Electron Beam Test System Research Articles

Thermal Performance of a Dual-Channel, Helium-Cooled, Tungsten Heat Exchanger

Helium-cooled, refractory heat exchangers are now under consideration for first wall and divertor applications. These refractory devices take advantage of high temperature operation with large delta-Ts to effectively handle high heat fluxes. The high temperature helium can then be used in a gas turbine for high-efficiency power conversion.Over the last five years, heat removal with helium was shown to increase dramatically by using porous metal to provide a very large effective surface area for heat transfer in a small volume. Last year, the thermal performance of a bare-copper, dual-channel, helium-cooled, porous metal divertor mock-up was evaluated on the 30 kW Electron Beam Test System at Sandia National Laboratories. The module survived a maximum absorbed heat flux of 34.6 MW/m2 and reached a maximum surface temperature of 593 °C for uniform power loading of 3 kW absorbed on a 2-cm2 area. An impressive 10 kW of power was absorbed on an area of 24 cm2.Recently, a similar dual-module, helium-cooled heat exchanger made almost entirely of tungsten was designed and fabricated by Thermacore, Inc. and tested at Sandia. A complete flow test of each channel was performed to determine the actual pressure drop characteristics. Each channel was equipped with delta-P transducers and platinum resistance temperature devices (RTDs) for independent calorimetry. One mass flow meter monitored the total flow to the heat exchanger, while a second monitored flow in only one of the channels.The thermal response of each tungsten module was obtained for heat fluxes in excess of 5 MW/m2 using 50 °C helium at 4 MPa. Fatigue cycles were also performed to assess the fracture toughness of the tungsten modules. A description of the module design and new results on flow instabilities are also presented.

Failure analysis of beryllium tile assemblies following high heat flux testing for the ITER program

The following document describes the processing, testing and post-test analysis of two Be-Cu assemblies that have successfully met the heat load requirements for the first wall and dome sections for the International Thermonuclear Experimental Reactor (ITER) fusion reactor. Several different joint assemblies were evaluated in support of a manufacturing technology investigation aimed at diffusion bonding or brazing a beryllium armor tile to a copper alloy heat sink for fusion reactor applications. Judicious selection of materials and coatings for these assemblies was essential to eliminate or minimize interactions with the highly reactive beryllium armor material. A thin titanium layer was used as a diffusion barrier to isolate the copper heat sink from the beryllium armor. To reduce residual stresses produced by differences in the expansion coefficients between the beryllium and copper, a compliant layer of aluminum or aluminum-beryllium (AlBeMet-150) was used. Aluminum was chosen because it does not chemically react with, and exhibits limited solubility in, beryllium. Two bonding processes were used to produce the assemblies. The primary process was a diffusion bonding technique. In this case, undesirable metallurgical reactions were minimized by keeping the materials in a solid state throughout the fabrication cycle. The other process employed an aluminum-silicon layer as a brazing filler material. In both cases, a hot isostatic press (HIP) furnace was used in conjunction with vacuum-canned assemblies in order to minimize oxidation and provide sufficient pressure on the assemblies for full metal-to-metal contact and subsequent bonding. The two final assemblies were subjected to a suite of tests including: tensile tests and electron and optical metallography. Finally, high heat flux testing was conducted at the electron beam testing system (EBTS) at Sandia National Laboratories, NM. Here, test mockups were fabricated and subjected to normal heat loads to 10 MW/m 2 (3 Hz) and abnormal heat loads to 250 MJ/m 2 (0.5 s) to determine their performance under simulated fusion reactor conditions for first wall components. Both assemblies survived the normal heat loads with no visual damage. Optical and electron microscopy were used to evaluate the extent of the damage at the interfaces following the VDE simulations.

