Coherent Diffraction Radiation Imaging Methods to Measure RMS Bunch

Diagnostics are crucial to the operation of all particle accelerator facilities. They provide a means of optimising beam parameters and monitoring beam quality for users. However, for the next generation of accelerators, operating in extreme parameter spaces, most current beam diagnostics will fail; either through material failure or lack of resolution. This thesis presents three new diagnostic concepts to address this imminent diagnostic need. These novel diagnostics are supported by a simulation-based algorithm, successfully benchmarked throughout this work. All work has been conducted by the Author unless otherwise stated and referenced. The first technique measures sub-micron transverse beam profiles using optical transition radiation (OTR). Simulations were used to design a new imaging system, which was then installed at KEK (Japan). OTR images were then collected for a range of beam sizes. Comparisons were then made with simulations to successfully achieve sub-micron beam size measurements. Validation of these results was found in the agreement across different imaging systems for fixed beam parameters, providing a self-consistency check for the algorithm in lieu of alternate corroboration. The next diagnostic is a bunch length monitor for ∼<100 fs particle bunches; based on imaging the spatial distribution of coherent transition radiation (CTR) in the THz regime. Simulations demonstrated a relationship between image width and intensity, with bunch length. A THz imaging system was then installed at MAX IV (Sweden). CTR images were taken for a range of compressions. Maximum compression was successfully identified by monitoring relative changes in the properties of the images. Bunch lengths were then acquired from these images through comparison with simulations. Finally, the optical performance of a Digital Micro-mirror Device (DMD) was assessed. Image resolution produced by a DMD was quantified by measuring the Point Spread Function (PSF) of an imaging system, which was capable of remotely replacing a DMD with a planar mirror. The PSFs were measured using the sub-micron focus of a laser. Results show no measurable alteration to a PSF with the introduction of a DMD. This provides a foundation for the development of future diagnostics centred around this device. This thesis provides several validated proof-of-principle experimental results and supporting simulations. Future work has been identified for each topic, only possible following the results presented here, which will provide an array of novel next generation diagnostics.

As is generally known, the integral of the electric field strength over all time for usual (bipolar) radiation is zero. The first demonstration of the possibility of unipolar radiation generation has been considered theoretically by Bessonov in 1981 [E.G. Bessonov, Zh. Eksp. Teor. Fiz. 80 (1981) 852]. According to this work, the unipolar radiation (or strange electromagnetic waves) is radiation for which the integral of the electric field strength over the entire duration of a pulse differs significantly from zero. Later, several theoretical papers devoted to this phenomenon have appeared in the literature, where authors investigated mainly synchrotron radiation. However, despite the critical interest, the experimental investigations ignored this effect. In this paper we present results of the first experimental investigation of the unipolar radiation generated by a relativistic electron beam. To detect the unipolar radiation the detector that is sensitive to the selected direction of the electric field strength has been elaborated and tested. We used a designed detector to observe the coherent backward diffraction radiation appearing when a bunched electron beam travels in the vicinity of a flat conductive target. The asymmetry of the electric field strength of the coherent backward diffraction radiation has been demonstrated.

A simple nonperturbing technique for the electron relativistic bunch diagnostics has been proposed which does not require the use of an interferometer for spectral measurements. The interferometer functions are performed by a slit target in which diffraction radiation is generated. The measurements of electron bunch length are carried out by shifting one half of the target relative to the other. A good agreement with the results of measuring the coherent radiation spectrum of relativistic electron bunches has been obtained.

Diffraction and transition radiation on conducting sphere and hemispherical bulge in conducting plane: Further development

Electron bunch shape measurement using coherent diffraction radiation

The longitudinal wake is calculated for a bunch of ultrarelativistic electrons that is deflected by a magnet that is much shorter than the formation length of its coherent synchrotron radiation. Using this wake and the Coulomb field of an image bunch, we obtain formulas for the wake of coherent transition radiation. By modeling the coherent diffraction radiation of an iris as the coherent transition radiation from a hollow bunch, we calculate the on-axis longitudinal wake of coherent diffraction radiation for an arbitrary target shape. We also calculate the influence of an upstream magnet's edge radiation upon the wake.

Coherent radiation from a short bunch of electron beams is expected to be utilized as a terahertz (THz) radiation source. We have conducted an investigation on a terahertz source based on coherent diffraction-radiation (CDR) that possesses a unique characteristic of radial polarization and is potentially useful for certain applications. Particularly, with the high repetition beam of an energy-recovery linac, it is possible to achieve a watt-class high power source. We have designed a CDR setup and THz transport line, and subsequently measured the THz beam profile at the end of the line. The results confirmed the preservation of the distinctive characteristics of CDR within the experimental area.

Measurements of coherent diffraction radiation from a slit of a variable width generated by short electron bunches were performed in millimeter and submillimeter range. Experimental data are compared with transition radiation case and theoretical predictions. More realistic description, than the conventional theory does, is necessary to correctly account for the data. No noticeable difference in the bunch length value was observed between the diffraction radiation mode in a wide range of the slit widths and transition radiation one in the bunch length evaluation.

We propose a method to generate isolated relativistic terahertz (THz) pulses using a high-power laser irradiating a microplasma waveguide (MPW). When the laser pulse enters the MPW, high-charge electron bunches are produced and accelerated to ∼100 MeV by the transverse magnetic modes. A substantial part of the electron energy is transferred to THz emission through coherent diffraction radiation as the electron bunches exit the MPW. We demonstrate this process with three-dimensional particle-in-cell simulations. The frequency of the radiation is determined by the incident laser duration, and the radiated energy is found to be strongly correlated to the charge of the electron bunches, which can be controlled by the laser intensity and microengineering of the MPW target. Our simulations indicate that 100mJ level relativistic-intense THz pulses with tunable frequency can be generated at existing laser facilities, and the overall efficiency reaches 1%.

