DC Electron Beam Research Articles

Enhanced corrosion resistance of strontium hydroxyapatite coating on electron beam treated surgical grade stainless steel

The surface of 316L stainless steel (316L SS) is irradiated by high energy low current DC electron beam (HELCDEB) with energy of 500keV and beam current of 1.5mA followed by the electrodeposition of strontium hydroxyapatite (Sr-HAp) to enhance its corrosion resistance in physiological fluid. The coatings were characterised by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and High resolution scanning electron microscopy (HRSEM). The Sr-HAp coating on HELCDEB treated 316L SS exhibits micro-flower structure. Electrochemical results show that the Sr-HAp coating on HELCDEB treated 316L SS possesses maximum corrosion resistance in Ringer's solution.

Electrical and thermo-mechanical analysis of beam recovery system for megawatt power gyrotron

The paper presents the electrical and thermo-mechanical design of single stage beam recovery system for 120GHz, 1MW gyrotron. The electrical study shows that the cylindrical shape single stage beam recovery system enhances the efficiency by 66.26%. The maximum power deposited to collector in depressed collector operation is 0.48MW for electronic efficiency, 30% and 1.44MW for DC electron beam. The thermo-mechanical analysis has been performed to evaluate the water cooling system. The cooling system has capability of accommodating a peak wall loading, 0.9kW/cm2 at flow rate of 1500l/min for safe operating time, 60ms. Further, a high voltage analysis is also carried out to appraise the electric field distribution in the collector.

Charge lifetime measurements at high average current using aK2CsSbphotocathode inside a dc high voltage photogun

Two ${\mathrm{K}}_{2}\mathrm{CsSb}$ photocathodes were manufactured at Brookhaven National Lab and delivered to Jefferson Lab within a compact vacuum apparatus at pressure $\ensuremath{\sim}{10}^{\ensuremath{-}11}\text{ }\text{ }\mathrm{Torr}$. These photocathodes were evaluated using a dc high voltage photogun biased at voltages up to 200 kV, and illuminated with laser light at wavelengths 440 or 532 nm, to generate dc electron beams at currents up to 20 mA. Some conditions produced exceptionally large photocathode charge lifetimes, without measurable quantum efficiency decay, even from the center of the photocathode where operation using GaAs photocathodes is precluded due to ion bombardment. Under other conditions the charge lifetime was poor due to extensive ion bombardment under severely degraded vacuum conditions, and as a result of localized heating via the laser beam. Following beam delivery, the photocathodes were evaluated using a scanning electron microscope to determine surface morphology.

Six-dimensional weak-strong simulation of head-on beam-beam compensation in the Relativistic Heavy Ion Collider

To compensate the beam-beam tune spread and beam-beam resonance driving terms in the polarized proton operation in the Relativistic Heavy Ion Collider (RHIC), we will introduce a low energy DC electron beam into each ring to collide head-on with the opposing proton beam. The device to provide the electron beam is called an electron lens. In this article, using a 6D weak-strong beam-beam interaction simulation model, we will investigate the effects of head-on beam-beam compensation with electron lenses on the proton beam dynamics for the RHIC 250 GeV polarized proton operation. Frequency maps, dynamic apertures, and proton beam loss rates are calculated for this study. Key beam parameters involved in this scheme are varied to search for the optimum compensation condition. The sensitivities of head-on beam-beam compensation to beam imperfections and beam offsets are also studied.

High Performance of GaN-Based Flip-Chip Light-Emitting Diodes with Hole-Shape Patterned ITO Ohmic Contact Layer and AgIn Reflector

The enhancement of light extraction efficiency is observed when the hole-shape patterned ITO ohmic contact layer and AgIn reflector is adopted in GaN-based flip-chip (FC) light emitting diodes (LEDs). ITO layer (140 nm) and AgIn (200 nm) was deposited on the top of p-GaN by in-line DC sputtering and electron beam evaporating system, respectively. The ITO ohmic contact layer showed a low specific contact resistance of 2.66 x 10(-5) Omega cm(-2) and high transmittance of >85% at visible spectral regions. The AgIn reflector exhibited a low specific contact resistance of 1.90 x 10(-5) Omega cm(-2) and high reflectance of approximately 84% at visible spectral regions. Comparing with unpatterned ITO/AgIn layer, the optical output power of GaN-based FC LEDs improves approximately 30% by the adoption of micro size hole-shape patterned ITO ohmic contact layer and AgIn reflector.

