- Email: [email protected]
CEA contribution to the ITER ICRH antenna design
Fusion Engineering and Design 88 (2013) 950–955
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
CEA contribution to the ITER ICRH antenna design J.M. Bernard a,∗ , A. Argouarch a , G. Berger-By a , C. Brun a , F. Clairet a , L. Colas a , C. Dechelle a , F. Durodié b , M. Firdaouss a , F. Ferlay a , J.C. Giacalone a , J. Hillairet a , J. Jacquot a , D. Keller a , D. Milanesio c , M. Missirlian a , M. Shannon d , A. Simonetto e a
CEA Cadarache, IRFM, F-13108 Saint-Paul-lez-Durance, France Laboratory for Plasmas Physics, 1000 Brussels, Belgium Politecnico di Torino, Dipartimento di electtronica (POLITO), 10129 Torino, Italy d Euratom/CCFE Association, Culham Science Centre, Abingdon, Oxon OX143DB, UK e Istituto di Fisica del Plasma, CNR, associazione Euratom-ENEA-CNR, 20125 Milano, Italy b c
a r t i c l e
i n f o
Article history: Available online 8 February 2013 Keywords: ITER ICRH RVTL Reflectometry Remote handling Faraday screen
a b s t r a c t The ITER ion-cyclotron range of frequency (ICRH) heating system is required to couple 20 MW of power in the frequency range 40–55 MHz for a large range of scenarios with Edge Localized Modes. To mitigate the associated risks, it is foreseen to design and install on ITER two port-plug antennas for a total of 20 MW coupled power on long pulse operation [1]. The CEA activity to this antenna design within the CYCLE consortium was focused on the Faraday screen design (Fig. 1) and associated radio frequency (RF) sheath modelling, the reflectometers design for edge density measurement in the antenna vicinity and a contribution to the remote handling/tooling of the antenna. This paper is an overview of each item and proposes some R&D activities on key components. © 2013 Elsevier B.V. All rights reserved.
1. Faradays screen (FS) bar design The FS is the part of the antenna the closest to the plasma. Its main purpose is to protect the antenna in general, and particularly the straps, from the heat loads coming from the plasma. The bars are actively cooled, composed by a sandwich of different materials. As the antenna, the screen is divided in four similar quarters. Each quarter of the screen is composed of bars, fixed on the frame around the quarter antenna. The study included a 2D analysis to define the cross section of the bars, and followed by a 3D analysis to assess the operational limits of the whole bars. 1.1. Thermo-mechanical loads on one bar The loads come from different sources. The thermal loads are composed of a heat flux involving radiation and particle charge exchange (0.35 MW/m2 ), parallel heat flux (up to 3.5 MW/m2 ), neutronic load (7 W/cm−3 ), variable convective cooling (around 60 kW/m2 ◦ C for 8 m/s water velocity) and ambient temperature. The mechanical loads come from the internal pressure and the attachment on both sides. Disruption forces are not taken into account at this stage of the design.
∗ Corresponding author. E-mail address: [email protected] (J.M. Bernard). 0920-3796/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.fusengdes.2013.01.040
Three operating modes are defined for the water cooling: baking mode (250 ◦ C/44 bar), operational mode (120 ◦ C/40 bar), and proof test mode (20 ◦ C/76 bar) (Fig. 1).
1.2. 2D analysis results Two conceptual designs have been compared (Fig. 2), for this optimization of the geometry to minimize the total height of the bars (better for plasma coupling) and the target lifetime of 35 × 103 cycles. The first one cooled by two standard copper tubes, the second one cooled by rectangular copper channel. Simulations show that with the use of hard copper (instead of pure copper), the rectangular channel is able to withstand the internal pressure. And because of its geometry, this concept is able to better extract the heat from the surface. Therefore it has been chosen for the possibility to lower the water velocity and thus decrease the amount of water required.
1.3. 3D analysis results The bar is a thin and long object with a constant cross section, attached on both side (Fig. 3). An angle of 6◦ has been added and optimized on the central end, in order to protect this side from parallel heat flux. It is 383 mm long and 32 mm wide. Its distance to the strap is 15 mm. This topology is susceptible to be revised.
