Picosecond pulsed 532 nm laser system for roughening and secondary electron yield reduction of inner surfaces of up to 15 m long tubes.

Laser-induced surface structuring is a promising method to suppress electron mulitpacting in the vacuum pipes of particle accelerators. Electrons are scattered inside the rough surface structure, resulting in a low Secondary Electron Yield (SEY) of the material. However, laser processing of internal pipe surfaces with a large aspect ratio is technologically challenging in terms of laser beam guidance and focusing. We present a 532 nm ultrashort-pulse laser setup to process the inner parts of 15 m long beam vacuum tubes of the Large Hadron Collider (LHC). Picosecond pulses at a repetition rate of 200 kHz are guided through an optical fiber toward an inchworm robot traveling inside the beam pipe. The system was installed, characterized, and tested for reliability. First surface treatments achieved the required scan precision. Cu2O-dominated nano-features were observed when processing at high average laser power (5 W) and slow scanning speed (5 mm s-1) in nitrogen flow, and the maximum SEY of copper was decreased from 2.1 to 0.7.

On the Use of Oxidation Induction Time as a Kinetic Parameter for Condition Monitoring and Lifetime Evaluation under Ionizing Radiation Environments.

The durability of polymeric materials is closely linked to their degradation under specific operating conditions when different stressors-general or specific, such as high temperature, sunlight or ionizing radiation, solvents, or mechanical stresses-act simultaneously, causing degradation. In the case of electrical cables, the durability of the electrically insulating materials used in their construction is an important parameter to ensure their operational security. In this work, we studied the degradation state of various types of electrical insulating materials from cables used in particle acceleration systems under European Organization for Nuclear Research (CERN) conditions (e.g., Super Proton Synchrotron, SPS) as a function of time and irradiation dose. A simple kinetic model was proposed based on the exponential decrease in the antioxidant amount in polymeric insulations. The onset oxidation time (OIT) values, used as an indicator of antioxidant concentration, were obtained from isothermal differential scanning calorimetry (DSC) and chemiluminescence (CL) measurements. Fourier transform infrared (FTIR) measurements were used to assess the degradation state and identify polymeric materials. The practical applicability of such a model in diagnosing degradation and in the subsequent evaluation of the remaining service life is of interest, as it can be adapted to a broad range of operating conditions and materials.

Brazing of Mo to Glidcop Dispersion Strengthened Copper for Accelerating Structures.

Alumina dispersion-strengthened copper, Glidcop, is used widely in high-heat-load ultra-high-vacuum components for synchrotron light sources (absorbers), accelerator components (beam intercepting devices), and in nuclear power plants. Glidcop has similar thermal and electrical properties to oxygen free electrical (OFE) copper, but has superior mechanical properties, thus making it a feasible structural material; its yield and ultimate tensile strength are equivalent to those of mild-carbon steel. The purpose of this work has been to develop a brazing technique to join Glidcop to Mo, using a commercial Cu-based alloy. The effects of the excessive diffusion of the braze along the grain boundaries on the interfacial chemistry and joint microstructure, as well as on the mechanical performance of the brazed joints, has been investigated. In order to prevent the diffusion of the braze into the Glidcop alloy, a copper barrier layer has been deposited on Glidcop by means of RF-sputtering.