Beam Divergence Measurements Research Articles

Study of Negative Ion Beamlets Produced in SPIDER by Beam Emission Spectroscopy

Among the beam diagnostics routinely employed in source for production of ion of deuterium (SPIDER), beam emission spectroscopy (BES) provides valuable information for beam characterization, thus driving source optimization methods. In particular, this technique is used to measure beam divergence and uniformity, which are crucial parameters to be optimized for application in International Experimental Thermonuclear Reactor (ITER). In this contribution, we focus on the characterization of H−/D− beamlets extracted during the first SPIDER Cs campaigns. In particular, we show parametric scans and preliminary broad component estimates on single beamlets.

Conceptual design of Doppler shift spectroscopy diagnostics for INTF

• Doppler Shift Spectroscopy diagnostics for ITER DNB at Indian Test Facility is conceptualised for neutral beam characterisation. • Modelling of the system suggests that 36 Line of Sights is required for a complete mapping of the beam. • A novel method of deconvolution of beam focusing effect in the total width is performed. • The error in divergence estimation of the 7 mrad focused divergent beam is less than 10%. INTF (Indian Test Facility) is a negative hydrogen ion source based neutral beam test facility to characterise 100 keV,60 A Diagnostic Neutral Beam (DNB), conceptualised for ITER. Several diagnostics are under development to monitor and characterise the performance of ion source and the beam properties. Doppler Shift Spectroscopy (DSS) diagnostics shall be used to estimate the beam divergence, beam inhomogeneity and the stripping losses of the extracted H − ion beam. In this work, the conceptualisation of the DSS diagnostics and the performance evaluation of the proposed system is presented. A forward model is developed to predict the signal strength and signal to noise ratio for various beam operation scenarios and for different optical setups. The model also estimates the expected error in the line width analysis carried for estimating the beam divergence. To reduce the error in the estimated beam divergence, a study on the error propagation was carried out by considering a range of viewing angles, different types of light collection systems and optical instruments. An optimum viewing angle, the light collection system and the instrumentation is chosen accordingly. An endoscopic design concept for each LOS has been adopted and the mechanical assembly of the same is presented in this work. The present work also reports that for a focused divergent beam, using conventional methods of line width analysis might lead large errors and impacts the beam divergence measurements obtained by DSS. A suitable algorithm has been developed to deconvolve the beam focusing spectral width contribution, thereby improving the preciseness of the beam divergence estimation.

2D broadband beamsteering with large-scale MEMS optical phased array

Optical-phased arrays (OPAs) enable complex beamforming, random-access beam pointing, and simultaneous scan and tracking of multiple targets by controlling the phases of two-dimensional (2D) coherent emitters. So far, no OPA can achieve all desirable features including large 2D arrays, high optical efficiency, wideband operation in wavelengths, fast response time, and large steering angles at the same time. Here, we report on a large-scale 2D OPA with novel microelectro-mechanical-system (MEMS)-actuated phase shifters. Wavelength-independent phase shifts are realized by physically moving a grating element in the lateral direction. The OPA has 160×160 independent phase shifters across an aperture of 3.1 mm×3.2 mm. It has a measured beam divergence of 0.042°×0.031°, a field of view (FOV) of 6.6°×4.4°, and a response time of 5.7 μs. It is capable of providing about 25,600 rapidly steerable spots within its FOV. The grating phase shifters are optimized for the near-infrared telecom wavelength bands from 1200 to 1700 nm with 85% optical efficiency.

Plasma beam structure diagnostics in krypton Hall thruster

AbstractKrypton Large Impulse Thruster (KLIMT) project was aimed at incremental development and optimization of a 0.5 kW-class plasma Hall Effect Thruster in which, as a propellant, krypton could be used. The final thermally stable version of the thruster (the third one) was tested in the Plasma Propulsion Satellites (PlaNS) laboratory in the Institute of Plasma Physics and Laser Microfusion (IPPLM) in Warsaw as well as in the European Space Agency (ESA) propulsion laboratory in the European Space Research and Technology Centre (ESTEC).During final measurement campaign, a wide spectrum of parameters was tested. The plasma potential, electron temperature, electron concentration, and electron energy probability function in the far-field plume of the thruster were measured with a single cylindrical Langmuir probe. Faraday probes were used for recording local values of ion current. Using several collectors in different locations and moving them on the surface of a sphere, the angular distribution of the expelled particles was reconstructed which was a local measure of beam divergence. Angular distribution of ion flux as measured with a central Faraday probe was parameterized with krypton mass flow rate, voltage, coil current ratio, and the cathode mass flow rate. Beam divergence measurements with Faraday probes as well as plasma parameters derived from Langmuir probe seem to be consistent with our understanding of the operating envelope. Obtained results will serve as a baseline in the design of plasma beam structure diagnostics system for the PlaNS laboratory.

