Emittance Measurements Research Articles

Statistical Characterization of Emitter Fabrication over Electrospray Array Thruster

A method for characterizing the variance in fabrication of emitters and extractors in a porous conical electrospray array thruster is presented. Coherence scanning interferometry is used to produce topographic maps of 543 of 576 sites within the array. The emitter and extractor geometries, features of size a few hundred micrometers, are modeled as a spherically capped cone recessed from a circular aperture. Regressing this model against the topographic maps yields a set of salient parameters that describe the geometry of a site, including the tip radius and height of the emitter and its offset from the extractor aperture. Statistics over the emitter geometries are computed, which represent manufacturing tolerances. It is found that key parameters like the emitter tip radius are highly variable (mean 25.8 μm and standard deviation 20.9 μm), highlighting the stochastic nature of the manufacturing process. Correlations between the tip radius and emitter height indicate that this variability arises from blunting of the emitters during fabrication, and the observation that emitters are shorter than nominal is explained by an increase in effective cutting diameter of the tools. Further analysis indicates that determining the mean emitter tip radius of the entire population within 5% error requires over 300 individual emitter measurements. These results indicate that accurately quantifying emitter variability at scale requires rigorous and extensive analysis, and the implications of this emitter variability for device performance and design are discussed.

Spectral emittance measurements for ytterbium disilicate‐based environmental barrier coatings

AbstractThe spectral reflectance and transmittance of two free‐standing ytterbium disilicate (Yb2Si2O7)—based environmental barrier coatings (EBCs) were measured from 25°C up to 1270°C. The measurements were collected over the spectral range of approximately 2–20 µm. The spectral emittance was then determined through conservation of energy and Kirchhoff's law of thermal radiation. The spectral emittance measurements for the EBCs were then compared to previous measurements for a thermal barrier coating (TBC).

Simulation and Measurement of Carbon Ion Beam Emittance in the Channel of Radiobiological Research at the Accelerator Complex U-70

The technique for determining the emittance of carbon ion beams by measuring their transverse dimensions at the end of the air gap of the channel is described. The inverse transformation of phase ellipses is considered, taking into account multiple Coulomb scattering of particles and the presence of dispersion in the carbon ion beam. The values of betatron emittance before the first quadrupole lens are given and compared with data obtained by direct calculation starting from the inner target. Inaccuracies in the calculated and measured emittance values are discussed. Simulations and measurements were performed at beam energies of 200, 300, and 400 MeV/nucleon in front of the target.

All-optical source size and emittance measurements of laser-accelerated electron beams

Novel schemes for generating ultralow emittance electron beams have been developed in past years and promise compact particle sources with excellent beam quality suitable for future high-energy physics experiments and free-electron lasers. Recent theoretical work has proposed a laser-based method capable of resolving emittances in the sub 0.1 mm mrad regime by modulating the electron phase space ponderomotively. Here we present the first experimental demonstration of this scheme using a laser wakefield accelerator. The observed emittance and source size are consistent with published values. We also show calculations demonstrating that tight bounds on the upper limit for emittance and source size can be derived from the “laser-grating” method even in the presence of low signal to noise and uncertainty in laser-grating parameters. Published by the American Physical Society 2024

Enhanced Production of Multicharged Ions by Mixing Low Z Gas and Emittance Measurement on Electron Cyclotron Resonance Ion Source

We have studied to enhance efficiency of producing multicharged ions in an electron cyclotron resonance ion source (ECRIS). The gas mixing method is known as an empirical method for highly efficient production of multicharged ions. This method is to mix low Z gas into the multicharged ions plasma. There are various explanations for the gas mixing effect. One of them is the ion cooling effect. It is necessary to obtain parameters related to the ion temperature in order to experimentally confirm the effect. We measured emittances for ion beams by using a wire probe and a multi-slit. He was mixed as a low Z gas into the operating Ar gas. Charged state distributions of ion beams was measured to confirm the gas mixing effect. We have also measured emittances for the multicharged Ar ion beams and compared root mean square emittances (ε rms) of those for pure Ar and Ar mixed by He. We confirmed that ε rms for Ar mixed by He was lower than that for pure Ar.

