Optical Diffraction Radiation Research Articles

EMITTANCE MEASUREMENT OF THE ACCELERATED BEAMS (A REVIEW)

A review of emittance measurement methods of the accelerated (ionic or electronic) beams on various accelerating facilities both foreign, and Ukrainian is presented. There are some ways of emittance measurements in their various modifications: a slit method ("two slits", "four slits", Allison scanner), pepperpot method, and also gradient method (quadrupole scanning). The most high-speed and exact enough way of emittance measurement what is pepperpot method in detail considered on example UNILAC GSI (Darmstadt, Germany). Possibility of a field angular distribution use in a distant zone of an optical diffraction radiation made electronic bunch, passing through rectangular apertures in screens (DESY, Hamburg, Germany) is shown.

Noninvasive Micrometer-Scale Particle-Beam Size Measurement Using Optical Diffraction Radiation in the Ultraviolet Wavelength Range

We present recent achievements in the application of optical diffraction radiation (ODR) to the measurement of the transverse beam size of a 1.3 GeV micrometer-size electron beam performed with an instrument installed in the extended extraction line of the KEK Accelerator Test Facility. ODR is a recent technique for the measurement of the transverse size and emittance of highly relativistic particle beams. ODR has the advantage of being a noninvasive and relatively inexpensive technique and is a candidate for the operation of linear particle accelerators, where no simple alternatives (e.g., synchrotron radiation) are available. In an effort to improve the resolution and performance, we establish an alternative target microfabrication technology, adopt solutions to improve the signal-to-noise ratio, and perform an experiment in the UV spectrum at 250 nm. With such a configuration, a transverse beam size as low as $3\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}\mathrm{m}$ is measured, drastically improving on past measurements reported in the literature. In light of these results, ODR, when combined with a high-resolution optical-transition-radiation monitor, represents a credible diagnostics solution for low-emittance high-intensity particle beams.

Optical diffraction radiation from a dielectric and a metal nanowire excited by a modulated electron beam

The optical diffraction radiation that accompanies the motion of a modulated beam of electrons near a dielectric and silver nanowire scatterers is investigated in the two-dimensional formulation. Our goal is to compute the field in the near and far zones and analyze how it depends on electron beam parameters. We demonstrate the excitation of internal resonances of such a scatterer that can be useful in the design of nanoscale non-invasive beam position monitors.

Different focalisations of Optical Transition Radiation and Diffraction Radiation

For beam diagnostics with Optical Transition Radiation and Diffraction Radiation, we consider the usefulness of focusing the optics on a plane at finite distance from the target. It gives informations on the beam emittance parameters which are complementary to those obtained by focusing on the target or at infinity.

Optical diffraction radiation for position monitoring of charged particle beams

In the framework of the future linear collider collaboration (CLIC, ILC), non-intercepting beam monitoring instruments are under development for very low emittance and high charge density beams. Optical diffraction radiation (ODR) was studied and developed during the last years focussing on beam size measurements. We propose in the paper to consider the use of diffraction radiation for ultra relativistic beams as position monitors with applications for the centering of scrapers, collimators and targets with high resolution. We present the experimental results obtained using small aperture slits on the ATF2 extraction beam line at KEK and on the Cornell Electron Storage Ring with 1.2GeV and 2.1GeV electrons respectively.

Ultrarelativistic electron beam spatial size estimation from angular distribution emission in thin crystals

The use of ultrarelativistic electron (positron) emission in thin crystals to estimate particle beam spatial sizes for projected electron–positron colliders is proposed. The existing position-sensitive X-ray range detectors restrict the minimum value of the measured beam size to a level of approximately 10μm, which is far greater than the planned sizes of collider beams. We propose to estimate the electron (positron) beam divergence over the diffracted transition radiation from angular distribution measurements. The spatial size can be obtained from the calculated beam emittance or the experimental emittance, which is measured during the earlier stage of acceleration using optical transition or optical diffraction radiation. The problem of crystal destruction under the influence of a high-intensity electron beam is discussed. The use of surface parametric X-ray radiation, where the problem of crystal destruction is almost absent, to measure the electron beam parameters is also discussed.

Advanced simulations of optical transition and diffraction radiation

Charged particle beam diagnostics is a key task in modern and future accelerator installations. The diagnostic tools are practically the ``eyes'' of the operators. The precision and resolution of the diagnostic equipment are crucial to define the performance of the accelerator. Transition and diffraction radiation (TR and DR) are widely used for electron beam parameter monitoring. However, the precision and resolution of those devices are determined by how well the production, transport and detection of these radiation types are understood. This paper reports on simulations of TR and DR spatial-spectral characteristics using the physical optics propagation (POP) mode of the Zemax advanced optics simulation software. A good consistency with theory is demonstrated. Also, realistic optical system alignment issues are discussed.

