Beam Mismatch Research Articles

Incoherent tune measurement of an ion storage ring using single ions

The measurement of betatron tunes is important in the studies of beam dynamics in circular accelerators. Here, we report a new method to extract the fractional tune values using revolution times of single ions stored for a few hundred turns in a heavy-ion storage ring utilizing a single time-of-flight detector. The experiment was done at the experimental Cooler Storage Ring (CSRe) in Lanzhou. The unbunched cocktail secondary beam was injected into the ring and allowed to coast without further excitation. Since the average number of simultaneously stored ions inside the 128.8 m-circumference ring was merely ∼20, the obtained tune values are considered to be incoherent. Given that the revolution time of an individual ion is related to its momentum, the chromaticity of the ring could be addressed. Moreover, the data indicate a possible beam mismatch in vertical direction y^ at the injection into CSRe. The new method is developed for ultralow beam intensities and is thus a sensitive approach to tune measurements. Thanks to its simplicity, the method can straightforwardly be employed at other circular accelerators by applying the same detection approach. Published by the American Physical Society 2024

Wavefront-modified vector beams for THz cornea spectroscopy.

Terahertz spectroscopy is a promising method to diagnose ocular diseases, where the cornea is typically imaged by Gaussian beams. However, the beam's mismatch with the cornea's spherical surface produces a 5-10 % error in analysis. We investigate cornea spectroscopy with wavefront-modified vector beams, reducing the original analysis error to less than 0.5 %. Vector beams are synthesized by our developed 3D Angular Spectrum Method expanded to vector spherical harmonic presentation, allowing wavefront modification and scattering analysis from 100-layer cornea models. We show that wavefront-modified spherical vector beams possess increased accuracy and non-sensitive focusing on cornea spectroscopy compared to the Gaussian beams. Additionally, we investigate wavefront-modified cylindrical vector beams, which show frequency-dependent scattering power arising from s- and p-polarizations. As a result, these beams are unsuitable for cornea spectroscopy, although they have potential for optical force applications. Wavefront-modified vector beams can be applied to spherical target spectroscopy and optical force applications, such as medicine, medical imaging, and optical tweezers.

Shift-variant deconvolution beamforming using Implicit Neural Representation for near-field acoustic image measurement

The conventional beamforming (CBF) output can be expressed as a convolution of the source distribution and the array dependent point spread function (PSF), which is defined as the response of the beamformer to a point source. The resolution and accuracy of sound source localization can be improved by deconvolution of CBF. The shift-invariant PSF assumption is only a good approximation when the source region is small compared to the distance between the array and the source. However, the PSF of the near-field underwater acoustic map measurement is shift-variant, whose mismatch with the beam could lead to performance degradation. In this paper, we proposed an optimized deconvolution method by using the neural network called implicit neural representation (INR) to solve the beam mismatch problem, due to its strong performance in learning and reconstructing spatial scenes. Rather than recompute the PSF for each pixel in the scene, INR predicts the complex-valued weight matrix in two-dimensional space that encapsulates both the spatially varying properties of the PSF and the scatter distribution of the scene. Numerical simulations and experimental results verify the effectiveness of our method. And this work can be broadly applied to arrays with shift-variant PSFs.

BEYONDPLANCK

We discuss the treatment of bandpass and beam leakage corrections in the Bayesian BEYONDPLANCKcosmic microwave background (CMB) analysis pipeline as applied to thePlanckLFI measurements. As a preparatory step, we first applied three corrections to the nominal LFI bandpass profiles, including the removal of a known systematic effect in the ground measuring equipment at 61 GHz, along with a smoothing of standing wave ripples and edge regularization. The main net impact of these modifications is an overall shift in the 70 GHz bandpass of +0.6 GHz. We argue that any analysis of LFI data products, either fromPlanckor BEYONDPLANCK, should use these new bandpasses. In addition, we fit a single free bandpass parameter for each radiometer of the form Δi = Δ0 + δi, where Δ0represents an absolute frequency shift per frequency band andδiis a relative shift per detector. The absolute correction is only fitted at 30 GHz, with a fullχ2-based likelihood, resulting in a correction of Δ30 = 0.24 ± 0.03 GHz. The relative corrections were fitted using a spurious map approach that is fundamentally similar to the method pioneered by the WMAP team, but excluding the introduction of many additional degrees of freedom. All the bandpass parameters were sampled using a standard Metropolis sampler within the main BEYONDPLANCKGibbs chain and the bandpass uncertainties were thus propagated to all other data products in the analysis. In summary, we find that our bandpass model significantly reduces leakage effects. For beam leakage corrections, we adopted the officialPlanckLFI beam estimates without any additional degrees of freedom and we only marginalized over the underlying sky model. We note that this is the first time that leakage from beam mismatch has been included forPlanckLFI maps.

