4 JET Operations. 4 JET Operations 4.1 INTRODUCTION 4.2 INSTALLATION OF NEW COMPONENTS

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1 4.1 INTRODUCTION UKAEA has had the responsibility for the operation and safety of the JET facilities since January 2000 under the European Fusion Development Agreement (EFDA). The legal and financial provisions are defined by the JET Operation Contract between the European Commission (that confers the contractual management to the EFDA Associate Leader for JET) and UKAEA. The JET research programme is carried out by Task Forces of visiting European scientists from fusion laboratories associated to EFDA, including UKAEA Culham (see Chapter 3), under the responsibility of the EFDA Associate Leader for JET. The 2007 Shutdown enabled the remaining tasks of the first JET Enhanced Performance programme ( JET EP1 ) to be completed. The initial activities of the second JET Enhanced Performance Programme ( JET EP2 ) were also undertaken. In addition, extensive maintenance and refurbishment activities were performed. Both the EP1 and the EP2 Programme are carried out through different Projects under the responsibility of various EFDA laboratories including UKAEA, which has the responsibility of the two major EP2 Projects. Tokamak operations ended on Wednesday 4 April, rather than Friday 20 April as planned, due to a water leak on the Octant 8 Neutral beam system and, separately, the jamming of the Octant 8 Rotary High Vacuum Valve. Investigations were required before the Shutdown work could start to identify the source of the water leak and to allow the necessary repair work in the Shutdown to be determined. Following these investigations, and systematic isolation of the machine and associated areas, Shutdown conditions were established on 3 May. The industrial workforce and supervisory teams were gradually increased in size from the start of the Shutdown to cater for the planned tasks, rising from approximately 100 to a peak of 132 during October. Following the Shutdown, which finished on 30 November, the JET systems were commissioned from December until the beginning of April 2008 prior to the start of the EFDA experimental campaigns. 4.2 INSTALLATION OF NEW COMPONENTS The following major installation activities were performed during the 2007 Shutdown: installation of two primary vacuum feed-throughs and outer poloidal arrays on the first wall to complete the upgrade of the magnetic diagnostic to enhance real time control of the plasma current, shape and strike points; installation of shields in the Torus to screen the feed-throughs of the halo current sensors installed in the previous Shutdown, which were subject to electrical noise pick-up. This completed the upgrade of the halo current sensors, which comprise Rogowski and toroidal field coils to measure both the current flowing through first wall tiles and the total poloidal halo current; exchange of four Positive Ion Neutral Injectors (PINIs) on the Octant 8 Neutral Injection Box (NIB). This was the start of the programme to modify the ion sources and accelerator grids of the PINIs to deliver higher power as part of the Neutral Beam Enhancement project of the JET EP2 Programme; 4.1

2 relocation of a vacuum-ultra-violet spectroscopy diagnostic from the Torus Hall to the Diagnostic Hall bunker to make it compatible with operation in future tritium campaigns. Redundant X-Ray diagnostics in the bunker area were decommissioned as part of this activity; installation of two 600 mm diameter water pipes connecting the main supply in the flywheel generator building to the J51 and J52 buildings that have been built to house the new high voltage power supplies procured under EFDA as part of the JET EP2 Neutral Beam Enhancement project; installation of the JET EP1 ITER-like ICRH antenna. This involved extensive remote handling (RH) work within the torus to prepare for the ex-vessel installation of the antenna structure, followed by RH installation of the antenna screen and protection tiles (See Figures 4.1 and 4.2). Figures 4.1 and 4.2: The ITER-like ICRH antenna inside the torus, and its blue transmission line assembly outside the torus at Octant 2 metrology and configuration surveys of the inside of the JET vacuum vessel to address design issues for the EP2 ITER-like Wall Project. Areas of particular interest were the upper high field side of the vacuum vessel and the exact location of existing diagnostic cable conduits; Installation of a second antenna for the excitation and detection of Toroidicity-induced Alfven Eigenmodes (TAEs), complementing the antenna installed in 2004; repairs to and installation of new diagnostics to allow measurements of the deposition of surface films by the plasma. This involved exchange and subsequent analysis of first wall samples and collectors. In addition the quartz micro-balance previously installed to monitor the deposition from a beryllium evaporator was realigned; installation of a High Frequency Pellet Injector (HFPI) for mitigation of Edge Localised Modes (ELMs) and deep fuelling studies in preparation for studies for ITER. This involved extensive ex-vessel work consisting of the 4.2

