30th IEEE Symposium on Fusion Engineering (SOFE 2023) JMM's viewpoint

SOFE 2023 was from the 9-13 July and there is plenty of action to be going forward. Since then, a Larger Project Bid has been submitted on ion-beam irradiation and plans are being put into motion on a longer-term study of cWC and RSBs on irradiation and activation.

However, the main aspect of this conference is that it showcases the scale of work that is required to make fusion power a practical power source.

While much progress has been made in demonstrating how to make fusing plasma, the practicality of high-temperature superconductors (HTS) and advances in power management, there is still the fact that a fusion power plant is at least 5 seperate large facilities that must work in concert for fusion power to be successful.

This provides a counterpoint to the headlines about recent achievements such as the record-breaking campaign at the National Ignition Facility in 2021 https://www.nature.com/articles/d41586-021-02338-4 or the success of the last deuterium-tritium campaign at JET in 2021 https://www.psfc.mit.edu/events/2022/jet-dte2-campaign-preparation-execution-and-selected-highlights are certainly significant they are also misleading to the general public.

While these achievements are critically important there is much that needs to be done before a a practical powerplant can be achieved.

For instance, there needs to be a whole new industrial supply chain that differs significantly from that established for fusion power not least in that there is the need to supply deuterium and tritium alongside reliable HTS magnets. While ITER is arguably a special case in that all the contributers are building part of the reactor itself, with the UK's JET which until recently was functioning as a mini-ITER (ITER now has a W-plasma face and is no longer using Be as the front-face material), the need to establish reliable supply lines and the associated industrial infrastructure still stands.

And here is where the earliest aspects of fusion infrastructure is starting. The UK Government is well on its way to writing fusion-specific legislation, taking into account the differences in risks betwen fusion and fission power - which also impact on the industrial infrastructure. To summarise the differences in risks (and why fusion is that much harder) is that one tries to contain fission; whereas one tries to sustain fission.

There is also the Spherical Tokamak Energy Production (STEP) site in West Burton, Nottinghamshire which will be a place where all the plants needed for a fusion power plant can be assembled and tested in one place. This is a critical part in establishing fusion power and the next set of steps to practical fusion.

Jessica Marshall : 01 Aug 2023 13:57 |  Tags: Conference Fusion Power |  Comments (0) |  Close comments |  Report a problem

30th IEEE Symposium on Fusion Engineering (SOFE 2023) Gurdev's viewpoint

This was the 2nd major nuclear fusion based conference after SOFT2022 which I was attended within last one year. SOFE2023 is on the prestigious conference in this field. It was hosted UK Atomic Energy Authority at University of Oxford, UK. We had a s great learning experience from this conference. It is always good to meet and discuss with persons from both academia and industries.

Plenary and invited talks were very beneficial regarding the current status of various nuclear fusion devices and technologies. We all had poster session on Wednesday (12th July 2023). It was very interactive session. People from industries (UKAEA, Tokamak Energy, Element Six, Oxford Sigma) and academia ( Imperial College London, University of Oxford, etc) were very keen to learn and understand about our work on reacted sintered borides and cemented tungsten carbides. Similarly, we also interacted with various experts during poster sessions and after talks.

It is always good to have researchers and technologist from similar field of interest. These interactions led to some future collaboration with UKAEA and few research groups. Overall, the conference has widen the understanding and specific needs of nuclear fusion industries. It has also given us the future directions about our research based on the inputs and suggestions from both academia and industry.

Jessica Marshall : 01 Aug 2023 12:58 |  Comments (0) |  Close comments |  Report a problem

The first ever RSB Big Sample and why it is so significant

A major step towards realization of Reacted Sintered Boride blocks for fusion applications

Establishing material properties of candidate materials for shielding is one part and manufacturing required materials with realistic dimensions for actual shielding is another. Till now the Radiation Dense Materials Group (RDMG) has worked extensively in reproducing Gen 1 RSBs in a lab based environment to produce Gen 2 RSBs.

This process also needs to be scalable. To test this we have attempted to make a much larger sample with a mass 20x greater than the standard samples. Successful densification of such samples is an important demonstration of how practical a sintering route is with respect to a specific material.

In general, most radiation shielding in a fusion reactor is in the form of tiles. These tiles are typically 20 - 30 mm thick with variable lateral sizes. Where materials made via powder metallurgy is concerned, the most important dimensional parameter is the part size.