Evaluation of beam divergence of a negative hydrogen ion beam using Doppler shift spectroscopy diagnostics

The Doppler Shift Spectroscopy (DSS) diagnostic is in the conceptual stage to estimate beam divergence, stripping losses, and beam uniformity of the 100 keV hydrogen Diagnostics Neutral Beam of International Thermonuclear Experimental Reactor. This DSS diagnostic is used to measure the above-mentioned parameters with an error of less than 10%. To aid the design calculations and to establish a methodology for estimation of the beam divergence, DSS measurements were carried out on the existing prototype ion source RF Operated Beam Source in India for Negative ion Research. Emissions of the fast-excited neutrals that are generated from the extracted negative ions were collected in the target tank, and the line broadening of these emissions were used for estimating beam divergence. The observed broadening is a convolution of broadenings due to beam divergence, collection optics, voltage ripple, beam focusing, and instrumental broadening. Hence, for estimating the beam divergence from the observed line broadening, a systematic line profile analysis was performed. To minimize the error in the divergence measurements, a study on error propagation in the beam divergence measurements was carried out and the error was estimated. The measurements of beam divergence were done at a constant RF power of 50 kW and a source pressure of 0.6 Pa by varying the extraction voltage from 4 kV to10 kV and the acceleration voltage from 10 kV to 15 kV. These measurements were then compared with the calorimetric divergence, and the results seemed to agree within 10%. A minimum beam divergence of ∼3° was obtained when the source was operated at an extraction voltage of ∼5 kV and at a ∼10 kV acceleration voltage, i.e., at a total applied voltage of 15 kV. This is in agreement with the values reported in experiments carried out on similar sources elsewhere.

Beam calorimetry at the large negative ion source test facility ELISE: Experimental setup and latest results

The test facility ELISE is the first step within the European roadmap for the development of the ITER NBI system. ELISE is equipped with a 1×0.9m2 radio frequency negative ion source (half the ITER source size) and an ITER-like 3-grid extraction system which can extract an H− or D− beam for 10s every 3min (limited by available power supplies) with a total acceleration voltage of up to 60kV. In the beam line of ELISE several beam diagnostic tools have been installed with the aim to evaluate beam intensity, divergence and uniformity.A copper diagnostic calorimeter gives the possibility to measure the beam power density profile with high resolution. The measurements are performed by an IR micro-bolometer camera and 48 thermocouples embedded in the calorimeter. A gaussian fit procedure has been implemented in order to characterize the large negative ion beam produced by ELISE.The latest results obtained from the beam calorimetry at ELISE show that the average beamlet group inhomogeneity is maximum 13%. The measured beam divergence agrees with the one measured by beam emission spectroscopy within 30%.

Comparison of objective lenses for multiphoton microscopy in turbid samples.

Optimization of illumination and detection optics is pivotal for multiphoton imaging in highly scattering tissue and the objective lens is the central component in both of these pathways. To better understand how basic lens parameters (NA, magnification, field number) affect fluorescence collection and image quality, a two-detector setup was used with a specialized sample cell to separate measurement of total excitation from epifluorescence collection. Our data corroborate earlier findings that low-mag lenses can be superior at collecting scattered photons, and we compare a set of commonly used multiphoton objective lenses in terms of their ability to collect scattered fluorescence, providing guidance for the design of multiphoton imaging systems. For example, our measurements of epi-fluorescence beam divergence in the presence of scattering reveal minimal beam broadening, indicating that often-advocated over-sized collection optics are not as advantageous as previously thought. These experiments also provide a framework for choosing objective lenses for multiphoton imaging by relating the results of our measurements to various design parameters of the objectives lenses used.

Emittance of positron beams produced in intense laser plasma interaction

The first measurement of the emittance of intense laser-produced positron beams has been made. The emittance values were derived through measurements of positron beam divergence and source size for different peak positron energies under various laser conditions. For one of these laser conditions, we used a one dimensional pepper-pot technique to refine the emittance value. The laser-produced positrons have a geometric emittance between 100 and 500 mm·mrad, comparable to the positron sources used at existing accelerators. With 1010-1012 positrons per bunch, this low emittance beam, which is quasi-monoenergetic in the energy range of 5–20 MeV, may be useful as an alternative positron source for future accelerators.

