3 JET Operations 3.1 INTRODUCTION 3.2 EP2 SHUTDOWN

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1 3.1 INTRODUCTION Since January 2000, CCFE has had the responsibility for the operation and safety of the JET facilities under the European Fusion Development Agreement (EFDA). The legal and financial provisions are defined by the JET Operation Contract (that confers the contractual management to the EFDA Associate Leader for JET). The JET research programme is carried out by Task Forces of visiting European scientists from fusion laboratories associated to EFDA, including CCFE, under the responsibility of the EFDA Associate Leader for JET. During the period covered by this report, the major shutdown for the installation phase of the second JET Enhancement Programme (EP2) was completed, formally marked by the start of pumpdown of the JET vacuum vessel on 18 May As reported in the 2010/11 Annual Report, the EP2 Shutdown to install the ITER-like Wall (ILW), the Neutral Beam Enhancement and a variety of upgrades to other systems (primarily diagnostics) continued into this reporting year because of delays caused by the need to modify new tiles to fit unexpected invessel features ( anomalies ) that only became apparent after removal of existing components. Bringing the JET machine into an operational state after such a complex and long shutdown was a very challenging and long task. The restart plan also needed to accommodate requirements from experimental Task Forces for JET to produce scientific results in the early stages of plasma operation, in order to examine the effect of the ILW on plasma behaviour from the first plasma onwards. This resulted in thorough optimisation of the restart plan with interleaved phases of restart activities and the experimental programme. The restart plan also incorporated installation and commissioning of the new system of Protection for the ILW (PIW), in parallel to machine operation. The first plasma was successfully obtained, at the first attempt, on 24 August 2011 (target date 19 August in planning released after pumpdown had been achieved). A total of four experimental campaigns, interleaved with four technical restart commissioning phases, were executed between 24 August 2011 and the end of the reporting year. 3.2 EP2 SHUTDOWN ITER-LIKE WALL INSTALLATION The largest activity in the EP2 Shutdown was to change the plasma-facing components and tiles protecting the wall of the JET vacuum vessel. This involved replacing the previous carbon plasma-facing surfaces with a combination of beryllium and tungsten tiles (some are solid tungsten but most are tungsten coated carbon fibre composite) supplied by the ITER-like Wall (ILW) project. CCFE led the ILW project as the JET Operator, rather than as an EFDA Associate. The shutdown work involved removing the old wall components and fitting over 3,500 new tile assemblies along with a new diagnostic conduit system, cables and vacuum feed-throughs to monitor the temperature of the tiles. During the installation of the tile assemblies, many anomalies (~250) were encountered as a result of the JET machine not being exactly as the drawings and CAD models 3.1

2 available during the design phase indicated. This required a large number of last minute modifications which, as the most of the tiles were beryllium, meant that stringent safety procedures needed to be observed. Despite the large additional workload and some near critical deliveries from suppliers the momentum in the installation work was maintained. However, the disruption to the installation sequence caused by the need to correct the anomalies and some delivery issues did make the shutdown activities substantially less efficient than originally planned, delaying the completion of the shutdown. The following is a summary of the components installed: Number of installed items: 2,880 Number of individual tiles: 5,384 Be tiles (~2 tons Be / ~ 1m 3 ) 1,288 W-coated CFC tiles 9,216 W-lamellas (~2 tons W / ~ 0.1m 3 ) 15,828 Total Total number of parts: 82,273 counting bulk W modules as one part Bulk tungsten total parts: 191,664 including 100,080 shims All ILW contracts are now completed, though the work needed to produce accurate drawings and CAD models of the interior of the JET vessel (both the structure and the components installed during the EP2 Shutdown) are continuing as a background activity within the Design Office under the JET Operation Contract (JOC). Figure 3.1: Remote handling installation operation inside JET vacuum vessel. 3.2

