Imagine a beam of neutral atoms accelerated at high speed and fired into the plasma; the atoms will collide with the plasma particles and transfer some of their energy, thus heating the plasma. To develop and test the source of these high-speed atoms and the injection system for ITER, two experiments are being constructed within the Neutral Beam Test Facility, a dedicated facility in Padova, Italy.

Prima construction site

Walking the Prima construction site: From left: Vanni Toigo, Maria Teresa Orlando, Adriano Luchetta, Roberto Pasqualotto, Pierluigi Zaccaria (Picture: Consorzio RFX)

Unique, in being the only main ITER plant not based in Cadarache, the Neutral Beam Test Facility (NBTF) is a big enterprise. The scope of the project is challenging: “providing a true reliable neutral beam injector for ITER, able to achieve full performance, giving confidence in terms of fatigue life predictions and identification of potential failures to avoid lost operation time in ITER” says Prof. Piergiorgio Sonato, from Consorzio RFX, while looking at the four Deputy Project Leaders to gain their agreement.
We are at a large area of the National Research Council, where the plant is being constructed. It will host two independent experiments: SPIDER, the negative ion source prototype, and MITICA, the neutral beam injector system. Construction activity is buzzing around us. About 400 foundation pillars and the 1000 m3 underground cooling water basins have already been laid out. The upwards construction is imminent. In a few months it will be ready to begin installing SPIDER. Technicians from the Cooperativa Ravennate company are working feverishly to make the deadline: to have the buildings ready to allow the start of SPIDER operation in early 2015 and that of MITICA around three years later.


The challenging nature of the enterprise lies in removing the large amounts of power that are dissipated in MITICA during the beam generation process. Of the approximately 60 megawatts (MW) supplied to the system, 16.5 MW will reach the plasma. The remaining 45 MW have to be removed. Peak power densities can reach 20 MW/m2, which is equivalent to 20.000 times the power of the sun on a sunny day. This calls for adequate surface cooling in the accelerator grids to avoid particle trajectory deviations. “Removal of heat loads will be guaranteed by keeping temperatures as well as mechanical tolerances and deformations tightly controlled, to ensure the required power, uniformity and aiming of the beam,” explains Dr. Pierluigi Zaccaria, Project Leader for the mechanical components. The MITICA injector components alone are cooled by two huge cryopumps – 2.5 meters high and eight meters long – kept cooled at four degrees Kelvin.

Power supply

“Just think about the high voltages involved in operating for a long time and of the systems connecting the supply to the injector. This has never been built before,” says Dr. Vanni Toigo, Project Leader for Power Supplies. He is responsible for construction and operation of the Power Supply and Voltage Distribution System, and collaborates with the Japanese ITER Domestic Agency which procures part of the high voltage power supplies. Generating one MV direct current (DC) voltage and transmitting it to MITICA requires technologies, especially for electrical insulation, which in part do not exist today.

Diagnostic and control

Optimising the injectors for ITER calls for extensive diagnostic systems and for innovative real-time system control. “Fast real-time control is unique among neutral beam injectors,” says Dr. Adriano Luchetta, Project Leader for the Control and Data Acquisition Systems, “it will allow us to iteratively optimise the beam operation without having to modify the power supply control systems.”
“A comprehensive set of measurements will be provided, using different techniques – some already exploited in other test facilities, others brand new”, adds Dr. Roberto Pasqualotto, Project Leader for the diagnostics systems. “The data is necessary to determine and verify the operating requirements. ITER provides only a limited number of diagnostic systems and there will be no time to optimise the injector performance. “
Talking about the innovative capabilities that are being brought into play in this endeavor, where fusion science and engineering integrate, the PRIMA team radiates confidence. After all, it can draw on the experience with the realisation of previous projects and experiments carried out by Consorzio RFX. Moreover, there is high confidence in the international collaboration for the PRIMA project.

Dr Maria Teresa Orlando, Consorzio RFX

Neutral Beam Heating systems heat a fusion plasma by injecting powerful beams of neutral particles. Traditionally, they accelerate positive ions and neutralise them before injecting them into the plasma. The ITER Neutral Beam system will use negative ion beams, because the efficiency of neutralising positive ions declines heavily with increasing beam power. Its beams have unprecedented energies of one megaelectronvolt (MeV) and they are on for a much longer time (up to one hour) than today’s systems (several tens of seconds). Each of the currently planned two injectors transmits 16,5 MW of power.

PRIMA – Padua Research on ITER Megavolt Accelerator
The objective of the PRIMA project is to develop, construct and test the full-size prototype of the ITER neutral beam heating system, NBTF. It comprises two independent test-stands: The negative ion source SPIDER produces hydrogen and deuterium ions and accelerates them with up to 100 kV. MITICA, a first full-size and full performance ITER injector, accelerates these ions up to 1 MeV.

The NBTF collaboration is a truly international collaboration, embedded in the agreements signed by the ITER Organization, F4E and RFX at the end of 2011. Coordinated by F4E, Europe is responsible for procuring the large majority of the NBTF components and it contributes financially to the NBTF design and operation. Other main components are procured by Japan and some contributions come from India. Consorzio RFX hosts the NBTF, provides the buildings, the necessary site adaptations and the team to design and operate the facility.