Beam Current Distribution Research Articles

Beam dynamics optimization of EuPRAXIA@SPARC_LAB RF injector

At EuPRAXIA@SPARC_LAB an X-ray FEL user facility is driven by a plasma accelerator in the particle-driven configuration where an ultra-relativistic beam, the driver, through a plasma generates a wake of charge density useful for accelerating a witness beam. The electron bunches are generated through the so-called comb technique in an RF injector that consists of a 1.6-cell S-band gun followed by four S-band TW accelerating structures. The main working point foresees a 30pC witness and a 200pC driver longitudinally compressed in the first accelerating structure operated in the velocity-bunching regime, which allows to accelerate and manipulate the beam to reach proper transverse and longitudinal parameters. The optimization of the witness emittance is performed with additional magnetic field around the gun and the velocity bunching S-band structures and by shaping the laser pulse at the cathode. The paper reports on beam dynamics studies performed also with the insertion of an X-band RF cavity after the gun that is proposed to shape the beam current distribution and stabilize it with respect to RF jitters.

Measurements of beam characteristics on a 70 MeV H− cyclotron system for ISOL beam production

A 70 MeV H− cyclotron system was commissioned in order to measure the beam characteristics for the isotope separation on line (ISOL) operation in the energies range between 40 and 70 MeV. Using internal beams, the cyclotron magnet was precisely isochronized by applying the Smith-Garren method, achieving a main-coil current margin of 0.2 A for the beam stability. In the center region, beam profiles were measured by a differential radial probe to verify the specified dee voltage of 50 kV, which allows well-defined turn separation. Extracted beams were then used to check the beam line alignment by monitoring beam losses on segmented collimators and measuring variations on beam profiles. We measured transverse emittances of the cyclotron beam at a current of 25 µA by observing the beam profiles with upstream quadrupole strengths varied, which was the first time for this kind of 70 MeV cyclotron. Transmission efficiency along the beam line was measured as above 98% at a current of 100 µA. A temporary beam line was installed in the ISOL area, and we measured beam current distributions using a beam profile monitor shaped by wobbling at 60 Hz at a target location for beam diameters of 2 and 5 cm. A specific current distribution is generally required to reduce the maximum thermal stresses induced on the target. Finally, a maximum beam power of 50 kW was successfully tested at 70 MeV for 6 h.

Reduced Plasma Frequency Calculation Based on Particle-in-Cell Simulations

We propose a scheme to calculate the reduced plasma frequency of a cylindrical-shaped electron beam flowing inside of a cylindrical tunnel, based on results obtained from Particle-in-cell (PIC) simulations. In PIC simulations, we modulate the electron beam using two parallel, non-intercepting, closely-spaced grids which are electrically connected together by a single-tone sinusoidal voltage source. The electron energy and the beam current distributions along the length of the tunnel are monitored after the system is operating at steady-state. We build a system matrix describing the beam's dynamics, estimated by fitting a 2x2 matrix that best agrees with the first order differential equations that govern the physics-based system. Results are compared with the theoretical Branch and Mihran model, which is typically used to compute the plasma frequency reduction factor in such systems. Our method shows excellent agreement with the theoretical model, however, it is also general. Our method can be potentially utilized to determine the reduced plasma frequencies of electron beams propagating in differently-shaped beam tunnels, where no theoretical model yet exists, such as the case of a cylindrical or elliptical electron beam propagating inside of a metallic beam tunnel of cylindrical, square, or elliptical cross-section. It can be applied also to electron beams composed of multiple streams.

GPU Simulation of Electron Beam Current Distribution during Pulsed Heating of a Metal Target

The GPU implementation by means of the OpenACC technology of the simulation of the current distribution in tungsten sample is heated by an electron beam pulse is presented.A special case of axial symmetry without taking into account electrical driving forces is considered. The temperature in the sample, calculated from the two-phase Stefan problem, is needed to solve the electrodynamic equations. The calculation time for different GPUs compared to CPU time is given.

Parallel Algorithm for Calculating the Dynamics of the Electron Beam Current Distribution during Pulsed Heating of a Metal Target

Speedup and efficiency of two parallel algorithms for calculating the dynamics of the current distribution when the surface of a tungsten sample is heated by an electron beam pulse are presented. The algorithms are implemented using OpenMP technology. A special case of axial symmetry without taking into account electric driving forces is considered. The temperature in the sample, calculated on the basis of the two-phase Stefan problem, is necessary for solving electrodynamic equations. To implement them, the methods of Jacobi and the successive over-relaxation methods were used. Pipelining is used to parallelize the successive over-relaxation algorithm. The current is considered as a possible source of rotation of the substance, which is observed in the experiment.