First non-intercepting emittance measurement by means of optical diffraction radiation interference

Transverse electron beam size measurements are required in order to determine the transverse emittance. In the case of high brightness electron beams produced by high repetition rate linear accelerators, conventional invasive diagnostics cannot sustain the intense power dissipated in intercepting devices. The analysis of the angular distribution of diffraction radiation has been proven to be a competent candidate for non-intercepting measurements of electron beam parameters. In addition, optical diffraction radiation interference (ODRI) has been demonstrated to be superior to the single slit ODR due to its shielding capability against the synchrotron radiation background and the possibility of avoiding complementary diagnostics. This paper reports the first transverse emittance measurement ever performed with the ODRI technique. In addition, the intrinsic non-intercepting and non-disturbing feature of the ODRI method has been checked in our experimental conditions by wakefield calculations.

Far- and near-field approximation for diffraction radiation

A new beam diagnostic technique based on the Optical Diffraction Radiation Interference (ODRI) has been recently proposed and experimentally investigated. The technique is based on the use of a two slits system. The far field approximation has shown rather accurate correspondence with experimental data when slits are centered with respect to the beam propagation line. Using formulas involving near field we point out in this work that a general treatment is needed with offset larger than 50μm.

Non-intercepting diagnostic for high brightness electron beams using Optical Diffraction Radiation Interference (ODRI)

High-gain Free Electron Lasers and future Linear Colliders require development of modern electron linacs with high brightness beams. Conventional intercepting transverse electron beam diagnostics, e.g. based on Optical Transition Radiation (OTR), cannot tolerate such high power beams without remarkable mechanical damages on the diagnostics device. Optical Diffraction Radiation (ODR) is an excellent candidate for measurements of the transverse phase space parameters in a non-intercepting way. One of the main problems of this method is the low signal to noise ratio, mainly due to the unavoidable synchrotron radiation background. This problem can be overcome by using two slits on metallic foils, placed at a distance shorter than the radiation formation zone. In this case a nearly background-free ODR interference pattern is produced allowing the determination of the beam size and angular divergence. The accuracy on these parameters can be increased by exploiting both ODR polarization states, as well as different wavelengths. Here we report measurements of the ODR interference between two slits with different aperture sizes in a non-collinear geometry, carried out at FLASH (DESY, Germany). Our results demonstrate the unique potential of this technique to determine the beam parameters.

Nonintercepting electron beam size monitor using optical diffraction radiation interference

In recent years, the use of diffraction radiation (DR), emitted when a charged particle beam passes through a rectangular slit, has been proposed and successfully tested as a nonintercepting diagnostic of high brightness beams. However, some problems related to the control of the particle trajectory through the slit still remain. If an additional slit is placed in front of the first one, at a distance shorter than the radiation formation length, interference between the forward diffraction radiation from the upstream slit and the backward diffraction radiation from the downstream slit can be observed. In this paper we report the first experimental observation of this effect, which we call here optical diffraction radiation interference (ODRI). If the two slits have different dimensions and are not aligned on the same axis, the properties of the ODRI pattern can be effectively used for nonintercepting beam diagnostics, especially for the unambiguously determination of the beam size. Indeed, the advantage of ODRI compared with a single aperture DR screen is due to the reduction of synchrotron radiation background, the increase of sensitivity for transverse beam dimensions, and the possibility to separate effects caused by the beam size and by beam offset within the slit.

NEW EXPERIMENTAL RESULTS WITH OPTICAL DIFFRACTION RADIATION DIAGNOSTICS

The characterization of the transverse phase space for high charge density and high energy electron beams is demanding for the successful development of the next generation light sources and linear colliders. Due to its non-invasive and non-intercepting features, Optical Diffraction Radiation (ODR) is considered as one of the most promising candidates to measure the transverse beam size and angular divergence. The recent results of our experiment, based on the detection of the ODR angular distribution to measure the electron beam transverse parameters and set up at FLASH (DESY), are presented. A thin stainless steel mask has been installed at 45° with respect to the DR target and normally to the beam propagation to reduce the contribution of synchrotron radiation (SR) background. In addition, interference between the ODR emitted on the shielding mask in the forward direction and the radiation from the DR target in the backward direction is observed. This is what we call Optical Diffraction Interferometry (ODRI). The contribution of this interference effect to the ODR angular distribution pattern and, consequently, its impact on the beam transverse parameters is discussed.

Phase control effects in optical diffraction radiation from a slit

Optical Diffraction Radiation (ODR) from a slit is becoming a real promising instrument for measuring the transverse beam size, or even the emittance of the very high brightness linacs driving SASE FELs or the future ILC which require non-intercepting diagnostic devices. But to correctly explain experimental data it is necessary to further develop the theory of this radiation emission. In this paper we discuss in particular the effects of a non-perfect coplanarity of the two halves of a slit, that introduces a phase difference in the field produced by the two half-planes. Such non-coplanarity can result from mechanical stress for instance.

Observation of focusing effect in optical transition and diffraction radiation generated from a spherical target

For the first time the focusing effect in optical transition and diffraction radiation generated by 1.28 GeV electrons in a tilted spherical target has been observed experimentally. A comparison of detected as well as simulated radiation spatial distributions produced by a flat and a spherical target has been made. It is shown that the application of such targets has allowed us to increase the radiation spectral-spatial density at the target focus without applying any additional focusing devices.

