DEOS: A New Scheme for Recording Electron Bunch Shapes With High Resolution and Record Recording Length - Principle and Tests at EuXFEL
S. Bielawski
PhLAM/CERCLA, Villeneuve d’Ascq Cedex, France
C. Evain, E. Roussel, C. Szwaj
PhLAM/CERLA, Villeneuve d’Ascq, France
C. Gerth, B. Steffen
DESY, Hamburg, Germany
B. Jalali
UCLA, Los Angeles, California, USA
Funding:CEMPI LABEX, CPER Photonics for society, ULTRASYNC ANR, METEOR CNRS MOMENTUM grant Recording electron bunch longitudinal profiles in single-shot, and non-destructively is largely needed in accelerator operation. A common strategy consists in probing the near-field of the bunch using femtosecond laser pulses. These two last decades, such electro-optic detection schemes have evolved to compact and reliable techniques. However, serious limitations have been limiting the time-resolution, when long recording lengths are needed. This has been recognized as a fundamental bottleneck and even coined the term "Fourier limit". We present here a novel electro-optic sampling strategy that is theoretically capable to overcome this limit and achieve femtosecond resolution for any recording length. This new approach is based on the mathematical concept of information diversity. We present first results of DEOS (Diversity Electro-Optic Sampling) obtained both in table-top experiments, as well as at the European XFEL. This technique opens the way to electric field shape characterization with femtosecond resolution in new situations, including longitudinal bunch profile monitoring, studies of microbunching instabilities, and THz pulses generated at free-electron lasers. https://arxiv.org/abs/2002.03782
Direct Observations of Sub-micropulse Electron-beam Effects from Short-range Wakefields in TESLA-type Superconducting RF Cavities
56
A.H. Lumpkin, D.R. Edstrom, P.S. Prieto, J. Ruan, R.M. Thurman-Keup
Fermilab, Batavia, Illinois, USA
J.A. Diaz Cruz, A.L. Edelen, B.T. Jacobson, F. Zhou
SLAC, Menlo Park, California, USA
Funding:Work supported by FRA, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Dept. of Energy, Off. of Sci./HEP. SLAC is supported by the U.S. Dept. of Energy, OS/BES, under contract DE-AC02-76SF00515. 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. * W.K.H. Panofsky and M. Bander, Rev. Sci. Instr. 39 , 206 (1968).
Observations of Optical Synchrotron Radiation from Ultra-low Charges Stored in a Ring Operating at 425 MeV
61
A.H. Lumpkin
AAI/ANL, Lemont, Illinois, USA
K.P. Wootton
ANL, Lemont, Illinois, USA
Funding:This research used resources of the Advanced Photon Source, operated for the U.S. Department of Energy Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. 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.
Bunch Length Measurements Using Beam Position Monitors
C.J. Richard
MSU, East Lansing, Michigan, USA
S. Cogan, S.M. Lidia
FRIB, East Lansing, Michigan, USA
Funding:Work supported by the US Department of Energy, Office of Science, High Energy Physics under Cooperative Agreement award number DE-SC0018362. Capacitive Beam Position Monitors (BPMs) are broadband pickups. For measurements of RF bunched beams, however, they typically use narrowband filters to measure one harmonic of the beam current to reduce noise and simplify the signal processing. If several harmonics are measured simultaneously, the longitudinal bunch shape, in principle, may also be measured. This can be accomplished by recording the waveforms from the BPMs with an oversampling measurement scheme before the narrowband analysis is applied. In order to reconstruct the bunch shape, the measured spectra should be corrected for non-relativistic effects, cable attenuation and filtering, and the geometry and impedance of the BPM pick up. These corrections are discussed as well as the procedure for calibrating the BPM system for measuring multiple harmonics. Measurements are presented that were taken in the medium energy beam transport line and the first linac section at the Facility for Rare Isotope Beams and are compared to simulations and measurements with a fast Faraday cup. Resolution and uncertainties of the reported bunch length measurements are described.