J.M. Bernard et al. / Fusion Engineering and Design 88 (2013) 950–955
951
Table 1 Equivalent von Mises stress, total strain and number of cycles in each material layer for both load cases. (MPa/%/cycles)
Be (1)
Cu (2)
CuCrZr (3/4)
Steel (5)
Case#1 Case#2
237/0.12/NA 221/0.16/NA
50.0/0.34/2e3 49.7/0.33/2e3
175/0.14/>1e5 174/0.16/>1e5
179/0.13/>1e5 174/0.13/>1e5
Fig. 3. Longitudinal cross section of the complete bar.
below the target. Note that the high stresses are concentrated on the bonding surface with Be. Fig. 1. View of the front antenna, with two quarter of the FS.
Temperature, mechanical stress, plastic strain and number of cycles achievable have been computed for two representative load cases and results are shown is the Table 1. These load cases are differing by the incident heat flux: one is representative of an important flux on the front face (up to 2.4 MW/m2 ) and the lateral face (up to 3.5 MW/m2 ), but on small area. The second one is representative of a moderate flux on the front face (up to 2 MW/m2 ) and the lateral face (up to 2.5 MW/m2 ), but on more important area. However, both cases give similar stress and strains (and thus cycles). The Cu interlayer appears to be the weak point of the component, with a number of cycles 10 times
2. Sheath modelling In order to estimate RF sheath effects in the vicinity of the ITER ICRF antenna structure, a new physics approach was followed that models self-consistently the interplay between the slow magnetosonic wave penetration and the resulting positive DC biasing of the scrape-off Layer (SOL) plasma: the SSWICH code [2], in an asymptotic version valid for large sheath widths. The private SOL limited by the two BSM (Blanket Schielding Modules) adjacent to the ICRF antenna was modelled in 3D parallelepipedic geometry with straight field lines normal to the lateral walls. In this region a low-density SOL profile was used [3], and was shifted radially by 8 cm towards the wall to provide an upper bound of sheath heat loads. The system was excited by imposing 2D (toroidal/poloidal) maps of the parallel RF electric field at an antenna aperture in
Fig. 2. Half of the two conceptual cross sections: tube (top left) and rectangle (top right) (1 = Be, 2 = compliance layer Cu, 3/4 = CuCrZi5 = SS). Complete cross section with dimensions (left).
952
J.M. Bernard et al. / Fusion Engineering and Design 88 (2013) 950–955
Fig. 4. 2D (radial/poloidal) distribution of parallel heat flux densities along the two BSM modules, for 20 MW RF power coupled using [00] toroidal strap phasing.
the outer vessel wall. These input maps were computed with the antenna code TOPICA in the absence of sheaths, using different realistic 3D geometries of the ITER antenna excited with five toroidal strap phasings. The maps were normalized to 20 MW coupled RF power. Sheaths effects were estimated on the BSMs, assimilated to plane walls normal to B0 . The most pessimistic output for each toroidal phasing is summarized in Table 2. Estimated rectified DC potentials are in the range 2 kV. Heat fluxes are in the range 6 MW/m2 parallel to B0 . Estimated RF power losses over BSM edges are about 125 kW. For overall losses a hierarchy of strap phasings emerges from the simulations: [00] > [CD−], [CD+] > [00] > [00], which is reminiscent of experimental observations with the four-strap A2 antennae on JET [4]. For the most pessimistic phasing [00] the 2D (radial, poloidal) distribution of parallel heat flux densities is illustrated on Fig. 4, showing that the maximal values in Table 2 are only reached very locally. This spatial distribution and its variation with strap phasing weakly depend on small changes of the antenna front face design (septum recessed or not by 20 mm behind the middle of the strap) or on the type of strap excitation (“Istrap” vs “Vmax” excitation). While the sheath voltage poloidal distribution is a relatively robust output, the quantitative amplitudes and radial penetration of rectified DC potentials are found sensitive to loosely constrained simulation parameters: toroidal and radial extension of the private SOL; transverse plasma DC conductivity. Table 2 provides upper bounds of the results over various parametric scans performed. 3. Reflectometer A critical issue for the ICRH heating is the coupling of the RF waves through the plasma boundary to the plasma bulk where the absorption takes place [5]. A density profile measurement is thus highly recommended in front of the ICRH antenna as it provides the information about the coupling efficiency of the ICRH wave [6].
