First accelerator test of vacuum components with laser-engineered surfaces for electron-cloud mitigation

Abstract

Electron cloud mitigation is an essential requirement for high-intensity proton circular accelerators. Among other solutions, laser engineered surface structures (LESS) present the advantages of having potentially a very low secondary electron yield (SEY) and allowing simple scalability for mass production. Two copper liners with LESS have been manufactured and successfully tested by monitoring the electron cloud current in a dipole magnet in the SPS accelerator at CERN during the 2016 run. In this paper we report on these results as well as the detailed experiments carried out on samples-such as the SEYand topography studies-which led to an optimized treatment in view of the SPS test and future possible use in the HL-LHC.

Cryogenic surface resistance of copper: Investigation of the impact of surface treatments for secondary electron yield reduction

“…In our case, δ can be estimated in the range 0.1-0.5 μm, depending on the frequency and on the RRR of copper. The grooves have a spacing of 24 μm and a depth of approximately 35 μm [20], both much larger than δ, while the fine copper nanoparticles attached to the surface have a size of the order of δ. Experimentally, we observe a large increase of the surface resistance for sample LESS1, where the surface currents are perpendicular to the grooves, and only a minor change for parallel currents, as is the case for sample LESS2. This particular behavior is indeed expected from the literature for grooves having dimensions t ≫ δ where, without going into the details of the modeling [26,14], the longer path traveled by the surface currents when crossing the grooves perpendicularly may intuitively explain the phenomenon.…”

“…The time between the laser treatment and the rf measurement was of the order of several weeks. Previous experiments indicate that copper with LESS maintains a stable low SEY when stored in air up to one year [20].…”

“…The surface was laser structured at the scanning speed of 10 mm=s, leading to approximately 240 pulses per spot being fired onto the target. All these values are equivalent to what was used for earlier accelerator validation experiments [12,20], to which the reader is referred for a detailed discussion of the laser parameter choices. A scanning electron microscope (SEM) image of a typical copper surface with LESS is shown in Fig.…”

Design of the future circular hadron collider beam vacuum chamber

“…The electrons become trapped inside the complex morphology, and the light incidence becomes perpendicular against the roughness peaks. e − cloud mitigation based on LASE has been recently demonstrated in an accelerator for the first time [58], with positive results.…”

Mitigating the electron cloud effect in the SuperKEKB positron ring

“…Hence, highly effective countermeasures against the ECE were required for the SuperKEKB LER [17,[21][22][23][24]. Various ECE countermeasures were prepared on the basis of studies in numerous laboratories, such as CERN [10,11,[25][26][27][28][29][30][31], Cornell University [15,[32][33][34], SLAC [12,[35][36][37], INFN [38,39], BNL [40,41], BINP [42,43], and of course, KEK [13,14,19,33,[44][45][46][47][48][49][50].…”