Holographic Back-Projection Method for Calibration of Fully Digital Polarimetric Phased Array Radar

Phased Array Radar (PAR) technology is rapidly rising as a candidate for future weather radars because it can provide focused, high-quality meteorological observations. Due to the need for precise measurements of polarimetric weather variables, it is desired that the radar simultaneously transmits and receives linearly polarized horizontal (H) and vertical (V) fields through beams that are well matched in gain and shape at every pointing direction. These scanning characteristics are difficult to achieve, especially with current methods such as the “park and probe” calibration, because the radiation patterns of PAR antennas are inherently dependent on their pointing direction. Thus, polarimetric array calibration is critical to produce matched H/V copolar antenna patterns. In this article, we present a polarimetric antenna calibration procedure for the fully-digital PARs based on the holographic back-projection of electric fields. The fully digital S-band Horus radar is used to implement and evaluate the proposed calibration method. First, near-field measurements of a fully active Horus antenna panel are back-projected onto the plane of the array to derive the copolar magnitude and phase of the H/V fields radiated by each antenna element. Then, digital calibration parameters are produced from back-projected fields to compensate for excitation differences and produce uniform radiation at the plane of the array. The performance of the back-projection calibration method is evaluated for broadside and for electronically scanned angles and compared to the more conventional park and probe calibration method. A robustness analysis is conducted using simulations to evaluate the impact of excitation amplitude and phase errors that could result from practical near-field environments and amplifier performance degradation. Preliminary results show that through precise digital calibration based on back-projected fields, beam matching can be significantly improved to achieve the desired polarimetric calibration levels. For electronically steered beams, back-projection calibration can reduce H/V beam mismatch biases by approximately 25%, from 0.34 dB to 0.08 dB. This improves measurement accuracy of fully digital PARs by mitigating antenna-induced biases in meteorological estimates.

Design of a compact RFQ linac for the transportable neutron source

A transportable accelerator-driven neutron source based on the Radio Frequency Quadrupole (RFQ) linac is developing at Xi’an Jiaotong University (X-TANS). It will be a promising tool for the non-destructive inspection of immovable objects. The neutron yield above 10 11n/s can be obtained via 7Li(p,n)7Be reaction with a proton beam energy of 2.5 MeV. To exactly guarantee the transportability of the neutron source, it is essential to achieve the light, compact and low-power consumption of RFQ linac. The operation frequency of 325 MHz is chosen considering the balance among cavity size, cavity consumption, and electrode aperture. In addition, compact dynamics scheme is adopted to achieve short RFQ by sacrificing a beam bunching efficiency. The beam dynamics design and optimization have been performed based on Parmteqm. Beam tracking results show that RFQ can accelerate the proton beam to 2.5 MeV with an electrode length of 2.6 m and an effective transmission efficiency of 93.8%. To enlarge the redundancy of the input beam mismatch and make the beam match easier from LEBT to RFQ, the electrode aperture is designed to shrink gradually in the RFQ entrance. In addition, we also performed the RF electromagnetic design and optimization based on the full-length 3D RFQ model. Multiphysics simulations of the cavity in different working conditions are investigated at last.