A frequency sweep X-mode bistatic reflectometry system installed into the ICRH antenna is foreseen to measure a density profile at four different positions to account for toroidal and poloidal asymmetries of the plasma boundary. The calculated cut-off frequencies range is then 50–150 GHz for plasma measurements at full and half magnetic field tokamak operation. The choice of oversized rectangular WR28 waveguides (7.1 mm × 3.6 mm) to route through the launcher has been done to account for the low space availability and to minimize the losses. Waveguide bends of radius larger than 1 m are required to minimize the mode conversions were tested with microwave wideband vector signal analyzer. Pairs of sectorial antennas provide sufficient directivity in the toroidal direction to recover enough reflected signal up to 40 cm in front of the launcher while a low directivity in the poloidal plane allows for leakage signal coupling which provide a convenient phase reference requested for the density profile reconstruction. Vacuum isolation is provided by pairs of quartz windows with wedges (Fig. 5). These windows provide about 0.1 dB transmission losses through the frequency bandwidth and minimize multireflections. They are classified safety important level 1 in the Safety ITER classification. Due to the long distance (∼45 m) between the launcher and the assembly hall, where the electronic of the reflectometers should be set, low loss (<0.005 dB/m) circular corrugated waveguides (31.75 mm int. diameter) will carry the signal. Optical tapers mode converter (TE01←→HE11), located in the port cell, will connect the WR28 waveguides to circular ones with estimated losses less than 2 dB. Sliding arrangement for the circular corrugated waveguides will be required, in the port cell, to cope with thermal expansion and radial shimming (∼6 cm in total) of the ICRH antenna. In the assembly hall, a JET equivalent set-up [7], using quasioptical boxes to connect circular waveguide to fundamental waveguide reflectometer systems based on fast sweep heterodyne
J.M. Bernard et al. / Fusion Engineering and Design 88 (2013) 950–955
953
Table 2 Upper bound of sheath rectification at 20 MW RF power coupled with 5 toroidal strap phasings. Maximum oscillating RF voltages over 2D maps on the 2 BSMs; maximum DC plasma potential; maximal heat flux densities parallel to B0 ; estimated power lost through the sheath over the two BSMs; and estimated lost power attributed to the RF waves (subtracting ohmic contribution of ∼20 kW). Phasing
[00]
[00]
[CD+ ]
[CD− ]
[00]
|VRFlmax | (V) |VRFrmax | (V) VDCmax (V) Q//lmax (MW/m2 ) Q//rmax (MW/m2 ) P//sh (kW) P//RF (kW)
633 472 623 2.4 2.3 46 26
488 650 640 2.4 2.5 56 36
1174 1587 1573 5.5 5.7 104 84
1363 1092 1350 4.9 4.8 116 96
1723 1840 1825 6.5 6.4 144 124
The associated assembly tools (Fig. 7) are composed with a port plug body frame, a grabber, a front frame and a rear frame. The eight RVTL are dismountable from the rear flange of the antenna installed on the port plug. The tool is composed by fixed frame, moving frame, guidance system, tractor, crane, storage tool and docking platform. This tool can be configured for each position of the eight RVTL (Fig. 8). 5. Remote handling (RH) for RVTL
Fig. 5. View of the future WR28 wide band window prototype (50–150 GHz).
system (three frequency bandwidths envisaged: V, W and D bands) will be in installed. 4. Assembly scheme and tooling The aim of the task is to describe the antenna assembly operation and the technical solution associated in manufacturing phase. To minimize the impact on the ITER operation and avoid work on the hot cell, we propose also the concept design for the hands-on dismounting of the RVTL (rear vacuum transmission line constituted by a service stub and two vacuum feeds thru allowing RF transmission to the front module) in the port cell, in non-active phase. A functional analysis has been performed to define the steps with three criteria: security (for workers), easy mechanical (to save budget) and fastness (to save time). After this analysis we have defined how to assemble the three sub-components (Fig. 6).