Landau Damping with Electron Lenses in Space-Charge Dominated Beams

Further progress of fundamental physics requires accelerated beams of high intensity. The intensities, however, are limited by many factors, including coherent beam instabilities. Usual methods to control the instabilities, such as octupole magnets, beam feedback dampers and employment of chromatic effects, may be ineffective or insufficient. Electron lenses were proposed as a means to provide stabilizing spread in the beam betatron frequencies. It was shown that electron lenses are uniquely effective for Landau damping of transverse beam instabilities in high energy particle accelerators, and that their employment does not compromise incoherent (single particle) stability, dynamic aperture and the beam lifetime. Here we consider effectiveness of the Landau damping with electron lenses when the space charge tune shift cannot be neglected. We demonstrate that the desired stability can be assured with proper choice of the electron beam parameters and current distributions.

Variable beam entrance Faraday cup system for pulsed electron beam current profile characterization.

A high accuracy variable beam entrance Faraday cup (VBEFC) system is designed in this work. The presented VBEFC system is designed for the beam current profile measurement of the transient hollow cathode discharge (THCD) generated pulsed electron beam, which is a new source of high energy flux for metallic material processing. By proper designs of the beam entrance array, fast response electron collector, grounding, and shielding, this VBEFC system is capable of determining the radial profile and its temporal evolution of the THCD generated electron beam. The results of the electron beam current and current density distributions collected at varying radial locations and times under multiple voltages are presented in this paper. The experimental results show that both the amplitude and the current density of the THCD electron beam at a given radius always increased with the increase in the accelerating voltage, which is coincident with the self-focused propagation of the electron beam promoted by the voltage.

Research on thermal effect of KDP crystal under ion beam cleaning

KDP crystal is difficult to fabricate for high precision. because it is brittle soft and with high heat expansion. Magnetorheological finishing (MRF) has been used to machine KDP for high precision. However, iron powders are easily embedded into KDP surface. Ion beam figuring (IBF) can clean iron powders embedded and enhanced laser-induced damage resistance. However, the thermal effect introduced by incident ions is a headachy problem. Temperature fields have been calculated by finite element simulation and measured by experiments. Thereof temperature fields of optical component bombarded by low energy ion beam were estimated and this estimate method is proved to be correct and feasible by comparing results of finite element simulation and experiments. And then, thermal stress of KDP under ion beam irradiation was calculated and discussed. Distributions of temperature and stress on KDP surface are accordant with beam current distribution. Temperature and stress rise quickly under ion beam irradiation, while decreases rapidly without ion beam irradiation. Peaks of temperature and thermal stress tend to periodicity. The period corresponds the period of ion beam moving spasmodically and fleetly in Y direction. Tensile stresses are not visible at X/Y/Z direction, but compressive stress at X direction is larger obviously than that of Y/Z direction.

Assessment of the SPIDER beam features by diagnostic calorimetry and thermography.

The full-size ITER ion source prototype SPIDER (Source for the Production of Ions of Deuterium Extracted from a Radio frequency plasma) has recently started beam operation, whose objective is to produce 100 keV, 60 A hydrogen negative ions for 1 h. The source is presently operated in the volume regime, and the beam power is consequently limited. In such a configuration, the high resolution calorimeter STRIKE (Short-Time Retractable Instrumented Kalorimeter Experiment), even though uncooled, may be used instead of the SPIDER beam dump without limiting the beam-on time. STRIKE is formed by unidirectional carbon fiber-carbon matrix (CFC) composite tiles that are exposed to the beam while their temperature is recorded by using two infra-red cameras. This setup, thanks to the moderate broadening of the temperature profile guaranteed by the anisotropy of CFC, allows for the determination of detailed features of the beam current distribution (spatial resolution is about 2 mm). Furthermore, positively biasing the CFC tiles permits a direct electrical measurement of the negative ion beam current. Besides the total beam current and beam uniformity, which can be retrieved both by calorimetry and electrical measurement, beamlet divergence and deflection can be determined by infra-red thermography. This contribution describes the characterization of the SPIDER negative ion beam as a function of the source and accelerator parameters by means of the diagnostic calorimeter STRIKE in the volume regime.