Study of magnetic fringe fields and interference effects on beam dynamics for proton facility gantry

ABSTRACT Proton therapy facilities require a beamline that effectively delivers particles to a nozzle that forms symmetric and achromatic beam spots. In the gantry lattice of the SC200 facility, the magnetic components are designed with a compact layout due to space constraints. This makes it important to properly deal with fringe fields and their interference when more accurate simulations of beam dynamics are required. In this paper, we establish field distributions based on real extracted magnetic maps and analyse the influences of linear fields on beam qualities by combining a perturbation model with Monte Carlo code in BDSIM. To verify the results, COSY INFINITY with the Enge function was used to quantify the beam variations at the isocenter; the results were in good agreement with those of BDSIM. Compared with the conventional hard edge model, beam mismatch at the isocenter is evidence of the impacts of fringe fields, which pose challenges to clinical dose planning. Hence, linear optical optimization on the gantry is also necessary to meet safety and precision requirements. These efforts will guide the commissioning of the beamline.

Optical Characterization of the Keck Array and BICEP3 CMB Polarimeters from 2016 to 2019

The BICEP/Keck experiment (BK) is a series of small-aperture refracting telescopes observing degree-scale Cosmic Microwave Background (CMB) polarization from the South Pole in search of a primordial $B$-mode signature. This $B$-mode signal arises from primordial gravitational waves interacting with the CMB, and has amplitude parametrized by the tensor-to-scalar ratio $r$. Since 2016, BICEP3 and the Keck Array have been observing with 4800 total antenna-coupled transition-edge sensor detectors, with frequency bands spanning 95, 150, 220, and 270 GHz. Here we present the optical performance of these receivers from 2016 to 2019, including far-field beams measured in situ with an improved chopped thermal source and instrument spectral response measured with a field-deployable Fourier Transform Spectrometer. As a pair differencing experiment, an important systematic that must be controlled is the differential beam response between the co-located, orthogonally polarized detectors. We generate per-detector far-field beam maps and the corresponding differential beam mismatch that is used to estimate the temperature-to-polarization leakage in our CMB maps and to give feedback on detector and optics fabrication. The differential beam parameters presented here were estimated using improved low-level beam map analysis techniques, including efficient removal of non-Gaussian noise as well as improved spatial masking. These techniques help minimize systematic uncertainty in the beam analysis, with the goal of constraining the bias on $r$ induced by temperature-to-polarization leakage to be subdominant to the statistical uncertainty. This is essential as we progress to higher detector counts in the next generation of CMB experiments.

Optical Design and Characterization of 40-GHz Detector and Module for the BICEP Array

Families of cosmic inflation models predict a primordial gravitational-wave background that imprints B-mode polarization pattern in the Cosmic Microwave Background (CMB). High sensitivity instruments with wide frequency coverage and well-controlled systematic errors are needed to constrain the faint B-mode amplitude. We have developed antenna-coupled Transition Edge Sensor (TES) arrays for high-sensitivity polarized CMB observations over a wide range of millimeter-wave bands. BICEP Array, the latest phase of the BICEP/Keck experiment series, is a multi-receiver experiment designed to search for inflationary B-mode polarization to a precision $\sigma$(r) between 0.002 and 0.004 after 3 full years of observations, depending on foreground complexity and the degree of lensing removal. We describe the electromagnetic design and measured performance of BICEP Array low-frequency 40-GHz detector, their packaging in focal plane modules, and optical characterization including efficiency and beam matching between polarization pairs. We summarize the design and simulated optical performance, including an approach to improve the optical efficiency due to mismatch losses. We report the measured beam maps for a new broad-band corrugation design to minimize beam differential ellipticity between polarization pairs caused by interactions with the module housing frame, which helps minimize polarized beam mismatch that converts CMB temperature to polarization ($T \rightarrow P$) anisotropy in CMB maps.

