To understand the underlying complex beam dynamics in electron storage rings often large numbers of single-shot measurements must be acquired continuously over a long period of time with extremely high temporal resolution. Photonic time-stretch is a measurement method that is able to overcome speed limitations of conventional digitizers and enable continuous ultra-fast single-shot terahertz spectroscopy with rates of trillions of consecutive frames. In this contribution, a novel ultra-fast data sampling system based on photonic time-stretch is presented and the performance is discussed. THERESA (TeraHErtz REadout SAmpling) is a data acquisition system based on the recent ZYNQ-RFSoC family. THERESA has been developed with an analog bandwidth of up to 20 GHz and a sampling rate of up to 90 GS s−1. When combined with the photonic time-stretch setup, the system will be able to sample a THz signal with an unprecedented frame rate of 8 Tf s−1. Continuous acquisition for long observation times will open up new possibilities in the detection of rare events in accelerator physics

Bielawski, S.

Bründermann, E.

Caselle, M.

Chilingaryan, S.

Dritschler, T.

Funkner, S.

Kopmann, A.

Manzhura, O.

Müller, A.-S.

Nasse, M. J.

Niehus, G.

Patil, M. M.

Roussel, E.

Steinmann, J. L.

Szwaj, C.

English

KITopen

TERAHERTZ SAMPLING RATES WITH PHOTONIC TIME-STRETCHFOR ELECTRON BEAM DIAGNOSTICSO. Manzhura1∗, M. Caselle1† , S. Bielawski2, S. Chilingaryan1, S. Funkner1, T. Dritschler1,A. Kopmann1, M. J. Nasse1, G. Niehues1, M. M. Patil1, J. L. Steinmann1,E. Bründermann1, E. Roussel2, C. Szwaj2, A.-S. Müller11Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, Germany2PhLAM/CERLA, Villeneuve d’Ascq cedex, FranceAbstractTo understand the underlying complex beam dynamicsin electron storage rings often large numbers of single-shotmeasurements must be acquired continuously over a longperiod of time with extremely high temporal resolution. Pho-tonic time-stretch is a measurement method that is able toovercome speed limitations of conventional digitizers and en-able continuous ultra-fast single-shot terahertz spectroscopywith rates of trillions of consecutive frames. In this con-tribution, a novel ultra-fast data sampling system based onphotonic time-stretch is presented and the performance isdiscussed. THERESA (TeraHErtz REadout SAmpling) is adata acquisition system based on the recent ZYNQ-RFSoCfamily. THERESA has been developed with an analog band-width of up to 20 GHz and a sampling rate of up to 90 GS s−1.When combined with the photonic time-stretch setup, thesystem will be able to sample a THz signal with an unprece-dented frame rate of 8 Tf s−1. Continuous acquisition forlong observation times will open up new possibilities in thedetection of rare events in accelerator physics.INTRODUCTIONMany scientific applications and experiments, especiallyin particle accelerator physics, require the continuous obser-vation of non-repetitive and statistically rare events occurringon very short time scales. This imposes high technologi-cal challenges on Data Acquisition (DAQ) systems such asoscilloscopes. One of them is the limited temporal resolu-tion of commercially available Analog-to-Digital-Converters(ADCs) [1]. In 1999 a first demonstration of a concept toovercome this limitation was presented [2]. To relax the de-mands on the data converter performance, prior to digitiza-tion, the signal under investigation is stretched in time usingchirped optical pulses and the chromatic dispersion in opti-cal fibers. This concept, also called Photonic Time-Stretch(PTS), is already successfully employed in combination witha real-time oscilloscope at the SOLEIL (Source optimiséede lumière d’énergie intermédiaire du LURE) synchrotronfacility [3].The second limitation is the short contiguous acquisitiontime of commercially available oscilloscopes, which is inthe range of few milliseconds. Therefore, the continuousacquisition over long observation time (up to hours), e.g.