Versatile by design

CHARM (CERN High energy AcceleRator Mixed field) is a new and unique testing facility that will complete CERN's radiation testing installations. Located in the East Area, CHARM will provide teams with a venue to test their equipment in radiation environments similar to those found in the accelerator chain.


Team at work in the irradiation zone of the CHARM facility.

First envisaged in 2007, the CHARM facility fulfils a growing demand for a large-scale tailor-made radiation testing facility. Unlike commercial facilities, CHARM features a wide spectrum of radiation types and energies (called mixed-field radiation environments), the space to test large equipment and even the possibility to adjust the environment using mobile shielding. "CHARM is versatile by design, allowing us to recreate any of the radiation environments found in the accelerator chain," says Markus Brugger, head of the R2E (Radiation to Electronics) project team that developed the CHARM facility. "We create our radiation in the same way it occurs in the accelerator complex: by colliding a beam against a fixed target (copper, aluminium or an aluminium sieve, depending on the required intensity). CHARM also has the space to test equipment as large as two cubic-metres and as heavy as one tonne, along with all the precise monitoring equipment that goes with it."

CHARM is located in the East Area just downstream of the PH Department's IRRAD facility, where high-flux radiation testing on smaller experimental equipment takes place. CHARM's installation unites CERN's experimental and accelerator equipment testing in a single area. "We will use the same beam as the upstream IRRAD facility, as the vast majority of the beam goes straight through their samples," says Brugger. "CHARM will exploit these beams, which would otherwise have been dumped."

"LS1 was the perfect opportunity to set up the CHARM facility," says Julien Mekki, who leads the CHARM facility team. "On top of their already heavy LS1 workload, CERN teams were able to remove the DIRAC experiment and still had time to construct a whole new facility." Although CHARM reuses an existing site, its construction has been a major undertaking, with over 2,000 tonnes of iron and 4,000 tonnes of concrete installed as shielding and a new control room that will also act as a secondary dry run testing facility. This is part of the East Area renovation, headed by project leader Lau Gatignon and technical activities coordinator Michael Lazzaroni. Together they have tackled numerous technical challenges and coordinated all renovation activities to ensure their completion.

View of CHARM's beam-line (with shielding) and the control/technical rooms (right).

While the challenging construction is being finalised, the CHARM team has been training in a dedicated and newly created mock-up of the facility, where they are successfully commissioning all the equipment that will be installed in CHARM.

In order to minimise radiation exposure, equipment being tested must be installed in CHARM's irradiated area without human intervention. It is the engineer's version of a locked-room mystery: how does a delicate one-tonne piece of equipment, with its complex cabling, make its way into an irradiated area without any human help? "With the help of many CERN groups and external companies, we were able to develop a set-up that allows us to carry out this feat," says Mekki. "Building on the experience of the CERN handling engineering group, we will use a custom-made, semi-remote lifting and transport vehicle to drive the heavy equipment around tight corridors and into the irradiated area. Cables will be attached to a rail on the ceiling that follows the same track. Once in the irradiated area, the test team will be able to use these cables through a patch-panel connecting the equipment to the user’s control and acquisition system."

CHARM will begin testing with beams this September. "This is thanks to the huge effort of many CERN service and equipment groups, who during the critical LS1 period found a way to support this vital project efficiently and often brought unique technical solutions – our many thanks to all of them!" says Brugger. "Now our first high-priority test subjects will be the new main LHC power converter control units, which will be installed next year. After that, we'll be tackling the equipment on our growing waiting list."

A very accurate simulator

Different areas of the accelerator complex bring with them different types of radiation and different types of damage. In the early stages of the LHC, the primary concern was single events: failures caused by a single interaction that, in certain cases, can lead to the destruction of the electronic device. This damage varies depending on its location in the LHC tunnel, where there are two primary types of radiation environments: one in the tunnel itself, with particles of very high energies, and another in adjacent shielded areas, where the energy spectrum is dominated by neutrons. With its movable shielding, CHARM can simulate all these environments very accurately.

However, in the LHC injector chain, the priority shifts from single-event failures to cumulative damage affecting the lifetime of the equipment. Cryogenic machines like the LHC have, on average, lower radiation levels than the traditional accelerators in the injector chain. The overall higher levels in the injector chain lead to more severe long-term damage constraints for the exposed equipment. CHARM's radiation spectrum can also be adjusted to reflect this more intense environment.


by Katarina Anthony