Improved MEMS piezoelectric vibratory stage with reduced off-axis error

Background: The piezoelectric microvibratory stage as a microelectromechanical system (MEMS) actuator can tilt around the X / Y axis and translate along the Z axis. However, when the vibratory stage is tilted around the X axis, it also has an undesirable tilting angle around the Y axis. It means that the X axis tilting and the Y axis tilting are not independent; therefore, it is significant to eliminate the coupling of two motions. Aim: The coupling of X / Y tilting motion is studied theoretically and decoupled by optimization of structural parameters. Approach: A structural model was established to analyze the reasons of the X / Y tilting coupling. Reasonable structure parameters of L-shaped piezoelectric beam were designed to eliminate the off-axis errors caused by X / Y tilting coupling. Results: The reason of X / Y tilting coupling is that the stiffness of the L-shaped piezoelectric support beam mismatch in the X axis and Y axis directions. The appropriate width ratio of the two segments of the L-shaped piezoelectric beam can reduce the off-axis error effectively. Conclusions: The test results show that the piezoelectric MEMS vibratory stage can achieve X / Y tilting motion with the relative off-axis error only at 1%.

Envelope dynamics and stability with non-linear space-charge forces

We developed a model to calculate the stability of Gaussian beam distributions with non-linear space-charge forces in the presence of random and skew-quadrupole errors. The effect of the space-charge force on the beam matrix is calculated analytically including full cross-plane coupling in 4D phase space, which allows us to perform fast parameter studies. For stability analysis, we find the fixed points of the beam including the space-charge forces and construct a Jacobi-matrix by slightly perturbing the periodic solution. The stability of envelope oscillations is inferred by eigenvalue analysis. Furthermore, we employ envelope tracking as a complementary method and compare the results of the eigenvalue analysis with FFT data from the tracked envelope. The non-linearity of the space-charge force in combination with lattice errors and beam coupling opens up for envelope-lattice resonances and envelope coupling resonances. Hitting these resonances leads to envelope blow-up, causing an effective beam mismatch. Therefore, we finally examine the effect of beam mismatch on the envelope tune-shift and its stability.

Improvements in the Beam-Mismatch Correction of Precipitation Radar Data After the TRMM Orbit Boost

The orbit of the tropical rainfall measuring mission (TRMM) satellite was boosted from 350 to 402.5 km in August 2001 to extend its lifetime by conserving fuel. Since the timing between transmission and reception by the precipitation radar (PR) onboard the TRMM satellite was a fixed constant for measurement from an original altitude of 350 km, the PR encountered a mismatch between the transmitting and receiving beams after the TRMM orbit boost. Although the PR algorithm in TRMM Version 7 employs a correction for the beam mismatch, its error remains as an underestimation of the precipitation estimates near surface in the second half of the swath. This paper aims to mitigate the beam-mismatch correction error in Version 7. The beam-mismatch correction needs to estimate the radar echo that would be measured in the virtual intermediate beam between the beam in question and the previous adjacent beam. The beam-mismatch correction developed in this paper assumes that the surface and precipitation echoes change linearly in the horizontal direction in parallel to the surface between the two beams. The new correction is tested with observational data, indicating that the method improves the accuracy of the correction at off-nadir angles. Statistics of the surface normalized radar cross sections and the bright band peak intensities at off-nadir angles are improved using the method. The asymmetric bias of the precipitation estimates with respect to the scan angle in Version 7 is mitigated by 95.9% over ocean and 72.5% over land with the new correction.

QuickPol: Fast calculation of effective beam matrices for CMB polarization

Current and planned observations of the cosmic microwave background (CMB) polarization anisotropies, with their ever increasing number of detectors, have reached a potential accuracy that requires a very demanding control of systematic effects. While some of these systematics can be reduced in the design of the instruments, others will have to be modeled and hopefully accounted for or corrected a posteriori. We propose QuickPol, a quick and accurate calculation of the full effective beam transfer function and of temperature to polarization leakage at the power spectra level, as induced by beam imperfections and mismatches between detector optical and electronic responses. All the observation details such as exact scanning strategy, imperfect polarization measurements, and flagged samples are accounted for. Our results are validated on Planck high frequency instrument (HFI) simulations. We show how the pipeline can be used to propagate instrumental uncertainties up to the final science products, and could be applied to experiments with rotating half-wave plates.