RH maintenance procedures for the replacement of removable vacuum transmission lines (RVTL) have been studied [8], in parallel with the design. The RVTL are 8 components of the antenna which interface between matching system and the four port junction feeding power to the straps. At the front and the rear of the RVTL are double RF windows that provide the first tritium barrier. In case of failure of the first window, all the RVTL has to be replaced. Due to the contamination and activation, the replacement must take place in the hot cell. The ITER requirements and the hot cell constraints have been used to extract specifications for the RH tooling (for handling, cutting, welding, etc.). Each step has been studied and suitable tools identified. For specific steps, mechanical principles for dedicated tools are proposed. Furthermore, the critical steps identified were simulated to check the feasibility. Scene animation, robotic and mechanical simulation with physic engine (contact and joints) and virtual reality immersion have been used to improve this study (Fig. 9). Involving simulation as early in the design was useful to confirm accessibility and to define specifications for the RH tooling. 5.1. Future prospects FS bars are able to withstand thermal loads during normal operating modes. However some concerns remains on the number of cycles achievable by the component, lower than the requirement in the Copper interlayer. The number of cycles achievable is probably underestimated, mainly because the properties of the junction are not really taken into account, because of the difficulties to model
Fig. 6. Three sub components of ICRH ITER antenna with four FMA (front module housing) left, PPB (port plug body) central, and eight RVTL one on right, which constitute the ICRH antenna.
954
J.M. Bernard et al. / Fusion Engineering and Design 88 (2013) 950–955
Fig. 7. Dedicated tools for assembly.
it. The real number of cycles would have to be estimated by the proper R&D. In the near future, it is planned to use the SSWICH asymptotic results as a first guess for an iterative resolution of the “more general” RF+DC problem using COMSOL. In order to get more confidence in the new physics model, assessment of its output has
started against experimental observations from Tore Supra with a new Faraday screen [9]. In a longer term several improvements of the physical model are envisaged [9]. Reflectometer remaining work will be concentrated on the waveguide window prototyping, which is a key component and safety important.
Fig. 8. Dedicated tools for RVTL dismounting.
J.M. Bernard et al. / Fusion Engineering and Design 88 (2013) 950–955
955
Fig. 9. Simulation of captive bolt dismounting.
Assembly sequence and RH of RVTL will be re visited at the end of the design. Mock-ups will be necessary to validate the conceptual design. Acknowledgements This work was set up in collaboration and financial support of Fusion for Energy in the framework of the grant F4E-2009-GRT-026. The views and opinions expressed herein do not necessarily reflect those of the ITER Organization and Fusion for Energy. References [1] P. Lamalle, et al., Proc. 27th SOFT Conf., Liège, 2012.
[2] L. Colas, J. Jacquot, et al. Self consistent RF wave propagation and peripheral DC plasma biasing: simplified 3D non-linear treatment in the “wide sheath” asymptotic regime, Physics of Plasmas, in press. [3] S. Carpentier, R.A. Pitts, ITER D 33Y59M-v2.3, ITER Baseline Documentation, 2010. [4] E. Lerche, et al., Proc. 18th RF Topical Conference, Ghent AIP Conf. proc. 1187, 2009, p. 93. [5] A. Messiaen, et al., PPCF 53 (2011) 085020; E. Lerche, et al., Proc. 18th RF Topical Conference, Ghent AIP conf. proc. 1187, 2009, p. 93. [6] F. Clairet, et al., Plasma Physics and Controlled Fusion 46 (2004) 1567. [7] A. Sirinelli, et al., Review of Scientific Instruments 81 (2010) 10D939. [8] F. Ferlay, et al., Proc. 27th SOFT Conf., Liège, submitted for publication. [9] J. Jacquot, D. Milanesio, et al., Proc. 39th EPS Conf. Plasma Physics and Controlled Fusion, Stockholm, 2012.
