CERN Accelerating science

Power converters specially designed for CERN can now be used by the wider accelerator community

The SOLEIL synchrotron facilities in Paris, France. (Image: SOLEIL)

The Electrical Power Converters (EPC) Group at CERN has developed new software layers to allow the broader particle accelerator community to use the CERN-specific power converters controls.

Power converters are a fundamental part of CERN’s accelerator complex, allowing it to function properly. In particle accelerators, the particle beams are guided by powerful magnets and are accelerated in metallic chambers called radiofrequency cavities. More than five thousand power converters electrically power both these structures. Many different types are needed, ranging in power from a few watts to more than one hundred megawatts. Some produce a steady current or voltage, while others must ramp, or pulse synchronously with all the other equipment in the accelerator. Therefore, the effective operation of each power converter depends on high-performance digital controls that regulate the current in the circuit.

Since the creation of the LHC, CERN power converters use specialised control computers called Function Generator/Controllers (FGCs), integrated into the power converters. An associated FGC software framework was developed to integrate the FGC hardware into CERN’s accelerator controls environment, which is unique to CERN. With the new software stack, the FGC hardware can now be integrated in the TANGO and EPICS control environments, which are the most common control frameworks used at other accelerator infrastructures. This update will open the door for FGCs and CERN-designed power converters to be deployed to other accelerator facilities, such as synchrotrons.

The project to integrate FGCs into the EPICS and TANGO frameworks was conceived in 2014 and resulted in the successful transfer of FGC converter controls to a European manufacturer, who supplied the new power converter to the main cyclotron magnet of the TRIUMF laboratory in 2018. In 2019, CERN provided power converter technology and the associated converter controls to the European Synchrotron Radiation Facility (ESRF). TRIUMF uses EPICS while ESRF uses TANGO.

Thanks to its potential for future technology transfer, the FGC update was one of the five projects selected to receive funding from the KT Fund in 2019. The objective is to continue the FGC framework integration with more commonly used control environments in the context of a collaboration agreement between CERN and SOLEIL.

During the first phase of this collaboration, CERN provided training and lent a standalone FGC and a small power converter controlled by an FGC to SOLEIL. “The SOLEIL upgrade builds on previous experience, gradually moving to a unified controls’ environment for which the FGC framework is particularly suitable,” explains Nick Ziogas, Knowledge Transfer Officer at CERN. In 2020, during phase 2 of the collaboration, eleven controllers of existing commercial power converters installed at the SOLEIL synchrotron (Paris, France) will be replaced by FGCs. SOLEIL intends to procure 1,700 power converters with digital controllers by 2025 for its major upgrade to higher brilliance and these could hopefully be CERN designs using FGC for controls.

At a time when the broader high-energy physics community debates the next-generation of accelerator machines, many laboratories have major upgrades in store for the next decades, aiming to achieve a performance that could lead to more complex science. This means higher luminosity in colliders and higher brilliance in light sources and, therefore, an upgrade of the accelerator infrastructure.

“The FGC framework comes with a powerful software stack that allows for monitoring and diagnosis of faults and the automatic configuration of the controllers following a change of hardware components,” explains Quentin King, head of the Converter Controls Software Section in the EPC Group. “Powerful management tools are vital when large numbers of converter controllers are used. This is a major requirement from all light sources: to have good insight and understanding of what is happening in their power converters.”

The integration of CERN’s FGC framework with the most common accelerator control frameworks, including TANGO, results in an important knowledge transfer opportunity, since it allows the power converters specifically developed for CERN to be used by both partner laboratories and industry, in fields from particle physics to medical and biomedical research.

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The CERN Knowledge Transfer Fund is a tool to bridge the gap between research and industry. It selects innovative projects based on a CERN technology with high potential for positive societal impact beyond high-energy physics. The fund is supported in part through revenues from commercial agreements concluded by CERN's Knowledge Transfer Group.

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How many points to direct the particle beam to collision?

Players of all ages lined up to play the Accelerator Game during the CERN Open Days. (Image: CERN)

How many points does one get for directing the particle beam to the collision? Unfortunately, one gets no points for the big collisions in real accelerator like the Large Hadron Collider, only enormous amounts of data. But in the Accelerator Game things work a bit differently. Developed specifically for the CERN Open Days by the Electrical Power Converters Group at CERN, this interactive activity aimed to explain the role of power converters in particle accelerators in a fun and engaging way for visitors of all ages.

