This week marks the launch of PRIMA, a project to fully develop and test the neutral beam facilities to be used in ITER. PRIMA, which stands for Padova Research on ITER Megavolt Accelerators, will be built at the Consorzio RFX in northern Italy.

“The aim is to have neutral beam injectors at ITER that work on Day 1,” says Deputy Project Leader of the Mechanical Division, Dr Diego Marcuzzi. To this end two systems based on ITER’s design are being built in advance and put through their paces, named SPIDER and MITICA.

MITICA – Megavolt ITER Injector and Concept Advancement - will be a copy of one of ITER’s three planned 16.7 megawatt heating neutral beam injectors. The name MITICA, meaning mythical in Italian, perhaps was chosen because these injectors will have a capacity far in advance of anything in existence today. “Because ITER has a very large plasma, we need a lot of energy to get the beams into the core,” says Dr Marcuzzi. “Although a megavolt of acceleration voltage has been done before, it was only for a few seconds. ITER will have a one hour shot length, and the beam size is larger too.”

Neutral beams are already in use on many facilities, for example JET, but it is not as simple as building a bigger version of the existing injectors – the higher voltage requires a different method. JET’s acceleration is done with positive ions, which are then neutralised just before they enter the vessel so they can penetrate the magnetic field. However positive ions present a problem because at the higher energies planned for MITICA it is almost impossible to re-attach the electrons and neutralise the ions. Instead MITICA will accelerate negative ions, which are harder to create and have a very short lifetime, but have a much higher neutralisation efficiency (around 60 percent at 1 megavolt).

The design of MITICA is more than 50 percent complete and the facility is planned to be up and running by the fourth quarter of 2017. In the meantime the lower energy accelerator and ion source SPIDER – Source for Production of Ions of Deuterium Extracted from RF plasma – will begin to produce results. It is already fully designed and has an expected completion time in the fourth quarter of 2014. Although its main role is as testbed for the ion source for MITICA, SPIDER’s 100 kilovolt acceleration is similar to the lower energy diagnostic neutral beams planned for ITER. The diagnostic injectors are not being developed by PRIMA but by the Indian ITER partners, who are also in charge of the procurement of two SPIDER components and so the obvious synergies are being exploited by both development teams. Some of the current highest energy beams are in plasma experiments in Japan and so there is also Japanese involvement in the project – collaboration in the beam source design and procurement of a significant part of the MITICA power supply system.

“Because there are several parties with different ways of seeing things, it might take a little more time to discuss and finalise all choices,” says Diego Marcuzzi, “but it’s worthwhile because we are utilising all the existing skills on earth, which gives us the best chance of getting it working!”

Source: EFDA