∗ olena.manzhura@kit.edu† michele.caselle@kit.edufor the study of the evolution of electron bunch profiles ona turn-by-turn basis, is not possible. To overcome theselimitations THERESA, a new digitizer system suitable forPTS measurements, has been developed. THERESA con-sists of sixteen parallel sampling channels operating in time-interleaved mode, which enables a sampling rate of over90 GS s−1 [4]. In the next sections an overview of the systemis given and a description of the firmware architecture andcalibration strategy is discussed.ARCHITECTUREThe digitizer architecture with the photonic time-stretchsystem is shown in Fig. 1. It consists of an opticaltime-stretching path, developed at Lille University [3], afast photo-detector and the THERESA sampling system.THERESA contains a wideband power-divider, a samplingboard and a readout card based on the recent ZYNQ-RFSoCtechnology.Time-Stretch SetupThe general principle of PTS is shown in Fig. 1. A broad-band, chirped carrier laser pulse is fed through an electro-optical crystal which encodes the ultra-fast signal to be sam-pled onto to the laser pulse. The modulated laser pulses arethen stretched in time by means of a long dispersive fiberuntil their duration is in the order of nanoseconds. The factor𝑆, by which the pulse is slowed down, can be calculated by𝑆 = 1 + 𝐿2𝐿1, (1)where 𝐿1 and 𝐿2 are the lengths of the two fibers [1, 3].Sampling BoardThe stretched and modulated pulse from the PTS is splitinto 16 identical signals by an active power divider. Each sig-nal is fed into the individual channels on the THERESA card.High-bandwidth Track-and-Hold Amplifiers (THA) [5] de-vice are employed to sample the input signal at a high rate.The sampling clock of the THAs is individually delayedby picosecond programmable delay chips [6]. One key fea-ture of the THERESA architecture is its high flexibility inthe sampling operation. The system can operate either incontinuous or in single-shot sampling mode. In continuousmode, the phase of the sixteen parallel sampling channelsare equally distributed over the sampling interval, which can13th Int. Particle Acc. Conf. IPAC2022, Bangkok, Thailand JACoW PublishingISBN: 978-3-95450-227-1 ISSN: 2673-5490 doi:10.18429/JACoW-IPAC2022-MOPOPT017MC6: Beam Instrumentation, Controls, Feedback and Operational AspectsT03: Beam Diagnostics and InstrumentationMOPOPT017263ContentfromthisworkmaybeusedunderthetermsoftheCCBY4.0licence(©2022).Anydistributionofthisworkmustmaintainattributiontotheauthor(s),titleofthework,publisher,andDOIFigure 1: Architecture of the photonic time-stretch setup and the THERESA digitizer [4].be a multiple of the sync clock period, as shown in figureFig. 2.In the single-shot sampling mode, the phase of sixteensampling channels is set with a minimum time distance of11 ps. In this mode, the system will sample an input signalat the frame rate of 90 GS s−1 [4].Figure 2: Working principle of the THERESA system incontinuous mode [4].Readout CardThe THERESA sampling card is connected to the XilinxZCU216 evaluation board, which is based on a ZYNQ Ul-traScale+ Radio Frequency System-on-Chip (RFSoC). ThisRFSoC integrates a Programmable Logic (PL), a ProcessingSystem (PS), sixteen 12-bit RF-ADCs and 14-bit RF-DACs,operating up to 2.5 GS s−1 and 10 GS s−1 respectively. Fur-thermore, the RFSoC hosts many peripherals on one singlechip and, therefore, is an ideal platform for the integrationof PL and System-on-Chip for data processing.FIRMWAREThe THERESA sampling board integrates two DAC chan-nels for the generation of test signals that can be employed forthe test and calibration of the sampling channels. Therefore,the first important