In particle accelerators like the Large Hadron Collider, particles are kept in a curved trajectory by magnets called dipoles, focused using magnets called quadrupoles, and accelerated in metallic chambers called radiofrequency (RF) cavities. All of these structures are electrically powered by hundreds of CERN-specific power converters. In the Accelerator Game, visitors needed to apply the right electrical pulse to make all these structures function properly. The game consisted of two distinctive parts: an arcade-like video game and a scaled-down model of an accelerator. The goal was to accelerate and guide a beam of particles, avoiding collisions with the accelerator pipe and obstacles – collimators. In real-life, collimators allow the deposition of beam losses in specific locations, minimising the radiation impact on the collider and detectors. “We took a few liberties to strike the perfect balance between realism and amusement,” explained Fulvio Boattini, the mastermind behind the idea for this activity. “And we would say, successfully so!”

If the beam collided with these obstacles, some particles in the beam would be lost. The player would interact with the game with two controller sticks for the two types of power converters: one powering dipoles and moving the beam on the horizontal and vertical plane, and the second powering quadrupoles, allowing the player to focus and defocus the beam and avoid the more difficult obstacles. As time progressed, the beam gained speed, accelerating the particles, and challenging the skills of the player.

If any particles remained after the one minute the game lasted, the player was rewarded with a stunning animation of two colliding beams and a final score. A scoreboard with the top ten players of the video-game was added to encourage some healthy competition among visitors and volunteers. “Each time the players managed to guide the beam through an obstacle, they got points equal to the product of velocity and number of particles they still had,” explains Dariusz.

The creation of this game was a joint effort by different sections of the EPC Group at CERN and the surprising contribution of two students from CERN’s High-School Students Internship Programme (HSSIP). The video-game itself was developed using the UNREAL engine by Christoph Merscher, with the collaboration of Dariusz Zielinski, who also designed the visually stunning animations and images, and Krzysztof Lebioda. “We started developing the game having almost no knowledge of the Unreal Engine. Every time we came up with a new challenge, we had to find out a solution, learning along the way. First, we were using block-based graphical programming, but soon we realized we had to write code in C++ to achieve the behaviour we wanted,” says Christoph.

To make the experience more tangible, Arnaud Bessonnat constructed a 1.2 meter scaled-down model of a circular collider, using 3D printing techniques. It included dipoles, quadrupoles, radiofrequency cavities, a detecting experiment and, of course, power converters. A LED strip around the accelerator simulated the two counter-rotating beams and the magnetic field. As particles gained speed, the LED beam rotated ever faster and the magnetic field glowed stronger. João Afonso wrote the code to switch each individual LED on and off in a predefined pattern, using an Arduino microcontroller. This program received instructions from the video-game through a communication protocol specifically designed for this purpose, and synchronised the LED beam with the progress of the player through the game. João based the program on the original work of two students from CERN’s High-School Students Internship Programme (HSSIP).

Accelerator Game display, with the model scaled-down accelerator and the interactive video-game developed by the Electrical Power Converters Group at CERN. (Image: CERN)

Over the CERN Open Days weekend, the Accelerator Game team estimate conservatively that about 600 visitors played the game. That is one player every two minutes, not counting all the visitors who stayed to watch and cheer the players as they tried to prove their worth, some coming back for multiple attempts at beating the highest score. “The reaction from the visitors is a clear sign that the hours we dedicated to this project paid off!” says Raul Murillo, the project supervisor for the game development, and the team agrees.

By all appraisals a successful exhibition, Raul attributes a great part of the activity’s success to the commitment and passion of the team. At a time when major developments are taking place for LINAC4 and ELENA in the context of LS2, Christoph, Dariusz, Arnaud, João and Krzysztof put a lot of effort in bringing the game to near perfection. “They were working weekends and after-hours to bring this game to a whole new level,” he says.

The CERN Open Days organisers have shown an interest in the Accelerator Game and would like to make it available to use in future events. For this, further development would be required, as the interactive game was designed to have the support of an Open Days volunteer, that is, the team would have to make the game more robust and low-maintenance, as well as provide instructing documentation. Hopefully one day the Accelerator Game might become a permanent activity for CERN visitors and the accelerator community.

References

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