. = 0.3 mm E. Max. = 0.25 mm

B

C

D

E

Free studVertical supporting stud

FW tile support concepts

R=1995 mm

511.5 mm

493.6 mm

Washer of 0.5

mm to 5mm

thickness

FW key fastner

Bonded to shell

Thk. Min= 1 mm

Thk. Max.= 3 mm

RFX-mod

Cu shell

m/c major axis

Plasma

center

Side thick element is for

vertical alignment of tile

Element: solid278

Element: Link33

Shell support

element

Temp = 294° K

Plasma flux

� 20 MJ of energy dissipated on FW (1.8 MW/m2)

� Pulse duration: 310 ms

� 20 min cooling between pulses

� Total 30 pulses considered for analysis

� At support 301 K temp. applied

� Radiation heat transfer is not included

Temp. distribution and mechanical behavior

Section - AA

Bottom_shell

Top_shell

BS_near_

support

Max. = 450 K Min. = 300 K

Plasma heat flux

Copper shell

Tile

Key

Supporting

washer

In-Washer

Heat conduction path

local displacements

Equivalent stresses

Due to change of vacuum boundary in RFX-mod2,

major change in internal systems will be,

� To design new support system for Cu-shell and

FW tiles

� As FW tiles will come nearer to Cu-shell, temp.will increase in Cu-shell.

Above model describe the concept of FW tile

support on Cu-shell.

Temp. distribution considering this configuration is

studied using FEA simulation as shown here.

Also structural study is going on for shell supporton TSS considering temp. distribution obtain by

FEA results.

Results shown that are within acceptable limit of

geometry displacement.

Results for equivalent stresses shows stress

concentration on single node due to coarse mesh at

support region which can be neglect.