Higher order mode beams mitigate halos in high intensity proton linacs

High intensity proton linacs (HIPLs) for applications such as Accelerator Driven Reactor Systems (ADRS) have serious beam dynamics issues related to beam halo formation. This can lead to particle loss and radioactivation of the surroundings which consequently limit the beam current. Beam halos are largely driven by the nonlinear space-charge force of the beam, which depends strongly on the beam distribution and also on the initial beam mismatch. We propose here the use of a higher order mode beam (HOMB), that has a weaker nonlinear force, to mitigate beam halos. We first show how the nonlinear space-charge force can itself be exploited in the presence of nonlinear solenoid fields, to produce a HOMB in the low energy beam transport (LEBT) line. We then study the transport of such a beam through a radio frequency quadrupole (RFQ), and show that the HOMB has a significant advantage in terms of emittance blow-up, halo formation and beam loss, over a Gaussian beam, even with a finite initial mismatch. For example, for the transport of a 30 mA beam through the RFQ, with an initial beam mismatch of 45%, the Gaussian beam sees an emittance blow-up of 125%, while the HOMB sees a blow-up of only 35% (relative to the initial emittance of $0.2\ensuremath{\pi}\text{ }\text{ }\mathrm{mm}\text{\ensuremath{-}}\mathrm{mrad}$). Similarly, the beam halo parameter and beam loss are 0.95 and 25% respectively for a Gaussian beam, but only 0.35 and 15% for a HOMB. The beam dynamics of the HOMB agrees quite well with the particle-core model, because of the more linear space-charge force, while for the Gaussian beam there are additional particle loss mechanisms arising from nonlinear resonances. Therefore, the HOMB suppresses emittance blow-up and halo formation, and can make high current ADRS systems more viable.

Electron-Beam Dynamics for an Advanced Flash-Radiography Accelerator

Beam dynamics issues were assessed for a new linear induction electron accelerator being designed for multipulse flash radiography of large explosively driven hydrodynamic experiments. Special attention was paid to equilibrium beam transport, possible emittance growth, and beam stability. Especially problematic would be high-frequency beam instabilities that could blur individual radiographic source spots, low-frequency beam motion that could cause pulse-to-pulse spot displacement, and emittance growth that could enlarge the source spots. Beam physics issues were examined through theoretical analysis and computer simulations, including particle-in-cell codes. Beam instabilities investigated included beam breakup, image displacement, diocotron, parametric envelope, ion hose, and the resistive wall instability. Beam corkscrew motion and emittance growth from beam mismatch were also studied. It was concluded that a beam with radiographic quality equivalent to the present accelerators at Los Alamos National Laboratory will result if the same engineering standards and construction details are upheld.

Beam halo studies in LEHIPA DTL

The Low Energy High Intensity Proton Accelerator (LEHIPA) project at Bhabha Atomic Research Centre (BARC) consists of a 20 MeV, 30 mA proton linac. The accelerator comprises of a 3 MeV Radio Frequency Quadrupole (RFQ) and a 20 MeV Drift Tube Linac (DTL). In such high intensity accelerators, beam halos are of concern as they not only cause an increase in emittance, but also lead to beam loss and radio activation. We have studied the effect of beam mismatch at the DTL input on halo formation and propagation. The particle core model is used to excite the three envelope eigen modes; the quadrupole mode, the fast mode and the slow mode by giving input beam mismatch. These modes get damped as the beam progresses through the DTL. The damping mechanism is clearly Landau damping and leads to increase in rms emittance of the beam. The evolution of these modes and the corresponding increase in beam emittance and maximum beam extent, as the beam propagates through the DTL, has been studied for different space charge tunes. The halo parameter based on the definition of Allen and Wangler has been calculated. It is seen that beam halos are very important for LEHIPA DTL, even at 20 MeV and leads to emittance and beam size increase and also to beam loss in some cases. The longitudinal halo is present even without mismatch and transverse halos arise in the presence of beam mismatch.

