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Detectors made from sub-micron-sized bridges of the high- ${T}_{c}$ superconductor Y–Ba–Cu–O have unique properties useful for the detection of THz radiation, namely evidence of a detector response with an additional sensitivity to the direction of the electric field of short THz pulses when used without a transport current in the so-called “zero-bias” regime. In order to examine the influence of the antenna design on the detector response, we have conducted electromagnetic simulations and performed experiments at a synchrotron light source and with a photomixing setup as sources for short THz pulses. In this paper, we evaluate a narrow-band double-slot antenna as well as a broadband log-spiral antenna design.

Coherent synchrotron radiation (CSR) is generated when the electron bunch length is in the order of the magnitude of the wavelength of the emitted radiation. The self-interaction of short electron bunches with their own electromagnetic fields changes the longitudinal beam dynamics significantly. Above a certain current threshold, the micro-bunching instability develops, characterized by the appearance of distinguishable substructures in the longitudinal phase space of the bunch. To stabilize the CSR emission, a real-time feedback control loop based on reinforcement learning (RL) is proposed. Informed by the available THz diagnostics, the feedback is designed to act on the radio frequency (RF) system of the storage ring to mitigate the micro-bunching dynamics. To satisfy low-latency requirements given by the longitudinal beam dynamics, the RL controller has been implemented on hardware (FPGA). In this article, a real-time feedback loop architecture and its performance is presented and compared with a software implementation using Keras-RL on CPU/GPU. The results obtained with the CSR simulation Inovesa demonstrate that the functionality of both platforms is equivalent. The training performance of the hardware implementation is similar to software solution, while it outperforms the Keras-RL implementation by an order of magnitude. The presented RL hardware controller is considered as an essential platform for the development of intelligent CSR control systems.

Detectors made from the high- T c superconductor YBa2Cu3O7-x are well suited to detect the high-intensity pulsed-terahertz (THz) radiation emitted by synchrotron light sources and free-electron lasers due to their fast response times. We propose a detection system consisting of an integrated planar array with four superconducting detectors coupled to narrowband double-slot antennas for the frequencies 140 GHz, 350 GHz, 650 GHz, and 1.02 THz, respectively. With the ability for spectroscopic measurements, it has the potential to further improve the understanding of accelerator science and the future application of THz radiation. In this paper, we present a new antenna and array design that has been especially optimized to match the high impedance of sub- μ m-sized detector bridges needed for high sensitivities, and measurements performed at the Diamond Light Source.

The behavior of submicrometer-sized thin-film YBa 2 Cu 3 O 7-x (YBCO) detectors under illumination with picosecond terahertz (THz) pulses was investigated. Real-time measurements with a temporal resolution of 15 ps full width at half maximum were performed at ANKA, the synchrotron facility of Karlsruhe Institute of Technology, and the UVSOR-III facility at the Institute for Molecular Science in Okazaki, Japan. The capability of YBCO detectors to reproduce the shape of a several picosecond long THz pulse was demonstrated. Single-shot measurements adhering to a reversal of the direction of the electrical field of the THz radiation were carried out. They provided evidence for the electrical field sensitivity of the YBCO detector. Exploiting the electrical field sensitivity of the YBCO detector, the effect of microbunching was observed at UVSOR-III.

In March 2005 a superconducting cold-bore undulator was installed in ANKA (ANSTROEM SOURCE IN KARLSRUHE) and since that time has been in operation. The purpose of the installation was to evaluate if such a device can be operated in a heavy duty synchrotron radiation user facility like ANKA without problems. In order to demonstrate this the generated spectra were measured and the heat load induced by the beam was investigated. It was shown that the heat deposited by the beam in the 8 mm gap is less than 1 W per 100 mA at 2.5 GeV and can be cooled by cryocoolers. Finally, reference is made to the spectra produced by sub-picosecond X-rays using a special ANKA optics.