This is defined as the diameter D of the largest sphere that can exist within a sintered part that is fully dense as shown in Figure 1:

Figure 1: Demonstration of part size of diameter D

The means that for a tile of dimensions 200 mm x 200 mm x 20 mm would require a part size D = 20 mm. Part sizes in most powder metal processes are seldom above 30 mm.

The real challenge comes when manufacturing lab based materials for practical applications. Thanks to Hyperion MT (Barcelona, Spain) for supplying sufficient milling media, we were able to manufacture decent size blocks of RSBs recently in the lab with the specification as given in Table 1.

Table 1: Specifications of RSB55_NFC regular* sample

Cross-sections show that the sample was defect free internally (figure 2c). Considering the fact that this sample was fabricated at one shot, the future of RSBs looks really bright in terms of industry scale fabrication. This is vital while aiming for better and bigger RSBs samples in near future. With further optimisation of the sample packing in sintering as well as the sintering run itself, the density and overall quality is expected to increase in the coming trials.

Figure 2: Various views for RSB55_NFC regular samples. a) To view b) Bottom view c) Cross-sectional view of as cut and polished sample

. A typical ITER identical monoblock tile geometry is shown in Fig. 3. In terms of geometry, the final aim is to fabricate RSBs with size and shape as used in ITER divertor. This aim looks more realistic now and this achievement is indeed a giant step towards this goal.

Figure 3: WEST plasma-facing unit (PFU) and the monoblock tile geometry. Monoblock tile geometry is identical to ITER.Source

Stay tuned for more interesting updates and insights from RDMG. Till then, keep researching, keep shielding!

*RSB55_NFC regular has about 30 at% Boron and NFC refers to no free carbon which means Carbon is added either in the form of Cr3C2 or WC. For more details, please check our latest publication (here) .

Jessica Marshall : 15 Jun 2023 13:32 |  Tags: Dense Materials Powder Metallurgy Rsb Sintering Success |  Comments (0) |  Close comments |  Report a problem

Publish or be damned?

Publishing is the lifeblood of academia and a main metric on how academic output is measured. Therefore it is critical to publish regularly and often, while avoiding pitfalls such as salami slicing, too much information and show don't tell.

Alongside this is the fact that the process of publication is as important as the publication itself. Currently this group is working on a selection of papers on RSB synthesis. These papers will cover every aspect of sintering from gas evolution, solid state sintering, microstructure and solid state properties including hardnesss and sintered density. The first paper will cover the early part of sintering and this includes a considerable amount of archive data from DTA/TGA and mass-spectrometry. This work was crucial in establishing the early sintering ramps which enabled the development of dense RSB materials.

All well and good although RSB processsing is still a long way from being fully optimized. It is unclear as to what the exact variables are but on writing the first paper it is apparent that some of the early gas-evolution data has been misinterpreted. In short, some of the issues from sintering such as large cavities near the surface of sintered bodies could be attributed to the fact that on closer examination the de-binding (organic binder removal) section was incomplete. While the current recipes focus on removing the bulk of the binder at low (~330C) temperature the part of the cycle at T > 330C was being neglected. This would mean that while most of the binder is removed not all the reactions have completed and this can lead to poor reproducibilty due to outgassing at higher temperatures. This would be consistent if there is excessive carbon present in a volatile form. Had this paper been started sooner it would have been possible to better optimised sintering before hand.

So this is a cautionary tale in making sure that processed data is scrutinized with a view to publication even if not immediate.

Jessica Marshall : 05 Mar 2023 18:48 |  Tags: Materials Synthesis Publishing |  Comments (0) |  Close comments |  Report a problem

Fusion Breakthrough at LLNL and its implications

Writing about web page https://www.llnl.gov/news/national-ignition-facility-achieves-fusion-ignition

On December 5th, Lawrence Livermore National Laboratory (LLNL) announced the first ever net energy gain from laser-powered inertial fusion. This campaign reported that from 2.05 MJ of input energy, 3.15 MJ was reported as the output. This is a world-first for controlled fusion and marks a critical achievement in demostrating the possibility of fusion power.

So what are the implications for magnetic tokamak confinement and the broader fusion community?

While it can be argued that inertial confinement fusion differs considerably from magnetic confinement fusion, both require considerable energy input and both require the fusion triple product and hence fulfil the Lawson Critierion for a sufficient amount of time to achieve ignition of the plasma. In the case of magnetic confinement it is the toroidal plasma, for inertial confinement, it is the plasma induced by the vapourization of the fuel pellet by the lasers. The fact that positive energy has been demonstrated by at least one method of fusion is an important demonstration about that positive energy is possible using current techniques.