Mismatch study of C-ADS main linac**Supported by China ADS Project (XDA03020000) and National Natural Science Foundation of China (11235012)

The ADS accelerator in China is a Continuous-Wave (CW) proton linac with 1.5 GeV beam energy, 10 mA beam current, and 15 MW beam power. To meet the extremely low beam loss rate and high reliability requirements, it is very important to study the beam halo caused by beam mismatch, which is one major sources of beam loss. To avoid envelope instability, the phase advances per period are all smaller than 90 degrees in the main linac design. In this paper, simulation results of the emittance growth and the envelope oscillations caused by mismatch in the main linac section are presented. To meet the emittance growth requirement, the transverse and longitudinal mismatch factors should be smaller than 0.4 and 0.3, respectively.

Mismatch characteristics of optical parametric chirped pulse amplification

The stability of an optical parametric chirped pulse amplifier (OPCPA) is influenced by time and the angular matching of the input beams. We derived the Gaussian dependence of the monochromatic signal gain on the small mismatch between the signal and pump beams. Gain characteristics were also calculated for polychromatic amplification and the impact of different beam mismatches and interaction geometries was explained. The asymmetry of the energy gain, and the square root dependence of the phase matched wavelength on beam angles were found. The predicted dependences were verified in a noncollinear OPCPA system with LBO and KDP crystal amplifying pulses of a Ti:sapphire laser around a central wavelength of 800 nm, pumped by the third harmonic frequency of an iodine gas laser at a wavelength of 438 nm. The widths of the gain curves in the dependence on both the pump–signal or the phase matching angles varied from several tenths to a few milliradians. The gain curve widths dependent on the pump–signal pulse delay were about two thirds of the pump pulse width for moderate pumping and about a half of the pump pulse width for pumping on the order of GW cm−2. A stable gain output is achieved if angular and temporal fluctuations are fractions of the measured gain curve widths, and when the signal direction is between the pump and the crystal principal axis (i.e. in the psz geometry).

Design of a CW high charge state heavy ion RFQ for SSC-LINAC

The new linac injector SSC-LINAC has been proposed to replace the existing Separator Sector Cyclotron (SSC). This effort is to improve the beam efficiency of the Heavy Ion Research Facility of Lanzhou (HIRFL). As a key component of the linac, a continuous-wave (CW) mode high charge state heavy ion radio-frequency quadrupole (RFQ) accelerator has been designed. It accelerates ions with the ratio of mass to charge up to 7 from 3.728keV/u to 143keV/u. The requirements of CW mode operation and the transportation of intense beam have been considered as the greatest challenges. The design is based on 238U34+ beams, whose current is 0.5pmA (0.5 particle mili-ampere, which is the measured 17 emA electric current divided by charge state of heavy ions). It achieves the transmission efficiency of 94% with 2508.46mm long vanes in simulation. To improve the transmission efficiency and quality of the beams, the phase advance has been taken into account to analyze the reasons of beam loss and emittance growth. Parametric resonance and beam mismatch have been carefully avoided by adjusting the structure parameters. The parameter-sensitivity of the design is checked by transportation simulations of various input beams. To verify the applicability of machining, the effects of different vane manufacturing methods on beam dynamics are presented in this paper.

Incidence-Angle Dependency of TRMM PR Rain Estimates

Abstract The incidence-angle differences of estimated surface rainfall obtained from the precipitation radar (PR) on board the Tropical Rainfall Measuring Mission (TRMM) satellite were investigated. The bias before the orbit boost in August 2001 relative to the near-nadir statistics was 2.7% over the ocean and −5.8% over land. After the boost, the bias was −3.2% and −9.5%, respectively. These biases were further quantified with respect to error sources, that is, the beam mismatch correction error, detection capability of storms with low-level storm-top height, and residual effects. For shallow storms lower than 3 km, most incidence-angle differences were caused by main lobe contamination. For nonshallow storms, several error factors resulted in 5.3% overestimates over the ocean and 5.1% underestimates over land for the period before the boost. The remaining uncertainty in local low-level profiles was identified as a controversial issue. The bias-corrected dataset updates the interannual variation in rainfall obtained from the TRMM PR. The increasing rainfall features and recent high-rainfall years were consistent with prior studies based on other microwave sensors. The coherent signals and slight differences in the temporal variation compared with the Global Precipitation Climatology Project (GPCP) data indicate the importance of further internal and cross validations based on long-term observation by multiple sensors.