The facility effects of a Hall effect thruster's relative exhaust direction in ground tests

This research focuses on understanding how the relative pumping orientation and backpressure of a vacuum facility affects the measured performance and plasma plume parameters of a Hall-effect thruster (HET). A HET was operated in two opposite directions: plume ejection towards the vacuum pump and plume ejection away from the pump. The HET plume for each orientation was individually characterized at three vacuum facility operating pressures to study the effect of the facility pumping orientation and backpressure on the measured plume parameters and thruster performance. The ion current density, divergence angle, beam current, and ion energy distribution were measured using a Faraday probe and a retarding potential analyzer (RPA). The variation in the direction of the plume with respect to the pumping orientation leads to a clear difference in the measured performance of the HET when operating at an elevated backpressure. These are the first experiments that take the effect of the pumping orientation of a vacuum facility with respect to the thruster's exhaust direction into consideration. The results here will aid future research in selecting an adequate thruster exhaust direction when performing different Hall thruster ground tests such as plume diagnostics, lifetime tests, and erosion tests.

Design of two by three element fractal tree antenna array for WLAN and WiFi applications

For more antenna miniaturization, novel fractal tree geometry designed for 5 iterations using rectangular and triangular patches that allow decrease in the resonance frequency without occupying more space. Impedance Matching can be improved without changing the main beam direction or current distribution to five iterations with branching half angle of 60 degrees. The antenna fed by a Coaxial or probe feed to improve the narrow bandwidth of Fractal Antenna. The proposed antenna achieves a bandwidth of 31.5% for 10 dB return loss, covering the frequency range 2.4–3.6 GHz for WLAN and WiFi applications. The antenna gain of the fractal element is about 3 dBi. Array is designed to increase the gain and radiation energy. Arrays are configured at operating frequency of 2.4 GHz by using six elements to enhance the gain up to 11 dBi. The obtained gain and frequency are suitable for WLAN and WiFi applications.

A 128-channel picoammeter system and its application on charged particle beam current distribution measurements.

A 128-channel picoammeter system is constructed based on instrumentation amplifiers. Taking advantage of a high electric potential and narrow bandwidth in DC energetic charged beam measurements, a current resolution better than 5 fA can be achieved. Two sets of 128-channel strip electrodes are implemented on printed circuit boards and are employed for ion and electron beam current distribution measurements. Tests with 60 keV O(3+) ions and 2 keV electrons show that it can provide exact boundaries when a positive charged particle beam current distribution is measured.

Electrospray of 1-Butyl-3-Methylimidazolium Dicyanamide Under Variable Flow Rate Operations

The ionic liquid 1-butyl-3-methylimidazolium dicyanamide ([Bmim][DCA]) is a propellant candidate for a standalone electrospray thruster or a dual-mode propulsion system. Characterization of positive polarity ions produced by [Bmim][DCA] capillary emitters with a nominal extraction voltage of 2.0 kV is presented, followed by predictions of propulsion performance. Flow rates from 0.27 to are used to investigate the impact variations in the flow parameter have on the electrospray plume. Measurements indicate the presence of (, 1, 2, 3, 4) cation species plus droplet contributions. At , the species dominates the mass spectrum contributing 56.5% of the total intensity, while at , the dominant species is , comprising 40.7%. Based on the retarding potential analysis, ions emitted from the capillary are formed below the emitter potential of 500 eV. Angular distributions indicate the broadening of both the beam current and mass distribution for increasing flow rates. As the flow rate increases from 0.30 to , derived thrust and specific impulse change from and 200 s to and 80 s, respectively.

Nanomachining with a focused neon beam: A preliminary investigation for semiconductor circuit editing and failure analysis

As the semiconductor device scaling trend continues, advancement in both focused ion beam source development and application innovations are needed to retain failure analysis and nanomachining application capabilities. In this work, a neon gas field ionization source was studied for its nanomachining properties. The authors have analyzed neon’s nanomachining precision at 10 and 20 keV on blank Cu and SiO2 thin films. Subsurface material amorphization from neon and its correlation with beam current distribution are characterized by TEM. In addition, some preliminary nanomachining work was performed on a 32 nm test chip and successfully demonstrated end-pointing on various device layers.