Beam characterization and spatial coherence measurement of F2 laser using Lumilass glass fluorescence

This paper presents the spectral emission and saturation properties of a Lumilass G9 fluorescence glass excited using a 157nm laser emitting ∼10ns duration pulses. This fluorescence glass can be applied in conjunction with a CCD array for beam profiling and divergence measurements. This method can also be used for deriving information on the spatial coherence function of the F2 laser. This constitutes one of the major contributions of the paper and is also discussed.

Design of a beam emission spectroscopy diagnostic for negative ions radio frequency source SPIDER

A facility will be built in Padova (Italy) to develop, commission, and optimize the neutral beam injection system for ITER. The full scale prototype negative ion radio frequency source SPIDER, featuring up to 100 kV acceleration voltage, includes a full set of diagnostics, required for safe operation and to measure and optimize the beam performance. Among them, beam emission spectroscopy (BES) will be used to measure the line integrated beam uniformity, divergence, and neutralization losses inside the accelerator (stripping losses). In the absence of the neutralization stage, SPIDER beam is mainly composed by H(-) or D(-) particles, according to the source filling gas. The capability of a spectroscopic diagnostic of an H(-) (D(-)) beam relies on the interaction of the beam particles with the background gas particles. The BES diagnostic will be able to acquire the H(α) (D(α)) spectrum from up to 40 lines of sight. The system is capable to resolve stripping losses down to 2 keV and to measure beam divergence with an accuracy of about 10%. The design of this diagnostic is reported, with discussion of the layout and its components, together with simulations of the expected performance.

Performance Evaluation of the T6 Ion Engine

*† * ‡ § ** The T6 ion engine is a 22-cm diameter, 4.5-kW Kaufman-type ion thruster produced by QinetiQ, Ltd., and is baselined for the European Space Agency BepiColombo mission to Mercury and is being qualified under ESA sponsorship for the extended range AlphaBus communications satellite platform. The heritage of the T6 includes the T5 ion thruster now successfully operating on the ESA GOCE spacecraft. As a part of the T6 development program, an engineering model thruster was subjected to a suite of performance tests and plume diagnostics at the Jet Propulsion Laboratory. The engine was mounted on a thrust stand and operated over its nominal throttle range of 2.5 to 4.5 kW. In addition to the typical electrical and flow measurements, an EB mass analyzer, scanning Faraday probe, thrust vector probe, and several near-field probes were utilized. Thrust, beam divergence, double ion content, and thrust vector movement were all measured at four separate throttle points. The engine performance agreed well with published data on this thruster. At full power the T6 produced 143 mN of thrust at a specific impulse of 4120 seconds and an efficiency of 64%; optimization of the neutralizer for lower flow rates increased the specific impulse to 4300 seconds and the efficiency to nearly 66%. Measured beam divergence was less than, and double ion content was greater than, the ring-cusp-design NSTAR thruster that has flown on NASA missions. The measured thrust vector offset depended slightly on throttle level and was found to increase with time as the thruster approached thermal equilibrium.

Use of the focusing multi-slit ion optical system at RUssian Diagnostic Injector (RUDI)

The upgrade of the diagnostic neutral beam injector RUDI in 2010 was performed to increase the beam density at the focal plane in accordance with the requirements of charge-exchange recombination spectroscopy diagnostics. A new focusing ion-optical system (IOS) with slit beamlets and an enlarged aperture was optimized for 50% higher nominal beam current and reduced angular divergence with respect to the previous multi-aperture IOS version. The upgraded injector provides the beam current up to 3 A, the measured beam divergence in the direction along the slits is 0.35°. Additionally, the plasma generator was modified to extend the beam pulse to 8 s.

A Continuously Operated 70mA, 50keV Proton Source for Plasma Diagnostic and Other Applications

A radio-frequency ion source has been developed in the Budker Institute of Nuclear Physics, Novosibirsk. Ion source is designed to operate in cw mode with beam modulation. The ion source works with hydrogen at 50kV producing an ion beam current of up to 70mA. The beam is extracted and accelerated by using a four electrode ion-optical system with single aperture. Initial beam diameter is 8 mm. The measured beam divergence is less than 0.5 deg. half angle.This paper describes the experimental results obtained during the ion source testing. Ion source can be applied in many areas including plasma diagnostic, accelerator technique, ion implantation, etc.

