Stanislav Baturin

Efficient extraction of high power THz radiation generated by an ultra-relativistic electron beam in a dielectric loaded waveguide

We have measured an intense THz radiation produced by a sub-picosecond, relativistic electron bunch in a dielectric loaded waveguide. For efficient THz pulse extraction, the dielectric loaded waveguide end was cut at an angle. For an appropriate choice of angle cut, such antenna converts the TM01 mode excited in the waveguide into a free-space fundamental Gauss-Hermite mode propagating at an angle with respect to the electron beam trajectory. Simulations show that more than 95% of energy can be extracted using such a simple approach. More than 40 oscillations of about 170 ps long 0.48 THz signal were explicitly measured with an interferometer and 10 μJ of energy per pulse, as determined with a calorimetric energy meter, were delivered outside the electron beamline to an area suitable for THz experiments.

Locally Resolved Electron Emission Area and Unified View of Field Emission from Ultrananocrystalline Diamond Films

In this paper we study the effect of actual, locally resolved, field emission (FE) area on electron emission characteristics of uniform semimetallic nitrogen-incorporated ultrananocrystalline diamond ((N)UNCD) field emitters. To obtain the actual FE area, imaging experiments were carried out in a vacuum system in a parallel-plate configuration with a specialty anode phosphor screen. Electron emission micrographs were taken concurrently with I-V characteristics measurements. It was found that in uniform (N)UNCD films the field emitting site distribution is not uniform across the surface, and that the actual FE area depends on the applied electric field. To quantify the actual FE area dependence on the applied electric field, a novel automated image processing algorithm was developed. The algorithm processes extensive imaging datasets and calculates emission area per image. By doing so, it was determined that the emitting area was always significantly smaller than the FE cathode surface area of 0.152 cm available. Namely, the actual FE area would change from 5× 10 % to 1.5 % of the total cathode area with the applied electric field increased. We also found that (N)UNCD samples deposited on stainless steel with molybdenum and nickel buffer layers always had better emission properties with the turn-on electric field <5 V/μm and β-factor of about 1,000, as compared to those deposited directly onto tungsten having the turn-on field >10 V/μm and β-factor of about 200. It was concluded that rough or structured surface, either on the macroor microscale, is not a prerequisite for good FE properties. Raman spectroscopy suggested that increased amount of the graphitic sp phase, manifested as reduced D/G peak ratio, was responsible for improved emission characteristics. Finally and most importantly, it was shown that when I-E curves as measured in the experiment were normalized by the field-dependent emission area, the resulting j-E curves demonstrated a strong kink and significant deviation from Fowler-Nordheim (FN) law, and eventually saturated at a current density of ∼100 mA/cm. This value was nearly identical for all studied (N)UNCD films, regardless of the substrate.In this paper, we study the effect of the actual, locally resolved, field emission area on electron emission characteristics of uniform planar conductive nitrogen-incorporated ultrananocrystalline diamond ((N)UNCD) field emitters. High resolution imaging experiments were carried out in a field emission microscope with a specialty imaging anode screen such that electron emission micrographs were taken concurrently with measurements of I-V characteristics. An automated image processing algorithm was applied to process the extensive imaging data sets and calculate the emission area per image. It was routinely found that field emission from as-grown planar (N)UNCD films was always confined to a counted number of discrete emitting centers across the surface, which varied in size and electron emissivity. It was established that the actual field emission area critically depends on the applied electric field and that the field emission area and overall electron emissivity improve with the sp2-fraction present in the film, irrespective of the original substrate roughness or morphology. Most importantly, when as-measured I-E characteristics were normalized by the electric field-dependent emission area, the resulting j-E curves demonstrated a strong kink and departed from the Fowler-Nordheim law, finally saturating at a value on the order of 100 mA/cm2. This value was nearly identical for all studied films regardless of substrate. It was concluded that the saturation value is specific to the intrinsic fundamental properties of (N)UNCD.

Electron emission projection imager

A new projection type imaging system is presented. The system can directly image the field emission site distribution on a cathode surface by making use of anode screens in the standard parallel plate configuration. The lateral spatial resolution of the imager is on the order of 1-10 μm. The imaging sensitivity to the field emission current can be better than the current sensitivity of a typical electrometer, i.e., less than 1 nA.