Development of an Image Analysis Method for Pepperpot Emittance Monitors

At the RIKEN Nishina Center for Accelerator-Based Science, we developed a pepperpot emittance monitor using a method that can change the distance between the pepperpot mask and the screen. The accuracy can be improved by correctly identifying the beam’s position at a close range followed by the increase of the distance; however, if the distance is increased excessively, the position matching will be difficult. To solve this problem, we developed a method for tracking continuous changes on a screen using optical flow. Using this method, the distance between the pepperpot mask and screen could be extended without plotting in the wrong area in the phase space, and the emittance measurement accuracy was successfully improved by more than 10%. This development will enable beam transport simulations to be performed more accurately.

Slice emittance measurements using a slit-grid system and a fast wall-current monitor.

The time evolution of beam properties in an electron bunch with the duration of a nanosecond was measured with a time resolution of several tens of picoseconds. A combination of horizontal and vertical slits cuts the beamlet from the original beam, with the current waveform of the beamlet measured using a fast wall-current monitor. The reconstruction of the waveform data obtained by scanning these two slits over the entire beam area provided the time evolution of the spatial profile. A similar measurement using two horizontal (vertical) slits separated by a certain distance also provides the time evolution of the phase-space profile. Using this method, the initial beam extracted from the CeB6 thermionic electron gun of the x-ray free-electron laser (XFEL) SACLA was evaluated. Although the slice emittance in the bunch was measured to be constant, the centroid of the spatial profile moved in the transverse direction by a few hundred micrometers in the 0.6ns flat-top region. This movement arises from the temporal variation in the rectangular high-voltage pulse of the beam chopper and can cause an increase in the projected emittance. These measurements are important for evaluating the conditions of the initial beam emitted from the cathode and processed downstream of the gun. Hence, the proposed diagnostic system will play an important role in developing an extremely low-emittance electron beam or an artificial electron beam with a multi-bunch or micro-bunch structure that enhances the brightness of the XFEL light.

The method to measure the UV emittance of low-pressure-lamps: a commentary on Schmalwieser et al. (2021)

Abstract In the paper by Schmalwieser and colleagues, the irradiance on the wall of a cylindrical UV reactor for water disinfection was measured. This is a useful way to measure/evaluate such UV devices. However, this measurement is not a solution for measuring the UV emittance of low-pressure-lamps. In fact, throughout the paper, the method and the emittance measurements that the title claimed were not really provided. The title of the paper claiming to be a ‘standardized method to measure the longitudinal UV emittance’ is misleading.

Effect due to Cs injection upon current oscillation of the beam extracted from the J-PARC negative hydrogen ion source

A high-speed emittance measurement system installed at the J-PARC RF negative hydrogen (H-) ion source test stand can construct emittance diagrams of the beam of a specific frequency component. The driving 2 MHz RF power produces small amplitude oscillating components at 2 MHz and at higher harmonic frequencies in the total H- ion beam detected by a Faraday installed downstream of the emittance measurement system. Magnitudes of oscillating component at 2 MHz and 4 MHz frequencies become appreciable as the slits of the emittance measurement system separate the H- ion beam into the position/angle resolved phase space elements. The reconstructed emittance diagrams of H- ion beams for the operation condition with continuous supply of Cs realizing large H- ion current to total extraction current ratios indicate that 2 MHz and 4 MHz frequency oscillating beam components propagate surrounding the center DC beam. Both 2 MHz and 4 MHz oscillating beam components comprise two to three beam particle groups in the phase space. The DC component of the H- ion beam exhibit a single peak in the angular distribution. Meanwhile, oscillating components often take the minima where the DC H- ion beam takes the maximum in the angular distribution diagram. Thus, the regions that produce large amplitude oscillations of the H- ion beam are considered located at the circumference of the beam extraction aperture. One possible explanation for observing larger amplitude beam oscillation can be the enhanced H- ion surface production at the plasma facing the wall of the beam extraction aperture. The operation without the Cs delivery to the source increased electron current coextracted with H- ions and changed the structure of the beam emittance diagram. In the direction perpendicular to the magnetic fields created by a magnetic filter and electron suppression magnets, the peak of the 4 MHz oscillating beam components appeared at the center of the DC beam. This observation suggests the extraction of H- ions formed in the central region by the volume production process near the internal RF antenna. Mechanisms that can excite and diminish the beam fluctuation amplitudes of the extracted H- ion beam are discussed.

