Structural and Electromagnetic Study of the Upper Port Plug for the

Structural and Electromagnetic Study of the Upper Port Plug for the
ECRH in ITER
D. Strauß1, R. Heidinger1, G. Gantenbein2, G. Hailfinger3, K. Kleefeldt1, A. Serikov3, P.
Späh1
Forschungszentrum Karlsruhe, Association FZK-EURATOM, (1) Inst. for Materials
Research I, (2) Inst. for Pulsed Power and Microwave Technology, (3) Inst. for Reactor
Safety, D-76021 Karlsruhe, Germany
e-mail: dirk.strauss@imf.fzk.de
Abstract
The ECRH system in the ITER upper launcher provides a stable structure during ITER operation. Besides of the
neutron and mm-wave loads during regular operation, plasma disruptions lead to fast changes in the magnetic
field, eddy currents are induced interacting with the static toroidal field. As a consequence, high mechanical
forces and torques act on the launcher structure. In numerical electromagnetic simulations these currents and the
resulting mechanical loads have been calculated. The loads are applied to a 3D finite element model of the upper
launcher structure, its deformation and occurring stresses are studied.
1. The upper launcher in ITER
External gyrotrons generate high power mm-waves which are guided by a system of
transmission lines to the ECRH launchers which inject up to 20 MW mm-wave power at 170
GHz into the ITER plasma [1]. The purpose of the upper launchers (upper port plugs shown
in FIG. 1) is to control plasma instabilities, especially to stabilize neoclassical tearing modes
by angular steering of the beam in poloidal direction towards the q=3/2 and q=2/1 flux
surfaces [2].
FIG. 1: The ECRH upper launcher is fixed exclusively at its back end.
This upper launcher structure is fixed at its back end to the vacuum vessel and swings free up
to the launcher tip facing the plasma. The mm-wave components are integrated into the
launcher main structure with diamond windows forming the first tritium barrier.
During operation plasma disruptions (centered disruption, vertical disruption or vertical
displacement events/VDE) cause high transient dynamic stresses due to electromagnetic loads
and transient thermal stresses with extremely high heat fluxes on the first wall [3]. As the
upper launcher is exclusively fixed at the back end flange the electromagnetic loads force the
launcher tip to deform. The structure must be stiff enough to withstand the forces and
moments without touching neighboring components. By design optimization the occurring
stresses have to be kept within an acceptable range to suppress cyclic failure scenarios.
2. Electromagnetic loads on the upper launcher
2.1. Disruption scenario
From the different disruption scenarios the upward VDE followed by a fast current quench
was assumed as the most severe for the upper launcher [4]. The EM loads calculated by
different simulation software show data for the complete launcher, the Blanket Shield Module
(BSM) and the internal shield (TABLE 1).
Load type
Frad (MN)
Fpol (MN)
Ftor (MN)
Mrad (MNm)
Mpol (MNm)
Mtor (MNm)
UPP loads projected on the
geometric center of the BSM [4]
0.33
-2.1
-2.2
1.62
Loads on BSM,
ANSYS [5]
-0.11
+0.26
-0.11
-0.56
-0.82
-0.19
Loads BSM and internal
shield, EMAS [6]
0.16
0.08
-0.22
-1.0
-1.45
-0.03
TABLE 1: VDE-III loads from different simulations.
2.2. The torus model
The torus is modeled as a 20° segment representing the symmetric nature of the VDE. The
ANSYS model [5] consists of the elements (FIG. 2) SOLID97 (vacuum: red, conductive:
light blue) and INFIN111 (dark blue).
FIG. 2: The torus segment and the modeled components.
The symmetry conditions suppress toroidal field components (the strong toroidal field is
added during post processing for the load calculation). Virtual vacuum loops represent the
poloidal field coils forming the static magnetic field. During the quench a current is induced
to the plasma facing modules. This transient current distribution is projected on a cell layer
artificially set to conductive vacuum directly in front of the blankets resulting in the fast
changing poloidal field affecting the outer components.
The upper port is filled with a simplified model of the launcher and a small vacuum gap
except for the launcher back end flange where the launcher is fixed to the vacuum vessel. The
blanket shield module includes shield blocks, the front steering mirror unit and an asymmetric
cut out in the first wall panel for the mm-wave beam line. The internal shield section is filled
with the first big neutron shield block followed by a second one filling the middle part of the
launcher. The rear part is a hollow structure representing the closure plate area where the first
tritium barrier in the beam lines is formed by the sophisticated thin CVD diamond windows.
2.3. Electromagnetic load calculation
The transient current distribution in the artificially conductive cell layer in front of the first
wall generates the fast changing poloidal field. Inside the upper port the simulation calculates
the formation of eddy currents. During post processing the strong toroidal field is added to
calculate the Lorentz force on each element. Force application points are created within the
geometric center of each component and associated with the summed up force and a torque
moment (TABLE 2).The segment border between BSM and internal shield cuts the major
current loop in two parts causing a sign flip in the radial and poloidal force components.
