Electron Light Source Research Articles

Ultra-compact plasmonic electron accelerator on chip

Electron accelerators are essential equipment in science and industry. However, their large footprint, ranging in length up to kilometers, limits their availability. Hence, compact solution to this problem is one of the major trends in advance accelerators. In this paper, a design of micro-scale electron accelerator based on surface plasmons is proposed. Due to the near-field enhancement effect of plasmons, this structure establishes extremely strong field for acceleration within less than 1μm. Simulation results shows that driven by infrared laser, the designed accelerator with 5 GV/m peak field deliver more than 0.39 keV energy to electrons. Cascaded in chain, this structure can realize fully electron acceleration, and has the potential of becoming the critical element of future integrated free electron light source lab on chip.

Observation of radio emissions from electron beams using an ice target

To observe high energy cosmogenic neutrinos above 50 PeV, the large neutrino telescope ARA is being built at the South Pole. The ARA telescope detects neutrinos by observing radio signals by the Askaryan effect. We performed an experiment using 40 MeV electron beams of the Telescope Array Electron Light Source to verify the understanding of the Askaryan emission as well as the detector responses used in the ARA experiment. Clear coherent polarized radio signals were observed with and without an ice target. We found that the observed radio signals are consistent with simulation, showing that our understanding of the radio emissions and the detector responses are within the systematic uncertainties of the ARAcalTA experiment which is at the level of 30%.

Coherent radio emission from the electron beam sudden appearance

We report on the measurement of coherent radio emission from the electron beam sudden appearance at the Telescope Array Electron Light Source facility. This emission was detected by four independent radio detector setups sensitive to frequencies ranging from 50 MHz up to 12.5 GHz. We show that this phenomenon can be understood as a special case of coherent transition radiation by comparing the observed results with simulations. The in-nature application of this signal is given by the emission of cosmic ray or neutrino induced particle cascades traversing different media such as air, rock and ice.

EUSO-TA, a JEM-EUSO pathfinder at the Telescope Array site

EUSO-TA is one of the prototypes of the JEM-EUSO space telescope, realized in the framework of the EUSO project. Its aims are to calibrate the detector response, test its performance in air and vacuum, raise the technological readiness level of some of the components and improve our knowledge of the various detector systems.EUSO-TA is located at the Telescope Array (TA) site in Black Rock Mesa, Utah, USA and is mainly devoted to study the detector response in conjunction with the TA fluorescence detector. The telescope is housed in a shed located in front of one of the fluorescence detectors of the Telescope Array experiment, pointing in the direction of the ELS (Electron Light Source) and CLF (Central Laser Facility), i.e. the artificial light sources at the Telescope Array site.The detector consists of two Fresnel lenses, 1×1 □m each, with a field of view of 11°×11°, able to focus the ultraviolet light generated by cosmic-ray showers as well as from artificial sources, on a focal surface identical to the ones that will be employed in JEM-EUSO.

Measurement of microwave radiation from electron beam in the atmosphere

We report the use of an electron light source (ELS) located at the Telescope Array Observatory in Utah, USA, to measure the isotropic microwave radiation from air showers. To simulate extensive air showers, the ELS emits an electron beam into the atmosphere and a parabola antenna system for the satellite communication is used to measure the microwave radiation from the electron beam. Based on this measurement, an upper limit on the intensity of a 12.5GHz microwave radiation at 0.5m from a 1018 eV air shower was estimated to be 3.96×10−16 W m−2 Hz−1 with a 95% confidence level.

EUSO-TA prototype telescope

EUSO-TA is one of the prototypes developed for the JEM-EUSO project, a space-based large field-of-view telescope to observe the fluorescence light emitted by cosmic ray air showers in the atmosphere. EUSO-TA is a ground-based prototype located at the Telescope Array (TA) site in Utah, USA, where an Electron Light Source and a Central Laser Facility are installed. The purpose of the EUSO-TA project is to calibrate the prototype with the TA fluorescence detector in presence of well-known light sources and cosmic ray air showers. In 2015, the detector started the first measurements and tests using the mentioned light sources have been performed successfully. A first cosmic ray candidate has been observed, as well as stars of different magnitude and color index. Since Silicon Photo-Multipliers (SiPMs) are very promising for fluorescence telescopes of next generation, they are under consideration for the realization of a new prototype of EUSO Photo Detector Module (PDM). The response of this sensor type is under investigation through simulations and laboratory experimentation.

