J. Plasma Fusion Res. SERIES, Vol.3 (2000) l0-15

CIEL in Tore Supra:

How to Master Power and Particles on very Long Discharges
GARIN Pascal*, on behalf of Tore Supra Team
Association EURATOM-CEA - Ddpartement de Recherches sur la Fusion Contrdl6e
CEA/Cadarache, I 3 I 08 SAINT- PAU L-LEZ-D U RANC E, F rance(Received: 2l January 2000 / Accepted: 7 July 2000)

Abstract
In order to prepare the next generation of tokamaks, a new goal has been assigned to Tore Supra.
Initially designed for handling 15 MW of power over 30 s operation, the original generation of plasma
facing components will be replaced by a set of new, high technology components, constituting the socalled "CIEL" project (French acronym for "Composants Internes Et Limiteur"), with the ultimate aim of
injecting 25 MW over 1000 s in the plasma. An overview of the developments associated to the various
components and of the main technological challenges is given. Installation of CIEL in Tore Supra will
last about l8 months; the new configuration will be operational mid of 2001.

Keywords:
Tore Supra, Plasma Facing Components, infrared, long discharges

1. Introduction
After I I years of operation, during which many

capability, in particular for the convected power. A totalof 25 MW power extraction becomes possible for 1,000s
discharges, with a pumping exhaust of 4 Pa.mr/s [2].
The development of a new generation of high heat
flux components makes possible an increase of about

new results have been obtained, as PEP or LHEP modes[] (regime where pellet injection or lower hybridenhances confinement), record energy coupled to theplasma (280 J, during two minute shot), comprehensive

one order of magnitude thermal removal capability.

studies on improved confinement regimes (internaltransport barriers, reversed shear), etc., Tore Supra is
now being dismantled in order to renew the wholeplasma facing component environment. Former results,
even if obtained for relatively long discharges, must be
confirmed for almost steady state operation.
It is the goal of this new environment, called CIEL
(French acronym for "Composants Internes Et
Limiteur", inner components and limiter) to provide
stable and reliable plasma facing component
configuration to extend former studies. They have

CIEL main object, so-called toroidal pump limiter
benefits of these developments, and enables a power
exhaust of 15 MW of convected power. The remaining
10 MW of radiated power will be evacuated by a set ofpanels enabling even a potential radiation up to 25 MW

for 1,000s, or peaked radiation up to a factor of 3.
Figure I below shows the main components of CIEL:.

A flat Toroidal Pump limiter (TPL) located at thebottom of the inner vessel:.

shown in particular the importance of the wall
preparation, its behavior for very long discharges (morethan one minute), and the overall power exhaust

A set of 6 poloidal bumpers, located on the highfield side of the machine;@2000 by The Japan Society of Plasma
Science and Nuclear Fusion Research

Corresponding author's e-mail: pascal. garin@ cea.fr
10Garin P. et al., crELinTore supra: How to Master Power and Particles on very tong Discharges

2. Heat Extraction

Stainless steel panels covering the whole surface of
the inner vessel, designed to evacuate up to 25MW,

Two generations of actively cooled components

and providing a stable temperature environment;.

have been already intensively used in Tore Supra'.

12 so-called neutralization cassettes located under
the limiter, in its throat, and connected via ducrs to

the first one, based on the brazing of carbon tiles
on stainless steel pipes, showed some limitation, inpumps.

particular with respect to runaway electrons which

destroyed some tiles, and their heat exhaust
Other components, as infrared endoscopes located in theupper ports are not visible on the drawing. They ensure
the safety of the limiter, and are a nice tool to measure
power deposition on it.
Cooling loop enhancement is also necessary.

capability;

a new generation was then installed on the highfield side of the inner vessel, based on carbon fiber
composite tiles, much more robust than the firstones, but always cooled down via stainless steel
heat sink.

In the meantime continuous development led to thepossibility to btaze CFC tiles on copper layer, with again of one order of magnitude in the thermal flux
removal capability with respect to stainless steel. This
new generation has been already successfully used onantenna bumpers for two years of experimental
campaign.

After l0 years of successful operation of theergodic divertor inside Tore Supra, a limiter
configuration has been chosen, in order to provide a
simple and stable environment to the plasma. It will
replace the main limiter used before (inner wall
bumper), which had some remaining gaps between thecooled stnrctures, because of its poloidal and toroidal
geometry (wider distance at the top and bottom than in
the equatorial plane).