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation P. Evtushenko, J. Coleman, K. Jordan, J. Michael Klopf, G. Neil, G. P. Williams; Bunch Length Measurements at the JLab FEL Using Coherent Transition and Synchrotron Radiation. AIP Conf. Proc. 20 November 2006; 868 (1): 193–201. https://doi.org/10.1063/1.2401405 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioAIP Conference Proceedings Search Advanced Search |Citation Search

This paper will review the basic concepts behind three types of plasma lenses for high energy charged particle beams, the Gabor lens, the ‘‘active’’ current‐carrying lens, and the ‘‘passive’’ lens. Also, recent experimental results of tests of these lenses will be discuss with emphasis on the ‘‘passive’’ plasma lens which is proposed as a possible final focusing element in future colliders. (AIP)

Nowadays, intense electromagnetic (EM) radiation in the far-infrared (FIR) spectral range is an advanced tool for scientific research in biology, chemistry, and material science because many materials leave signatures in the radiation spectrum. Narrow-band spectral lines enable researchers to investigate the matter response in greater detail. The generation of highly monochromatic variable frequency FIR radiation has therefore become a broad area of research. High energy electron beams consisting of a long train of dense bunches of particles provide a super-radiant regime and can generate intense highly monochromatic radiation due to coherent emission in the spectral range from a few GHz to potentially a few THz. We employed novel coherent Cherenkov diffraction radiation (ChDR) as a generation mechanism. This effect occurs when a fast charged particle moves in the vicinity of and parallel to a dielectric interface. Two key features of the ChDR phenomenon are its non-invasive nature and its photon yield being proportional to the length of the radiator. The bunched structure of the very long electron beam produced spectral lines that were observed to have frequencies upto 21 GHz and with a relative bandwidth of 10–4 ~ 10–5. The line bandwidth and intensity are defined by the shape and length of the bunch train. A compact linear accelerator can be utilized to control the resonant wavelength by adjusting the bunch sequence frequency.

Coherent Cherenkov diffraction radiation in super-radiant regime as a tool for longitudinal diagnostics

Current measurements of the weak lensing signal induced by large-scale structure provide useful constraints on a range of cosmological parameters. However, the ultimate success of this technique depends on the accuracy with which one corrects for the effect of the point spread function (PSF), in particular the correction for the PSF anisotropy. With upcoming large weak lensing surveys, a proper understanding of residual systematics is necessary. In this paper, we examine the importance of the adopted model for the spacial variation of the PSF anisotropy using images of fields with a large number of stars. A wrong parametrization of the PSF anisotropy leads to a residual signal in the data, affecting the cosmic shear measurements. We use data taken with the Canada‐France‐Hawaii 12k (CFH12k) camera, and note that some of the results might not be valid for other instruments. We select a random subset of stars which are used to characterize the PSF and to correct the shapes of the remaining stars. The ellipticity correlation function of the residuals is studied to quantify the effect of residual PSF anisotropy on cosmic shear studies. In order to single out the effect of the parametrization, we assume a perfect method for the actual correction of galaxy shapes. The PSF anisotropy is typically modelled for each individual chip of a mosaic; consequently, the residuals are coherent on small scales. As a result, the systematic signal decreases rapidly with increasing angular scale. Separation of the signal into ‘E’ (curl-free) and ‘B’ (curl) components can help to identify the presence of residual systematics, but in general, the amplitude of the ‘B’ mode is different from that of the ‘E’ mode. The study of fields with many stars can be beneficial in finding a proper description of the variation of PSF anisotropy, and consequently can help to improve the accuracy with which the cosmic shear signal can be measured significantly. We show that such an approach can lead to an appreciable reduction in systematics. The results suggest that the prospects for accurate measurements of the cosmic shear signal on scales larger than ∼10 arcmin are excellent.

The ability to track single fluorescent particles within a three dimensional (3D) cellular environment can provide valuable insights into cellular processes. In this paper, we present a modified nonlinear image decomposition technique called K-factor that reshapes the 3D point spread function (PSF) of an XYZ image stack into a narrow Gaussian profile. The method increases localization accuracy by ~60% with compare to regular Gaussian fitting, and improves minimal resolvable distance between overlapping PSFs by ~50%. The algorithm was tested both on simulated data and experimentally. This work presets a novel use of the nonlinear image decomposition technique called K-factor that reshapes the three dimensional (3D) point spread function (PSF) of an XYZ image stack into a narrow Gaussian profile. The experimentally obtained PSF of a Z-stack raw data that is acquired by a widefield microscope has a more elaborate shape that is given by the Gibson and Lanni model. This shape increases the computational complexity associated with the localization routine, when used in localization microscopy techniques. Furthermore, due to its nature, this PSF spreads over a larger volume, making the problem of overlapping emitters detection more pronounced. The ability to use Gaussian fitting with high accuracy on 3D data can facilitate the computational complexity, hence reduce the processing time required for the generation of the 3D superresolved image. In addition it allows the detection of overlapping PSFs and reduces the effects of the penetration of out of focus PSFs into in focused PSFs, therefore enables the increase in the activated fluorophore density by ~50%. The algorithm was tested both on simulated data and experimentally, where it yielded an increase in the localization accuracy by ~60% with compare to regular Gaussian fitting, and improved the minimal resolvable distance between overlapping PSFs by ~50%, making it extremely applicable to the field of 3D biomedical imaging,