Fabrication and Bioconjugation of Micro- and Nanoscale Structures Intended for Cancer-Specific Antigen Detection

Cleanroom processes can be used for fabricating microscale and nanoscale structures, and such structures, when bioconjugated, can be used for detecting low levels of cancer-specific circulating antigens. The concentration of such circulating antigens in human serum continues to increase with cancer progression, and therefore, detection of cancer at very early stages of the disease can be facilitated by monitoring small increases in circulating antigen concentration. Therefore, fabrication and bioconjugation are the first steps in the development of bio-assays for cancer detection. In this work, microscale and nanoscale Au/Cr thin film structures have been fabricated on Si substrate using dc sputtering and electron-beam (e-beam) evaporation in combination with photo and e-beam lithography. Using the fabricated device material stack (Au/Cr/Si), we have assessed the binding affinity of Au, Cr, and Si with Protein G, and antibodies for prostate specific antigen and cancer antigen 125, an ovarian cancer-associated antigen. Based on our experiments, we see that the thin gold layer of the Au/Cr/Si samples provides increased biomaterial binding affinity, and the chromium layer has a similar, if not less, binding affinity compared with the silicon chip alone. Thus, this work demonstrates that the fabricated material stack provides an appropriate platform for antigen detection.

Fore-vacuum plasma-cathode electron sources

AbstractThis paper presents a review of physical principles, design, and performances of plasma-cathode direct current (dc) electron beam guns operated in so called fore-vacuum pressure (1–15 Pa). That operation pressure range was not reached before for any kind of electron sources. A number of unique parameters of the e-beam were obtained, such as electron energy (up to 25 kV), dc beam current (up 0.5 A), and total beam power (up to 7 kW). For electron beam generation at these relatively high pressures, the following special features are important: high probability of electrical breakdown within the accelerating gap, a strong influence of back-streaming ions on both the emission electrode and the emitting plasma, generation of secondary plasma in the beam propagation region, and intense beam-plasma interactions that lead in turn to broadening of the beam energy spectrum and beam defocusing. Yet other unique peculiarities can occur for the case of ribbon electron beams, having to do with local maxima in the lateral beam current density distribution. The construction details of several plasma-cathode electron sources and some specific applications are also presented.

Coating characteristics of electron beam cured bisphenol A diglycidyl ether diacrylate resin containing 1,6-hexanediol diacrylate on wood surface

Electron beam curing of bisphenol A diglycidyl ether diacrylate resin (BDGDA) mixed with varying amount of 1,6-hexanediol diacrylate monomer (HDDA) was investigated using low energy DC electron beam accelerator. Cured coating films were analyzed by Fourier transformed infrared spectroscopy (FTIR), gel fraction, swelling ratio and thermogravimetric (TG) techniques. The wood surfaces cured with different coating compositions were tested for their end use performance properties like gloss, pencil hardness, scratch resistance, mar resistance, abrasion resistance, chemical resistance, steam resistance and cigarette burn resistance. FTIR studies indicated that the density of acrylate functionality and degree of curing increased with the HDDA content in the feed mixture. This observation was supported by gel fraction and swelling studies as well. The thermal stability, pencil hardness, mar resistance, abrasion resistance and solvent resistance properties of coating were observed to improve with the incorporation of HDDA. However, there was significant decrease in gloss and scratch resistance at higher HDDA content. The coating showed excellent steam and stain resistance but poor resistance to cigarette burns.

Experimental Demonstration of Relativistic Electron Cooling

We report on an experimental demonstration of electron cooling of high-energy antiprotons circulating in a storage ring. In our experiments, electron cooling, a well-established method at low energies (<500 MeV/nucleon), was carried out in a new region of beam parameters, requiring a multi-MeV dc electron beam and an unusual beam transport line. In this Letter, we present the results of the longitudinal cooling force measurements and compare them with theoretical predictions.