Thermal performance and flow instabilities in a multi-channel, helium-cooled, porous metal divertor module

Pressurized helium is under consideration for cooling Langmuir probes and plasma facing components of next generation fusion experiments. Helium is non-corrosive, does not activate, separated easily from tritium, vacuum compatible, and undergoes no phase transformations. Recently, the thermal performance of a bare-copper, dual-channel, helium-cooled, porous metal divertor mock-up, designed and fabricated by Thermacore Inc., was evaluated on Sandia's 30 kW Electron Beam Test System equipped with a closed helium flow loop. The module uses short circumferential flow paths to minimize pressure drops and pumping requirements while achieving optimal thermal performance by providing a very large effective surface area. The module was tested under both uniform and non-uniform heat loads to assess the effects of mass flow instabilities. It survived a maximum absorbed heat flux of 29.5 MW/m 2 on a 2-cm 2 area. Results on the power sharing between the two channels is presented and compared with that of a previous design. These experimental results coupled with appropriate modeling provide insight on flow instabilities in multi-channel, helium-cooled heat exchangers.

Fabrication and high heat flux testing of plasma sprayed beryllium ITER first wall mock-ups

Plasma-sprayed beryllium ITER first wall mock-ups have survived 3000 thermal fatigue cycles at 1 MW/m 2 without damage during testing at the Plasma Materials Test Facility at Sandia National Laboratory in New Mexico. This heat flux level is twice the expected design heat flux for ITER first wall modules. Plasma sprayed beryllium mock-ups were vacuum plasma sprayed at the Los Alamos National Laboratory's Beryllium Atomization and Thermal Spray Facility. Results will be reported on the fabrication, high heat flux testing and post-mortem analysis of two beryllium plasma sprayed mock-ups (1) beryllium plasma sprayed directly on a CuNiBe heat sink and (2) beryllium plasma sprayed on a compliant layer of aluminum which was explosion-bonded to a CuCrZr copper heat sink. The high heat flux tests utilized the 30 kW Electron Beam Test System at a Sandia National Laboratory.

Low cycle thermal fatigue testing of beryllium

A novel technique has been used to test the relative low cycle thermal fatigue resistance of different grades of US and Russian beryllium, which is proposed as plasma facing armor for fusion reactor first wall, limiter and divertor components. The 30 kW electron beam test system at Sandia National Laboratories was used to sweep the beam spot along one direction at 1 Hz. This produces a localized temperature `spike' of 750°C for each pass of the beam. Large thermal stresses in excess of the yield strength are generated, due to very high spot heat flux, 250 MW m −2. Cyclic plastic strains on the order of 0.6% produced visible cracking on the heated surface in less than 3000 cycles. An in-vacuo fiber optic borescope was used to visually inspect the beryllium surfaces for crack initiation. Grades of US beryllium tested included: S-65C, S-65H, S-200F, S200F-H, SR-200, I-400, extruded high purity, HIP′d spherical powder, porous beryllium (94 and 98% dense), Be/30% BeO, Be/60% BeO, and TiBe 12. Russian grades included: TGP-56, TShGT, DShG-200, and TShG-56. Both the number of cycles to crack initiation and the depth of crack propagation, were measured. The most fatigue resistant grades were S-65C, DShG-200, TShGT and TShG-56. Rolled sheet Be (SR-200) showed excellent crack propagation resistance in the plane of rolling, despite early formation of delamination cracks. Only one sample showed no evidence of surface melting, Extruded (T). Metallographic and chemical analyses are provided. Good agreement was found between the measured depth of cracks and a 2-D elastic-plastic finite element stress analysis.

Hierarchical VLSI Fault Tracing by Successive CircuitExtraction from CAD Layout Data in the CAD-Linked EB TestSystem

A hierarchical VLSI fault tracing method is proposed which is applicable to the case where only CAD layout data is available in the CAD-linked electron beam test system. The CAD layout data is assumed to be hierarchically structured. The method uses the expansion of a previously proposed integrated algorithm which combines a transistor-level fault tracing algorithm and a successive circuit extraction from a non-hierarchically or a flat structured CAD layout data. The method allows us to trace a fault hierarchically from the top level cell to the lowest primitive cell and from the primitive cell to the transistor-level circuit in a consistent manner independent of circuit functions even when the cell data and the transistor-level circuit data exist in a level as a mixture. An application of the method to a hierarchically structured CMOS model layout with about 600 transistors shows its validity.

