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The initial observations of optical synchrotron radiation (OSR) emitted over millions of passes from a few electrons circulating in the Particle Accumulator Ring (PAR) at the Advanced Photon Source have been done with a digital CMOS camera and a synchroscan streak camera operating at 117.3 MHz. The discrete changes of integrated counts in the CMOS image region of interest are ascribed to single electron steps at ~3500 cts per electron. Circulations of a single electron at 375 MeV and at 425 MeV were demonstrated in the 12-bit digital FLIR USB3 camera images. The Hamamatsu C5680 streak camera operating at the 12th harmonic of the fundamental revolution frequency at 9.77 MHz was used to measure the zero-current bunch length from 0.5 nC circulating charge down to 10s of electrons or 10 aC. The latter cases were performed with 6-ps temporal resolution for the first time anywhere, to our knowledge. We report a preliminary effective bunch length of 276 ± 36 ps for 57 electrons (9.1 aC) stored based on a fit to a single Gaussian peak. The results will be compared to the standard zero-current model for the ring., Proceedings of the 9th International Beam Instrumentation Conference, IBIC2020, Santos, Brazil

In recent years, the THz part of the electromagnetic spectrum has attracted special attention due to the broad range of possible applications deriving from it and its presence in multiple natural phenomena. T-rays are able to pass almost unobstructed through a wide range of non-polar materials such as fabrics, paper, wood, ceramics, plastics and plasma. Radioastronomy, spectroscopy, molecular sensing, plasma diagnostics, security and biomedical imaging are only a few possible uses of the THz spectrum. Such wide range of possible applications demands a similarly wide range of detection techniques and devices. The methods presented in this overview have been organized in four groups, based on the physical principia they rely on: thermal, direct detection, superhet and sampling detection. For each of the techniques, the operational limits and the most frequent applications are also presented., Proceedings of the 9th International Beam Instrumentation Conference, IBIC2020, Santos, Brazil

9th International Beam Instrumentation Conference, IBIC2020, Santos, Brazil, 14 Sep 2020 - 18 Sep 2020; JACoW Publishing, Geneva, Switzerland 145-149 (2020). doi:10.18429/JACOW-IBIC2020-WEPP21, The all-optical synchronization systems used in various Xray free-electron lasers (XFEL) such as the European XFEL depend on transient fields of passing electron bunches coupled into one or more pickups in the Bunch Arrival Time Monitors (BAM). The extracted signal is then amplitude modulated on reference laser pulses in a Mach-Zehnder type electro-optical modulator. With the emerging demand of the experimenters for future experiments with ultra-short FEL shots, fs precision is required for the synchronization systems even with 1 pC bunches. Since the sensitivity of the BAM depends in particular on the slope of the bipolar signal at the zero crossing and thus, also on the bunch charge, a redesign with the aim of a significant increase by optimized geometry and bandwidth is inevitable. In this contribution a possible new pickup concept is simulated and its performance is compared to the previous concept. A significant improvement of slope and voltage is found. The improvement is mainly achieved by the reduced distance to the beam and a higher bandwidth., Published by JACoW Publishing, Geneva, Switzerland

Multibunch Feedback systems in Diamond use the RF reference signal to sample the BPM signals. Uncertain reference phase variations due to upstream adjustments to the RF system previously necessitated regular manual realignment of the sampling phase. Locking the sampling phase to the measured beam phase has been investigated to improve the stability and robustness of the system and remove the dependence on absolute RF phase. Significant improvements have been achieved using a Beam Locked Loop architecture based on an IQ modulator and cartesian feedback to phase align the local 500MHz reference signal to the BPM RF frequency component under closed loop digital control with remote management via EPICS. The system has been successfully deployed on the storage ring at Diamond and has been operating live since October 2019. Live data captured from the operational storage ring demonstrates the ability to tolerate a wide variation in beam phase whilst maintaining accurate beam sampling and robust acquisition of the reference phase over the operating range of beam currents and fill patterns., Proceedings of the 9th International Beam Instrumentation Conference, IBIC2020, Santos, Brazil