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
CEA contribution to the ITER ICRH antenna design J.M. Bernard a,∗ , A. Argouarch a , G. Berger-By a , C. Brun a , F. Clairet a , L. Colas a , C. Dechelle a , F. Durodié b , M. Firdaouss a , F. Ferlay a , J.C. Giacalone a , J. Hillairet a , J. Jacquot a , D. Keller a , D. Milanesio c , M. Missirlian a , M. Shannon d , A. Simonetto e a
CEA Cadarache, IRFM, F-13108 Saint-Paul-lez-Durance, France Laboratory for Plasmas Physics, 1000 Brussels, Belgium Politecnico di Torino, Dipartimento di electtronica (POLITO), 10129 Torino, Italy d Euratom/CCFE Association, Culham Science Centre, Abingdon, Oxon OX143DB, UK e Istituto di Fisica del Plasma, CNR, associazione Euratom-ENEA-CNR, 20125 Milano, Italy b c
a r t i c l e
i n f o
Article history: Available online 8 February 2013 Keywords: ITER ICRH RVTL Reflectometry Remote handling Faraday screen
a b s t r a c t The ITER ion-cyclotron range of frequency (ICRH) heating system is required to couple 20 MW of power in the frequency range 40–55 MHz for a large range of scenarios with Edge Localized Modes. To mitigate the associated risks, it is foreseen to design and install on ITER two port-plug antennas for a total of 20 MW coupled power on long pulse operation [1]. The CEA activity to this antenna design within the CYCLE consortium was focused on the Faraday screen design (Fig. 1) and associated radio frequency (RF) sheath modelling, the reflectometers design for edge density measurement in the antenna vicinity and a contribution to the remote handling/tooling of the antenna. This paper is an overview of each item and proposes some R&D activities on key components. © 2013 Elsevier B.V. All rights reserved.
1. Faradays screen (FS) bar design The FS is the part of the antenna the closest to the plasma. Its main purpose is to protect the antenna in general, and particularly the straps, from the heat loads coming from the plasma. The bars are actively cooled, composed by a sandwich of different materials. As the antenna, the screen is divided in four similar quarters. Each quarter of the screen is composed of bars, fixed on the frame around the quarter antenna. The study included a 2D analysis to define the cross section of the bars, and followed by a 3D analysis to assess the operational limits of the whole bars. 1.1. Thermo-mechanical loads on one bar The loads come from different sources. The thermal loads are composed of a heat flux involving radiation and particle charge exchange (0.35 MW/m2 ), parallel heat flux (up to 3.5 MW/m2 ), neutronic load (7 W/cm−3 ), variable convective cooling (around 60 kW/m2 ◦ C for 8 m/s water velocity) and ambient temperature. The mechanical loads come from the internal pressure and the attachment on both sides. Disruption forces are not taken into account at this stage of the design.
∗ Corresponding author. E-mail address: [email protected] (J.M. Bernard). 0920-3796/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.fusengdes.2013.01.040
Three operating modes are defined for the water cooling: baking mode (250 ◦ C/44 bar), operational mode (120 ◦ C/40 bar), and proof test mode (20 ◦ C/76 bar) (Fig. 1).
1.2. 2D analysis results Two conceptual designs have been compared (Fig. 2), for this optimization of the geometry to minimize the total height of the bars (better for plasma coupling) and the target lifetime of 35 × 103 cycles. The first one cooled by two standard copper tubes, the second one cooled by rectangular copper channel. Simulations show that with the use of hard copper (instead of pure copper), the rectangular channel is able to withstand the internal pressure. And because of its geometry, this concept is able to better extract the heat from the surface. Therefore it has been chosen for the possibility to lower the water velocity and thus decrease the amount of water required.
1.3. 3D analysis results The bar is a thin and long object with a constant cross section, attached on both side (Fig. 3). An angle of 6◦ has been added and optimized on the central end, in order to protect this side from parallel heat flux. It is 383 mm long and 32 mm wide. Its distance to the strap is 15 mm. This topology is susceptible to be revised.
