The injector CW campaign was interrupted during a few weeks to fix two technical issues which appeared in a row just after resuming this activity at the beginning of 2023. For the first one, a fuse and few transistors were found damaged in the power supply of the second source coil. Procurement of new components was relatively fast and allowed fixing the power supply in a timely manner. The second difficulty came immediately after resuming injector operations and was linked to the power supply of the magnetron. On-site investigations did not allow to determine the reason of this failure. The power supply was replaced by a spare one from same manufacturer with different remote control interfaces. Yet few adjustments were needed to accommodate a different communication protocol and physical interfaces. The control system group worked closely with the injector group to update the local control system. Tests were performed in manual and remote modes to confirm signal synchronization with timing system, interlocks and operability from injector OPI (Operator Interface). Eventually, the injector operations with deuteron beam resumed on 29 March with the 11mm PE (plasma electrode). While plasma conditioning is organized during nights, beam extractions is performed during evening shifts and reached 150 mA extracted current at 100% DC (duty cycle) in the last days. Emittance measurements are performed at 5% DC for different beam extraction conditions. The objective is to gather enough data to compare results with the ones of previous injector campaign in 2022 using same PE diameter.

The main reason preventing injector operations during the daytime is related to RFQ activities. Indeed, the assembly of the Oring couplers was performed in a cleanbooth mounted in the vault. After each assembly, the coupler was mounted on a local vacuum chamber next to the cleanbooth to perform vacuum leak test. Though the coupler assembly procedure was well detailed, the percentage of successful leak tests was rather low for the first assemblies. A number of adjustments were introduced in the assembly sequence in order to obtain vacuum tight assemblies. Once validated on the vacuum test bench, each Oring coupler was mounted on the RFQ. Special care was given to the cleanliness aspects with the use of a large cleanbooth installed on both sides of the RFQ and able to host 2 operators. A smaller cleanbooth was installed in the first one around the RFQ port on which was mounted the Oring coupler. After completing the installation of the 8 Oring couplers, vacuum was pulled in the RFQ for a global leak test. After tightening further few bolts, the RFQ vacuum leak test was validated. The RFQ was brought back to atmospheric pressure to allow the assembly of the coaxial lines, which should start just after removing all the scaffoldings used for coupler assembly and also after reconnection of water piping and cables on the couplers.

Meanwhile, the conditioning of the first pair of brazed couplers on RFQ RF chain 4A was terminated in March. It reached 96.3% duty cycle at 196 kW but with 130 kW of reflected power. While the first brazed coupler can be considered as fully conditioned, the second coupler was not exposed to full RF power and its conditioning should be completed later. The HPTB (High-Power Test Bench) was dismounted last month to allow activities on the MEBT SSPA and remounting of the coaxial lines in view of the LIPAc beam operations.

Another RF test bench was mounted on the RFQ RF chain 3B to condition the spare ceramic disks of the Oring couplers. A first ceramic disk was mounted and conditioned up to 150kW at 55% DC, but the test was put on hold as temperatures were reaching 86°C on the RF window flanges. A second ceramic disk was mounted for comparison and is under testing.

After their delivery and unpacking in Rokkasho BA site, the circulators 1A and 1B have been mounted on the RFQ RF module #1. Besides the heavy components and the limited space between RF modules and control cubicles, the detailed procedure prepared in advance allowed a smooth assembly operation. A water pressure test was performed after reconnection of water piping and get successful after fixing a few leaks. Measurements of RF characteristics for each circulator were performed successfully at different temperatures. The position of the circulators was adjusted during an alignment campaign with laser tracker. Before connecting the circulators to the RFQ with coaxial lines, a last RF power test will be performed by mounting a RF load at the output of each circulator.

The 15^th LIPAc Technical Meeting (LTM15) was held remotely on February 16 2023, to share a general overview of the LIPAc Unit present and future activities.

