Sub-THz Waveguide Spectroscopy of Coating Materials for Particle Accelerators

Abstract

The electromagnetic characterisation of different materials for the inner wall coating of beam pipes is a long-standing problem in accelerator physics, regardless the purpose they are used for, since their presence may affect in an unpredictable way the beam coupling impedance and therefore the machine performance. Moreover, in particle accelerators and storage rings of new generation very short bunches might be required, extending far in frequency the exploration of the beam spectrum and rendering therefore more and more important to assess the coating material response up to hundreds of GHz. This paper describes a time domain method based on THz waveguide spectroscopy to infer the coating properties at very high frequencies. The technique has been tested on Non Evaporable Getter thick films deposited by DC magnetron sputtering on copper plates.

Characterisation of copper and stainless steel surfaces treated with laser ablation surface engineering

“…The depth of microstructure (grooves and superimposed nanoparticles) under pulse durations between 50 ps to tens of nanosecond can be between several microns to hundreds of microns [22,23,24]. The presence of such features on the inner surface of the vacuum vessel will reduce the SEY to the desirable threshold but at the same time will increase the RF surface resistance which leads to undesirable effects such as [25,26,27,28]:…”

Terahertz as a Frontier Area for Science and Technology

“…As, in storage rings and linear accelerators of new generation, very short bunches might be required, extending the exploration of the beam spectrum far in frequency is required to assess the coating material response up to hundreds of GHz. The paper of Passarelli et al [22] describes a time domain method based on the waveguide spectroscopy to infer the coating properties at very high frequencies. The approach is extremely useful for the evaluation of the real part of the surface impedance, currently used for modeling the resistive wall component of the beam impedance in accelerators.…”

Design of 94GHz Dual-Polarization Antenna Fed by Diagonal Horn for Cloud Radars

“…A three-dimensional (3D) printed cassegrain antenna for THz near-field focusing is used in back scattered side-channel detection, and the parameters and performance of 3D printed cassegrain antenna were analyzed in [7]. To achieve excellent gain, bandwidth, polarization, and radiation patterns, diagonal horn antennas are widely used in MMW and THz applications [8]- [10]. Two symmetrical pyramidal horn antennas are used to enhance electromagnetic signal collection and radiation in the sub-THz measurement system [8].…”

“…To achieve excellent gain, bandwidth, polarization, and radiation patterns, diagonal horn antennas are widely used in MMW and THz applications [8]- [10]. Two symmetrical pyramidal horn antennas are used to enhance electromagnetic signal collection and radiation in the sub-THz measurement system [8]. A modification of the traditional diagonal horn design using a spline-curve "S" shape modulation in the depth of the "V" groove was introduced in [9].…”