Development of a scintillation screen monitor and emittance measurement experiment at the National Cancer Center Korea

Development of a scintillation screen monitor and emittance measurement experiment at the National Cancer Center Korea

FAST Low-Energy Beamline Studies: Toward High-Peak 5D Brightness Beams for FAST-GREENS

The FAST beamline is the injector for the planned Gamma-Ray Electron ENhanced Source (GREENS) program, which aims to achieve the demonstration and first application of a high-efficiency, high-average-power free-electron laser at 515 nm. FAST-GREENS requires high 5D peak brightness; transverse normalized projected emittances of 3 mm-mrad and a peak current of 600 A are the minimum beam requirements for the FEL to reach the 10% efficiency goal. In this work, studies of the low-energy section of the FAST beamline are presented toward these ends, including preliminary measurements of beam compression and beam emittance. An effort toward developing a high-fidelity simulation model that could be later optimized for FAST-GREENS is presented.

Applying fully convolutional networks for beam profile and emittance measurements

The transverse cross-sectional size and emittance are critical beam parameters that characterize the performance of the accelerator and assess the state of the beam. Inspired by the success of machine learning in image processing tasks, we have crafted a bespoke measurement system with a primary focus on accurately determine the transverse cross-sectional size and emittance of the beam. The system utilizes a beam spot detector to convert the beam spot to a light spot image, which is then projected onto the CCD camera through the telecentric lens for the acquisition. The image data collected by the camera is subsequently imported into the EPICS database developed based on ADAravis software. We employ the Gaussian fitting technique on the collected images to accurately calculate the cross-sectional size of the beam. Furthermore, by incorporating the four-level iron scanning method, the lateral emittance of the beam is calculated in a comprehensive manner. To suppress the salt and pepper noise introduced due to the presence of dark current and beam shooting phenomena on the transmission line, we propose a novel fully convolutional neural network (FCN) design with preactivated residual units. The test conducted at HLS-II confirms that the measurement uncertainty of this system is superior to 27.5 μm. Moreover, when operating at an electron beam energy of 800 MeV, the measured emittance of the accelerator is found to be 38.515 nm·rad, a value closely aligning with the theoretical value of 36.2 nm·rad. These compelling results provide strong evidence supporting the reliability of the emittance measurement algorithm, making it suitable for deployment in the forthcoming terahertz accelerator.

Single-shot emittance measurement and optimization of a hybrid photo-cathode gun beam

A unique hybrid photo-cathode S-band gun accelerator is in operation at Ariel University. The accelerator produces an ultra-fast relativistic electron beam with beam characteristics of 6 MeV kinetic energy, 30 pC charge, and 150 fs pulse duration. In this paper, we present a compact transverse emittance measurement system using the multi-slit mask technique. The system is calibrated using a fully automatic calibration routine, and the results are obtained instantaneously. To find the optimal parameters required to obtain the lowest transverse emittance value, we scan the currents in the focusing coils surrounding the gun including a bucking coil current scan to minimize the magnetic field upon the photo-cathode. In the last step, we verify the relation between transverse emittance and electron beam charge in RF guns emitted from a photo-cathode. The verification is done by a beam charge scan.

Measurement of the longitudinal bunch-shape distribution for a high-intensity negative hydrogen ion beam in the low-energy region

A bunch-shape monitor (BSM) is a useful device for performing longitudinal beam tuning using the pointwise longitudinal phase distribution measured at selected points in the beam transportation. To measure the longitudinal phase distribution of a low-energy negative hydrogen (${\mathrm{H}}^{\ensuremath{-}}$) ion beam, highly oriented pyrolytic graphite (HOPG) was adopted for the secondary-electron-emission target to mitigate the thermal damage due to the high-intensity beam loading. The HOPG target enabled the measurement of the longitudinal phase distribution at the center of a 3-MeV ${\mathrm{H}}^{\ensuremath{-}}$ ion beam with a high peak current of about 50 mA. The longitudinal bunch width was measured using HOPG-BSM at the test stand, which was consistent with the beam simulation. The correlation measurement between the beam transverse and longitudinal planes was demonstrated using HOPG-BSM. The longitudinal Twiss and emittance measurement with the longitudinal Q-scan method was conducted using HOPG-BSM. The measured longitudinal emittance is consistent with the beam simulation using the radio-frequency quadrupole design input.

The application of encoder–decoder neural networks in high accuracy and efficiency slit-scan emittance measurements

A superconducting radio-frequency (SRF) photo injector is in operation at the electron linac for beams with high brilliance and low emittance (ELBE) radiation center and generates continuous wave (CW) electron beams with high average current and high brightness for user operation since 2018. The speed of emittance measurement at the SRF gun beamline can be increased by improving the slit-scan system, thus the measurement time for one phase space mapping can be shortened from about 15 min to 90 s. The convolution neural networks are applied to improve the efficiency and accuracy of beamlet images processing. In order to estimate the uncertainty in the calculation of normalized emittance, we analyze the main error contributions.