In the first session about the LIPAc status and commissioning plan, the Project Leader presented the progress of LIPAc with respect to the injector continuous wave campaign, the circulator 1B repair, and the couplers strategy (O-ring couplers are used, with an enhanced cooling capability to reduce the temperature at the inner conductor coupling part, see photo below) in order to resume operation in a timely manner. The SRF Linac assembly, the maintenance strategy and the commissioning objectives were also addressed.

The significanceof the LIPAc contributions to the preparation DONES and A-FNS was pointed out, in addition to the qualification of the accelerator concept and components. Other presentations and discussions included the revised experimental plan and the RFQ power couplers activities, on the critical path to restart beam operation.

The second session was about the LIPAc design enhancement. Regarding the injector, the scope of its upgrades has been updated based on the maintenance and the operational feedback in order to optimize maintainability and operability. As for the Radio-Frequency Power Systems, its maintenance aims to improve the system availability, while a prototype Solid State Power Amplifier is under design for its planned upgrade. Lastly, the Machine Protection System upgrade of the Control Systems is progressing well as its Preliminary Design Review was scheduled on the 28/29 of March 2023.

The Project Leader and LIPAc Unit Leader thanked all for the fruitful discussions and congratulated the team about the quantity and quality of work performed.

The 1^st Fusion Neutron Source Technical Meeting (FNS TM1) was held remotely on February 09, 2023, to share the status of the FNS Unit activities.

The first session was focused on the Lithium Target Facility activities (LF) that are the engineering validation activities in BA phase II (from 2020) aiming to perform additional R&D in order to improve the reliability of the individual systems from the viewpoints of long-term operation.

The progress of the construction of Li loop facilities were presented for both the 1:10 scale pilot plant (Japan) and the full-scale test loop (EU). The first experimental results of the erosion-corrosion of Target Assembly and ELTL (EVEDA Lithium Test Loop) material were discussed before being used to feed its modelling. The experimental setup for the study of the stabilization method of used/leaked Li including radioisotopes was completed and enabled the start of the experiments. Following the finalization of the Li fire experimental setup, the conclusion of the first experiments on Li fire risks identified the levels of humidity without ignition.

The second session was focused on the Engineering Design activities (ED) that are theactivities in BA phase II (from 2020) aiming to obtain relevant information for the design of an IFMIF-like Neutron Source concerning the safety reduction. Many modelling and experimental studies were presented. 

The possibility of storing the lithium after its stabilization was investigated within the tritium migration estimation. Experimental studies on a stabilization treatment are currently underway.

The erosion-deposition modelling in the target system for FNS enabled the evaluation of the absorbed dose rate of the primary heat exchanger oil due to the activated erosion-corrosion products. The modelling activities are now focused on the corrosion.

In order to complement the accident analysis in safety, an environmental impact assessment was performed using the PUFF code developed to study the tritium atmospheric release from FNS facilities. Additionally, the first draft of failure mode analyses activities is expected to be available in June 2023 including references to the top-level safety regulations.

The irradiation campaigns of the candidate oils for the heat transfer fluid in the primary heat exchanger were performed with simulations in JA using the dibenzyl toluene properties and experiments in EU using hydrogenated terphenyls to investigate the behaviour at different gamma dose rates. As main results, a good stability under gamma irradiation has been found up to 13 MGy (dose expected in DONES after 40 years of nominal operation).

The last IFMIF/EVEDA Project Committee recommended to resume LIPAc beam operations in a timely manner. For what concern the RFQ couplers, this recommendation resulted in the re-use of viton Oring solution for ceramic window sealing with improved cooling capacity while the ceramic-metal brazed couplers would be conditioned as much as possible in parallel.

Indeed, the design of the RFQ Oring coupler has been updated to improve its cooling capability. On vacuum side, an upgraded anchor is meant to ease the heat extraction from the internal conductor and the RF windows ceramic. A prototype was built and tested in Rokkasho, confirming its assembly procedure and vacuum tightness. On atmospheric side, flanges of the RF windows were machined to allow compressed air-cooling injection and extraction by 6 holes. The series of upgraded anchors and air flanges were delivered in Rokkasho beginning of February. The re-installation of the Oring couplers with upgraded elements on the RFQ is starting this week.