Short pulse, high power seed lasers have been implemented to improve the longitudinal coherence and shot-to-shot reproducibility of Free Electron Lasers (FEL). The laser pulse duration is typically 100 - 200 fs with wavelengths in the 260 nm range produced from third harmonic generation of a Ti:sapphire laser. The pulse duration must be measured accurately for seeded FEL operation. The Ultraviolet (UV) pulse width measurement can be carried out with intensity cross-correlation based on the difference frequency generation (DFG) in ultrathin ß-Barium Borate (BBO) crystals. The DFG output pulse broadened due to group velocity mismatch between the 266.7 nm and 800 nm components. The broadening effect depends on the BBO crystal thickness so we explored 0.015 mm, 0.055 mm and 0.1 mm thick samples. To the best of our knowledge, this is the first time that ß-BBO crystal with thickness of only 0.015 mm has been used to measure the UV seed laser pulse width. Experiment results show the measured pulse width broadens with increased BBO thickness in agreement with a theoretical model., Proceedings of the 9th International Beam Instrumentation Conference, IBIC2020, Santos, Brazil

The Shanghai high repetition rate XFEL and extreme light facility (SHINE) is planned to be built into one of the most efficient and advanced free-electron laser user facilities over the world to provide a unique tool for kinds of cutting-edge scientific research. The measurement of bunch arrival time is one of the key issues to optimize system performance. This is because the FEL facility relies on the synchronization of electron bunch and seeded lasers. Currently, there are mainly two methods to measure the bunch arrival time: the electro-optical sampling method and the RF cavity-based method. Considering the latter one has a simpler system and lower cost, the method has been adopted by SXFEL. The previous results show that the measurement uncertainty of bunch arrival time has achieved to be 45 fs, which can be further optimized. For SHINE, the bunch arrival time resolution is required to be better than 25 fs@100pC, and 200 fs@10 pC. The RF cavity-based method will also be applied. This paper will present the system prototype design and related simulation results., Proceedings of the 9th International Beam Instrumentation Conference, IBIC2020, Santos, Brazil

The use of THz-driven split ring resonator (SRR) as a streak camera for sub-ps bunch length measurement has been proposed for a few years. Since then, the feasibility of such a method has been experimentally demonstrated for both keV and MeV electron beam. The structural dimensions of SRR has a substantial impact on the resonance frequency, the field enhancement factor and the interaction region of the streaking field, eventually determining the temporal resolution of the bunch length measurement. Here we discuss the quantitative dependence of the streaking field on the structural dimensions of SRR. Combining with an analytical streaking model, we propose a method to optimize the structural dimensions of SRR such that the finest temporal resolution is achieved with given THz pulse., Proceedings of the 9th International Beam Instrumentation Conference, IBIC2020, Santos, Brazil

In this paper, the radio-frequency (RF) phase modulation method is exploited to investigate the variations in the transverse beam size and emittance at Hefei Light Source (HLS-II). Meanwhile, a certain quantitative analysis was performed on the stability and practicability of the beam transverse profile measurement systems. The experiments show that the RF phase modulation method can effectively explore the robustness and stability of beam transverse profile measurement systems over the range of 20.0-22.5 kHz, which is close to the first-harmonic of the synchrotron frequency. It is concluded that when the modulation amplitude of the external phase perturbation is less than 0.04 rad, this optical system can be capable of maintaining reliable and stable working status. This is also useful for analyzing the influence of RF phase noise on the subsequent beam measurement and diagnostics, which including the deterioration of beam quality, emittance blowup, beam jitter, and beam loss., Proceedings of the 9th International Beam Instrumentation Conference, IBIC2020, Santos, Brazil

Relativistic electron beams in storage rings radiate a significant fraction of beam energy per turn. As demonstrated in previous experiments, with the radiofrequency accelerating structures off, the turn-by-turn time of arrival of the electron bunch can be observed from the synchrotron radiation that it produces using a streak camera. In the present work, we present measurements of the energy loss per turn of an initially short electron bunch (~1 ps RMS) from a photocathode electron gun in the Advanced Photon Source Particle Accumulator Ring (375 MeV, 10² ns revolution period). With the streak camera synchroscan locked to the twelfth harmonic of the revolution frequency (117.3 MHz), we observe an injection transient in the horizontal direction., Proceedings of the 9th International Beam Instrumentation Conference, IBIC2020, Santos, Brazil