Thermal analysis of the diamond compound refractive lens

Two dimensional compound refractive lenses (CRL) made out of single crystal diamond had been recently demonstrated [1, 2]. The use of compound refractive lens is inevitably associated with high x-ray absorption. One of the benefits of diamond as a material for CRL is its ability to withstand high instantaneous and average heat load. We used finite element method to simulate thermal effects in the lens. A steady state simulation is done for high average heat load conditions of ultimate storage rings. A time domain simulation is used for high peak power XFEL case. We compare diamond with beryllium, a common material for the CRL, and find that diamond temperature rise is less even though its x-ray absorption is higher.

Scanning probe microscopy and field emission schemes for studying electron emission from polycrystalline diamond

The letter introduces a diagram that rationalizes tunneling atomic force microscopy (TUNA) observations of electron emission from polycrystalline diamonds as described in recent publications. The direct observations of electron emission from grain boundary sites by TUNA could indeed be evidence of electrons originating from grain boundaries under external electric fields. At the same time, from the diagram it follows that TUNA and field emission schemes are complimentary rather than equivalent for results interpretation. It is further proposed that TUNA could provide better insights into emission mechanisms by measuring the detailed structure of the potential barrier on the surface of polycrystalline diamonds.

Beam-driven linear and nonlinear THz source technology

Advances in dielectric resonators and materials have arisen in the context of research into new particle acceleration techniques. In the wakefield accelerator, electromagnetic fields excited by an electron beam in a low loss dielectric structure are used to accelerate a second, trailing beam to high energy. Energy can be efficiently extracted from the beam in this manner and thus the accelerating structure can also be used as an RF source, with frequencies extending into the THz. New ferroelectrics are also finding significant uses in this technology; some of the applications discussed are nonlinear frequency multiplication and frequency agile (tunable) cavities.

Field emission microscopy of ultra-nano-crystalline diamond films

Nitrogen-incorporated ultrananocrystalline diamond, (N)UNCD, is an unconventional field emitter that performs in planar thin film configuration and has turn-on fields on the order of 10 V/ m. To shed more light on fundamental field emission properties of (N)UNCD, we have designed and commissioned a field emission microscope (FEM). The microscope can directly image the field emission site distribution on a cathode surface by making use of anode screens in the standard parallel plate configuration with the lateral spatial resolution 1–10 m.

Locally resolved field emission area and its effect on resulting j-E characteristics: Case study for planar thin film ultrananocrystalline diamond field emitters

In this work we present the results of numerical processing of extensive datasets of electron field emission (FE) micrographs obtained from planar nitrogen-incorporated ultra-nanocrystalline diamond ((N)UNCD) films deposited on different substrates. The micrographs were acquired concurrently with the FE measurements performed in a parallel-plate configuration. The extracted electrons were collected by a phosphor imaging anode screen, which converted an electron emission pattern into a light emission pattern representing electron emission site distribution on the surface of (N)UNCD. We establish a quantitative correlation between the effective emission area and the applied electric field S(E). Moreover, we find that, when the measured current is normalized by S(E), all current density curves demonstrate a strong kink and saturate at about 100 mA/cm2 independently of the substrate, whereas normafization by the total area of a cathode does not lead to such behavior.

Vacuum effect on field emission I-V curves

In this paper, we report our first experimental findings that evidence the vacuum level in the test chamber can be responsible for variation in the field emission (Fowler-Nordheim) response of an electron source. This situation is exampled using a carbon nanotube sample measured in a parallel plate configuration.

Stroboscopic High-Duty-Cycle GHz Time-Resolved Microscope: Toward Hardware Implementation and Commissioning

1. Euclid TechLabs, 365 Remington Blvd., Bolingbrook, IL 60440, USA 2. Integrated Dynamic Electron Solutions, 5653 Stoneridge Dr., Suite 117, Pleasanton, CA 94588, USA 3. Materials Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA 4. Department of Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton, NY 11973, USA * s.baryshev@euclidtechlabs.com