On the other hand, actively cooled stainless steel
panels will be used in the new geometry, this cheap
technology being compatible with the flux to extract.
Only slight optimization, in particular with respect towater flow rate has been made, as explained hereafter.

2.1 Toroidal Pump Limiter
A flat limiter configuration procures a flexible way
plasmaforshaping, control and HF additional heating
coupling; simple feedback control on the local shape in
the throat can be used to optimize heat deposition andpumping. The Toroidal Pump Limiter covers 7.5 m2 of
the bottom area of the inner vessel and has been
designed to sustain a convective power of 15 MW in. NeuiralizationCa66suos
Fig. 1 Overview of CIEL Components

steady state.

This horizontal disk, tangent to the plasma, islinked to a supporting structure (Fig. 2), used as areference plane and manifold [3]. It allows the accuratellGarin P. et al., CIEL\nTore Supra'. How to Master Power and Particles on very Long Discharges

positioning of the limiter leading edge, can be moved
vertically and is electrically isolated from the vacuum
vessel by ceramic rings, allowing a biasing up to +lkV.

A remarkable manufacturing accuracy, measured by two
different techniques, has been obtained: +0.2 mm offlatness, +0.3 mm of circularity and +0.2 mm ofcircularity between the external and inner crowns.

The head of the limiter (horizontal disk) is
composed of high heat flux components, called fingers,
manufactured by the Austrian company Plansee. These

fingers are cooled by pressurized water (40 bar at

150'C) provided by the TPL structure. Flux
performance of these elements has been measured on a
special facility, an electron gun called FE200: up to
l5MWm2 on the flat part of the finger and I I MWm2
on the leading edge with safety. They are composed of asheath of 6 mm carbon fiber composite linked to a thin

Fig. 2 TPL Supporting Structure

copper layer by a technique called "Active Metal
Casting" [4]. This copper layer is itself welded byelectron beam on the body, made of CtCrZr alloy. A

d50

s

*ff

n 860

!m
rm

final systematic check by means of infrared camera on a
specific test bed is carried out to measure individual
thermal transfer from finger surface to inner water
channel, and guaranty the overall performance of the

.E

Erm

-2#'

Fr*
Flm
t0

TPL.

o

o

2.2 Inner Wall Protection Panels
Protection of the inner vessel against radiatedILu

2.3 Bumpers
Transient events (disruptions, runaways...), as well

the following main reasons:as permanent radiated power will be absorbed by a setof 6 pairs of poloidal bumpers (Fig. l). Their

Suppression of all slots between panels, resulting intechnology, developed in the framework of a NET
contract, is based on the concept of thick CFC tiles
cooled on a CuCrZr heat sink via a sheath of carbon

a transparency lower than l7o;.

o.a 0.6 ca-

Forqlleaitr 0IWrnJ

Fig. 3 FE200 Test of Inner Wall Panels

power is devoted to a set of stainless steel panels. Zore
Supra has already experienced this kind of panels, but it
was necessary to replace them by a new generation for.

ot*fn*i&tlaA)*Fm*dla{Ltdj+Blltddr (f r&

In order to optimize water flow rate, the thicknessof panels was decreased from 12 (present
configuration) down to 8 mm. Thus the
manufacturing technology is also different: preembossed plates were welded, while the first
generation consisted in hydroformed panels.

paper, called papyex, and springs. The latter ensure a
constant pressure, whatever the surface temperature of
the CFC tiles. Their thickness and shape are calculated

to spread the flux on a large surface, with a deep
penetration of the runaways, without any risk of damage

for the cooling structure. The temperature is less than600"C for the maximum radiated power (25 MW) after

Figure 3 shows the experimental results of test
under flux of one panel on FRAMATOME-CEA

1,000 s.

installation F8200 (water velocity: I and 2.5 m/s). Even
with a low water velocity of I m/s, up to 0.5 MWm2
can be applied with a maximum temperature of 300'C.
This flux corresponds to an overall radiated power of
25MW, with a peaking factor of almost 2.

