Conceptual design finalization of the ITER In-Vessel Viewing and Metrology System (IVVS) G. Dubusa, A. Puiua, C. Damiania, M. Van Uffelena, A. Lo Buea, J. Izquierdoa, L. Semeraroa, and J. Palmerb a

Fusion for Energy, c/ Josep Pla, n°2 - Torres Diagonal Litoral - Edificio B3, 08019 Barcelona, Spain b ITER Organization, Route de Vinon sur Verdon, 13115 Saint Paul Lez Durance, France

Abstract The In-Vessel Viewing and Metrology System is a fundamental tool of the ITER Remote Maintenance System, aiming at performing inspections as well as providing information related to the erosion of in-vessel components. Periodically or on request, the IVVS probes will be deployed into the Vacuum Vessel from their storage positions (still within the ITER primary confinement) in order to perform both viewing and metrology on plasma facing components (blanket, divertor, heating/diagnostic plugs, test blanket modules) and, more generically, to provide information on the status of the in-vessel components. In 2011, the IO proposed to simplify and strengthen the six IVV penetrations situated at the divertor level. Among other important consequences, such as the relocation of the GDC electrodes at other levels of the machine, this design change had a major impact on the layout of the IVV port extension itself. It implied the need for a substantial redesign of the IVVS plug, which took part to an on-going effort to bring the integrated IVVS concept – including the scanning probe and its deployment system – to the level of maturity suitable for the Conceptual Design Review. This poster describes the current concept design for IVVS. It also gives an overview the various design and R&D activities in progress.

Current conceptual design

Latching systems A traverse latch secures the carrier trolley: two lobed arms extend through the carrier sides and engage with pockets machined in the guide tube. They are moved by a non-backdriveable leadscrew mechanism actuated by piezoelectric technology, whose benefit is to be immune to the surrounding magnetic field. A tilt latch operates in a similar manner: arms mounted within the carrier body clamp inwards onto a toothed rack, locking the tilt body. In normal operation, both latches cannot be released simultaneously. If the traverse latch is released, the push rod acts on the carrier and linear motion is achieved. If the tilt latch is released, the push rod acts on the tilt mechanism to raise the probe. Once in position, both latches are locked. As they operate at discrete positions, the probe is deployed in a very repeatable way.

Probe The probe is the active scanning tool. It is a hybrid viewing and ranging system relying on the amplitude modulation of a coherent single mode laser [1]. Greyscale 2D images are obtained from the intensity of the backscattered light, while range data is generated from its phase shifting.

Cable reeling system Since the various services connected to the probe and carrier must accommodate the 5-6 m radial translation, the umbilical management relies on a system able to control both tension and bending applied on the cables. This cable reeling system is made of the arrangement of four pulleys: two of them are fixed to the rear of the cartridge and the other two are mounted on a sliding carriage. The motion of this carriage is controlled by a ball screw mechanism attached to the chain drive, so that the pulleys move at the exact required speed.

Its optical box hosts an arrangement of lenses, mirrors and optical fibres connectors, segregated into one transmitting stage and one receiving stage. A step focus is realized by means of nano/micropositioning linear piezo motors. Its rotating head comprises a fused silica prism actuated, in both pan and tilt, by ultrasonic piezo rotary stages equipped with optical encoders.

Main actuation The selected transmission method is a single stepper motor located at the rear of the cartridge, where the toroidal field allows the use of magnetic motors. Through an inline planetary gearbox, this motor extends a rigid chain from the back of the port. The chain front interface is connected to the carrier such that, when the chain is pulled out of its magazine, the carrier is pushed forward, and vice versa. Comparable rigid chains already proved their reliability in the nuclear industry. Similar stepper motors and gearboxes were successfully tested for radiation hardness up to 10 MGy. All ball bearings use MoS2 or WS2 solid lubrication, which makes the system operational in both vacuum and air.