3 erection of a new platform, installation of the injector and flight tubes system and significant associated services. (See Figures 4.3 and 4.4.); Installation of new cables for spectroscopy, neutron and lost alpha particle diagnostics that form part of the JET EP1 and EP2 projects to enhance the diagnostic capability of JET. A total of 10 km of multi-core and specialised individually screened cables was installed, linking different areas and diagnostics via shielded penetrations through the biological shield. Figures 4.3 and 4.4: Services installation, and main platform, for the High Frequency Pellet Injector 4.3 KEY OPERATOR MAINTENANCE ACTIVITIES Key activities in 2007/08 included the following. A water leak occurred on the Centre Support Column (CSC) of the Octant 8 Neutral Injection Box in the latter stages of the experimental campaign in the spring of Repair of the water leak required this large, 50- tonne assembly, which carries the major power-handling components of the beam line, to be transferred into a ventilated tent in the JET Assembly Hall. After an extensive period of drying out the water channels of the CSC by vacuum pumping, leak testing identified two water leaks which were successfully repaired. (See Figures 4.5 and 4.6.) 4.3

4 Figures 4.5 and 4.6: The water pipes that leaked in the CSC, and the whole CSC during one of the lifts to move it between the Torus and Assembly Halls Replacement of the motor that powers the impeller of the gas circulator in the plant used to heat the JET vessel to its operating temperature (of between 200 o C and 320 o C) was necessary because it had suffered a failure that prevented it from operating at full speed. As well as replacing the motor, a variable speed control was installed to eliminate the mechanical shocks to the system when the motor is started or increased in speed. Replacement of the leaking welded diagnostic window in the Octant 7 main horizontal port. This was a like for like replacement of the double window assembly which had developed a leak between the inter-space and the torus. This task necessitated re-calibration of an adjacent microwave diagnostic since temporary removal of the associated waveguide had been unavoidable. Preventative maintenance on the rarely operated 11 kv and 3.3 kv circuit breakers, particularly the spring charging mechanisms, the open current and the earth fault protection devices. In addition, transformer oil was inspected, a water leak was repaired and 415 V switch-gear cleaning and inspection was undertaken. Repairs were made to corroded sections of the Site Cooling Water system. Following extensive surveying and excavations, two sections of carbon steel pipe were repaired with proprietary injection-sealed bandage fittings. The screw pump used to maintain the Diagnostic Crown below atmospheric pressure was exchanged. (The Diagnostic Crown is the common exhaust line of the JET diagnostic vacuum systems.) Ingress of water from a failed oil-cooling circuit in a diagnostic roughing pump is 4.4

5 thought to have been responsible for the rotor damage in the pump which necessitated this exchange. Endoscopic inspections were made of the waveguides of the Lower Hybrid Current Drive system to see if any internal damage had been caused by oil ingress found to have occurred from weeping oil-cooled bellows sections in the waveguides. Fortunately no arcing damage was discovered, and the oil was subsequently removed. The turbomolecular vacuum pumps on the NIBs were upgraded to new generation types without drag (i.e. integrated exhaust pumping) stages. Some of the torus vacuum pumps were exchanged with identical spares, as a preventative maintenance measure to mitigate against bearing failure. Metal protection shields were installed to protect the vacuum bellows assemblies above these turbopumps from debris in the event of a failure of a pump rotor. The Octant 8 Rotary High Vacuum Valve was exchanged. This valve provides isolation between the torus and NIB vacuum vessels when required. The seal between the rotor and the stator had been found to be defective and the rotor actuating mechanism had also become dysfunctional. (See Figures 4.7 and 4.8.) Figures 4.7 and 4.8: A view upwards through the space where the Rotary High Vacuum Valve would usually be, between the NIB and the duct into the torus, and (figure 8) a view through the duct scraper lining the duct, into the torus (showing the remote handling manipulator, MASCOT) Extensive preventative maintenance was undertaken of the bus-bars that connect the power supplies to JET to address recommendations of the enquiry held following a failure in 2005 caused by an overheating bus-bar joint. The joints were visually inspected, their resistance was measured, and if this was found to be too high, they were disassembled, cleaned, remade and measured again. 4.5