2.4 Cooling Loop Modifications
CIEL project also includes modifications of thecooling loop, which ensures Tore Supra's baking at
230"C and heat removal at about 150'C. A total amountt2

Garin P. et al., cIBLinTore supra: How to Master Power and particles on very Long Discharges

of 1,000 t/hours is indeed necessary for all CIEL
components, but also RF antennas, plasma facing
diagnostics, etc. The upgraded loop primary circuit(40 bar - 23O"C) will extract 25 MW overall power for
1,000 s discharges.

2.5 Particle Control
In steady state, one cannot rely on wall pumping,
and an active pumping must be provided. Control of theedge density will be made by means of neutralizer sets,located below the limiter, and connected to the pumps.

Pellet injectors will mainly fuel the plasma, at afrequency of 10 Hz.
A total pumping capacity of 4 Pa.m3/s seems to be

Fig. 4 Schematic of Neutralization Cassetteenough to maintain a constant density, whatever the
scenario.
E

2.6 Neutralization Ca*settes€6

Below the TPL throat are located 12 cassettes asshown in Fig. l. Four fingers (same technology as forthe flat part of the TPL) are assembled in a V-shape sothat each quadruplet of neutralizers is at the shadowing
limit of the next toroidal one.
A bellows under the cassette plate is connected to
the vertical port of Tore Supra and enables evacuationof neutralized species towards the pumps.
Figure 4 shows also optical fibers and the final
mirror that monitors finger surface temperature.
Gases are then pumped via cylindrical ducts locatedwder Tore Supra. After neutralization on the fingers,
thermalization in the box below the plate, molecular
recombination occurs all along the pipe towards thepumps. EIRENE code has been intensively used tocompute and dimension all these elements. As a result,Fig. 5 shows the necessary flux to extract versus
deuterium pressure at the bottom of Tore Supra'slower

3€s
.EEr

rU

Ev3

i8.
go&
5r
F]

o

0.1

0.01
D2

I

Pmurc at the Port Bottom €a)Fig. 5 Computed Flux vs. D2 Pressure

3.5
3

'12.s

Mrxim

7

^c^ /

./tTon SunroC,

2vertical port. The calculation is made assuming l0 ports
available under the machine (two of them are occupied

1.5

by traversing diagnostics: Thomson scattering andinterfero-polarimetry). Data are given with a gas

o.00r

0.0r

o.1

I

R-Pc(m.Pa)

temperature of 300 K.

Fig. 6 Possible Gain vs. Pressure and Radius

2.7 Cryomechanical Pumps
The principle of the cryomechanical pump is basedon the relation between volume and temperature at asection shrinks, it converges to the square root of thegiven pressure. When the section is infinite, theresulting gain in the pumping speed is with the ratio of
the temperatures (i.e. a factor 3.3 for 80 K pump,temperatures, as shown in the Fig. 6 below, which plots

including a l0 K gradient between the gas and theshown.

the gain vs. the product ofthe radius R and the pressure
Pc above the pump. Tore Supra typical operation, is also

pump, with respect to room temperature). But when thet3Garin P. et al., CIEL in Tore Supra: How to Master Power and Particles on very Long Discharges

Power deposition measurement on the TPL is avery important challenge (15 MW - 1000 s is the design

As shown in Fig. 8, the endoscopes are full plasma
facing components and must withstand, not only theradiated power, but also electrons lost in the magnetic
ripple. They are composed of the following elements:

value). The most commonly used model is based on theconventional exponential decay out of the scrape-of.

3. Temperature Monitoring and Safety
3.1 TPL Surtace lnfrared Monitoringlayer, with a characteristic length called 1.a. Present
power deposition analysis on the so-called Inner Wall
Protection, in spite of very important recent progress,
leads to surprisingly very small heat decay length ,tq,

A head in CtCrZr alloy, actively cooled as theother plasma facing components at 150'C inoperation; this head is protected duringboronizations by a rotatable protection.

.

and needs to be better understood. The flat geometry of

the TPL will help a lot in the construction of a modeland its understanding. Recently this model was
improved by including self-shadowing of the limiter on
itself, as shown in Figure 7 [5].
On the other hand, the safety of such an expensive
instrument must be particularly robust and enable also a
feedback action on plasma itself (position, shape), oreven to its heating.
All these functions will be devoted to a set of 6
infrared cameras, analyzing and combining 12 images of
the 360' of the TPL. 6 endoscopes are thus located in
the upper vertical ports of the machine, every 60". Each
one has 3 lines, 2 of them looking to the TPL surface, athird one towards one RF antenna. Spatial resolution isforeseen to be better than 9 mm. A specific line will
have even a better resolution (4 mm), to make detailed
power deposition physics analysis.