3 Figure 3.2: Photogrammetry survey on trial limiter assembly, and on installed in-vessel components using remote handling. Whilst taking detailed survey photographs at the end of the shutdown, physical contact was identified between a poloidal limiter flux excluder and the adjacent screen bar knuckles on ICRH Antenna B. This was due to an inconsistency between the configuration model and the true situation in the machine (i.e. a further in-vessel anomaly) that was not noticed during installation. It was decided not to take remedial action immediately because of the large impact on the shutdown duration that this would cause. The consequence of this anomaly was the decision not to operate one half of Antenna B during the 2011/12 campaigns and the necessity to re-design the flux excluder for installation during the 2012 intervention. Antennae B and A are powered by the same generator through 3dB hybrid couplers, so the full use of antenna A was also slightly compromised. By reconfiguration of the RF transmission line connections to antennae A and B the total available ICRH power was however reduced only by about 20%. The in-vessel installation work was completed on 10 May when the Octant 5 RH boom was removed. The vessel pump down took place on 18 May, which formally marked the completion of the shutdown and the transition to restarting the JET systems. This represented a delay with respect to the planning released in December 2010 of one month, and a delay of four months with respect to planning released in December NEUTRAL BEAM ENHANCEMENT INSTALLATION The other major activity in the EP2 Shutdown was the installation of components and equipment as part of the project to increase the power (by 40%) and pulse length capability (by 100%) of the JET neutral beam injection systems. This project has been carried out as an EFDA EP2 Enhancement, with CCFE in the role of lead Association as part of the range of activities performed under EFDA- JET Orders described in Chapter 4. The shutdown installation work within this project comprised: 3.3

4 Replacement of the protection panels of the torus beam entry ducts (known as duct scrapers ) with new actively-cooled components to withstand the higher incident power and the longer pulse duration; Refurbishment of the central column assemblies in the two Neutral Beam Injectors Boxes, which carry all the main beamline components, so that they can handle the increased power; The completion of the exchange programme of the sixteen individual Positive Ion Neutral Injector (PINI) beam sources, including testing and conditioning of modified PINIs in the JET Neutral Beam Test Bed (NBTB). The target agreed as part of the shutdown planning, i.e. that the availability of the beam-line components should not affect the critical path, was achieved. Although there was a loss of operational time on the NBTB due to a number of technical problems on the facility, the availability of PINIs was nevertheless achieved because their reconditioning on the Neutral Beam Test Bed proceeded more quickly than expected, allowing the full complement of 16 PINIs to be installed before the end of the shutdown. Figure 3.3: Beam s eye view of neutral beam torus entry port, showing the installed actively cooled duct scraper DIAGNOSTICS A large number ( 30) of new or upgraded plasma diagnostic systems are included within the JET EP2 enhancements. These can be classified into three groups according to their function: Package I: Diagnostics in support of the new wall Package II: Diagnostics with strong in-vessel and vacuum-boundary implications Package III: Improved detection and test of techniques for measurement of profiles of various plasma emissions (neutrons, gamma rays, neutral particles, microwave reflectometry etc.) The majority of these diagnostic enhancements have been led by EFDA Associates, including four led by CCFE, with a further three led by CCFE under the JET Operating Contract. The installation of the new equipment and implementation of the associated data acquisition systems for the diagnostic 3.4