散斑相关在椭圆高斯光束发散角测量中的应用

散斑相关在椭圆高斯光束发散角测量中的应用

About the correlation between the centre and the wings of a hard-apertured Gaussian beam

The paper considers the influence of near-field clipping upon the accuracy of angular divergence measurement of a laser beam. We have shown that power fraction that contain the centre and the wings of a diffracted beam are not necessarily correlated. This effect can lead to systematic important errors on laser beam divergence measurement even when the beam under consideration is weakly truncated. In particular, the monitoring of any variable lensing effect can be greatly affected by such effects since one could be mistaken about its sign (converging or diverging).

Wide-aperture no-moving-parts optical beam profiler using liquid-crystal displays

To the best of our knowledge, we demonstrate the first no-moving-parts largest aperture profiler design that is also cost effective. Specifically exploited is the large-scale production of thin-film transistor liquid-crystal displays (LCDs) to produce a high intrinsic reliability low-cost profiler. Today, the maximum beam diameter under test can reach 70 cm using 117 cm diagonal LCDs. Experiments conducted with the laboratory LCD profiler include 1D and 2D knife-edge profiling, 2D pinhole profiling, and beam divergence measurements.

Simultaneous Measurements of Proton Ratio and Beam Divergence of Positive-Ion-Based Neutral Beam in the Large Helical Device

A spectroscopy system was installed on the diagnostic neutral beam injector in LHD. The Hα lines spectrum emitted by full, half and one-third energy component are clearly observed, and the proton ratio and the beam divergence were estimated by the line intensity and the line width, respectively. The proton ratio of 85∼90 % is achieved in high arc power discharge. The beam divergence of them shows their minimum with the same perveance. It was experimentally confirmed that the spectroscopy system is useful for the monitor of the proton ratio and the divergence of the beam.

Xenon ion beam characterization in a helicon double layer thruster

A current-free electric double layer is created in a helicon double layer thruster operating with xenon and compared to a recently developed theory. The Xe+ ion beam formed by acceleration through the potential drop of the double layer is characterized radially using an electrostatic ion energy analyzer. For operating conditions of 500W rf power, 0.07mTorr gas pressure, and a maximum magnetic field of 125G, the measured beam velocity is about 6kms−1, the beam area is about 150cm2, and the measured beam divergence is less than 6°.

Acceleration of MeV-class energy, high-current-density H−-ion beams for ITER neutral beam system

For the ITER neutral beam system, reasearch and development of a vacuum-insulated MeV accelerator has been carried out at Japan Atomic Energy Research Institute. After a successful 1MV insulation in vacuum for more than 2h, H−-ion-beam acceleration test is in progress to fulfill the ITER requirement of the current density of 200A∕m2 at 1MeV, with good beam optics quality of <7mrad divergence. For such a high-current-density H−-ion-beam acceleration, the Kamaboko negative-ion source was operated at high input power, with increased filament number and magnetic filter strength. The optimum perveance was investigated by scanning the extraction and acceleration voltages, together with the beam divergence measurement. As a consequence, H−-ion beams of 146A∕m2 (total ion-beam current: 206mA) were obtained at 836keV, of which power density is in the “ITER relevant” level. Such high-power-density beams with a divergence as low as 5mrad were obtained at the optimum perveance corresponding to that of the ITER (200A∕m2 at 1MeV).

Measurement of neutron flux and beam divergence at the cold neutron guide system of the new Munich research reactor FRM-II

A sophisticated neutron guide system has been installed at the new Munich neutron source FRM-II to transport neutrons from the D 2 cold neutron source to several instruments, which are situated in a separate neutron guide hall. The guide system takes advantage of supermirror coatings and includes a worldwide unique “twisted” guide for a desired phase space transformation of the neutron beam. During the initial reactor commissioning in summer 2004, the integral and differential neutron flux as well as the distribution of beam divergence at the exit of two representative and the twisted neutron guide were measured using time-of-flight spectroscopy and gold-foil activation. The experimental results can be compared to extensive simulation calculations based on MCNP and McStas. The investigated guides fulfill the expectations of providing high neutron fluxes and reveal good quality with respect to the reflective coatings and the installation precision.