While this is important, it is critical to know the reliable positive energy is only one of the earliest critieria that need to be met. For fusion power to be practical, the energy has to be tranferred into a useful form. A practical reactor of any type must be capable of fusion pulses on a regular basis and to withstand the conditions caused by the heat and radiation by the fusing plasma. This leads to aspects of fusion reactor design whereby reactor components such as the cryogenics plant, diagnostics and gyrotrons to name a few require power and effectively reduce the net power generated from the fusion reactor such that the actual energy released/energy input is << 1

The result of this will be that a considerable period of fusion development when the next major development will be when gross energy input = energy output. That is, a fusion reactor which gives no net energy to the Grid but does not take energy out of the Grid unlike every single fusion experiment to date. This will demonstrate the fusion power has a level of maturity in that it can support its own reactions which will be the next signficiant milestone.

To summarise, while care must be taken to not overstate the importance of the LLNL result it does show that fusion power is well on its way from transitioning from a physics problem to an engineering problem. That isn't to say there will not any surprises on the physics front on the race to practical fusion but this is another piece of good news alongside the latest JET result. We await with bated breath for ITER's first plasma in 2026.

Jessica Marshall : 24 Dec 2022 13:39 |  Tags: Inertial Fusion Llnl Positive Energy |  Comments (0) |  Close comments |  Report a problem

And now we have a group!

A critical part of ensuring the success of a project and that it has a useful legacy is to ensure that it is not dependant on a handful of people. To this end this proposal aimed to acquire 2 PDRAs and a PhD student for this duration.

For much of 2022, the Radiation Dense Materials Group was composed of myself and Gurdev, a significant leap from 2021. Much has been accomplished this year as part of the project:

• Reproduction of Reactive Sintered Borides by Ar atmosphere sintering
• Exploration of the RSB phase diagram
• Initiation of collaborative research with Hyperion MT
• Irradiation of cWC and RSB samples at the Dalton Cumbrian facility

So far, one paper has been accepted and another is currently under review. But like an iceberg there is more under the surface. There are two papers on RSB sintering planned and underway; an in-depth analysis of irradiated cWC and RSB samples and plans for brazing and dilatometry of cWC, RSB and joined cWC and RSB on steel.

This is an ambitious body of work and would not be feasible so with this we can now welcome the two newest members of the group from November: Joe Gillham and Suresh Srinivasen who will be working with more of a focus on cWC and its qualification and testing as a fusion material. There will be numerous challenges since a fusion material has to be more than just a good shield; it has to be compatible with other reactor components and be suitably tractable when being put into place for example. This is going to form a significant part of the planned work in 2023 where equipment and working practices within the group consolidate with the formal start of the collaboration with external partners and further use of central facilties. 2023 is going to be a year to remember and will be made feasible with a full group.

Jessica Marshall : 15 Dec 2022 13:17 |  Comments (0) |  Close comments |  Report a problem

SOFT32 – A Reality Check for what fusion power really is

A belated entry considering that SOFT32 took place way back in September (incidently just after we had reproduced decent Gen2 RSB samples)

This is the first in a somewhat belated set of entries but this blog aims to be unlike others and not just get abandoned because things are busy, since that is more or less a given.

The 32nd Symposium on Fusion Technology (SOFT32) in Dubrovnik, Croatia took place from the 18th-23rd of September. This was the first hybrid/live conference since before 2020 since SOFT31 was a virtual conference held online. This conference is not long after JET's record-breaking dueterium-tritium campaign, holding a fusing plasma for 5s and ITER director Dr Bigot's untimely death in May.

Certainly, while there is a lot that can be done online, nothing beats the immersion that happened when you are interacting informally with people as well as being in the talks and the posters. It has given us a greater appreciation for the international effort to get fusion working and on how far ITER and JET has come.

The biggest takeaway was that each fusion reactor is more than just a reactor. For a tokamak reactor, the plasma chamber is only 1 part of the reactor. The reactor also has to comprise of the following facilities:

Cryoplant: Cooling the magnetic coils (LTS/HTS and copper) and cooling the dueterium/tritium for the fuel plant

Fuel plant: Harvesting and handling tritium from the fuel blanket within the reactor prior to use as fuel. Making the fuel pellets and injecting them into the reactor to fuel the plasma.

Gyrotrons: Powerful microwave resonators to pre-heat and energise the plasma prior to initiating fusion.

Neutral beam injector: Linear accelerator to initiate fusing plasma reactions once the plasma is energised from the gyrotrons:

Monitoring and diagnostics: Monitoring the status of the plasma, vacuum, shielding, magnets and blanket.