5 enhancements was largely complete by the beginning of the JET restart to allow commissioning to be progressively carried out with plasma. All diagnostic projects were expected to collect data and allow a detailed evaluation of their performance by the end of the 2012 campaigns (with the exception of the lithium beam diagnostic for which an issue of reduced field of view can only be remedied in the 2012 intervention). A series of calibrations of existing diagnostics was planned to be carried out during the EP2 Shutdown. In 2010 calibration of the Electron Cyclotron Emission and spectroscopy diagnostics was performed. However, in early 2011 it was decided not to proceed with the planned neutron calibrations to reduce the time needed to complete the shutdown. This decision was taken on the grounds that the neutron calibrations could be carried out in the 2012 intervention with little increase in its duration and that the programmatic impact of delaying the calibration to 2012 is small. These calibrations are now a high priority item on the plan for the 2012 intervention PROTECTION OF THE ITER-LIKE WALL The installation of ITER-like Wall in JET imposes new limits and restrictions on the plasma operation, because the new metallic wall protection is less resilient than the carbon fibre composite tiles used previously. This is compounded by the fact that the increased heating power resulting from the neutral beam upgrade will lead to higher heat fluxes on inner and outer divertor tiles. In October 2009 a new project called Protection for the ITER-like Wall (PIW) was launched to integrate monitoring of surface and bulk temperatures into the JET protection system. These measurements are available for the JET protection systems in real time using robust visible cameras with infra-red (IR) filters and image processing algorithms, as well as pyrometers and thermocouples. Protection of the wall is based on surface temperature limits defined in the corresponding JET Operating Instructions, based on rigorous engineering analysis. The protection strategy under normal and abnormal operation and during termination sequences has also been developed within the project, this includes: Improved software models for real-time calculation of the surface and bulk temperature evolution of critical components based on actual plasma parameters, power input etc. within the WALLS protection system in addition to the measured surface temperature from the PIW cameras; Changes to Real Time Protection system (RTPS) including changes to Pulse Termination Network (PTN) logic to facilitate appropriate protection actions e.g. on plasma heating systems; Modifications to the local management systems of the neutral beam, RF and Lower Hybrid heating systems, and the gas introduction system to allow their integration into the overall PIW protection system. The real time processing system was designed, installed and commissioned in 2011 with the involvement of three Associations (CEA, IST and CCFE). For each PIW camera a dedicated hardware system, connected to the real time control network (RTC), computes temperatures of pre-defined Regions-of-Interest (RoI) using image processing algorithms. The algorithms include calibration and calculation of RoI temperature; neutron pixel hit detection and removal, detection 3.5

6 and removal of light emitted from specks of dust in the plasma, recognition of surface layers and correction of vibrations. To improve the IR calibration data for the cameras used within the JET PIW project, measurements to validate the thermal data provided by the PIW cameras against a pyrometer and a thermocouple using the W-coating test facility at the NILPRP (MEdC Association) have been carried out in This data has formed the basis for the calibration data used by the PIW cameras. This project also included the investigation of the emissivity and thermal properties of the beryllium tiles using the JET Neutral Beam Test Bed. 3.3 RESTARTS AND OPERATIONS After a major shutdown there is a significant amount of work required to recommission the JET systems to a state that permits plasma operation. This period of re-commissioning is referred to as the restart. After previous shutdowns under EFDA, the restart activities have also included a period of plasma operations to condition the walls of the vacuum vessel and the heating systems to a state that allows routine operation at the performance levels needed by the experimental campaigns. The restart after the EP2 Shutdown was significantly different in several respects: Important scientific results would be produced from the start of plasma operations since this would represent the first operation with the combination of wall materials planned for ITER. Hence there needed to be a strong involvement of the EFDA Task Forces in planning and executing even the initial plasma operation without additional heating; The change of the materials used to make the plasma-facing components meant that JET was effectively a new machine hence previous experience could not be relied upon; The use of beryllium (which has a relatively low melting temperature of 1280 C) and tungsten (both solid and in the form of thin coatings on carbon fibre composite tiles, which have operational limits of about 1200 C because of, respectively, re-crystallisation and damage to the coating) meant that the wall of JET is now far less robust than when it was made of carbon. Consequently, systems to protect the ITER-like Wall against overheating during plasma operations that had been installed during the shutdown (see Section 3.2.4) needed to be commissioned and proven before embarking on operation with high power additional heating. This required the additional heating to be increased progressively as the protection systems were proven to work; The neutral beam heating systems had also been enhanced via the Neutral Beam Enhancement project (see Section 3.2.2), which meant that they also needed to be progressively commissioned over a significant period of time. Hence the usual approach of commissioning all systems near to full performance during a restart phase before the start of experimental campaigns was not appropriate. Consequently a sequence of inter-leaved restart phases and experimental campaigns were planned to explore behaviour with the new ITERlike Wall with progressively increasing heating power. 3.6