High heat flux testing of CFC composites for the tokamak physics experiment

High heat flux (HHF) testing of carbon fiber reinforced carbon composites (CFC's) was conducted under the General Atomics program to develop plasma-facing components (PFC's) for Princeton Plasma Physics Laboratory's tokamak physics experiment (TPX). As part of the process of selecting TPX CFC materials, a series of HHF tests were conducted with the 30 kW electron beam test system (EBTS) facility at Sandia National Laboratories, and with the plasma disruption simulator I (PLADIS-I) facility at the University of New Mexico. The purpose of the tests was to make assessments of the thermal performance and erosion behavior of CFC materials. Tests were conducted with 42 different CFC materials. In general, the CFC materials withstood the rapid thermal pulse environments without fracturing, delaminating, or degrading in a non-uniform manner; significant differences in thermal performance, erosion behavior, vapor evolution, etc. were observed and preliminary findings are presented below. The CFC's exposed to the hydrogen plasma pulses in PLADIS-I exhibited greater erosion rates than the CFC materials exposed to the electron-beam pulses in EBTS. The results obtained support the continued consideration of a variety of CFC composites for TPX PFC components.

Manufacturing and testing of a Be/OFHCCu divertor module

Beryllium, carbon-based materials and tungsten are considered as plasma facing materials for the next generation of fusion machines such as the international thermonuclear experimental reactor (ITER). Beryllium is one of the primary candidate materials because of its low atomic number and lack of tritium codeposition. However, joining of a beryllium armor to a copper heat sink remains a critical problem due to the formation of brittle intermetallics at the interface. To address this concern, the Japan Atomic Energy Research Institute manufactured a beryllium/Cu divertor module with Cr and Ni diffusion barriers. This Be/Cu module was tested in the electron beam test system of Sandia National Laboratories in the framework of the US—Japan Fusion Collaboration. The divertor module consisted of four beryllium tiles, 25 mm × 25 mm, and a square copper heat sink with convolutions like a screw nut inside the coolant channel. To evaluate the integrity of the brazed bonds under various heat fluxes, beryllium tiles of two different thicknesses, 2 and 10 mm, were bonded to the copper heat sink. Cooling conditions of 10 m/s water flow velocity at 1 MPa, and a water inlet temperature of 20°C were selected based on the thermal analysis. During high heat flux testing the 10 mm thick Be tiles detached at an absorbed heat flux around 5 MW/m 2 for several shots due to flaws at the braze joint confirmed by optical observation after manufacturing. One of the 2 mm thick Be tiles failed after 550 cycles at the steady state heat flux of 6.5 MW/m 2. Most likely the failure was caused by brittleness at the interface caused by the presence of BeCu intermetallics.

Thermal Fatigue Testing of a Diffusion-Bonded Beryllium Divertor Mock-Up under ITER-Relevant Conditions

Thermal response and thermal fatigue tests of four 5 mm thick beryllium tiles on a Russian divertor mock-up were completed on the Electron Beam Test System at Sandia National Laboratories. The beryllium tiles were diffusion bonded onto an OFHC copper saddleblock and a DSCu (MAGT) tube containing a porous coating. Thermal response tests were performed on the tiles to an absorbed heat flux of 5 MW/m{sup 2} and surface temperatures near 300{degrees}C using 1.4 MPa water at 5.0 m/s flow velocity and an inlet temperature of 8-15{degrees}C. One tile was exposed to incrementally increasing heat fluxes up to 9.5 MW/m{sup 2} and surface temperatures up to 690{degrees}C before debonding at 10 MW/m{sup 2}. A third tile debonded after 9200 thermal fatigue cycles at 5 MW/m{sup 2}, while another debonded after 6800 cycles. In all cases, fatigue failure occurred in the intermetallic layers between the beryllium and copper. No fatigue cracking of the bulk beryllium was observed. During thermal cycling, a gradual loss of porous coating produced increasing sample temperatures. These experiments indicate that diffusion-bonded beryllium tiles can survive several thousand thermal cycles under ITER relevant conditions without failure. However, the reliability of the diffusion bonded Joint remains a serious issue.

High-Heat-Flux Testing of Helium-Cooled Heat Exchangers for Fusion Applications

High-heat-flux experiments on three types of helium-cooled divertor mock-ups were performed on the 30-kW electron beam test system and its associated helium flow loop at Sandia National Laboratorie...