Transition Radiation Based Diagnostics for Non-Relativistic Ion Beams
R. Singh, T. Reichert, B. Walasek-Höhne
GSI, Darmstadt, Germany
The usage of optical transition radiation for profile monitoring of non-relativistic electron beams is well known. In this contribution, we study the application of transition radiation in optical and GHz regime for non-relativistic ion beams. The light emitted from a metal target after ion beam irradiation consists of polarized transition radiation as well as significant amount of unpolarized photons. The dependence of light yield on beam current and comparison of measured transverse profiles with alternative devices is shown. Simulations and pilot measurements demonstrating the potential usage of coherent transition radiation in GHz regime for bunch-by-bunch longitudinal profile measurements is also discussed.
Streak Camera Measurement of Electron Beam Energy Loss Per Turn in the Advanced Photon Source Particle Accumulator Ring
66
K.P. Wootton, J.R. Calvey, J.C. Dooling, K.C. Harkay, A.H. Lumpkin, Y. Sun, B.X. Yang
ANL, Lemont, Illinois, USA
Funding:This research used resources of the Advanced Photon Source, operated for the U.S. Department of Energy Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. 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.
Novel Trends in Bunch Length Diagnostics Based on Coherent Polarization Radiation
A. Curcio
NSRC SOLARIS, Kraków, Poland
Bunch length and temporal profile diagnostics is of primary importance for accelerator facilities. It provides a huge variety of applications, ranging from the optimization of the accelerators’ performances to the delivery of light bursts of controlled duration for experiments. During the last years, efforts have been made in demonstrating the beneficial aspects of exploiting Coherent Cherenkov Diffraction Radiation for bunch length characterizations, as its non-intercepting nature, the directionality, the tunability, the high resolution and the high signal-to-noise level. This technique has been compared to others based on more standard mechanisms of polarization radiation as Coherent Transition and Diffraction Radiation. Bunch length measurements have also been benchmarked with more conventional techniques as the use of RF-deflectors and time-domain measurements of Optical Transition Radiation. In conclusion we report on diagnostic solutions already adopted or foreseen in the next future for the SOLARIS facility, both for the LINAC injector and the storage ring.
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F. Mazzocchi, D. Strauß
KIT IAM-AWP, Eggenstein Leopoldshafen, Germany
E. Bründermann, A.-S. Müller, T.A. Scherer
KIT, Eggenstein-Leopoldshafen, Germany
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.
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Optimization of Lasers in Electron Accelerator Applications
S. Vetter
SLAC, Menlo Park, California, USA
Lasers are increasingly used at electron accelerator facilities both to produce high brightness beams and to modify the properties of the bunches to optimize FEL performance at the LCLS. We describe techniques for controlling and measuring the position, intensity and spatial profile of the laser at the cathode. These measurements must be performed on a bunch by bunch basis in order to monitor stability and pulse to pulse jitter at 120 Hz in our copper linac and up to 1 MHz in the new superconducting linac for LCLS-II. Additionally, IR laser beams are overlapped with the electron beam within a wiggler to modulate the energy of the electron bunch to increase the slice energy spread and offset microbunching instabilities that degrade the FEL performance. We describe the critical laser parameters for such laser heaters and the techniques for controlling the spatial and temporal overlap of laser and electron beams. Moreover diagnostics such as cross-correlation measurements are performed to verify the cathode drive laser pulse length. Finally, we give an overview of laser measurements applied to novel bunch compression schemes for producing attosecond bunches at the XLEAP experiment.
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Non-invasive Longitudinal Profile Measurements of Electron Bunches Simultaneously to FEL Operation at MHz Rates
N.M. Lockmann, C. Gerth, B. Schmidt, S. Wesch
DESY, Hamburg, Germany
Hard X-ray FELs require ultra-short electron bunches with peak currents of several kiloamperes. Therefore, longitudinal bunch profile characterization with femtosecond resolution is essential for a successful operation and control of the accelerator as well as a wide field of photon experiments. The high electron beam energies of hard X-ray FELs enable non-invasive longitudinal form factor monitoring down to a few micrometers utilizing coherent diffraction radiation spectroscopy. For this purpose, a 4-staged grating spectrometer has been recently installed at European XFEL. Here, current profiles are reconstructed with femtosecond time resolution based on phase retrieval algorithms which are in excellent agreement to results obtained with a transverse deflecting structure. The fast pyroelectric detectors allow, for the first time, to measure the current profile of all bunches inside the bunch train with repetition rates of up to 2.2 MHz. The low latency electronic readout of the 120 channels of the spectrometer provides high potential for fast compression feedbacks and machine learning applications.