7 The dates of the restart periods and experimental campaigns during the reporting period were as follows: Preparations for plasma operation: 18 May to 23 Aug Restart with plasma, R1: 24 Aug to 1 Sept Campaign C28a: 1-20 Sept Restart phase R2: 21 Sept to 3 Nov Campaign C28b: Oct Restart phase R3: 7-28 Nov Restart phase R4a: 30 Nov to 6 Dec Campaign C28c: 21 Nov to 21 Dec Restart phase R4b 3 9 Jan Campaign C29 10 Jan to 30 Mar C28a was executed with ohmic plasmas (i.e. no additional plasma heating), C28b using up to 4 MW of heating, while C28c used up to 10 MW of heating to study both the low confinement (L-mode) and first high confinement (H-mode) plasmas with the new wall. The restart phases had well defined tasks (milestones) in order to prepare for the subsequent campaigns. However, due to delays in system availability (in particular the upgraded neutral beam injection system) some of the restart activities were incorporated into the experimental campaigns. For example, the first sessions of C28c were interleaved with R3 and R4a. The planned campaign C29 (exploration of H-modes) was postponed until More details of the individual restart and operational periods are given below PREPARATION FOR PLASMA OPERATION The shutdown formally finished on 18 May 2011 when the JET vacuum vessel was pumped down. A specific set of restart activities and commissioning procedures are required before commencing plasma operation. For the restart in 2011 preparing for plasma operation the following sequence of tasks was performed: Vacuum leak checking with the vessel at room temperature and rising to 200 o C: test for leaks in the torus, diagnostics, connections to Active Gas Handling Systems and the two Neutral Beam Injection (NBI) boxes, including the rotary high vacuum valves between torus and the NBI boxes; Commissioning the cooling and cryogenic systems: demineralised water system, liquid nitrogen loops and liquid helium loops; Baking of the vacuum vessel to remove water from components: initially at 200 o C, followed by 320 o C for 4 weeks, then cooling down to 200 o C; Glow discharge cleaning in deuterium: several periods, totalling ~100 hours, with regular vacuum assessments (including estimation of the water removal rate); Vacuum conditioning of ICRH and Lower Hybrid systems during vessel baking at 320 C; 3.7

8 Power supply commissioning: Protection systems; Poloidal Field and Toroidal Field power supplies; power supplies of additional heating systems; Extensive diagnostic installation and alignment, including the cameras viewing the new inner wall of JET (both as part of the PIW project and to provide data for the science campaigns); Testing without plasma the Plasma Control Systems, including those upgraded during the shutdown needing complete system commissioning; Final vacuum checks: calibration of the vacuum gauges, mass spectrometers and gas introduction systems; Detailed leak search: identifying and rectifying small leaks on torus and attached diagnostic systems. The vacuum leak testing proved to be a complicated task taking ~2 weeks longer than planned. Despite this search there remained a significant air leak of ~8x10-4 to 2x10-3 mbarls -1 into the JET vacuum vessel. Various attempts continued throughout the remainder of the reporting year to try to localise the leak when time permitted. Conventional leak detection using helium clearly demonstrated the existence of a leak but because it showed poor time response failed to localise it. The most promising alternative technique has been to increase the argon levels in the torus hall atmosphere; this resulted in a prompt response when the argon is released, confirming that the leak is directly from the air in the Torus Hall into the vacuum vessel (rather than being from a remote vacuum system or via a vacuum interspace). However, a dedicated search on individual machine octants had still failed to locate the leak by the end of the reporting year. The magnitude of the leak was at the upper limit of the range that could be accepted for operations, and did not significantly compromise operations or the quality of scientific measurements (the leak was eventually located, using a development of the argon method, early in the following reporting year) RESTART PHASE R1 AND CAMPAIGN C28A A period of 14 weeks of restart without plasma was required to commission the basic systems required for plasma operation. On 24 August at 18:29 JET had its first plasma with the new wall (Figure 3.4). 3.8