Ground-based tests of JEM-EUSO components at the Telescope Array site, “EUSO-TA”

We are conducting tests of optical and electronics components of JEMEUSO at the Telescope Array site in Utah with a ground-based “EUSO-TA” detector. The tests will include an engineering validation of the detector, cross-calibration of EUSO-TA with the TA fluorescence detector and observations of air shower events. Also, the proximity of the TA’s Electron Light Source will allow for convenient use of this calibration device. In this paper, we report initial results obtained with the EUSO-TA telescope.

Hybrid modeling of relativistic underdense plasma photocathode injectors

The dynamics of laser ionization-based electron injection in the recently introduced plasma photocathode concept is analyzed analytically and with particle-in-cell simulations. The influence of the initial few-cycle laser pulse that liberates electrons through background gas ionization in a plasma wakefield accelerator on the final electron phase space is described through the use of Ammosov-Deloine-Krainov theory as well as nonadiabatic Yudin-Ivanov (YI) ionization theory and subsequent downstream dynamics in the combined laser and plasma wave fields. The photoelectrons are tracked by solving their relativistic equations of motion. They experience the analytically described transient laser field and the simulation-derived plasma wakefields. It is shown that the minimum normalized emittance of fs-scale electron bunches released in mulit-$\mathrm{GV}/\mathrm{m}$-scale plasma wakefields is of the order of ${10}^{\ensuremath{-}2}\text{ }\text{ }\mathrm{mm}\text{ }\mathrm{mrad}$. Such unprecedented values, combined with the dramatically increased controllability of electron bunch production, pave the way for highly compact yet ultrahigh quality plasma-based electron accelerators and light source applications.

Absolute energy calibration of the Telescope Array fluorescence detector with an electron linear accelerator

The Electron Light Source(ELS) is a new light source for the absolute energy calibration of cosmic ray Fluorescence Detector(FD) telescopes. The ELS is a compact electron linear accelerator with a typical output of 109 electrons per pulse at 40 MeV. We fire the electron beam vertically into the air 100 m in front of the telescope. The electron beam excites the gases of the atmosphere in the same way as the charged particles of the cosmic ray induced extensive air shower. The gases give off the same light with the same wavelength dependence. The light passes through a small amount of atmosphere and is collected by the same mirror and camera with their wavelength dependence. In this way we can use the electron beam from ELS to make an end-to-end calibration of the telescope. In September 2010, we began operation of the ELS and the FD telescopes observed the fluorescence photons from the air shower which was generated by the electron beam. In this article, we will reort the status of analysis of the absolute energy calibration with data which was taken in September 2010, and beam monitor study in November 2011.

Future plans for the Telescope Array experiment

The Telescope Array (TA) experiment is world's first and only air shower detector to be directly calibrated by an on-site accelerator beam. For wider and deeper understanding of cosmic rays via high precision measurements, we have several future plans for TA experiment. The first extension plan is an on-going project, called as TA low energy extension (TALE), to extend sensitive energy range to 10 16.5 eV in order to study second knee, predicted galactic-extragalactic transition of dominant sources and air shower phenomena comparing with LHC measurements. The second proposition is exchanges of FDs and SDs between TA and Pierre Auger Observatory, toward understanding systematic uncertainties of these experiments and to solve discrepancies in energy scales and Xmax. The third plan is a huge air shower array, the world observatory, consisting of a huge number of SDs and/or FDs for world's largest exposure and finest accuracy to open a new window on astronomy with ultra high energy particles. surface detectors (SDs) arrayed with a spacing of 1.2km between each SD in an area of approximately 680km 2 , and air fluorescence detectors (FDs) in three stations located around SDs facing inward and looking over array. The full operation of detectors have been started in March 2008. In TA experiment we have most valuable calibration facility which is a electron linear accelerator, called Electron Light Source (ELS) (2). ELS installed 100m away from south-east FD station (called BRM station) shoots calibrated electron beams for FDs. The typical energy per electron and number of electrons are 40MeV and 10 9 , respectively. With this equipment we will achieve an end to end calibration for FDs. After four years of very stable operations, we have successfully released our results in this conference, although some of these are still preliminary. The results are briefly summarized as follows: The energy spectrum has a clear ankle at 10 18.7 eV and a sharp cutoff above 10 19.7 eV. The flux is consistent with HiRes result. The shape of spectrum curve, it means spectral indexes and break points on curve, are fitted to spectrum curves by HiRes and that by Auger, However, to fit our curve with that by Auger we need to shift primary energies about 20%. Our preliminary results of mass composition analyses, which are averaged Xmax and their distributions, show that protons dominate primary composition of observed showers. This preliminary conclusion contradicts Auger's results (3), which show a transition of dominant composition from light to heavy, derived from averaged Xmax values and their distributions. From arrival direction distribution analyses, we do not observe

