CERN Large Hadron Collider

Robotics for Laser Engineered Surface Structures

LESS

The Large Hadron Collider (LHC) is the world’s largest and most powerful particle accelerator. It first started up on 10 September 2008, and remains the latest addition to CERN’s accelerator complex. The LHC consists of a 27-kilometre ring of superconducting magnets with a number of accelerating structures to boost the energy of the particles along the way.

Jointly developed by researchers from the University of Dundee and the Science and Technology Facilities Council (STFC), the technology – which is known as LESS (Laser Engineered Surface Structures) –increases the range of experiments possible on the LHC by helping to clear the so-called “electron cloud”: a cloud of negative particles which can degrade the performance of the primary proton beams that circulate in the accelerator.

This in-situ surface treatment must be carried out in relatively long (up to 15 meters) and narrow pipes, which means that the laser light must be delivered over long distances in a very limited space. For the in-situ treatment of the LHC magnets, the access to the beam screens is limited to a 15-cm long entry slot created by dismantling part of removable interconnection unit called plug-in module. Additionally, the chosen pattern of grooves requires high precision in treatment head movement (10 micro meter). All these requirements led to a sophisticated hardware and software development, namely the optical fibre with the beam delivery system, the robot that carries the fibre and provides the treatment inside the beam screen and the control system that manages the whole process.

Cross-section of LESS treated surface

Top view of LESS treated surface.

Project

The project goal for Inspection Robotics is to learn from and with our partners and to further develop our robotic capabilities.

CERN

Project goals

The LESS treatment robot is a novel solution designed and manufactured by GE Inspection Robotics for the in-situ treatment of the LHC beam screens. The dimensions of the robot are limited longitudinally by the interconnection entry slot and by the beam screen crosssection shape. The robot moves along the beam screen using the inchworm movement principle, by means of a pneumatically-driven clamping system. The robot movement along the beam screen is disentangled from the treatment head movement that is carried out by an electrical motor coupled with a precision driving screw.
During LESS structuring the robot remains rigidly clamped to the beam screen and only the rotating treatment head moves longitudinally engraving the spiral pattern in the beam screen.

Tests have shown that it is possible to reformulate the surface of the metals in the LHC vacuum chambers to a design that under a microscope resembles the type of sound padding seen in music studios. The surface can trap electrons, keeping the chambers clear of the cloud. The University of Dundee said that initial tests at the Super Proton Synchrotron, the LHC injector, have shown the LESS method is very effective at controlling the electron yield, as electron clouds have been fully eradicated.

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