The whole body of the endoscope is also cooled at
the same temperature.

I o.?

!:^
1,,
,22
i27
i32
:zl
42
5?

:47

iea
167

Fig. 7 Computation of Power Deposition on the Toroidal

Pump Limiter

Soparafa Pumf,ing d trt€ Endos@p6 Sody

Rippl€ Lcs Prolactbn

Th€ whole Endoscope Body is sctively cool€dRolatabl€ Windo$ Prcletion (e.9. during Borcnisalisr)

Fig. 8 Overall View of one Endoscope and its Cameras

14

Garin P. et al., ClELinTore Supra: How to Master Power and Particles on very Long Discharges.

.

completion and final acceptance tests. Removal ofexisting components, in particular the ergodic divertor
modules, has started in December 1999 and CIEL

The inner lenses, which propagate the images, arecooled with another loop at 2O"C, to avoid image
contamination by higher temperatures, andmaintain a good transmission coefficient (some of
the materials become opaque at high temperature).

installation is scheduled during the three last quarters of

2000. The new machine should be ready forconditioning beginning of 2001, and the first plasma is

Two infrared cameras, one devoted to the TPL

expected mid-2001.

measurement, the other one to the antenna

The upgrade of the injection part, second half of"Tore Supra Continu" is now in study, as well as thenecessary upgrade of plasma facing diagnostics(windows, valves...). Because of the limitation ofpresent heating systems, a first objective of I GJ (e.g.
4 MW - 500 s) can be set for the first years of CIEL

monitoring.

3.2 Neutralizer lnfrared Monitoring
Computations performed in the frame of an"advanced scenario" with a total power of 25 MW
coupled to the plasma show that the thermal flux whichhits the front face of the most exposed neutralizer finger
reaches locally 20 MWm2, in spite of a specific shaping
to spread this flux.
In order to monitor this critical component, theoperation, 2001,2002.

References

tll

X. Litaudon et al., Stationary regimes of Improved

Confinement in Tore Supra, Plasma Phys. Control.
Fusion 38, A25l-A268 (1996).
l2l A. B€coulet, Heating and Current Drive System forfollowing original concept is in study. A triplet offiberglass will look at the edge of the neutralizer. Then,after separation of the signal, a bi-chromatic pyrometer
will allow absolute temperature measurement. The

Tore Supra in Steady State Operation, thisbundle of 12 times 3 signals will be separated by means

t3l L. Doceul, J. Schlosser, Ph. Chappuis, M.

conference.

of a beam-splitter. The resulting signals will pass

Chatelier, J.P. Cocat, C. Deck, F. Faisse, A.
Grosman, R. Mitteau and G. Tonon, Conceptual
design of a high heat flux toroidal pumped limiter
for Tore Supra, lSth SOFT August 22-26, 1994,

through two narrow interferential filters. The
comparison and ratio between the two signals will givethe surface temperature, whatever the transmission.
Preliminary experiments carried out in the laboratory

Karlsruhe. Germany.

t4l T. Huber, L. Pltichl, N. Reheis, J.P. Cocat and J.
Schlosser, The Manufacturing and Testing of the
Toroidal Pumped Limiter Prototype Elements forTore Supra, IEEE/SOFE, Champaign, 1995, pp.

show that blackbody emission intensity (the foreseen
wavelength range is 0.8-2 pm) is much higher thanmolecular rays, and should not be affected by them. But
a non-Lorenzian distribution has been observed, leading
to some difficulty in the interpretation of the measured
signal. Thus an absolute measurement is also

716-719.

t5l R. Mitteau, S. Berebi, P. Chappuis, Ph Darses, A.

project "Tore Supra Continu" has been launched in

Dufayet, L. Garampon, D. Guilhem, M. Lipa, V.
Martin and H. Roche, Non Destructive Testing of
Actively Cooled Plasma Facing Components bymeans of Thermal Transient Excitation and Infrared
Imaging, l9th SOFT, September 16-20, 1996,

February 1996. After 3 years of design andLisbon, Portugal, pp. 443-446.

implemented.

4. Conclusion
CIEL project, the extraction part of the more global

manufacturing, all components are now in the phase of15