Stories – 75 years in business

75 years in business – How Comet is exploring for better

Enlightening, or: The world’s most powerful x-ray tube.

By developing the 600 kV x-ray tube, Comet blazed a trail where no one had gone before. The path to success was long and rocky.

“Comet achieves breakthrough in x-ray technology,” proclaims the headline of the Swiss business newspaper “Finanz und Wirtschaft” on October 15, 2011. The groundbreaking innovation reconciles extremes of large and small: Even relatively huge objects can be x-rayed in minute detail thanks to this Comet technology. In the words of the newspaper: “Structures barely thicker than a human hair can be recognized in components that are several square meters in size.” Making this possible is the 600 kilovolt x-ray source that enables three-dimensional imaging in stunning resolution.

This technological breakthrough almost eluded Comet. Let’s take a look back at its origin. In 2006, the company’s X-Ray Tubes department, now the Industrial X-Ray Modules division (IXM), has to acknowledge that its most powerful tubes, those with an operating voltage of 450 kilovolts (kV), no longer meet the needs of numerous customers. They now require stronger tubes that allow even larger products and denser materials to be inspected in little time – for example, to screen steel shipping containers at customs, or for non-destructive inspection of high-absorbing turbine blades in aircraft engines. The mission for the R&D department is clear: A new x-ray tube with 600 kilovolts of power is needed!

The task is formidable: How can 600 kV – that is 600,000 volts, or 40 times the voltage of a suburban railroad overhead line – be reliably insulated in a 35-centimeter-long metal-ceramic tube for several thousand hours of operation? So far, no one has managed to do this. The developers at the X-Ray Tubes department get to work.

A ten-centimeter-thick steel layer is irradiated for four minutes, first with a 450 kV x-ray tube (left), then with a 600 kV tube (right). The 600 kV model provides a much more detailed image (Bavendiek, Heike, Kosanetzky et al: “Best Energy Selection for Different Applications with DDAs – from 20 keV to 600 keV”, 2011).
About Adrian Riedo

Mechanical engineer Adrian Riedo has worked at Comet for over 25 years, first as R&D Project Manager, then as Head of R&D for X-Ray Tubes, later as a Technology Specialist, and, since 2020, as Director of the Technology Group at IXM. He embodies the spirit of the many long-time employees at Comet and is the president of the 10-year seniority club. His latest landmark achievement: the invention of the MesoFocus tube technology.

Try tungsten

Soon, however, it also becomes clear to the project team in Flamatt why no competitor has yet ventured to develop a 600 kV x-ray tube. The first challenge: The x-ray source needs a generator that is able to produce an operating voltage of this level in the first place. Such a generator does not exist on the market, which means Comet’s development work is doubled at a stroke.

Another difficulty: At 600 kV of operating voltage, the radiation cannot be shielded by a lead covering as in conventional x-ray tubes, because it would be much too thick and heavy. Instead, the developers use a tungsten alloy in the anode. The chemical element, which is highly absorbent of x-rays, is designed to block the radiation where it is generated. However, this approach too comes with challenges. Adrian Riedo, the head of R&D and project manager at the time, remembers the dedicated development team working through the weekends to find solutions during this “hot phase”.

The complete system: generator, controller, cooler, and 600 kV tube

The hard work and perseverance pay off. In the fall of 2011, Comet can declare victory: The 600 kV x-ray tube is ready for the market – and immediately finds buyers worldwide. A Chinese customer uses it to test ceramic tiles for aerospace applications, and a little later a customer from the USA orders ten modules at once – tube, high-voltage generator, controller and cooler – for several hundred thousand Swiss francs.

About Christoph Walther

Christoph Walther is a physicist and has been with Comet for more than 11 years. As one of his early responsibilities at Comet, he was assigned to lead the task force to optimize the 600 kV tube. In 2014, Walther, who wrote his doctoral thesis on terahertz quantum cascade lasers at ETH Zurich, became Director of R&D, X-Ray Tubes.

A task force is needed

Now that demand is gaining momentum, new challenges suddenly emerge: Product defects and “teething problems” arising in use must be corrected in order to satisfy Comet’s own standards and those of its customers. It’s nothing unusual in innovations, but reason enough for immediate action.

In 2013, a twelve-member task force led by the physicist Christoph Walther tackles the technological problems. Soon the team discovers one of the causes of the issues: As a result of the ceramic insulation, the electrical charges inside the tube cannot dissipate, which causes disruptive discharges and flashovers. Together with suppliers from the USA and Comet manufacturing engineers, Walther and his team develop a novel, ultra-thin coating of chromium oxide that allows the charge to dissipate. “The new coating is as conductive as necessary and as insulating as possible,” Walther says. “The difficulty was finding the right balance.” In 2017, the chromium oxide coating will become standard on all Comet x-ray tubes from 320 kV on up. From then on, production scrap is significantly reduced.

Richer by important experience

Since its market launch in 2011, Comet has sold over one hundred of the 600 kV modules. Although this does not make the world’s most powerful x-ray tube a bestseller, its luminosity is nevertheless of considerable significance for Comet’s history.

First of all, the 600 kV x-ray tube has underscored Comet’s claim to global technology leadership. Second, the project drove the developers to overcome ever new challenges for more than ten years, until the ultimate success. During the development process, Comet discovered technologies whose benefits go far beyond the original product, such as the chromium oxide coating. And finally, it established new standards and processes, like the creation of a testing team that puts new products through their paces. All of which goes to show that the 600 kV x-ray tube is more than just an impressive piece of technology – its genesis gave Comet valuable insights to take forward.