Broadband Air-Coupled Ultrasound Emitter and Receiver Enable Simultaneous Measurement of Thickness and Speed of Sound in Solids.

Air-coupled ultrasound sensors have advantages over contact ultrasound sensors when a sample should not become contaminated or influenced by the couplant or the measurement has to be a fast and automated inline process. Thereby, air-coupled transducers must emit high-energy pulses due to the low air-to-solid power transmission ratios (10-3 to 10-8). Currently used resonant transducers trade bandwidth-a prerequisite for material parameter analysis-against pulse energy. Here we show that a combination of a non-resonant ultrasound emitter and a non-resonant detector enables the generation and detection of pulses that are both high in amplitude (130 dB) and bandwidth (2 µs pulse width). We further show an initial application: the detection of reflections inside of a carbon fiber reinforced plastic plate with thicknesses between 1.7 mm and 10 mm. As the sensors work contact-free, the time of flight and the period of the in-plate reflections are independent parameters. Hence, a variation of ultrasound velocity is distinguishable from a variation of plate thickness and both properties are determined simultaneously. The sensor combination is likely to find numerous industrial applications necessitating high automation capacity and opens possibilities for air-coupled, single-side ultrasonic inspection.

Transverse emittance measurement in 2D and 4D performed on a Low Energy Beam Transport line: benchmarking and data analysis

2D and 4D transverse phase-space of a low-energy ion-beam is measured with two of the most common emittance scanners. The article covers the description of the installation, the setup, the settings, the experiment and the benchmark of the two emittance meters. We compare the results from three series of measurements and present the advantages and drawbacks of the two systems. Coupling between phase-space planes, correlations and mitigation of deleterious effects are discussed. The influence of background noise and aberrations of trace-space figures on emittance measurements and RMS calculations is highlighted, especially for low density beams and halos. A new data analysis method using noise reduction, filtering, and reconstruction of the emittance figure is described. Finally, some basic concepts of phase-space theory and application to beam transport are recalled.

Measurement of electron beam transverse slice emittance using a focused beamline

Abstract A single-shot measurement of electron emittance was experimentally accomplished using a focused transfer line with a dipole. The betatron phase of electrons based on laser wakefield acceleration (LWFA) is energy dependent owing to the coupling of the longitudinal acceleration field and the transverse focusing (defocusing) field in the bubble. The phase space presents slice information after phase compensation relative to the center energy. Fitting the transverse size of the electron beam at different energy slices in the energy spectrum measured 0.27 mm mrad in the experiment. The diagnosis of slice emittance facilitates local electron quality manipulation, which is important for the development of LWFA-based free electron lasers. The quasi-3D particle-in-cell simulations matched the experimental results and analysis well.

Conceptualization of Multidimensional Finite Impulse Response (FIR) Filter for Projected Emittance Images-sets

Photoemission in modern high-brightness electron sources is under study at the DESY-PITZ photo injector. The electron source optimization process is under continuous upgrading. The developments in modern digital signal processing provide an opportunity for building intelligent algorithms that implement mathematical methods unattainable by analogue technology which can support the related image of emittance measurements from PITZ system. In this work, we provide an intriguing technique for designing multilayer FIR filters with minimal computing effort. As a result, the filter design is particularly effective at reducing complicated noise and performs quickly and efficiently.

Measurement of transverse beam emittance of split beams for the CERN Proton Synchrotron Multi-Turn Extraction

Crossing a horizontal nonlinear resonance is the approach that can be used to split a beam in several beamlets with the goal to perform multi-turn extraction from a circular particle accelerator. Such an approach has been successfully implemented in the CERN Proton Synchrotron and is used routinely for the production of high-intensity proton beams for fixed-target physics at the Super Proton Synchrotron. Recently, thanks to the deployment of diamond detectors, originally installed to monitor the beam losses at extraction, it has been possible to measure the horizontal beam emittance of the split beam just prior to extraction. This is the first time that an emittance measurement is attempted for split beams, i.e. in a regime of highly nonlinear beam dynamics. In this paper, the technique is presented and its application to the analysis of the experimental data is presented and discussed in detail. This result is essential for the performance assessment of the splitting process and for the design of further performance improvements.