Multicomponent measurements of the Jefferson Lab energy recovery linac electron beam using optical transition and diffraction radiation

High brightness electron accelerators, such as energy recovery linacs (ERL), often have complex particle distributions that can create difficulties in beam transport as well as matching to devices such as wigglers used to generate radiation from the beam. Optical transition radiation (OTR), OTR interferometry (OTRI) and optical diffraction-transition radiation interferometry (ODTRI) have proven to be effective tools for diagnosing both the spatial and angular distributions of charged particle beams. OTRI and ODTRI have been used to measure rms divergences and optical transverse phase space mapping has been demonstrated using OTRI. In this work we present the results of diagnostic experiments using OTR and ODR conducted at the Jefferson Laboratory 115 MeV ERL which show the presence of two separate components within the spatial and angular distributions of the beam. By assuming a correlation between the spatial and angular features we estimate an rms emittance value for each of the two components.

Imaging of optical diffraction radiation in pre-wave zone and spatial resolution of non-invasive beam size diagnostics

A simple model to evaluate the imaging shape of an optical diffraction radiation (ODR) source focused by a lens on a detector, taking into account the pre-wave zone effect has been developed. The characteristic size of an ODR image does not depend on the Lorentz-factor and is defined by the impact-parameter (minimal distance between a particle trajectory and ODR target edge) only. Using the ODR intensity component polarized parallel to the target edge it is possible to significantly improve the spatial resolution of an ODR beam profile monitor.

Experimental observation and investigation of the prewave zone effect in optical diffraction radiation

Transition radiation (TR) and diffraction radiation (DR) has widely been used for both electron beam diagnostics and generation of intense radiation beams in the millimeter and the submillimeter wavelength range. Recently, it was theoretically predicted that TR and DR properties change either at extremely high energies of electrons or at long radiation wavelengths. This phenomenon was called a prewave zone effect. We have performed the first observation and detailed investigation of the prewave zone effect in optical diffraction radiation at 1.28 GeV electron beam at the KEK-Accelerator Test Facility (KEK-ATF). The beam energy at KEK-ATF is definitely not the highest one achieved in the world. Since we could easily observe the effect, at higher energies it might cause serious problems. We developed and applied a method for prewave zone suppression valid for optical wavelengths. Furthermore, a method for prewave zone suppression applicable for longer radiation wavelengths is discussed.

Non-intercepting electron beam transverse diagnostics with optical diffraction radiation at the DESY FLASH facility

Linear colliders (LCs) and short wavelength free electron lasers (FELs) require ultra-high brilliant electron beams of so much power density that no intercepting device can sustain it. The development of suitable beam diagnostics, non-invasive and non-intercepting, is necessary to measure the properties of such beams. Optical diffraction radiation (ODR) is considered as one of the most promising candidates, as testified by the interest of many laboratories all around the world. An experiment based on the detection of ODR has been set-up at DESY FLASH Facility and it is under operation to measure the electron beam transverse parameters. The radiation is emitted by a high energetic electron beam passing through a sub-millimeter slit, opened on a screen made of aluminum deposited on a silicon substrate. Radiation is then detected by a low noise, high sensitivity CCD camera. We report here the preliminary results for a 680 MeV electron beam energy going through a 0.5 mm slit.

Imaging of high-energy electron beam profile with optical diffraction radiation

Optical transition radiation (OTR) has been widely used in electron beam profile imaging. Optical diffraction radiation (ODR) has recently been used to measure the electron beam's transverse size with the angular distribution. Because of the close relationship between OTR and ODR, it is natural to ask whether ODR could be used to image the beam profile as is done with OTR. In this paper, the image formation process is investigated as a two-dimensional (2D) convolution. The image formed with ODR as a single electron passes through a circular aperture, through a rectangular slit, and beneath a semi-infinite plane is studied from first principle and taken to be the point spread function (PSF) of the imaging system. It is found that, unlike the OTR case, the PSF of ODR is space variant and largely depends on the shape of the ODR target. With this characteristic, the beam image formed with ODR differs greatly from the real beam profile, and the deconvolution process is generally needed in order to retrieve the real beam distribution from the ODR image. The possibility of using an image formed with ODR from a rectangular slit and a semi-infinite plane to determine beam profile in the direction parallel to the edge of the slit or plane and monitoring the beam's position are estimated. The theoretical prediction is compared to recently reported experimental results and a qualitative agreement is achieved.

Near-field imaging of optical diffraction radiation generated by a 7-GeV electron beam

We report the first unambiguous demonstration of near-field imaging of optical diffraction radiation (ODR). The source of the ODR was an aluminum metal reflective surface with a 7-GeV electron beam passing nearby its single edge. Because of the high Lorentz factor involved, appreciable ODR is emitted at visible wavelengths even for impact parameters of 1 to 2 mm, so standard imaging techniques were employed. The experimental results are compared to a simple near-field model. We show that the ODR signals are sensitive to both beam size and position. Applications to multi-GeV beams in transport lines in the major synchrotron radiation facilities, x-ray free-electron lasers, energy recovering linacs, and the International Linear Collider are possible.