Non-Destructive Monitoring of Electron Beam Micro-Bunching Periodicity
I.V. Konoplev, H. Zhang
JAI, Oxford, United Kingdom
G. Doucas
Oxford University, Physics Department, Oxford, Oxon, United Kingdom
Electron beam microbunching can either occur naturally in high current accelerator facilities, or can be induced artificially for wide range of studies. Microbunching has applications in LINAC driven tunable sources of coherent radiation and wakefield acceleration. In all cases, an accurate, non-destructive monitoring of the beam microbunching is needed to validate theory, improve the accelerator and light source operations and understanding of the phenomenon observed. However, it is still a challenge to monitor the beam microbunching non-destructively and we discuss the possibility of measuring the femtosecond periodic microstructure of the beam without strong interference (i.e. in a non-destructive way) via analysis of the amplitude modulation of the coherent Smith-Purcell radiation (cSPr) signal generated by a partially or fully microbunched beam. The results of the numerical studies of the cSPr generated by the partially and fully microbunched beam and proof-of-principle experiments demonstrating the measurements of the distance between micro-bunches will be presented. The theoretical predictions are compared with the experimental data and the limitations are discussed.
Measurements of Ultraviolet FEL Seed Laser Pulse Width Broading in Thin ß-BBO Crystals
140
C.L. Li, X.T. Wang, W.Y. Zhang
Shanghai Advanced Research Institute, Pudong, Shanghai, People’s Republic of China
L. Feng, B. Liu
SARI-CAS, Pudong, Shanghai, People’s Republic of China
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.
Evaluation of a Novel Pickup Concept for Ultra-Low Charged Short Bunches in X-Ray Free-Electron Lasers
145
B.E.J. Scheible, A. Penirschke
THM, Friedberg, Germany
W. Ackermann, H. De Gersem
TEMF, TU Darmstadt, Darmstadt, Germany
M.K. Czwalinna, H. Schlarb
DESY, Hamburg, Germany
Funding:This work is supported by the German Federal Ministry of Education and Research (BMBF) under contract no. 05K19RO1. 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.
Submicropulse Energy-Time Correlations of 40-Mev Electron Beams at Fast
150
R.M. Thurman-Keup, A.H. Lumpkin
Fermilab, Batavia, Illinois, USA
Funding:This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics. 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.
Optimization of GaAs Based Field Effect Transistors for THz Detection at Particle Accelerators
R. Yadav, S. Preu, S. Regensburger
IMP, TU Darmstadt, Darmstadt, Germany
A. Penirschke
THM, Friedberg, Germany
For pump probe experiments employing a free-electron laser and a near infrared (NIR) laser, there is no natural locking between the two. Therefore only the repetition rate of the two lasers can be synchronized leading to jitter and drift on the picosecond scale. GaAs-based field-effect transistors (FETs) allow for simultaneous detection of the amplitude and timing of picosecond-scale THz and NIR pulses*. They cover the whole THz band and beyond up to the MIR (0.1 - 22 THz) with the exception of the GaAs Reststrahlen band*. Large-area FETs feature a high damage threshold (>65 kW) and large linearity range*. Antenna-coupled FETs show a noise equivalent power (NEP) of 250 pW/√Hz at 600 GHz**. FET based THz detectors can be used both for THz beam on a single pulse level, as well as for the beam diagnosis. For further optimization of the detector for the needs of beam diagnosis with low incident intensity, a more precise modeling of the FET is developed. Therefore, the incoupling of THz to the rectifying element is investigated. The S-Parameters of the 2DEG are measured with on-wafer probes up to 67 GHz and de-embedded with on-wafer TRL*** calibration. * Regensburger, S.,et al.,DOI:10.1364/OE.23.020732. ** Regensburger, S.,et al.,DOI: 10.1109/TTHZ.2018.2843535. *** Guoping, T.,et al.,DOI: 10.1088/1674-4926/36/5/054012.
Prototype Design of Bunch Arrival Time Measurement System Based on Cavity Monitor for SHINE
154
Y.M. Zhou, S.S. Cao, J. Chen, Y.B. Leng
SSRF, Shanghai, People’s Republic of China
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.