J.M. Bernard et al. / Fusion Engineering and Design 88 (2013) 950–955
951
Table 1 Equivalent von Mises stress, total strain and number of cycles in each material layer for both load cases. (MPa/%/cycles)
Be (1)
Cu (2)
CuCrZr (3/4)
Steel (5)
Case#1 Case#2
237/0.12/NA 221/0.16/NA
50.0/0.34/2e3 49.7/0.33/2e3
175/0.14/>1e5 174/0.16/>1e5
179/0.13/>1e5 174/0.13/>1e5
Fig. 3. Longitudinal cross section of the complete bar.
below the target. Note that the high stresses are concentrated on the bonding surface with Be. Fig. 1. View of the front antenna, with two quarter of the FS.
Temperature, mechanical stress, plastic strain and number of cycles achievable have been computed for two representative load cases and results are shown is the Table 1. These load cases are differing by the incident heat flux: one is representative of an important flux on the front face (up to 2.4 MW/m2 ) and the lateral face (up to 3.5 MW/m2 ), but on small area. The second one is representative of a moderate flux on the front face (up to 2 MW/m2 ) and the lateral face (up to 2.5 MW/m2 ), but on more important area. However, both cases give similar stress and strains (and thus cycles). The Cu interlayer appears to be the weak point of the component, with a number of cycles 10 times
2. Sheath modelling In order to estimate RF sheath effects in the vicinity of the ITER ICRF antenna structure, a new physics approach was followed that models self-consistently the interplay between the slow magnetosonic wave penetration and the resulting positive DC biasing of the scrape-off Layer (SOL) plasma: the SSWICH code [2], in an asymptotic version valid for large sheath widths. The private SOL limited by the two BSM (Blanket Schielding Modules) adjacent to the ICRF antenna was modelled in 3D parallelepipedic geometry with straight field lines normal to the lateral walls. In this region a low-density SOL profile was used [3], and was shifted radially by 8 cm towards the wall to provide an upper bound of sheath heat loads. The system was excited by imposing 2D (toroidal/poloidal) maps of the parallel RF electric field at an antenna aperture in
Fig. 2. Half of the two conceptual cross sections: tube (top left) and rectangle (top right) (1 = Be, 2 = compliance layer Cu, 3/4 = CuCrZi5 = SS). Complete cross section with dimensions (left).
952
J.M. Bernard et al. / Fusion Engineering and Design 88 (2013) 950–955
Fig. 4. 2D (radial/poloidal) distribution of parallel heat flux densities along the two BSM modules, for 20 MW RF power coupled using [00] toroidal strap phasing.
the outer vessel wall. These input maps were computed with the antenna code TOPICA in the absence of sheaths, using different realistic 3D geometries of the ITER antenna excited with five toroidal strap phasings. The maps were normalized to 20 MW coupled RF power. Sheaths effects were estimated on the BSMs, assimilated to plane walls normal to B0 . The most pessimistic output for each toroidal phasing is summarized in Table 2. Estimated rectified DC potentials are in the range 2 kV. Heat fluxes are in the range 6 MW/m2 parallel to B0 . Estimated RF power losses over BSM edges are about 125 kW. For overall losses a hierarchy of strap phasings emerges from the simulations: [00] > [CD−], [CD+] > [00] > [00], which is reminiscent of experimental observations with the four-strap A2 antennae on JET [4]. For the most pessimistic phasing [00] the 2D (radial, poloidal) distribution of parallel heat flux densities is illustrated on Fig. 4, showing that the maximal values in Table 2 are only reached very locally. This spatial distribution and its variation with strap phasing weakly depend on small changes of the antenna front face design (septum recessed or not by 20 mm behind the middle of the strap) or on the type of strap excitation (“Istrap” vs “Vmax” excitation). While the sheath voltage poloidal distribution is a relatively robust output, the quantitative amplitudes and radial penetration of rectified DC potentials are found sensitive to loosely constrained simulation parameters: toroidal and radial extension of the private SOL; transverse plasma DC conductivity. Table 2 provides upper bounds of the results over various parametric scans performed. 3. Reflectometer A critical issue for the ICRH heating is the coupling of the RF waves through the plasma boundary to the plasma bulk where the absorption takes place [5]. A density profile measurement is thus highly recommended in front of the ICRH antenna as it provides the information about the coupling efficiency of the ICRH wave [6].