VLSI testing with CAD-linked electron beam test system

Two approaches for efficient fault diagnosis are proposed where only CAD layout data is available in the CAD-linked electron beam test system. One is a circuit logical function extraction method from the CAD layout data. In the method, after extracting transistor-level circuit data in a unit of a primitive logic gate from a flat structured CAD layout data, the data are translated to higher cell-level data automatically in order to trace a fault hierarchically. The other is a hierarchical fault tracing method for a hierarchically structured CAD layout data. The method allows us to trace a fault hierarchically from the top level cell to the lowest primitive cell and from the primitive cell to the transistor-level circuit da a consistent manner independent of circuit functions even when the cell data and the transistor-level circuit data exist in a level as a mixture.

Quantitative electron-beam tester for defects in semiconductors (CL/EBIC/SDLTS system)

A pulsed electron beam testing system was developed for quantitative analysis of optical and/or electrical properties of defects in semiconductors. This system can control not only the electron beam but also detect and record the absolute values of light intensity: cathodoluminescence (CL), electron-beam-induced current (EBIC), and scanning deep level transient spectroscopy (SDLTS). Several improvements were made to enable accurate quantitative measurement. An optical system with an ellipsoidal mirror of low magnification was designed to make uniform collection efficiency of CL over a wide specimen area. A photon counting system and a lock-in amplifying system were implemented to measure absolute value of light intensity. A quantitative EBIC or SDLTS system was also incorporated to this system. The combined system of CL/EBIC/SDLTS can both image the distribution of defects and study their characteristics.

Mechanisms for cold sintering of copper : M.M. Ristic et al (Serbian Academy of Arts and Sciences, Belgrade, Yugoslavia), Science of Sintering, vol 25, no 3, 1993, 145–153

The tested divertor targets were designed by the NET Team with emphasis on a high overall melting temperature, which is attractive for off-normal operating conditions, providing a wide margin in passive safety. The mock-up samples were manufactured by Metallwerk Plansee. The high heat flux experiments were performed in the Electron Beam Test System of Sandia National Laboratories, the testing parameters were chosen to match NET/ITER requirements. The power density of electron beam testing was increased stepwise up to 14 MW/m2, the loading time was adjusted to reach steady-state temperature conditions – pulses of up to 500 s were applied. In addition the loading procedure was observed and recorded with an on-line diagnostics system. Numerical methods using known materials data of the refractory metals and the carbon armor were applied to estimate the general thermal response of the test pieces. The excellent agreement with the observed surface and bulk temperatures as well as the good resistance to heat fluxes up to 12.3 MW/m2 is rather promising for an application in future fusion devices. The observed surface temperature for the CC armored target was 1000°C at 6 MW/m2, and 2400°C at 14 MW/m2. However, for some CC-tiles an increased surface temperature was detected after continued loading at heat fluxes between 12.3 and 14 MW/m2. After 1000 loading cycles applied on a graphite tile brazed atop a heat sink of TZM/Mo.41Re neither a visible damage nor a change in the thermal response was observed; the steady-state surface temperature ranged between 1000 and 1050°C.

Time delay measurements using conventional E-beam technology

Abstract The ability to resolve sub-nanosecond phase shifts on internal IC nodes is central to the utility of electron beam test systems. In this work, the obtainable time delay resolution has been investigated both experimentally and via computer modeling. Initial time delay resolution results were obtained at working distances from 1 to 32 mm in a conventional electron beam test system. In order to obtain these results, a signal generation system was developed. This system proved to be adequate for resolution measurements down to 10 ps. Monte Carlo simulated waveforms were generated and used to develop a consistent method of determining the minimum detectable delay. This method, which is based on linear regression and confidence intervals, corresponded well with visual judgments of the resolution. The minimum detectable delays using this criteria ranged from 8 to 44 ps at a static beam current of 20 nA, a pulse width of 150 ps and a 100 kHz repetition rate. The degradation of resolution with increasing working distance was attributed to the transit time effect since there was no significant jitter noise and no increase in noise with working distance evident in the acquired waveforms.

