Electromagnetic characterization of nonevaporable getter properties between 220–330 and 500–750 GHz for the Compact Linear Collider damping rings

Abstract

Due to its effective pumping ability, nonevaporable getter (NEG) coating is considered for the vacuum chambers of the Compact Linear Collider (CLIC) electron damping rings (EDR). The aim is to suppress fast beam ion instabilities. The electromagnetic (EM) characterization of the NEG properties up to ultrahigh frequencies is required for the correct impedance modeling of the damping ring (DR) components. The properties are determined using rectangular waveguides which are coated with NEG. The method is based on a combination of complex transmission coefficient S 21 measurements with a vector network analyzer (VNA) and 3D simulations using CST Microwave Studio® (CST MWS). The frequency ranges discussed in this paper are 220-330 and 500-750 GHz.

Sub-THz Waveguide Spectroscopy of Coating Materials for Particle Accelerators

“…Results agree fairly well both with previous data obtained on different NEG samples using the circular waveguide [16] and DC (direct current) conductivity values extracted using the frequency domain approach [10]. Nevertheless, differently to these latter measurements, a TD method allows to evaluate the electromagnetic properties of coatings in a reliable and simple way exploiting tailored (and reusable) waveguides.…”

“…During the process, in order to prevent thermal induced deformations the plate is held in an aluminum frame, that in turn is placed on a rotating axis to ensure a homogeneous deposition on both sides of the slab (see Figure 1b). Local composition and thickness of the coating have been checked using X-ray fluorescence (XRF) measurements along the median line of the slab (the waveguide longitudinal axis), showing that samples keep the target composition within 10% and a uniform profile ±2% with an average surface roughness of 0.2 µm [10,17]. For the spectroscopy measurements, we use a gold plated brass device (shown in Figure 2) consisting in a parallelepiped of 16 × 12 × 140 mm 3 machined in two identical pieces.…”

“…Recently, the impedance of NEG films has been measured in frequency domain in the sub-THz range, directly depositing 1-2 µm of the material on the lateral walls of a calibrated waveguide [10,11]. This method can be easily extended to the characterisation of other coating in thin film form, however has its own drawbacks, specifically local in-homogeneity with blistering and peel-off, constraints in sample dimensions, and impossibility to re-use the test system (the waveguide) for further measurements.…”

Novel measurement technique for the electromagnetic characterization of coating materials in the sub-THz frequency range

“…Frequency domain simulations have been performed by imposing the first mode propagation and comparing the scattering parameter, S 21 , to evaluate the attenuation. We used an estimated NEG conductivity value of σ coat ¼ 3.5 × 10 5 S=m, as reported in [22]. The agreement between the results of Eq.…”

“…Recently, frequency characterization of different NEG samples deposited on the lateral walls of a calibrated millimeter waveguide has been carried out by using two port VNA measurements [22,23]. However, this approach has some relevant drawbacks: (1) the nonhomogeneous deposition with unpredictable thickness and relevant peeloff and blistering; (2) the impossibility to reuse the system for further measurements on different coating materials;…”