Meanwhile, an important effort was dedicated to the setup of the High-Power Test Bench (HPTB) in the RF area with the objective to condition the RFQ brazed couplers. The LIPAc building was not designed to host this kind of HPTB and the RF area was already occupied by many equipment. Resources from the different groups of the LIPAc Unit were involved to find solutions for the HPTB, finding adequate position, re-using existing components and adapting the RF system and control system to operate the HPTB in standalone. Careful conditioning of the first pair of brazed couplers started in Dcember 2022 and reached 96% Duty Cycle (DC) last week. The objective is to reach 100% DC in order to validate the design of this brazed couplers. The 3 other pairs will need to be conditioned as well to validate their manufacturing, presumably on a different test bench as the HPTB will be shortly dismounted.

The circulator 1B was checked and repaired at the premises of the manufacturer (Ferrite Company owned by MEGA) in Gorham, near Portland, ME-USA. The Factory Acceptance Tests (FAT) were organized last week with the attendance of 3 LIPAc Unit experts. For the FAT, the circulators 1A and its twin unit 1B were mounted together in the same configuration as for LIPAc (see picture below). Electrical performance tests and water tightness tests were passed successfully. After reaching thermal stability, RF parameters were measured on circulator 1B to check the success of the repair. The measurements were repeated after removing circulator 1A, resulting in a strong mismatch that can be corrected applying adequate current to the coil. This series of measurements will be useful to setup the spare circulator which aims to have an interchangeable position between side A and B. Both circulators will be packed for shipment to be back in Rokkasho by end of March.

Injector operation

The measurements with the new EMU (Emittance Meter Unit) were interrupted at the end of April because of an HV standoff issue due to a broken ceramic insulator placed at the repeller electrode. As the replacement of the ceramic insulator implies to open the injector chamber and break the vacuum, it was pointless to resume EMU qualitative characterization. It was then decided to change the PE (plasma electrode) to the 12mm size (as already planned).

During the inspection the BN (Boron Nitride) disks were also found strongly damaged and therefore replaced, it was to be expected considering the number of beam extraction and operational hours since their last replacement. We have currently a major intervention on going on the RFQ couplers. The vault is then open in the day time and injector operation can resume at around 17h30, for a shift until 21h30. While during the night and over weekends, plasma conditioning is performed. Until now efforts have been made to increase the extracted beam current remaining at 5 or 10%DC (duty cycle); current was progressively increased from 130 to 150 mA before some arcs appeared. From this week, beam characterization with the 12mm PE will start.

RFQ couplers

The RFQ cavity is currently vented with N2 at atmospheric pressure. The intervention on the couplers was slowed down mainly due to the technical difficulties (including long and delicate preparation work) and necessity to train adequately the staff by the experts. INFN supported remote training sessions on a spare coupler before the intervention was authorized. After the previous leak tests, the RFQ coupler#3b was suspected to leak and thus it has been the first disassembled and inspected. The window was found with sign of Cu deposition and with partly melted o-ring. The RF window parameters have been measured with network analyzer and the data are analyzed. Considering the time needed to inspect each coupler and replace the o-rings, we will not be able to have few weeks of beam operation in July. Accelerating the activity on the couplers implies unacceptable and not justified technical risks, additionally contractual maintenance onsite starts on August 1^st.

We have also started to prepare a high power test bench (using a bridge cavity that was available onsite) to be able to tests at high power the new RF windows before their installation on the RFQ itself. This will eliminate the risk that a window with imperceptible impurities could break when used at full RF power. The bridge cavity is currently being characterized that is the measurement of RF parameters and tuning, while mechanical interfaces, possible location, cooling options are studied.