Ion clearing in an ERL

The rest-gas in the beam-pipe of a particle accelerator is readily ionized by effects like collisions, synchrotron radiation and field emission. Positive ions are attracted to electron beams and create a nonlinear potential in the vicinity of the beam which can lead to beam halo, particle loss, optical errors or transverse and longitudinal instabilities. In an energy recovery linac (ERL) where beam-loss has to be minimal, and where beam positions and emittances have to be very stable in time, these ion effects have to be avoided. Here we investigate three measures of avoiding ion accumulation: (a) A long gap between linac bunch trains that allows ions to drift out of the beam region, a measure regularly applied in linacs; (b) a short ion clearing gap in the beam that leads to a time varying beam potential and produces large excited oscillations of ions around the electron beam, a measure regularly applied in storage rings; (c) Clearing electrodes that create a sufficient voltage to draw ions out of the beam potential, a measure used for DC electron beams and for antiproton beams. For the parameters of the X-ray ERL planned at Cornell University we show that method (a) cannot be applied, method (b) is technically cumbersome, and (c) should be most easily applicable.

Attainment of an MeV-range, DC electron beam for the Fermilab cooler

To prepare a beam generation device for Fermilab's future Recycler Electron Cooling system, an experimental set-up with a simplified beam line has been commissioned at Fermilab. Stable operation was achieved at an electron energy of 3.5MeV and a DC beam current of up to 0.5A. The main reason for interruptions of the operation was found to be microsecond long bursts of the cathode current. While the frequency of the interruptions is determined primarily by a flow of secondary ions, the resulting reduction in the duty factor depends on the beam optics, the protection systems, and the tube electric field strength.

Ultra-cold electron source with a GaAs-photocathode

A source of ultra-cold magnetically guided DC electron beams with a transmission mode GaAs-photocathode has been developed. The mA currents and the required stability are obtained by using state-of-the-art technology of photocathode fabrication and cleaning in UHV. To optimize energy spreads from photocathodes, studies of the complete (longitudinal and transverse) energy distribution of the magnetized electron beam were performed. They allowed us to get a detailed look on the energy loss and momentum scattering of the electrons at the interface and finally, to obtain narrow electron energy spreads (below 10meV) from the photocathode.

A new 5 MeV–300 kW dynamitron for radiation processing

The high beam power required to deliver reasonably effective levels of X-rays for processing food and medical products has driven the development of a new high-power Dynamitron ® system. For many years, RDI accelerators have been providing up to 200 kW of DC electron beam power at energies up to 5.0 MeV. This new system, designed to operate at 300 kW of beam power at 5.0 MeV, is also capable of producing up to 75 mA of beam current when operating at lower voltages. Achieving this high power level and maintaining the high reliability that Dynamitrons are known for has required new designs offering lower power losses yielding higher efficiency and reducing stress in critical components. Improvements in beam control and optics add to the stability and reliability of the system providing a basis for a highly reliable high-power system.

Investigation of the interfacial structure of ultra-thin platinum film deposited by cathodic–arc

Ultra-thin films are of interest in the production of X-ray mirrors that use a multilayer structure. The most commonly used deposition techniques are dc magnetron sputtering and electron beam evaporation; this paper presents results of cathodic–arc deposition. Ultra thin films of platinum with nominal thicknesses in the range 15–65 Å were deposited on silicon substrates and the film structure investigated using X-ray reflectivity and X-ray photoelectron spectroscopy. It has been found that the structure of the deposited films consists of three layers—the platinum film, a silicon oxide layer and a platinum silicide layer. In contrast to dc magnetron and electron beam deposited films, the silicide layer of cathodic–arc deposited films have a higher density and greater thickness, which is attributed to the higher energy process of this deposition technique. These attributes of the cathodic–arc deposited films suggest that the deposition technique is not suitable for production of mirrors of materials that react with each other, but for materials that do not the deposition technique is potentially more favourable than that of e-beam and magnetron sputtering.

Probe diagnostic development for electron beam produced plasmas

A variety of diagnostics have been fielded in different plasma sources to provide new information about the large area plasma processing system (LAPPS) at NRL. Specifically, a high resolution digital Langmuir probe system and ion flux/energy diagnostics have been employed in pulsed and dc electron beam produced plasmas as well as in an inductively coupled source as a baseline experiment. rf induced dc bias, ion flux, electron and ion temperature, and plasma potential in the proximity of rf powered electrodes placed into these plasmas were measured. It is found that the LAPPS plasma channel is essentially unaffected by the presence of the rf voltage, with the net ion flux unchanging in the presence of rf. These findings are consistent with earlier theoretical models of LAPPS [Manheimer et al., Plasma Sources Sci. Technol. 9, 370 (2000)].