9 Figure 3.4: JET Control Room activity during the first plasma pulse with the ITER-like Wall, obtained successfully at the initial attempt on 24 August The 1 MA plasma discharge lasted 15 seconds, significantly exceeding expectations. Previously, with the carbon wall, only a brief flash of plasma would have been produced, limited by the effects of impurities. This success was even more notable given the known air leak. Subsequent operation has confirmed that plasma operation with a beryllium wall can be easier (particularly there is less radiated power and cooling from impurities at plasma initiation due to the strong gettering effect of beryllium) than with a carbon wall. In general, plasma initiation (breakdown) also showed less variability with the ITER-like Wall; successful plasma initiation is obtained in a large range of gas prefill values without the need to adjust the conditions for successful plasma initiation after disruptions. Since the first plasma with the ITER-like Wall JET has operated with almost no plasma initiation issues and no need for glow discharge cleaning. This experience shows that control of the cleanliness of the components during manufacture and installation was successful as well as the beneficial properties of the beryllium. The first phase of restart had the task to complete the commissioning of ohmic operation up to 2 MA plasma currents with diverted plasmas in one configuration. Most of the restart targets were achieved; including the commissioning of the basic plasma position and current controller and shape controller, the gas introduction matrix (GMX), the Active Gas Handling System (AGHS) and the minimum level of protection of the plasma facing components using the WALLS system (see Section 3.2.4). This met the requirements to conduct the experiments in the first experimental campaign C28a with the ITER-like Wall. A notable departure from the plan was the inability to test plasma operation up to the normal maximum value of the toroidal field of 3.45 T, due to the failure of a plug-braking transformer in the TF Flywheel Generator that limited the maximum field to 3.1 T using static units only. This did not, however, impact upon the C28a campaign. Restart phase R1 was completed using 41 successful pulses within 8 sessions (ahead of the scheduled 10 sessions) with a total delay for system faults during sessions of ~8 hours and no unplanned maintenance and repairs. 3.9

10 3.3.3 RESTART PHASE R2 AND CAMPAIGN C28B This aim of this restart phase was to commission the Neutral Beam Injection (NBI), Ion Cyclotron Resonance Heating and Lower Hybrid Current Drive (LHCD) systems, to start the commissioning of the ITER-like Wall protection (PIW), to start the vacuum commissioning of the pellet injection system and to finish the commissioning of the plasma control and plasma protection systems. The additional heating power targets for this phase were the levels that were required for C28b, namely 4 MW of ICRH at two frequencies, 1 MW of LHCD and 7.7 MW of NBI power. Most of the due milestones were achieved by the end of this phase. However, the NBI system was not yet available for routine plasma operation because only five out of the eight PINI beam sources of the Octant 8 NBI box had been successfully commissioned (up to the initial target of 80kV beam energy). In particular, one pair of Octant 8 PINIs was served by the first of the six new HV power supplies due to be commissioned as part of the NB Enhancement project. As a result of a number of technical problems on other NBI power supplies (not connected with the enhancement) it was necessary to delay the start of the new HV power supplies commissioning and operation of the associated PINIs. Whilst that delayed commissioning was being carried out (asynchronously from JET pulsing) it was not possible to use the Octant 8 NBI box for routine experiments. Three ICRH frequencies were commissioned, one more than the required milestone, with 42 MHz up to 4 MW, 33 MHz up to 2 MW and 51 MHz up to 2 MW (in the various required antenna phasings). All of the PIW alarms were commissioned and the temperature validation was completed. An additional test for one camera was performed, by using one of the installed beryllium-evaporator heads as a known heat source to check the validity of the temperature measurement. The first new strategies were developed and tested to respond to protection system requests to terminate the plasma if overheating of plasma facing components were detected. All required commissioning of the plasma position and current control system was also completed RESTART PHASE R3 The purpose of this phase was mainly to: finish the commissioning of Octant 8 neutral beam heating system and start the commissioning of Octant 4 system; to finish the commissioning of the remaining ICRH frequencies; to continue the commissioning of the pellet injection system; and to finish the commissioning of PIW, including a demonstration of the protection in H-modes. The Octant 8 NB system was however still not available for plasma operation; the commissioning of 6 out of the 8 PINIs had started but not finished. Due to knockon effects of having to redeploy power supplies staff resources to resolve the problems encountered in restart phase R2, integrated commissioning of the Octant 4 NBI box had to be delayed until R4b (see below). Good progress was made on ICRH, finishing the commissioning of all the frequencies and antenna phasings required for the campaigns. This was done with a 6-7 cm distance from the plasma to the outer limiter distance and typical power levels up to 4 MW, which gives conservative power loads to the beryllium wall components. The PIW project installed and commissioned the narrow filters that allow the cameras to measure from 600 C up to the JET Operating Instruction limit of 950 C for the beryllium wall. The main-chamber protection was 3.10