6 Remedial work was done on some of the Glow Discharge Cleaning (GDC) electrodes to remove particulate build-up which was reducing the insulation resistance between the electrode and the torus. The insulators of these electrodes have to tolerate a high voltage in order to initiate breakdown of gas in the torus for GDC of the first wall. The main isolation valve on an X-Ray spectroscopy diagnostic beam line, which was failing to seal in the closed position, was replaced. 4.4 EXECUTION OF SHUTDOWN ACTIVITIES To achieve the planned work-load of this significant engineering shutdown, activities were performed using a two-shift system with six days per week working for the vast majority of the period. Daily shutdown activities began at 6.00am and finished the following day at 1.30am. Overall the Shutdown activities necessitated almost 1,000 man-hours of working in full pressurised suits across a number of facilities, resulting in a total collective dose of msv. Following isolation of the machine and establishing access to the torus, the critical path of the baseline Shutdown plan consisted of four distinct remote handling phases needed to cater for approximately 240 in-vessel tasks. Phase one principally consisted of divertor removal and preparation activities for later tasks. Phase two covered the installation of the magnetic field diagnostics components. Phase three dealt with the installation of the ICRH antenna screen and phase four the installation of the TAE Antenna and re-installation of the divertor tiles. Following the completion of remote handling operations within the torus, the main pumping chamber doors were closed on 14 November The various In-vessel Access Facilities were then removed from the Torus Hall. To cater for the equipment failures identified immediately prior to the shutdown and the need for remedial work following inspections, the shutdown task list grew to over 360 critical path in-vessel activities, including a short interim manual phase to cater for the cleaning of the GDC electrodes. The increased scope resulted in an increase of the planned duration from just over six months to just under eight months; the achieved Shutdown duration was very close to the revised planned duration and finished on 30 November. 4.5 FACILITY INFRASTRUCTURE PREPARATIONS FOR EP2 Preliminary planning for the EP2 Shutdown planned for 2009 identified a number of new requirements for infrastructure facilities. Good progress has been made in enhancing the facilities infrastructure during the reporting period, as detailed below: a new assembly and test area for the extended Octant 1 articulated boom has been provided in the Assembly Hall; enhancements have been made to the existing Remote Handling Maintenance Facility, to allow docking of standard ISO containers to assist in shutdown logistics; temporary re-location of a storage area to make way for the construction of a new ventilated beryllium goods in Inspection Facility on a mezzanine floor; construction and commissioning of a general goods in facility within the Assembly Hall has been completed to improve quality control of incoming items, as recommended following the EP1 post Shutdown Review; 4.6