Preparation and performance of transmission-mode GaAs photocathodes as sources for cold dc electron beams

Photoemission from GaAs cathodes with negative electron affinity (NEA) is applied for producing electron beams with very low longitudinal and transverse velocity spread. GaAs transmission-mode cathodes were activated with Cs and either O2 or NF3 in an extremely high vacuum setup (base pressure below 10−12 mbar). Quantum efficiencies of 20%–25% (at 670 nm) and long dark lifetimes (about 1000 h) could be achieved for both types of activation in a reproducible way. Using a method based on the adiabatic transverse expansion of an electron beam in a spatially decreasing magnetic field, the mean transverse energy (MTE) of the photoemitted electrons was measured systematically, recording longitudinal energy distribution curves. Both the MTE and the longitudinal energy spread strongly depend on the value of NEA and the position of the extracted distribution relative to the bulk conduction band minimum. Electrons with energies above the conduction band minimum are thermalized with the lattice temperature of the cathode, while electrons with energies below this level show a non-Maxwellian distribution with enhanced transverse energies. Thus, when extracting all electrons in a current limited emission mode, the MTE increases with the absolute value of NEA and reaches values up to ≈100 meV. By cutting off the low energy electrons with an external potential barrier, the longitudinal as well as transverse energy spread of the extracted electron ensemble are reduced. The MTE could be reduced down to about 28 meV at room temperature and to about 14 meV at liquid nitrogen temperature. The behavior of the MTE was found equivalent for (Cs, O) and for (Cs, F) activation layers on the same cathode. Conclusions about energy loss and scattering in the emission of photoelectrons from NEA GaAs cathodes are discussed.

Simulation of a dc electron beam strongly influenced by self-fields

A method is presented to simulate the transport of a dc charged particle beam strongly influenced by its self-fields. If the initial phase space of the beam is chosen to be a Kapchinskij-Vladimirskij distribution, the simulation is in agreement with the Kapchinskij-Vladimirskij envelope equations. The simulation was initialized with a Gaussian transverse momentum distribution to investigate the origin of current profiles measured in a 130 keV, 635 mA plasma-focused electron beam.

Pelletron-based MeV-range electron beam recirculation

Abstract In this paper we describe the successful recirculation of a DC electron beam at energies 1–1.5 MeV and currents up to 0.7 A with typical relative losses of 5–20×10−6. Currents of 200 mA were maintained for periods of up to five hours without a single breakdown. We found that the aperture-limiting diaphragm in the gun anode significantly increased the stability of the recirculation. We also found that the stability depended strongly on vacuum pressure in the beamline. The performance of the collector with transverse magnetic fields was found to be adequate for beam currents up to 0.6 A, which is in agreement with our low-energy bench test results.

Electron beam simulations of a multi-stage depressed collector, including secondary and scattered electrons

The Fusion FEM is the prototype of a high power, rapid-tunable mm-wave source, operating in the range 130–260 GHz (Urbanus, Nucl. Instr. and Meth. A 375 (1996) 401) [1]. The device is driven by a 2 MeV, 12 A DC electron beam. A decelerator and depressed collector will be mounted behind the mm-wave cavity, for energy recovery of the unspent electron beam. This way the device will have a high system efficiency of over 50%. The unspent beam has a high-energy spread due to the FEM interaction. We report on the design of the depressed collector and on the beam transport system from the decelerator into the collector. The current streaming back has to be below 0.1%. Secondary electrons with low energy have little influence. Much attention had to be paid to prevent scattered electrons with high energies from streaming back. Two design solutions will be presented, one completely cylindrical symmetric and one with an a-symmetric bending scheme.

Vacuum ultraviolet rare gas excimer light source

A dc electron beam at 20 keV is used for the excitation of pure rare gases at pressures up to 1.7 bar. The well known second excimer continua of argon, krypton, and xenon observed under these excitation conditions provide an efficient light source in the vacuum ultraviolet spectral region between 120 and 200 nm. Thin (300 nm) SiNx foils are used as entrance windows for the low energy electron beam. Due to the flexibility of the production process of the thin foils one can consider various shapes and sizes of the light emitting region to be manufactured. Efficiencies of ∼30% are observed for the conversion of electron beam energy into light.