11 made active with protection action triggered when the measured temperature reached 750C (conservative limit). It was not possible to carry out the functional testing of the PIW cameras as originally foreseen at this time, as this would have required higher levels of additional heating power than available. Instead, the camera was calibrated using the beryllium-evaporator head measurements mentioned in Section and estimates of the beryllium emissivity. The plasma position and current control system was commissioned to provide the appropriate response to these protection action triggers. However, the control of the additional heating waveforms in response to PIW action through the local managers for NBI, ICRH and LHCD could not be yet be commissioned. The High Frequency Pellet Injector, providing deuterium ice pellet injection for control of Edge Localised Mode plasma instabilities or ELMs, commenced commissioning with plasma during phase R RESTART PHASE R4A AND CAMPAIGN 28C At the end of this short restart phase, the NBI interlock commissioning, including functional testing to prove the correct operation of the fast beam interlock signals to inhibit the beams when plasma conditions for NBI become invalid, was completed. Conditioning of the Octant 8 duct scraper (by firing pulses of progressively higher power and pulse length in order to degas the duct surfaces) was successfully carried out, with 6 PINIs operating up to a maximum voltage of 110 kv providing 9.3 MW of NBI power to the plasma. The commissioning of the Error Field Correction Coil (EFCC) controller had to be delayed until R4b due to problems with the 36kV pulsed power distribution system.. This prevented commissioning and operation of the EFCC amplifier, which had been reconfigured in the shutdown to provide improved EFCC functionality. Controls and interlocks for the Disruption Mitigation Valve (DMV) were successfully commissioned in ohmic plasmas, and commissioning of DMV interlocks with NBI was completed parasitically during C28c. These fast DMV interlocks are necessary in order to protect the additional heating and some diagnostic systems from the effect of the massive gas injection from the DMV. During R4a, a temporary replacement plug-brake transformer was installed and successfully commissioned with the toroidal field flywheel generator on 1 December, but a subsequent problem with the bearings of the generator led to its being taken out of service, pending further investigations (see section below) RESTART PHASE R4B AND EXPERIMENTAL CAMPAIGN C29 This period of three months JET operation contained the last block of the restart and experimental campaign C29. The reference plan for 2012 allocated only 10 sessions to R4b, with 112 sessions allocated to C29. The main restart activity during this period was the outstanding commissioning of the NBI heating systems. The commissioning of Octant 4 NIB only started in January This was a considerable task, as six out of eight PINIs of the Octant 4 NIB were to be operated for the first time using new HV power supply units. However, the commissioning progressed very much faster than on the Octant 8 NBI box and, by the end of March, both NBI boxes were available for plasma operation, with most of the PINIs operated at beam energies above 100 kev, which corresponds to available total neutral beam power above 25 MW. Towards the end of March, the NBI system was routinely delivering MW of heating power into JET plasma. PINI number 5 on Octant 4 NBI box was taken 3.11

12 out of service at the end of February due to a leak that developed in the gas introduction system, which could only be repaired in the 2012 intervention. At the end of R4a most elements and functionality of the PIW system had been commissioned except for Divertor protection. Sufficient additional power to reach surface temperatures visible by the PIW divertor cameras became available during R4b, but the observation of static hot spots (with temperatures above to the protection levels) caused by poorly connected coating and mobile hot spots probably caused by dust made the commissioning difficult as these hot spots cannot be easily eliminated from the regions of interest, causing the pulse to be tripped by PIW. With the higher NBI power available, the validation for the two available wide angle cameras, using the outer limiters, and the divertor cameras became possible. Furthermore, a methodology that allows the hot spot issues to be worked around was successfully developed. The results with strong additional plasma heating have shown that the attention paid to the detail of the tile geometry and control of installation tolerance has been rewarded by good power handling of the beryllium tiles (unlike the previous JET beryllium limiters). The tungsten coatings have performed well so far as has the bulk tungsten divertor. During this period the commissioning of various other JET subsystems was completed. The wave heating systems (ICRH and LHCD) achieved all required targets. The Error Field Correction Coils were commissioned for operation with coil currents up to 6kA and were successfully used during the experimental campaign. All CCFE operated diagnostics were commissioned including those dependent on neutral beams. Commissioning of new and modified plasma control systems was also fully completed. Considerable time was dedicated to increasing the reliability and reproducibility of the High Frequency Pellet Injector, with some significant improvement achieved towards the end of March. All various machine services were fully functional, and operated reliably throughout the entire period. The cryoplant, in particular, achieved very high levels of reliability and also performance in terms of helium liquefaction rate, following a major refurbishment of the control system in the shutdown. The toroidal field flywheel generator was not used to supply current to the coils, as there were concerns related to vibrations detected during off-line operation in January. Considerable time was dedicated to the identification of the cause of the vibration. The experimental programme did not require toroidal field above 3T and Static Units were used instead. Unfortunately, in the last week of February a fault developed on one of these units (a flashover caused by a shorted capacitor in a snubber circuit). This resulted in the loss of several days of operation and in further reduction of the maximum available toroidal field to 2.65T, since only three quarters of the Static Unit power supply could be used. Some experimental days were also lost during the recovery from the leak in the gas introduction system of Octant 4 NIB PINI 5. A summary of the planned and achieved sessions for R4b and C29 is given in Table 3.1 below. 3.12