RF system

After receiving the spares onsite, the circulator of the RF-RFQ chain#1b was repaired following the instructions provided by the supplier. We are ready to perform some quick functional tests in these days. As the possibility to have beam operation is summer has been discarded, the circulator will be finally shipped back to the supplier for a repair at their premises. Even though it wastechnically the best option since the beginning, but it was not adopted for the long time needed (4 months), non-compatibility with operation in summer and the non-null chances of success of the repair onsite. As the conditioning will resume now in October, it becomes the appropriate option.

We target to have the #1b chain operational by end of October along with the RFQ. Depending on the outcome of inspections and analyses of the RF windows, the best option for the experimental campaign after the summer break will be considered: resume RFQ conditioning aiming at CW or resume beam operation at low power, low DC.

Since beginning of May, after more than 2 years of entry ban in Japan, we could welcome 5 new colleagues from Spain. 2 senior experts from CIEMAT (and old acquaintance of the project) and 3 new engineers for Granada University. We could immediately feel the positive energy and the increase of our working force in the commissioning of the HEBT and BD and in the maintenance activities. Among whom, 4 of them will stay in Rokkasho for at least 1 year.

Disclaimer: the information reported is not meant to be technically complete and doesn’t cover all the activities currently carried out on LIPAc. 

Injector conditioning campaign

After several long runs (each one of ~10hours of CW operation) the Injector CW campaign with the 11mm PE is now considered completed. The last few days of operation were dedicated to collect data for the beam profile measurements and their analyses are on-going (see below profiles). As the RFQ conditioning campaign needs to be extended, the way forward for the injector CW campaign was agreed with CEA as follows. At first the validation of the new EMU will take place with its calibration using the 11mm PE. Then, following a short maintenance of the source (also changing the BN disk), the campaign will proceed with the 12mm PE with the goal to repeat the CW operation. The target in any case is to complete this CW campaign by mid-June, when RF-RFQ conditioning should also be completed.

Extracted current=142-145 mA, Intermediate Electrode Voltage=18 kV

RF-RFQ conditioning campaign

While the RF-RFQ conditioning reached 15%DC at nominal (for deuteron acceleration) cavity voltage of 132kV and 35%DC at 80% level cavity voltage of 106kV, it was stopped on March 30 due to vacuum interlock events. Preliminary investigation pointed out that the time needed by the system to recover the RFQ base vacuum after the vacuum peaks follows the same trend than the temperatures measured in correspondence of the RFQ couplers ceramic windows (see below graphs). Consequently, leaks at the RF couplers viton O-rings are suspected. Intensive leak checks have been performed, first by using Kr gas sprayed in pockets around the windows to be detected by the RFQ RGAs and then by using Helium, following a more standard He leak test by isolating the cryopump and using a mobile trolley. Following the increase of DC during the last months of conditioning campaign, the ceramic windows may also have experienced metallization. Further inspection of the couplers will tell us more if changing ceramic windows and O-rings should be considered. Even though spares are available on-site, the diagnosis of the issue (with the great support of INFN) is our first focus to clearly identify the coupler to be opened because the intervention will be quite invasive (with the need to disassemble the coaxial lines and disconnect them in the pit for couplers located on the north side).

HEBT/BD commissioning

The remote sessions with CIEMAT are progressing well. In particular the new radiation resistant RGA installed in the HEBT is now fully operative (see the below screenshot of its OPI). The noise issues at the HAL02 accelerometer in the BD was solved and the final debugging of the mass flow controllers and cRIO is on-going. The monitoring of the BPMs is ongoing after the new PV gateway service through the Data-diode was started. It appears that an overrun memory issue was causing the segmentation fault observed in the last BPMs operations. These activities will speed up when two CIEMAT colleagues together with the 3 new colleagues from Granada University will join us on-site as soon as May.

Control System

Meanwhile, the Control system supported the modification of the OPI for the isolation valve of the injector vacuum sector 2, while the modification of the chopper interlock module is on-going.

Disclaimer: the information reported is not meant to be technically complete and doesn’t cover all the activities currently carried out on LIPAc.