Heat rejection: Removal of heat both for useful work and 'cool' heat from the magnets and cryoplant.

When the scale of setting up a tokamak is understood it becomes clear that the reason fusion power takes such a long time is that it is very difficult and it has taken a long time just to appreciate what needs to be done alone.

So from this we can see that ITER is a very important project, not just because it was the only international collaborative project initiated between the USSR and America in 1987 but that it has also carved out a path to industrialization for companies and universities working on fusion power. This has also stimulated research and development into related technologies and facilities that are critical to a wide range of applications inside and outside of fusion power.

What is for certain is that we are now in a situation where practical fusion power is no longer falling in the trope of '20 years away and always will be' but there will be plenty of challenges involved.

With respect to the cWC-RSB project it has also shown just how much qualification reactor candidate materials require. Not just the shielding but also materials that form the blankets, divertors, coolant networks, steels and plumbing adjacent to the inner shielding. This goes a long way to why W is still the main candidate shielding material since it has the most testing and data. The recent succesful JET campaign was used in part to qualify the W:Be inner wall, referred to as the ITER-like wall.

So the biggest conclusion we can take from SOFT32 alongside all the networking and knowledge about fusion is what is needed for a practical shielding material and the experimental data needed. W has blazed the trail so that cWC-RSB can follow.

Jessica Marshall : 24 Nov 2022 15:27 |  Tags: Fusion Power Iter Jet Soft32 |  Comments (0) |  Close comments |  Report a problem

12 g/cc mark has been breached!

Why this is important? Significance of this milestone can be well understood from the fact that the most common material used for radiation shielding was lead whose density is 11.29 g/cc. That’s why this number 12 g/cc is important. In addition to that density/porosity has direct effect on radiation atenuation. The goal was to achieve similar densities under lab based environment with different sintering technique. In this case, horizontal furnace with Ar as inert atmosphere. These samples were sintered at 1450 ^oC for 4h under Ar atmosphere. Sintering with different composition and sintering conditions (table 1) were performed, so that the final density can be fine-tuned.

Table 1: Densities of various compositions at specific sintering conditions for RSB55

What next? In the upcoming weeks, we will be using N₂ as the atmosphere for sintering. Hopefully, we will achieve the final density of 12.3 g/cc and with that it will be the time for gen. 3 materials. With present milestone, stay tunned for more details at SOFT22. Figure : RSB55_Large_2Cr sample: Needle like structure of WB

Gurdev Singh : 16 Sep 2022 21:36 |  Tags: Hardmetals Tungsten |  Comments (0) |  Close comments |  Report a problem

News from Plansee 2022

Writing about web page https://www.plansee-seminar.com/

After being delayed by COVID from 2021, the long-awaited Plansee 2022 conference took place in Ruette, Austria from 29th-May -3rd June.

This is a four-yearly conference that is the place to be for anyone who works with hard metals and refractory metals - essentially most metals from group 5,6,7 of the Transition metals - namely W and elements next door.

This Seminar did not disappoint and there was a surprisingly significant number of talks on nuclear materials in terms of how W and similar materials have their place in fusion power.

There have also been numerous opportunities to connect with academic and industrial partners as well as groups such as the European Powder Metals Group (EPMA). Maintaining networks and setting up new once is as crucial to research as doing research itself - no advances get made if they are not communicated,

Alongside this were talks on exciting topics such as additive manufacture and 3-D printing techniques - both of which are significant when considering parts for fusion reactors since complex geometries are required.

The work our group presented gained some interest in that this conference is an ideal platform to demonstrate the cWC-RSB concept and the progress made so far despite setbacks. Certainly, the contacts made at Plansee will show a significant role later this year as the full demonstration of Gen 2 RSBs is realized.

Simply put, 3-D printing of powder metallurgy fabrication can be split into two main categories:

1. Direct powder bed sintering, where a laser draws out a part from a powder bed in a protective atmosphere as for 3-D printing. The aim is ultimately a near net shape part that can then be annealed and finished as for conventional PM.

2. 3-D printing of green PM materials. This comprises of a selection of techniques involving green materials including 3-D printing of organic binder into powder constituents - useful for for complex geometries - prior to a standard debinding cycles or from filaments which can be shaped and bonded into a more robust structure prior to sintering.

Both techniques show promise both for cWC and RSB materials in the later stages of this project when there will be need for demonstrator parts and full-sized boilerplace items by the mid 2020s

While it might be a long time until Plansee 2026 the work starts now to ensure that fusion-realated applications will be front and centre.

