Quality Factor Enhancement of 650 MHz Superconducting Radio-Frequency Cavity for CEPC

Medium-temperature (mid-T) furnace baking was conducted at 650 MHz superconducting radio-frequency (SRF) cavity for circular electron positron collider (CEPC), which enhanced the cavity unloaded quality factor (Q0) significantly. In the vertical test (2.0 K), Q0 of 650 MHz cavity reached 6.4 × 1010 at 30 MV/m, which is remarkably high at this unexplored frequency. Additionally, the cavity quenched at 31.2 MV/m finally. There was no anti-Q-slope behavior after mid-T furnace baking, which is characteristic of 1.3 GHz cavities. The microwave surface resistance (RS) was also studied, which indicated both very low Bardeen–Cooper–Schrieffer (BCS) and residual resistance. The recipe of cavity process in this paper is simplified and easy to duplicate, which may benefit the SRF community.

Enhancement of corona discharge thresholds in microstrip bandpass filters by using cover-ended resonators

This paper studies the corona discharge power thresholds in microstrip bandpass filters (BPFs) and, in particular, is focused on a solution based on λ/2 cover-ended resonators to enhance their peak power handling capability (PPHC). First, a parametric analysis is carried out to evaluate the variation of the maximum electric field and the unloaded quality factor (Q u ) as a function of the cover's geometrical dimensions (i.e. height, length, and width). Next, several microstrip BPFs centered at 1.6 GHz are designed, and their behaviors under moderate-to-high applied RF power signals are simulated to corroborate the previous study. A suitable number and size of covers are selected to enhance PPHC without barely degrading the filters’ electrical performance and, consequently, without hardly increasing the insertion losses. Finally, two third-order filters with covers and without covers (benchmark prototype) are manufactured, by way of illustration, and they are tested in the European High-Power RF Space Laboratory to validate the good performance of the proposed solution, where a PPHC enhancement of 3.1 dB at high pressures is achieved as compared to the benchmark prototype.

A multilayer substrate integrated filter using dual dielectric modes

In this paper, a novel multilayer substrate integrated dual-mode dielectric resonator (DR) filter is proposed. The square dual-mode DR is made of the high permittivity substrate by removing the undesired portions and the surface coppers so that the relatively high unloaded quality factor of the dominate TM11 pair can be obtained which compared to these fully dielectric-filled substrate integrated waveguides. Meanwhile, it can be easily integrated in an equivalent cavity implemented by multilayer printed circuit boards for filter design, showcasing low in-band loss, light weight, and compact size. For demonstration, a multilayer substrate integrated DR bandpass filter centered at X-band is designed and measured. Good agreement between the simulated and measured results can be observed, and the measured insertion loss at the passband center frequency (8.38 GHz) is 1.1 dB.