A frequency sweep X-mode bistatic reflectometry system installed into the ICRH antenna is foreseen to measure a density profile at four different positions to account for toroidal and poloidal asymmetries of the plasma boundary. The calculated cut-off frequencies range is then 50–150 GHz for plasma measurements at full and half magnetic field tokamak operation. The choice of oversized rectangular WR28 waveguides (7.1 mm × 3.6 mm) to route through the launcher has been done to account for the low space availability and to minimize the losses. Waveguide bends of radius larger than 1 m are required to minimize the mode conversions were tested with microwave wideband vector signal analyzer. Pairs of sectorial antennas provide sufficient directivity in the toroidal direction to recover enough reflected signal up to 40 cm in front of the launcher while a low directivity in the poloidal plane allows for leakage signal coupling which provide a convenient phase reference requested for the density profile reconstruction. Vacuum isolation is provided by pairs of quartz windows with wedges (Fig. 5). These windows provide about 0.1 dB transmission losses through the frequency bandwidth and minimize multireflections. They are classified safety important level 1 in the Safety ITER classification. Due to the long distance (∼45 m) between the launcher and the assembly hall, where the electronic of the reflectometers should be set, low loss (<0.005 dB/m) circular corrugated waveguides (31.75 mm int. diameter) will carry the signal. Optical tapers mode converter (TE01←→HE11), located in the port cell, will connect the WR28 waveguides to circular ones with estimated losses less than 2 dB. Sliding arrangement for the circular corrugated waveguides will be required, in the port cell, to cope with thermal expansion and radial shimming (∼6 cm in total) of the ICRH antenna. In the assembly hall, a JET equivalent set-up [7], using quasioptical boxes to connect circular waveguide to fundamental waveguide reflectometer systems based on fast sweep heterodyne
J.M. Bernard et al. / Fusion Engineering and Design 88 (2013) 950–955
953
Table 2 Upper bound of sheath rectification at 20 MW RF power coupled with 5 toroidal strap phasings. Maximum oscillating RF voltages over 2D maps on the 2 BSMs; maximum DC plasma potential; maximal heat flux densities parallel to B0 ; estimated power lost through the sheath over the two BSMs; and estimated lost power attributed to the RF waves (subtracting ohmic contribution of ∼20 kW). Phasing
[00]
[00]
[CD+ ]
[CD− ]
[00]
|VRFlmax | (V) |VRFrmax | (V) VDCmax (V) Q//lmax (MW/m2 ) Q//rmax (MW/m2 ) P//sh (kW) P//RF (kW)
633 472 623 2.4 2.3 46 26
488 650 640 2.4 2.5 56 36
1174 1587 1573 5.5 5.7 104 84
1363 1092 1350 4.9 4.8 116 96
1723 1840 1825 6.5 6.4 144 124
The associated assembly tools (Fig. 7) are composed with a port plug body frame, a grabber, a front frame and a rear frame. The eight RVTL are dismountable from the rear flange of the antenna installed on the port plug. The tool is composed by fixed frame, moving frame, guidance system, tractor, crane, storage tool and docking platform. This tool can be configured for each position of the eight RVTL (Fig. 8). 5. Remote handling (RH) for RVTL
Fig. 5. View of the future WR28 wide band window prototype (50–150 GHz).
system (three frequency bandwidths envisaged: V, W and D bands) will be in installed. 4. Assembly scheme and tooling The aim of the task is to describe the antenna assembly operation and the technical solution associated in manufacturing phase. To minimize the impact on the ITER operation and avoid work on the hot cell, we propose also the concept design for the hands-on dismounting of the RVTL (rear vacuum transmission line constituted by a service stub and two vacuum feeds thru allowing RF transmission to the front module) in the port cell, in non-active phase. A functional analysis has been performed to define the steps with three criteria: security (for workers), easy mechanical (to save budget) and fastness (to save time). After this analysis we have defined how to assemble the three sub-components (Fig. 6).