Jessica Marshall : 29 Jul 2022 20:54 |  Tags: Hardmetals Nuclear Materials Plansee 2022 Processing Methods Tungsten |  Comments (0) |  Close comments |  Report a problem

Snatching Victory from the Jaws of Defeat part 2

Picture the scene. The critical equipment you have been waiting to have ready is online and practical work is going well. You are on track to have results ready for the conference you are going to at the end of the month.

You now have a new gauge on the furnace so you aren't having to borrow one. It's in Torr not mbar but that isn't a worry since 1 torr = 1.333 mbar.

A new set of samples are loaded into the samples. First pumpdown goes without a hitch. Time to do the argon purge so follow the Standard Operating Procedure (SOP). All valves are checked, valve on vacuum pump is closed and Ar gas cylinder is carefully opened to allow gas to pressurize vacuum chamber to 1 bar Ar. Cylinder valve, flowmeter valve and lower chamber valve is opened in order.

Pressure starts to increase from its baseline near 2 x 10^-1 torr baseline but starts to slacken off near 43.3 torr, despite the positive pressure at the Ar cylinder and flowmeter.

Two operators in the room, one manning the Ar tank adjacent to the flow meter and the other manning the chamber valve. Both can check the valve.

Chamber valve is opened further, pressure increases to 82 torr and levels. Valves still open but pressure just fluctuates - still short of the 760 torr target pressure-

POP!

Top of furnace arcs 10 cm from the neck of the tube and embeds itself in the lab floor. Operators act to shut off cylinder, turn off vacuum pump and shut all the valves.

Now it is time to take photos and file an incident report. Here is the resulting damage:

Here is the top vacuum assembly post incident:

In terms of damage, the top assemblage with the exception of the vacuum gauge is still intact. The worktube has kept its integrity with the exception of a 30 mm spall damage at the top of the tube. This will need to be removed before a seal can be established.

So while the incident report is filed, the next questions are how did it happen?

Identification of the fault showed that the over-pressure from the misreading of the gauge was 1.1 bar, which was not sufficient to trigger the failsafe valve set at 1.2 bar.

The tube was overpressured as a result of a hitherto unknown nonlinearity in the behaviour of Ar at sub-atmosphere. For Pirani-type guages that rely on convection, diatomic and monatomic gasses behave differently at low pressures. The net result is that while N₂ and O₂ behave mostly linearly with respect to measured pressure, monatomic gasses do not:

As can be seen, it is very easy to overpressure a furnace with Ar using a Pirani gauge, which relies on convection. Gauges that rely on absolute pressure via a plate are more reliable for this type of operation.

The actual fault was a result of a sudden loss of friction between the O-ring and worktube when at overpressure, resulting in the loss of upper vacuum assemblage while overpressure. This resulted from distortion of the o-ring at elevated temperature.

From this evidence it is apparent that the current assemblage is not fit for purpose when at high temperature, despite the highest temperature recorded at the gasket. This has lead to the following faults that need to be remedied before the furnace can be recommisioned.

• A thermal shield is required for the top part of the furnace. This will need to sit in the neck of the furnace and sit on the top of the furnace so it can stay in place during a furnace cycle. Can be fabricated from an existing thermal shield with an additional thermal plug at the top. This will significantly cut the thermal load at T_max when radiation is the main contributor.
  
• Larger bore tubing for the vacuum pump exhaust to prevent pressure build up on turning pump on.
• For general use, use N₂ line for purging since this will prevent the risk of overpressure. This will require an additional 6-7 m of PVC tubing to connect the spare N₂ line to the gas inlet.
• A regulator can be added to the Ar cylinder to prevent gas overpressure and to limit the outlet pressure to 1 bar.
• A new pressure gauge that does not rely on convection and will not go nonlinear at sub-atmosphere pressure.
• Repair of worktube to enable fitting of o-rings.

Additional safety features to be added are as follows:

• Bolting the top assemblage onto the top of the furnace cage to prevent loss of top vacuum system and enable triggering of safety valve.
• Use of fans at top of furnace to keep top cool and increase the longevity of the seals.
• Amending SOP to better reflect the operation of the furnace.

Once all these items are addressed the furnace can be recommisioned. Once thing is for certain, no practical work is so important that operator safety can be compromised.

Jessica Marshall : 06 Jun 2022 16:46 |  Tags: Accident Incident Laboratory Safety Standard Operating Procedures Vacuum Systems |  Comments (0) |  Close comments |  Report a problem