7 a high ceiling clean room assembly area for the embedded diagnostic components being procured as part of the ITER-like Wall project has been identified and a building refurbishment programme has now started; caged storage areas in the Assembly Hall have been cleared and rationalised for use as a bonded store for ITER-like Wall beryllium tile components; a location has been identified and clearance begun of a laboratory to provide the location for a beryllium machining facility, as a risk mitigation measure for the ITER-like Wall project; the existing Centre Support Column (CSC) ventilated containment tent within the Assembly Hall has been repositioned to improve local access and egress, particularly given the need to accommodate the second such tent near-by; clearance of a mezzanine area and a structural integrity assessment of supporting steel-work has been completed, as part of preparation of an area for making modifications to the Neutral Beam Duct Scrapers in support of the Neutral Beam Enhancement project; phase one enhancement of the Active Ventilation system in the Assembly Hall, necessary to accommodate the three new tritium containment tents for the CSC and Duct Scraper work, has been completed, and design work has begun for phase two. 4.6 RESTART After the Shutdown, the process of restarting JET began on 26 November with the reconnection of the auxiliary electrical supplies to the JET Torus Hall. This allowed re-commissioning of key systems to begin and vacuum pumping of the JET torus started on 30 November. Initial leak testing identified several leaks that required partial machine vents to effect repairs: significant leaks were found on a weld on the Torus side of the Octant 8 Rotary High Vacuum Valve which was replaced during the shutdown and on the top flange of a turbo pump. Both of these leaks were repaired and further leak testing carried out during which an air leak from a damaged metallic gas introduction pipe on a PINI on the Octant 8 NIB was found and repaired. The vacuum vessel was the baked at 200ºC from 18 to 27 December and further leak testing was then carried out after the vessel was cooled down. This revealed an air leak in the 5x10-3 mbar l/s range that proved difficult to identify but it was ultimately found on 17 January to be due to a trapped volume between a vacuum valve and a blanked off vacuum flange on the Low Field Side flight line of the new, partially installed auxiliary systems of the pellet injector. Once the leak had been identified and repaired, the vessel was then baked to 320 o C. This was the first time that this temperature has been achieved since 2003 and was possible following the replacement of the baking plant motor. Liquid nitrogen was introduced to the Pumped Divertor on 28 January and the commissioning of the new Nitrogen Recovery Plant, which will lead to a significant saving in liquid nitrogen consumption, was completed on 1 February. Vessel conditioning continued with a total of 89.5 hours of GDC before a successful first plasma attempt on 5 February. Following the 320 o C bake vacuum conditions were excellent indicated by the rapid achievement of good operation at high plasma density within two weeks of first plasma. Double shift operations commenced on 15 January. For the first three days power supply and additional heating commissioning was carried out on the early shift and further vacuum leak testing was carried out on the late shift. 4.7

8 Subsequently the main Power Supply commissioning was completed on 29 January which gave an opportunity to complete on 1 February the commissioning to high current of the system to produce toroidal field ripple. Commissioning of the Neutral Beam heating systems progressed very well with the Octant 4 Neutral Beam system progressing to asynchronous operation on 29 January and then synchronous with plasma operations on 27 February. This was followed by the Octant 8 Neutral Beam system going asynchronous on 4 February and finally synchronous on 12 March. Excellent progress was made and on 25 March a record 4.9 GJ of Neutral Beam energy were injected into the plasma in 42 plasma shots (compared with a daily target of 25 shots). Diagnostic systems were also commissioned in parallel with the commissioning of the neutral beam systems. Where necessary, specific shifts were dedicated to running specific plasma configurations required for certain diagnostics. All plasma and Neutral Beam milestones were met comfortably within the restart period. A notable effort from the diagnostics team was to replace the visible light camera at Octant 1 (which had a periscope assembly with a shutter which would not open) with one at Octant 7. Without this plasma operations would not have been possible. Other new diagnostic systems which have been commissioned during restart are an Infra Red camera. High Resolution Thomson Scattering is now operating and producing data. The commissioning of the other additional heating systems, namely Radio Frequency (RF) heating and Lower Hybrid (LH) Current Drive, progressed less quickly due to plant and power supplies faults together with the heavy load on the team because several new systems were also being brought into operation. A pragmatic approach to bringing these systems on line was taken, concentrating on delivering the performance required for the first experiments of the campaign. At the end of restart, the RF system had achieved 4.2 MW at 42 MHz and 2.8 MW at 37 MHz and the LH system had coupled 1 MW to plasma. Good progress on commissioning of the ITER-like antenna and installing the external conjugate T matching system was also achieved. The other new system which was installed during the 2007 shutdown was the High Frequency Pellet Injector a fuelling system designed to inject deuterium and hydrogen ice pellets into the plasma at high velocity. During restart this system was locally commissioned producing both large and small volume pellets at 1-15 Hz at velocities of 300 m/s. At the end of restart the final connections of the flight lines to the Torus and the commissioning of the flight line vacuum systems remained to be completed. Unfortunately on 2 April an internal water leak was detected on the Octant 8 NIB which requiried an intervention to replace one of the PINIs. In spite of this the experimental campaign commenced during the week commencing 7 April, though the RF and LH systems still had not reached full power, which meant that conditioning of these systems had to be continued in parallel with the first few weeks of plasma operations. Overall this has been a successful restart, bringing the key systems to readiness in time for the experimental campaign, although in some cases not up to full operational performance. 4.7 ITER-LIKE WALL PROJECT The ITER-like Wall (ILW) project is part of the second programme ( JET-EP2 ) of major enhancements to JET under EFDA. The project to implement the ILW is part of the JOC (JET Operation Contract) work by UKAEA, with core engineering 4.8

