Enough of the tourist blog this is about Fusion! The ITER site is another 30 minutes drive from Aix through some beautiful mountainous french countryside. Once we arrived, after a wait we were met by our guide who took us to the main visitor centre. As experts in Fusion we immediately grilled our guide about breeder blankets and diverter configurations but she held her ground and made Joe look silly multiple times.
We then had a drive around the site to where the pulsed power is supplied from the supergrid. This is a particular area of interest for Joe and Chad who both work on power supplies at JET. The main difference with ITER is that JET uses Flywheels as it cannot legally take all the power it needs straight from the grid during a pulse, ITER however takes all it's power straight from the grid. Joe and Chad were very impressed with this, particularly by the apparent robustness of the European grid to deliver such high power capability to a relatively remote site. Doug and Ian didn't know what was happening at this point.
Next we were taken to the most developed part of ITER; the Poloidal Field Coil Winding Facility. Most of the buildings at ITER are not yet built, or have to remain so clean they do not allow visitors, or are actually dangerous. Meaning the PF winding building is the only operational building which is allowed for visitors, luckily it's very big.
Poloidal describes a magnetic field confined to a 'radial or meridian plane', although it's easier to remember it just as the shape of a polo. There are two main types of poloidal field coils on JET and ITER There is the central solonoid which is used mainly for initial ohmic heating of the plasma. The other coils are much larger and wrap around the exterior of the Tokamak, they are used more for the control and shaping of the plasma. What we saw was the winding of these large exterior coils, an incredibly long and slow process which requires very high precision. The reason for this precision is that these coils will very likely never be removed from ITER so any defects would affect the machine for it's whole lifetime which is on the order of decades. So clearly it's worth getting it right, let's go through the process of winding a perfect PF coil.Stage 1: Conductor checks; cleaning, bending and sandblasting the outside of the conductor. This is the first stage where the prefabricated conductor is rolled into a poloidal shape while being treated. The sandblasting is to create a slight texture on the exterior of the conductor which helps the insulation stick.
Stage 2: Insulation and winding of the Double Pancake (DP). Each PF coil is made up of a number of 'Pancakes' which are like single layers, each tested to their own high standards then combined to form a stack.
Stage 4: Forming a Winding Pack. This stage is simply stacking multiple DP's and impregnating the stack with resin under vacuum as before to ensure rigidity, other components are added at this stage such as clamps and helium pipes.
Stage 5: Cold testing. The stack is then cooled to 80 Kelvin to simulate some of the thermal stresses that it will undergo on ITER. Once a stack passes this test then it is ready.
The most impressive part of the winding facility for me were the cranes. The PF coils weigh up to 400 tonnes, part of the reason they are being manufactured on site as opposed to being shipped in like many of the other ITER components. The cranes are designed to lift this huge weight in a perfectly symmetrical way to avoid any stress or damage.
Visiting ITER was a great experience for all those involved, we learn a lot and got to see the reality of the biggest engineering challenge in the world. Until it is complete ITER will be visually similar to a regular building site on a massive scale. We can't wait to go back when it's finished and see how it's changed and what it can achieve for fusion research, also the beaches are nice.