Photoinjector Driver Laser Temporal Shaping and Diagnostics for Shanghai Soft X-ray Free Electron Laser
C.L. Li, X.T. Wang, W.Y. Zhang
Shanghai Advanced Research Institute, Pudong, Shanghai, People’s Republic of China
L. Feng, B. Liu
SARI-CAS, Pudong, Shanghai, People’s Republic of China
It is known that the intensity distribution plays an important role in the electron bunch character, such as its transverse emittance, longitudinal structure. Compared with longitudinal Gaussian distribution, Driver laser pulse with longitudinal flattop structure can produce electron bunch with lower emittance. This paper presents electron beam structure and emittance under different driver laser structure, specifically, laser pulse temporal shaping method for producing Gaussian beam and flattop beam are presented. The advantage and disadvantage of the two method are also discussed. Flattop beam produced from BBO stacking is more benefit for producing electron beam with lower emittance, but significantly increase the microbunch effect. However, Gaussian beam has the advantage to help reducing the mircobunch effect. Moreover, cross correlation method for characterization the laser pulse temporal structure are also presented, particularly, the group velocity mismatch effect induced by the sum frequency BBO crystal are discussed.
Effect of phase modulation on the transverse beam size and emittance of the HLS-II ring
158
Y.K. Zhao, S.S. Jin, B.G. Sun, J.G. Wang, F.F. Wu
USTC/NSRL, Hefei, Anhui, People’s Republic of China
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.
Measurement of Cs2Te Cathode Response in a High-Gradient Photoinjector
G. Loisch, M. Groß, D.K. Kalantaryan, C. Koschitzki, M. Krasilnikov, X. Li, O. Lishilin, D. Melkumyan, R. Niemczyk, A. Oppelt, F. Stephan, G. Vashchenko, T. Weilbach
DESY Zeuthen, Zeuthen, Germany
Y. Chen
DESY, Hamburg, Germany
L. Monaco, D. Sertore
INFN/LASA, Segrate (MI), Italy
Cesium-Telluride is a widely used semiconductor photocathode material in electron photoinjectors for its high quantum efficiency and its stability in a high-gradient RF-gun environment. Even though the properties of such cathodes have been studied in the past decades, the emission process is still not fully modeled. One of the parameters that has not been directly quantified in experiment is the lengthening of electron bunches in Cs2Te with respect to the incident UV laser pulse length - often referred to as cathode response time - due to photon penetration depth variations and scattering processes. Especially for applications such as novel accelerator technologies, ultrafast electron diffraction and free electron lasers with ever higher demands on short bunch durations, the minimum attainable bunch length from the electron gun is a decisive quantity. We present the first direct measurement of Cs2Te cathode temporal response by measuring electron bunch lengths and profiles with a few tens of femtoseconds resolution at the Photoinjector Test facility at DESY Zeuthen (PITZ). We also show first results on the impact of photocathode properties on cathode response.
Virtual Slit for Improved Resolution in Longitudinal Emittance Measurement
241
K.J. Ruisard, A.V. Aleksandrov, A.P. Shishlo
ORNL, Oak Ridge, Tennessee, USA
Funding:This manuscript has been authored by UT-Battelle, LLC, under Contract No. DE-AC0500OR22725 with the U.S. Department of Energy. 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.
Design and Development of a Novel Stripline Fast Faraday Cup to Measure Ion Beam Profile
246
A. Sharma, R.K. Gangwar
IIT (ISM), Dhanbad, Jharkhand, India
B.K. Sahu
IUAC, New Delhi, India
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. 1. M. Bellato et al, "Design and tests for the Fast Faraday cup of ALPI post-accelerator", NIM A 2. C. E. Deibele, "Fast Faraday Cup with High Bandwidth", US Patent no. 7012419B2.
A THz-Driven Split Ring Resonator for Temporal Characterization of Femtosecond MeV Electron Beam
250
Y. Song, K. Fan
Huazhong University of Science and Technology, State Key Laboratory of Advanced Electromagnetic Engineering and Technology,, Hubei, People’s Republic of China
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.
Tracking Frequency Reference Phase Changes at Point of Use Based on BPM Measurements
254
A. Tipper, M.G. Abbott, G. Rehm
DLS, Harwell, United Kingdom
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.