Calibration and testing of a prototype of the JEM-EUSO telescope on Telescope Array site

Aim of the TA-EUSO project is to install a prototype of the JEM-EUSO telescope on the Telescope Array site in Black Rock Mesa, Utah and perform observation of natural and artificial ultraviolet light. The detector consists of one Photo Detector Module (PDM), identical to the 137 present on the JEM- EUSO focal surface. Each PDM is composed by 36 Hamamatsu multi-anode photomultipliers (64 channels per tube), for a total of 2304 channels. Front-End readout is performed by 36 ASICS, with trigger and readout tasks performed by two FPGA boards that send the data to a CPU and storage system. Two, 1 meter side square Fresnel lenses provide a field-of-view of 8 degrees. The telescope will be housed in a container located in front of the fluorescence detector of the Telescope Array collaboration, looking in the direction of the ELF (Electron Light Source) and CLF (Central Laser Facility). Aim of the project is to calibrate the response function of the EUSO telescope with the TA fluorescence detector in presence of a shower of known intensity and distribution. An initial run of about six months starting from end 2012 is foreseen, during which we expect to observe, triggered by TA electronics, a few cosmic ray events which will be used to further refine the calibration of the EUSO-Ground with TA. Medium term plans include the increase of the number of PDM and therefore the field of view.

Three dimensional field calculations for a short superconducting dipole for the UCLA Ultra Compact Synchrotron

The Ultra Compact Synchrotron (UCS), proposed for UCLA, is a compact 1.5 GeV electron light source with superconducting magnets to produce X-rays with a critical energy of about 10 keV. The design physical length (cold length) for the dipole is 418 mm. The synchrotron requires that a uniform field be produced in a region that is 180 mm wide by 40 mm high by about 380 mm long. The end regions of the dipole should be short compared to the overall length of the dipole field region. A Vobly H type of dipole was selected for the synchrotron bending magnets. In order for each dipole to bend a 1.5 GeV electron beam 30 degrees, the central induction must be in the range of 6.4 to 6.9 T (depending on the dipole magnetic length). The pole width for the dipole was set so that over 90 percent of the X-rays generated by the magnet can be extracted. The three dimensional field calculations were done using TOSCA. This report shows that Vobly type of dipole will behave magnetically as a conventional water cooled iron dominated dipole. The uniformity of the integrated magnetic field can be controlled by varying the current in the shield coil with respect to gap and cross-over coils. The two dimensional in center of the magnet can be tuned to be very uniform over a width of 110 to 120 mm. The three dimensional calculations show that the magnetic length along a particle track in the dipole is about 29 mm longer than the length of the iron pole pieces. This report presents the three dimensional design of the UCS Vobly dipole and the results of the field calculations for that magnet.

The Interaction between Low Velocity Electron Beams and Insulating Surfaces under Electron Bombardment and Photo Induced Excitations

The electron absorption coefficient (1 − δ̄) of an insulating surface held at an average potential V̄s between zero and the first crossover potential is observed to increase substantially when the insulator is subject to excitation from a separate electron beam or light source. This effect is apparently caused by the migration of holes to the vacuum interface under influence of the applied field. A vidicon gun in the low-velocity scanning mode was used to establish a potential V̄s of the exposed surfaces of thin films of As2S2 and As2S3 up to 5 μ in thickness which were evaporated onto electron-permeable or light-transparent conducting substrates. The average insulation excitation current ĪT was measured as a function of IB, the low velocity beam current, for fixed values of VT, the potential of the conducting substrate, under constant excitation conditions from either a light source or a 20 keV electron beam extended area source. The average electron absorptivity (1 − δ̄) of the insulator is determined as a function of V̄s, using the equation ĪT = (VT − V̄s)/R = (1 − δ̄)IB on the assumption that resistance R of the insulating film is independent of the field gradient applied across it, for a fixed value of electron bombardment (or light) excitation. Observations also include measurements on changes in (1 − δ̄) after evaporating thin layers of different, metal and insulating films over the exposed surfaces of the insulating films.