13 R4b C29 Total Reference plan for Maintenance 6 6 Saturdays 5 5 Achieved 22* Required Maintenance 6 6 Unscheduled Repairs *13 sessions extra (5 by working on Saturdays and 8 during campaign time) Table 3.1: Sessions for restart phases and campaigns during January March OUTSTANDING EP2 COMMISSIONING ACTIVITIES At the end of the reporting period the main outstanding EP2 commissioning issue was demonstration of the performance objectives for the Neutral Beam Enhancement. By the end of March 20MW total NB power was routinely available to plasma from both NB boxes. However, an operational limitation in beam voltage of around 105kV (cf. 125kV design value) on some of the new HV power supplies had been experienced, due to triggering of an overcurrent protection in the HV output circuit, identified as a consequence of the longer cable run from the new HV power supply buildings (compared with that of the older identical units installed in 2003). A simple modification of the circuit to overcome this limitation has been designed, due for testing in the final two weeks of operation before the 2012 intervention. Project closure is dependent upon completing a series of reference neutral beam injection pulses into plasma, designed to confirm both the high-power and long-pulse objectives of the upgrade. For the reasons described, including loss of operation of PINI number 5 on the Octant 8 NBI box, the power and energy objectives required to close the NBE project were not met during the reporting year. However, for those PINIs not affected by the voltage limitation mentioned, the target value of power per PINI for the upgrade has been achieved in the asynchronous commissioning mode (short-pulse beams fired into the beamline calorimeter rather than the JET plasma), giving high confidence that the design performance can be achieved providing the tests of the minor HV circuit modification are successful. 3.4 PREPARATIONS FOR 2012 INTERVENTION The Follow-on ITER-like Wall Project (FILW) was implemented by CCFE as Operator in order to address in-vessel issues and component preparation for the 2012 intervention. The FILW project will provide the necessary components to enable the replacement of existing ILW assemblies with new ones where required, including the replacement of marker tiles and samples to be removed for assessment of fuel retention, and erosion, migration, deposition and mixing of plasma-facing materials, as well as assessment and partial replacement of the Quartz Microbalances (for in situ plasma redeposition measurements). The project also includes the design, procurement and assembly of replacement for 3.13

14 the ICRH antenna flux excluders to avoid the configuration issues reported in Section 3.2.1, assessment and improvement of the protection from radiofrequency loads for wide outer poloidal limiter tile assemblies, re-design of the ICRH antenna Horizontal tile assemblies to make them robust to variability in their support position, assessment and repositioning of dump-plate (a plasma facing vessel protection tile) thermocouples. The deliverables of the FILW project are, at the time of writing, all on schedule to meet required installation dates. Installation of these components is planned to be entirely by remote handling (RH) means. Following the intensive RH operations on the shutdown, major refurbishments of the RH equipment (booms and control systems, including electrical cubicle remedial work) have been required. At the time of writing, this RH refurbishment work is in progress and the complete RH system will be fully recommissioned before the start of the FILW installation phase. 3.14