9 and installation related activities based at JET involving some secondees from other EURATOM Fusion Associations. Certain specialist technical tasks have been undertaken by other Fusion Associations but under the overall management of the JOC ILW team. The objective of the ITER-like Wall (ILW) Project is to install in JET a beryllium (Be) wall and an all tungsten (W) divertor, which is now the planned material configuration for the deuterium-tritium phase of ITER. In combination with other JET-EP2 enhancements to JET (the most significant of which are described in Chapter 3), the ILW will provide a test bed for developing integrated scenarios with ITER relevant edge conditions and testing plasma compatibility with these wall materials, thus speeding up the early phases of ITER. The total number of parts required to replace the 5,000 existing carbon fibre composite (CFC) tiles in JET is around 80,000 and involves about 2,000 distinct new component designs. Due to the higher electrical conductivity and lower melting point of beryllium compared to CFC a completely new approach to the design was required in order to meet its overall objective of maintaining the same thermal performance as achieved with CFC wall materials. The resulting tile designs are significantly more complex, involving many more parts, than the CFC tiles that are being replaced because of the need to: cut the Be tiles into slices to reduce the electrical current flowing in them during plasma disruptions and hence reduce the force on them; partially cut through each slice from the plasma-facing surface to produce castellations to avoid cracking that would otherwise result from differential thermal stress. The slices of the Be are then assembled onto inconel carriers to produce tile assemblies to replace the CFC tiles. As reported in previous years, the tungsten tiles have also required a significant R&D programme. The ILW project activities divide into two main strands: Engineering Design and Manufacture, in which the design and procurement of all the new components required inside JET is managed; and Installation Preparation, in which all of the preparatory work and procurements required to install the new wall are organised. Because most of the installation will be by remote handling the effort involved in tool design and manufacture, procedure preparation and training is a very substantial part of the overall work. All of the contracts for the procurement of the major components required by the project have now been placed by European Commission and four of these were completed by the end of this period. The project has required a total of 19 such contracts with a total budget of 33MEuro. The overall management of these contracts is performed by the EFDA JET Close Support Unit at Culham with the technical management being done by UKAEA. By early 2008 the main focus of the project had moved from design to manufacturing. Figure 4.9 shows one of the first manufacturing prototypes (aluminium rather than beryllium) undergoing a fit check in the JET in-vessel training facility. 4.9

10 Figure 4.9: Picture of a production prototype of an ILW tile undergoing a fit check in the JET invessel training facility In previous shutdowns, all in-vessel remote handling operations have been carried out with a single long boom and mascot manipulator with the components being supplied to the mascot manipulator via a second, much shorter boom. Due to the time required to move the long boom to collect individual components from the short boom, this system would be too slow to install the large number of components associated with the ILW project. For this reason the components necessary to extend the short boom to make a second long boom are being procured to allow a complete set of tiles and tools to be delivered directly to the area of work of the mascot manipulator. A virtual reality simulation of co-operative working with the two booms is shown in Figure The primary mechanical elements of the new boom were procured under a UKAEA contract and accepted at the manufacturer in April Figure 4.10: Virtual reality simulation showing the new extended JET boom (on the left) bringing a package of tiles and tools into the torus for delivery to the mascot manipulator 4.10