tasks of the firmware are the generationof the calibration signal and the data acquisition from thesampling channels. The firmware architecture employedfor the calibration of the system takes advantage of the Xil-inx RF Evaluation Tool [7], which provides an evaluationsoftware combined with a hardware test platform for datageneration and acquisition. The hardware-test platform canbe easily extended with custom designs according to userrequirements. The simplified block diagram of the currentfirmware is shown in Fig. 3. The data generated by the PSare stored to an external DDR memory via Direct MemoryAccess (DMA) and then converted to an analog signal bythe Xilinx RF data converter Intellectual Property (IP) block.The signal from the DAC channels is propagated to the sam-pling channels on the THERESA board and digitized by theADCs integrated in the RFSoC. The digital samples from theADCs are temporarily stored in the memory and accessedby the processor for further data analysis. The PS hosts anembedded Linux system with an user space application thatallows the access to all peripheries and communicates withthe evaluation tool software. The software implements con-trol, data generation, acquisition, visualization and analysisfunctions and, therefore, provides all necessary tools forassessing the THERESA system performance.CALIBRATION ANDCHARACTERIZATIONThe software [7] provides all the tools necessary for char-acterization and calibration of the system. Online spec-tral analysis is performed on the acquired signals and pre-sented to the user for a fast way of analyzing the spec-tral components. Furthermore, dynamic performance char-acteristics such as the Total Harmonic Distortion (THD),Signal-to-Noise Ratio (SNR) and Effective Number of Bits(ENOB) can be computed by the software. The calibrationof the THERESA system is necessary to correct several mis-matches intrinsic to the time-interleaving sampling method,like the additional spurs in the spectrum due to offset, gain,13th Int. Particle Acc. Conf. IPAC2022, Bangkok, Thailand JACoW PublishingISBN: 978-3-95450-227-1 ISSN: 2673-5490 doi:10.18429/JACoW-IPAC2022-MOPOPT017MOPOPT017ContentfromthisworkmaybeusedunderthetermsoftheCCBY4.0licence(©2022).Anydistributionofthisworkmustmaintainattributiontotheauthor(s),titleofthework,publisher,andDOI264MC6: Beam Instrumentation, Controls, Feedback and Operational AspectsT03: Beam Diagnostics and InstrumentationFigure 3: Block diagram of the firmware. It consists of the Xilinx RF evaluation platform [7] for signal generation,acquisition and the slow-control interface for configuration of the sampling board components. The processor hosts anembedded Linux system and is responsible of the communication with the RF Evaluation GUI running on a PC.timing and bandwidth mismatches of the ADCs. Gain mis-match creates a frequency spur at 𝑓𝑠/𝑀, while all of the othermismatches create components at 𝑓𝑠/𝑀 ± 𝑓IN, where 𝑓𝑠 is thesampling frequency, 𝑀 the number of ADCs in the arrayand 𝑓IN the frequency of the input signal1 [4, 8]. The offsetand gain mismatches can be measured by applying a lowfrequency signal by the DAC. In order to compensate thesemismatches, one ADC is taken as reference and the offsetand gain of the other converters are matched to it. Phaseand bandwidth mismatches can be measured by applyingsinusoidal signals with different frequencies as describedin [4]. To reduce these mismatches, the sampling clocks andanalog traces are routed with a precise timing/length matchin order to have a time skew down to 1.2 ps.An example test setup for characterization and calibrationis shown in Fig. 4. The output from the DAC channel isfed back via a power-divider to four ADC channels. Thedata converter reference sampling clock is provided by thePhase-Locked Loop (PLL) on the sampling board.CONCLUSIONThe