Component vs. loads
Frad (MN)
Fpol (MN)
Ftor (MN)
Mrad (MNm)
Mpol (MNm)
Mtor (MNm)
BSM
-0.1
0.2
-0.08
-0.45
-0.7
0
Internal Shield
0.75
-0.17
-0.12
-0.7
-0.7
0.05
Middle
0.15
0.03
-0.03
-0.32
-0.17
0
Rear
0.01
0
0
-0.02
-0.01
0
TABLE 2: Forces and loads on different launcher components relative to their geometric center.
3. Deformations under electromagnetic loads
3.1. The model and the load application
In the present design stage the internal components as shield blocks and their fixation are still
subject of change. As a first approach of an analysis of the launcher structural under the
calculated EM load distribution the load peaks are taken to perform a static elastic analysis of
the launcher deformation. The actual CATIA model was imported and simplified at the back
end fixation to the vacuum vessel where the launcher is supposed to be fixed rigidly.
FIG. 3: The modeled front steering upper launcher.
Further simplifications affect minor geometric details without significant importance to the
analysis. The model was meshed using ANSYS workbench 11.0 and the element types
Solid186, Solid187 and Surf154. For the load application usual multi-point constraints with
element types Conta174 and Targe170 were applied for the different components as well as
gravity for the whole model.
3.2. Deformations
Due to the trapezoid structure the upper launcher is especially sensible to bending in toroidal
direction and tilting around the launcher main axis. The bending of about 8mm in the critical
toroidal direction is mainly caused by Ftor and Mpol. An additional tilting by Mrad increases the
toroidal launcher deformation to 10.2mm. In comparison the maximum spacing to
neighboring components is 20mm where tolerances still have to be considered.
FIG. 4: Axial bending and tilting of the launcher.
The comparison of the deformation under the different EM loads show a reduction in toroidal
direction of 10% compared to the EMAS calculations and 15% compared to the older
reference loads. As the simulations were performed statically the transient analysis might
show higher deformations. However for a detailed transient analysis the fixation of the
internal shield blocks has to be defined as this influences significantly the launcher stiffness
respectively the launcher natural frequency.
Deformations
[mm]
Radial
Poloidal
Toroidal
Differential loads
(TABLE 2)
1.2
0.8
-10.2
EMAS loads for BSM
and int. shield (TABLE
1)
1.3
0.7
-11.4
UPP loads applied to the
BSM (TABLE 1)
1.8
2.5
-11.8
TABLE 1: Launcher deformation under different loads.
The deformations result in stresses that are concentrated at the transition from the trapezoid
structure at the closure plate to the stiffer launcher back end. The stress maximums occur on
the upper two corners of the trapezoid reaching 200MPa (FIG. 5) compared to
Sy(125°C)=210MPa [7]. As the simulation was performed static these values can only be
taken as a first idea of occurring stresses. However the stress peak is in a range tolerable to
level C events, where local permanent deformations are allowed as long as immediate fracture
can be excluded with reasonable confidence [7].
FIG. 5: Von Mises stresses [MPa] under differential loads in the rear part are significant for the
deformation at the free launcher tip.
4. Conclusions
The EM loads for the upper launcher could be refined to a load distribution over launcher
segments with different mechanical stiffness. Static simulations showed a reduced
deformation of 10% - 15% compared to the preliminary loads. The stress peaks at the closure
plate aren't critical but subject to further observation in transient analysis when the shield
blocks are added.
In a next step the internal components will be included and fixed to reduce stresses and the
critical toroidal deformation. A service access opening in the middle of the launcher is under
investigation. At the end of this design freeze a reasonable transient structural analysis of the
complete launcher will be performed fulfilling the simulation criteria of ITER quality control.
Acknowledgement
This work, supported by the European Communities under the contract of Association
between EURATOM and Forschungszentrum Karlsruhe, was carried out within the
framework of the European Fusion Development Agreement. Views and opinions expressed
herein do not necessarily reflect those of the European Commission.
References
[1] HEIDINGER, R., et al., “Design and Analysis of the ECH Upper Port Plug Structure at
ITER”, Fusion Energy 2006 (Proc. 21st IAEA Conf. Chengdu 2006), to be published in
Fusion Energy
[2] SAIBENE, G., et al., “Design of the ITER Electron Cyclotron Wave Launcher for NTM
Control”, Fusion Energy 2006 (Proc. 21st IAEA Conf. Chengdu 2006), to be published in
Fusion Energy
[3] MIKI, N., et al., “VDE electromagnetic analysis for the ITER-FEAT vacuum vessel and
in-vessel components”, Fusion Eng. & Design 58 – 59 (2001)
[4] UTIN, Y., et al., “Mechanical Loading Conditions for the Equatorial and Upper Port
Plugs”, https://users.iter.org/users/idm/get_document?document_id=ITER_D_22FACL
(2005)
[5] ROCCELLA, M., Internal note on EM ANSYS-simulations (2005)
[6] ROCCELLA, M., Internal note on EM EMAS-simulations (2004)
[7] BARABASH, V., et al., “Structural Design Criteria for ITER In-vessel Components”,
https://users.iter.org/users/idm/get_document?document_id=ITER_D_222RHC (2005).