RH maintenance procedures for the replacement of removable vacuum transmission lines (RVTL) have been studied [8], in parallel with the design. The RVTL are 8 components of the antenna which interface between matching system and the four port junction feeding power to the straps. At the front and the rear of the RVTL are double RF windows that provide the first tritium barrier. In case of failure of the first window, all the RVTL has to be replaced. Due to the contamination and activation, the replacement must take place in the hot cell. The ITER requirements and the hot cell constraints have been used to extract specifications for the RH tooling (for handling, cutting, welding, etc.). Each step has been studied and suitable tools identified. For specific steps, mechanical principles for dedicated tools are proposed. Furthermore, the critical steps identified were simulated to check the feasibility. Scene animation, robotic and mechanical simulation with physic engine (contact and joints) and virtual reality immersion have been used to improve this study (Fig. 9). Involving simulation as early in the design was useful to confirm accessibility and to define specifications for the RH tooling. 5.1. Future prospects FS bars are able to withstand thermal loads during normal operating modes. However some concerns remains on the number of cycles achievable by the component, lower than the requirement in the Copper interlayer. The number of cycles achievable is probably underestimated, mainly because the properties of the junction are not really taken into account, because of the difficulties to model
Fig. 6. Three sub components of ICRH ITER antenna with four FMA (front module housing) left, PPB (port plug body) central, and eight RVTL one on right, which constitute the ICRH antenna.
954
J.M. Bernard et al. / Fusion Engineering and Design 88 (2013) 950–955
Fig. 7. Dedicated tools for assembly.
it. The real number of cycles would have to be estimated by the proper R&D. In the near future, it is planned to use the SSWICH asymptotic results as a first guess for an iterative resolution of the “more general” RF+DC problem using COMSOL. In order to get more confidence in the new physics model, assessment of its output has
started against experimental observations from Tore Supra with a new Faraday screen [9]. In a longer term several improvements of the physical model are envisaged [9]. Reflectometer remaining work will be concentrated on the waveguide window prototyping, which is a key component and safety important.
Fig. 8. Dedicated tools for RVTL dismounting.
J.M. Bernard et al. / Fusion Engineering and Design 88 (2013) 950–955
955
Fig. 9. Simulation of captive bolt dismounting.
Assembly sequence and RH of RVTL will be re visited at the end of the design. Mock-ups will be necessary to validate the conceptual design. Acknowledgements This work was set up in collaboration and financial support of Fusion for Energy in the framework of the grant F4E-2009-GRT-026. The views and opinions expressed herein do not necessarily reflect those of the ITER Organization and Fusion for Energy. References [1] P. Lamalle, et al., Proc. 27th SOFT Conf., Liège, 2012.
[2] L. Colas, J. Jacquot, et al. Self consistent RF wave propagation and peripheral DC plasma biasing: simplified 3D non-linear treatment in the “wide sheath” asymptotic regime, Physics of Plasmas, in press. [3] S. Carpentier, R.A. Pitts, ITER D 33Y59M-v2.3, ITER Baseline Documentation, 2010. [4] E. Lerche, et al., Proc. 18th RF Topical Conference, Ghent AIP Conf. proc. 1187, 2009, p. 93. [5] A. Messiaen, et al., PPCF 53 (2011) 085020; E. Lerche, et al., Proc. 18th RF Topical Conference, Ghent AIP conf. proc. 1187, 2009, p. 93. [6] F. Clairet, et al., Plasma Physics and Controlled Fusion 46 (2004) 1567. [7] A. Sirinelli, et al., Review of Scientific Instruments 81 (2010) 10D939. [8] F. Ferlay, et al., Proc. 27th SOFT Conf., Liège, submitted for publication. [9] J. Jacquot, D. Milanesio, et al., Proc. 39th EPS Conf. Plasma Physics and Controlled Fusion, Stockholm, 2012.