Primary electron pulse shape evaluation in an EBT system

The time resolution of an electron beam testing system (EBT) is mainly related to the primary electron (PE) sampling pulse width. Signal deconvolution techniques are available to enhance the time resolution of the system, provided the PE pulse shape is known with high accuracy. While for high energies this shape has already been evaluated, for the low energies commonly used in MOS IC testing, some additional difficulties must be accounted for, such as increased PE beam spot dispersion, charge trapping into passivation oxides, and lower SIN ratio at the detector. Here, we describe the direct measurement of the PE current used to sample internal voltage waveforms through the use of a fast avalanche photodiode. A numerical simulation has also been performed to help in the correct interpretation of the results. Using a known signal as an input to a matched-impedance microstrip line, a numerical deconvolution technique has been applied to the signal sampled by finite-duration current pulses to evaluate the goodness of the restoration of the original signal.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

FACE: A failure analysis and characterization environment for E-beam testing

VLSI circuits diagnosis demands a test environment with high automation degree. The FACE project has been defined for failure analysis and IC characterization with an electron beam test system. The purpose of this paper is to present Dynamic Fault Probing, one of the analysis methods of FACE, a tool for automatic waveform measurement and comparison. This requires the combination of probe fine positioning and waveform processing techniques, which insures the optimized acquisition, automatic processing and comparison of the signals.

Aspects of dimensional control during manufacture of bronze self-lubricating bearings: J.P. Lagier et al (University of Paris, France)

The tested divertor targets were designed by the NET Team with emphasis on a high overall melting temperature, which is attractive for off-normal operating conditions, providing a wide margin in passive safety. The mock-up samples were manufactured by Metallwerk Plansee. The high heat flux experiments were performed in the Electron Beam Test System of Sandia National Laboratories, the testing parameters were chosen to match NET/ITER requirements. The power density of electron beam testing was increased stepwise up to 14 MW/m2, the loading time was adjusted to reach steady-state temperature conditions – pulses of up to 500 s were applied. In addition the loading procedure was observed and recorded with an on-line diagnostics system. Numerical methods using known materials data of the refractory metals and the carbon armor were applied to estimate the general thermal response of the test pieces. The excellent agreement with the observed surface and bulk temperatures as well as the good resistance to heat fluxes up to 12.3 MW/m2 is rather promising for an application in future fusion devices. The observed surface temperature for the CC armored target was 1000°C at 6 MW/m2, and 2400°C at 14 MW/m2. However, for some CC-tiles an increased surface temperature was detected after continued loading at heat fluxes between 12.3 and 14 MW/m2. After 1000 loading cycles applied on a graphite tile brazed atop a heat sink of TZM/Mo.41Re neither a visible damage nor a change in the thermal response was observed; the steady-state surface temperature ranged between 1000 and 1050°C.

Electron beam testing of monolithic integrated micro- and millimeterwave circuits

An electron beam testing system has been developed, consisting of a new type of electron beam blanking system and a specimen holder designed for applying GHz-frequencies to the device under test. First quantitative measurements have been done on a special test structure, showing the influence of the transit-time-effect on quantitative measurements. These experimental results were compared with results obtained by simulations, showing good agreement. Although the electron beam testing system works in a frequency range from 8 to 18 GHz the results show that quantitative measurements are only practical for frequencies below 2.5 GHz, assuming a maximum measurement error of 10%.

Multi-channel vs. conventional retarding field spectrometers for voltage contrast

This paper will assess the possible advantages of using multi-channel voltage contrast spectrometers in place of conventional retarding field spectrometers in electron beam test systems. The comparison is based on calculating the signal-to-noise characteristics of both spectrometers types. Experimental results on a time-of-flight voltage contrast spectrometer are used to confirm the theoretical predictions made.

Methods for the determination of the static accuracy and linearity of electron-beam test systems

In conjunction with the development of a new test chip for qualification and characterisation of electron-beam testers by the “ITG Fachgruppe 5.6 Kontaktloses Testen von elektronischen Bauelementen” (Head: Prof. Dr.-Ing. E. Kubalek) suitable test methods have been investigated. In this paper several methods for determining the static accuracy and linearity are presented. The recommended procedure can be carried out without great effort and gives easily interpretable results.