Myrrha protons accelerated for first time

20 July 2020

Researchers at Belgium's Nuclear Research Centre (SCK-CEN) have for the first time succeeded in accelerating a proton beam through the recently connected radio frequency quadrupole (RFQ). The RFQ is a component of the particle accelerator that will drive the Myrrha sub-critical research reactor.

The Myrrha RFQ (Image: SCK-CEN)

Myrrha is intended to replace Belgium's ageing BR2 research reactor, and will be used in a range of research functions including the demonstration of the concept of transmutation of long-lived radionuclides in nuclear waste, as well as producing radioisotopes for medicine. Myrrha will also be used for conducting fundamental scientific research in areas such as nuclear physics, atomic physics, fundamental interactions, solid-state physics and nuclear medicine.

Myrrha - Multipurpose Hybrid Research Reactor for High-tech Applications - will be a sub-critical assembly relying on accelerated protons producing neutrons in the target to achieve periods of criticality in a low-enriched uranium core. It will be a 57 MWt accelerator-driven system in which a proton accelerator will deliver a 600 MeV proton beam to a liquid lead-bismuth (Pb-Bi) spallation target that is in turn coupled to a Pb-Bi cooled subcritical fast nuclear core.

The Myrrha accelerator team connected the RFQ component with the already existing low-energy beam transmission line (LEBT). The next step consisted of fine-tuning the RFQ in order to accurately match it to the LEBT. Another major preparatory step consisted of upgrading the ion source amplifier. In addition, an RF power amplifier for the RFQ was developed and constructed.

Last year, the first proton beam was generated in the ion source and sent through the LEBT. The accelerator team has now succeeded in sending the first proton beam ever from the ion source via the LEBT through the RFQ with an acceleration of up to 1.5 MeV. Preliminary results confirm the team's confidence that the accelerator's high reliability requirements will be met. The initial tests were performed with short (200 µs at 0.5 Hz) pulses at nominal (115 kW) RF peak power and 4 mA peak beam current.

Dirk Vandeplassche, leader of the linear accelerator team, said: "The RFQ's geometry and built quality have proven themselves with this initial test. Our next step is now to obtain detailed proton beam measurements in order to further optimise the setup. Next, we will complete the installation by adding CH accelerating cavities to the system. That will enable us to increase the beam's energy to 2 MeV and eventually to 5.9 MeV. The beam will then undergo further optimisation to bring its reliability to the required level. Upon achieving that level, the linear accelerator will be transferred from our UCLouvain partner site to the Myrrha site at SCK-CEN in Mol."

The French National Institute of Nuclear and Particle Physics (IN2P3), a division of the National Centre for Scientific Research, co-developed the LEBT and built the low-level RF control unit. In addition, matching the RFQ successfully with the LEBT was the result of beam dynamics simulations jointly accomplished by IN2P3 and SCK-CEN. The RFQ was made in close cooperation with two German partners. The Institute of Applied Physics within Goethe University in Frankfurt-am-Main developed the component, which was built by engineering company NTG. The RFQ's RF power amplifier was developed and built by accelerator and amplifier experts IBA of Belgium, who based their solution on solid state technology.

The project forms part of the European Strategy Forum on Research Infrastructures, and is one of three new research reactors forming the cornerstones of the European Research Area of Experimental Reactors, alongside the Jules Horowitz Reactor at Cadarache in France and the Pallas reactor at Petten in the Netherlands. Construction of the Myrrha reactor is expected to begin in 2026, with full-operation from 2034.

Researched and written by World Nuclear News