The preservation of the low emittance of electron beams during transport in the accelerating structures of large facilities is an ongoing challenge. In the cases of the TESLA-type superconducting rf cavities currently used in the European X-ray Free-electron Laser (FEL) and the under construction Linac Coherent Light Source upgrade (LCLS-II), off-axis beam transport may result in emittance dilution due to transverse long-range and short-range wakefields (SRW)*. To investigate such effects, experiments were performed at the Fermilab Accelerator Science and Technology (FAST) facility with its unique two-cavity configuration after the photocathode rf gun. We used optical transition radiation (OTR) imaging with a UV-visible synchroscan streak camera to display sub-micropulse y-t effects in the 41-MeV beam. The head-tail transverse kicks within the 11-ps-long micropulses were observed at the 100-micron level for steering off-axis in one cavity and several 100 microns for two cavities. Since the SRW kick angles go inversely with energy, these results may inform the commissioning plans of the LCLS-II injector where beam will be injected at ~1 MeV into a cryomodule., Proceedings of the 9th International Beam Instrumentation Conference, IBIC2020, Santos, Brazil

A technique to reduce point-spread originating from physical slit width in emittance measurements is described. This technique is developed to improve phase resolution in a longitudinal emittance apparatus consisting of a dipole magnet, energy-selecting slit and bunch shape monitor. In this apparatus, the energy and phase resolutions are directly proportional to the width of the slit, but the virtual slit method enables sub-slit resolution. The bunch phase profile is measured at two points in the energy distribution with a separation less than the physical slit width. The difference of these two profiles is used to reconstruct the profile from a virtual slit of width equal to the separation., Proceedings of the 9th International Beam Instrumentation Conference, IBIC2020, Santos, Brazil

Present day heavy ion accelerators use bunched ion beams of sub-nanosecond time scale for beam acceleration. In order to monitor its longitudinal profile, fast faraday Cups are employed. Owing to the advent of microstrip technology and its fabrication process, planar structures have become easier to fabricate. A novel design using the same is developed with a special provision for mounting edge launch connectors through a microstripline, followed by a microstrip to stripline transistion to again a microstrip structure in the beam interaction hole. The entire structure is a 50 Ω is bidirectional. An experimental study on via placement around central strip has also been conducted to not only ensure the field containment around the strip but also for bandwidth enhancement. To measure ion beam currents from 10-100 nA and a bunch width of 1ns, device has been beam interaction hole of around 10mm. 3 dB bandwidth is measured >6 GHz with a rise time of ~60 ps. The devices are also provided with a bias ring on the topmost layer of the 3 layer architecture for electron suppression. In this paper, design, fabrication and RF testing stripline fast faraday cup is presented., Proceedings of the 9th International Beam Instrumentation Conference, IBIC2020, Santos, Brazil

We have recently extended our ability to explore submicropulse effects in relativistic electron beams to energy-time (E-t) correlations. The Fermilab Accelerator Science and Technology (FAST) facility consists of a photoinjector, two superconducting TESLA-type capture cavities, one superconducting ILC-style cryomodule, and a small ring for studying non-linear, integrable beam optics called IOTA. The linac contains, as part of its instrumentation, an optical transport system that directs optical transition radiation (OTR) from an Al-coated Si surface to an externally located streak camera for bunch length measurements. For the first time, an OTR screen after the spectrometer magnet was used for measurements of submicropulse E-t correlations. The projected, micropulse time profile was fit to a single Gaussian peak with σ = 11.5 ± 0.5 ps for 500 pC/micropulse and with a 200-micropulse synchronous sum, in agreement with the upstream bunch-length measurement at a non-energy-dispersive location. The submicropulse E-t images were explored for four rf phases of CC1, and the E vs. t effects will be presented., Proceedings of the 9th International Beam Instrumentation Conference, IBIC2020, Santos, Brazil