Probe elevation This system identically actuates the probe tilt motion. In that case, the movement of the push rod equipping the carrier is transferred into a tilt motion thanks to a lever mechanism at the hinge, assisted by two counterbalance springs. The choice between the two motions is carried out by the selective deployment of latches.

On-going design and R&D activities

Definition of a testing programme

Development of a metrology strategy

Objectives:

Plug design integration

• to prepare a pre-concept design of on-site test stands, required for testing and/or commissioning of the IVVS after maintenance or upgrade

Objectives: • to bring together results yielded by other activities into a well-integrated concept • to address the areas of the design which still need substantial development It includes: • mechanical structures design refinement • service umbilicals and connectors integration • probe size reduction • vacuum feed-throughs design • control cubicles and cabling [2], • definition of maintenance processes and interfaces • development of built-in recovery features • derivation of a cask-based rescue strategy F4E-GRT-282 (ENEA) / F4E-OMF-272-01-03 (OTL)

Probe concept validation under environmental conditions

• to establish clear interface definitions with both Hot Cell Facility (HCF) and RH Test Facility (RHTF) F4E-GRT-282 (ENEA)

Objective: • to verify the selection of the probe components (optics, motorization, cabling and cubicle) in relation to operation under the expected environmental conditions It includes: • gamma irradiation of an ultrasonic piezo rotary stage • neutron irradiation • test under magnetic field up to 8T • test under vacuum and high temperature • design, prototyping and testing of a FBG-based accelerometer • practical validation of a vibration compensation scheme [4] F4E-GRT-282 (ENEA)

Alternative design It considers the presence of a vacuum tank situated in the port cell and linked to the port extension by a double bellow surrounded by two gate valves. During plasma operations, the probe is retracted in the tank (neutron flux significantly reduced) and is totally isolated from the primary vacuum. Another benefit of this concept is the ability to remove the whole tank for maintenance without breaking the primary vacuum, by shutting off the gates valves. The tank is equipped with its own vacuum pump, pressure control and baking system. The probe alignment is achieved with external actuators arranged in a Stewart platform. Still several options for the system main actuation: internal vacuum-compatible motor-gearbox assembly external standard motor through a vacuum-tight magnetic coupling

The views and opinions expressed herein do not necessarily reflect those of the ITER Organization.

Nuclear analysis Objective: • to identify the neutron fluence and gamma activation in the various parts of the 8-m long plug It includes the calculation of: • the neutron flux for different shielding configurations • the complete nuclear response (absorbed dose rate, activation, nuclear heating…) for the layout providing the most adequate shielding • the equivalent dose rate map (Sv/hr) for an isolated IVVS • the neutron map up to the IVVS front end electronics F4E-2008-OPE-02-01-06 (CCFE)

Objective: • to build a robust strategy for the use of IVVS in the evaluation of the amount of mobilisable dust inside ITER [5] It includes: • developing high-speed performance simulation tool • producing a mapping study predicting the effectiveness of the IVVS in terms of coverage, viewing resolution and metrology data accuracy • evaluating potential upgrades to the current IVVS design • proposing a metrological strategy helping to achieve the required accuracy – by making use of reference markers for instance • identifying feasible solutions for a metrological simulation tool • experimentally validating a procedure for dust quantity estimation from IVVS measurements

F4E-2008-OPE-07-02-01-06 (SRS) / F4E-GRT-282 (ENEA) / F4E-2011-EXP-080 (I. Piacentini)

Acknowledgments The authors would like to thank all the contributors taking part to the activities touched upon in this paper.

References [1] [2] [3] [4] [5]

C. Neri et al., FusEngDes vol. 86, n° 9-11, p.1237, 2011. M. Florean et al., Proc. of SOFT-27, Liege, 2012. P. Rossi et al., Proc. of SOFT-27, Liege, 2012. C. Neri et al., Proc. of SOFT-27, Liege, 2012. M. Shimada et al., Proc. of PSI-20, Aachen, 2012.