Nonlinear processes of probe formation of a beam with inhomogeneous phase density at nuclear microprobe

The work describes nonlinear processes of probe formation on the target with allowance for an inhomogeneous density of ion distribution in phase space in the object collimator plane taken from experimental data. The chromatic aberrations, intrinsic aberrations of the 3rd order and parasitic aberrations caused by sextupole and octupole components of the magnetic quadrupole lens field have been taken into account in the object-target phase coordinate transformation. The criterion of obtaining the optimal resolution was defined as the minimum spot size (FWHM) for a fixed ratio IFWHM/I0 of beam current in this spot to the total beam current. The conditions for which the initial density of ion distribution in phase space is matched with the ion-optical characteristics of the probe-forming system were considered. The influence of axial brightness and parasitic sextupole and octupole field components on the beam current distribution at the target has been determined.

Influence of the beam current density distribution on the spatial resolution of a nuclear microprobe

The paper discusses the effect of nonuniform distribution of the ion beam phase density on the nuclear microprobe resolution. The deconvolution of the beam brightness distribution parameters was performed on the base of the beam current distribution measurements in the object collimator plane. This information gives a possibility to define the ion distribution in the phase set for a beam to be transformed by the probe-forming system into the target plane. A criterion for selecting the optimum collimator dimensions was the highest beam current for the fixed beam spot size (FWHM). This approach, with allowance for the initial distribution, makes it possible to obtain a higher beam current intensity at the center of the spot.

Upgrade of the beam profile ionization monitor for the KOMBAS fragment separator

The results from upgrade of an ionization beam profile monitor (IBPM) are presented. The IBPM consists of a conventional capacitor that extracts the ionization products of the residual gas and analyzing capacitors. The main objective of this upgrade was to create a device with uniform spatial resolution. For this purpose, an additional difference of potentials, the ramping of which allows the beam cross section to be scanned, is applied between the capacitors of the monitor, while the electric fields in the capacitors themselves remain constant. Two IBPMs have been developed as a result of the facility’s upgrade: an IBPM for on-line monitoring of the vertical and horizontal beam current distributions in the beam line in an area of 8 × 8 cm2 with a uniform 1-mm resolution, and an IBMP for detailed beam profile monitoring with a uniform resolution of 1 × 1 mm2 over the scanning region. It was established experimentally that the proposed scanning technique provides good results in beam profile measurements when the ion component of the ionized residual gas is extracted; for the electron component, the result is much worse.

Diagnostics for intense heavy-ion beams in the HIF-VNL

Modern diagnostic techniques provide detailed information on beam conditions in injector, transport, and final focus experiments in the HIF-VNL. Parameters of interest include beam current, beam energy, transverse and longitudinal distributions, emittance, and space charge neutralization. Imaging techniques, based on kapton films and optical scintillators, complement and, in some cases, may replace conventional techniques based on slit scans. Time-resolved optical diagnostics that provide 4-D transverse information on the experimental beams are in operation on the existing experiments. Current work includes a compact optical diagnostic suitable for insertion in transport lines, improved algorithms for optical data analysis and interpretation, a high-resolution electrostatic energy analyzer, and an electron beam probe. A longitudinal diagnostic kicker generates longitudinal space-charge waves that travel on the beam. Time of flight of the space-charge waves and an electrostatic energy analyzer provide an absolute measure of the beam energy. Special diagnostics to detect secondary electrons and gases desorbed from the wall have been developed.

Signal formation analysis of the electron beam current distribution measurements

The Fourier spectra of signals and the modulation transfer functions are chosen as main characteristics of the electron beam (EB) analyzers. This approach can be used for EB analyzer design and optimization. It is concluded that the space–frequency characteristics of the scanning (modulation) system are the limiting factors for the signal distortion. A matrix of more than 32×32 sufficiently short impulses and at a transfer rate twice higher than the maximum spectrum frequency can create an adequate image of the beam current radial or angular distribution. At the data processing of the rotating probe or of the moving slit measurements an inverse transformation is needed and a false minimum can appear in the calculated current distributions.

High-resolution primary ion beam probe for SIMS

High-brightness negative ion beams, especially O − beams, from a compact gaseous plasma source are studied to evaluate the suitability for high-resolution SIMS. Ion-optical calculations are made using the beam parameters from the new source. Results suggest that sub-100 nm spot with O − beam current of 10 pA is achievable. Beam focusing, the resulting beam current distributions at the target and the expected instrumental performance are discussed.