measurement of events occurring in the time range offemtoseconds over long observation times poses great tech-nological challenge on DAQ systems. It requires carefullydesigned high-bandwidth and low-noise sampling circuitsand a readout systems capable of high data-throughput andprocessing. The latest generation of ZYNQ UltraScale+ RF-1 Assuming equidistant sampling points.Figure 4: THERESA test setup for characterization andcalibration.SoC has proven to be an efficient platform that simplifieshardware and software design. The THERESA samplingsystem is a result of a close collaboration between engineersand beamline scientists. This collaboration has producedone of the fastest digitizer available in the scientific commu-nity with an analog bandwidth up to 20 GHz and a samplingrate up to 90 GS s−1. When combined with the PTS setup de-veloped at Lille University, the system will be able to samplean incoming optical signal with an unprecedented frame rateof 8 Tf s−1. The continuous acquisition for long observationtimes by high data throughput readout electronics will openup new possibilities for real-time data processing and fastdetection of rare events nowadays considered very difficultto observe.13th Int. Particle Acc. Conf. IPAC2022, Bangkok, Thailand JACoW PublishingISBN: 978-3-95450-227-1 ISSN: 2673-5490 doi:10.18429/JACoW-IPAC2022-MOPOPT017MC6: Beam Instrumentation, Controls, Feedback and Operational AspectsT03: Beam Diagnostics and InstrumentationMOPOPT017265ContentfromthisworkmaybeusedunderthetermsoftheCCBY4.0licence(©2022).Anydistributionofthisworkmustmaintainattributiontotheauthor(s),titleofthework,publisher,andDOIREFERENCES[1] A. Mahjoubfar, D. V. Churkin, S. Barland, N. Broderick, S.K. Turitsyn, and B. Jalali, “Time stretch and its applications”,Nature Photonics, vol. 11, pp. 341–351, 2017.[2] A. S. Bhushan, F. Coppinger, and B. Jalali, “Time-stretchedanalogue-to-digital conversion”, Electronics Letter, vol. 34,no. 9, pp. 839–841, 1998. doi:10.1049/el:19980750[3] E. Roussel et al., “Observing microscopic structures of a rela-tivistic object using a time-stretch strategy”, Scientific Reports,no. 10330, 2015. doi:10.1038/srep10330[4] M. Caselle et al., “Terabit sampling system with photonictime-stretch analog-to-digital converter”, SPIE Real-time Mea-surements, Rogue Phenomena, and Single-Shot ApplicationsVII, vol. 11986, pp. 21–33, 2022.[5] Analog devices, “Ultra-wideband 4 GS/s Track-and-Hold Amplifier DC - 18 GHz”, 2015, accessed05.06.2022, https://www.analog.com/media/en/technical-documentation/data-sheets/hmc661.pdf[6] ON semiconductors, “2.5V / 3.3V Dual Channel Pro-grammable Clock/Data Delay with Differential LVPECL Out-puts”, 2012, accessed 05.06.2022, https://www.onsemi.com/pdf/datasheet/nb6l295-d.pdf[7] Xilinx, “Zynq UltraScale+ RFSoC ZCU208 and ZCU216RF Data Converter Evaluation Tool”, 2021, accessed05.06.2022, https://docs.xilinx.com/v/u/en-US/ug1433-zcu216-rfsoc-eval-tool[8] J. Harris, “The ABCs of Interleaved ADCs”, 2019, ac-cessed 05.06.2022, https://www.semanticscholar.org/paper/The-ABCs-of-Interleaved-ADCs-Harris/9c5dbadbe8236328b933476326e37878792acb5313th Int. Particle Acc. Conf. IPAC2022, Bangkok, Thailand JACoW PublishingISBN: 978-3-95450-227-1 ISSN: 2673-5490 doi:10.18429/JACoW-IPAC2022-MOPOPT017MOPOPT017ContentfromthisworkmaybeusedunderthetermsoftheCCBY4.0licence(©2022).Anydistributionofthisworkmustmaintainattributiontotheauthor(s),titleofthework,publisher,andDOI266MC6: Beam Instrumentation, Controls, Feedback and Operational AspectsT03: Beam Diagnostics and Instrumentation

Terahertz sampling rates with photonic time-stretch for electron beam diagnostics

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Terahertz sampling rates with photonic time-stretch for electron beam diagnostics

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