Important properties and applications of CVD SILICON CARBIDE^TM with particular emphasis on high heat loads are reviewed. Data on the mechanical and thermal properties of CVD-SiC as function of temperature are presented. Further, the effect of different high temperature treatments on flexural strength of CVD-SiC is discussed and the thermal shock resistance of CVD-SiC is compared to other competing materials. Finally, several high heat flux applications in the areas of optics, semiconductor processing and wear parts are discussed.

The advanced photon source is a state-of-the-art synchrotron light source that will produce intense x-ray beams, which will allow the study of smaller samples and faster reactions and processes at a greater level of detail than has ben possible to date. The beam is produced by using third- generation insertion devices in a 7-GeV electron/positron storage ring that is 1,104 meters in circumference. The heat load from these intense high-power devices is very high, and certain components must sustain total heat loads of 3 to 15 kW and heat fluxes of 30 W/mm$_2). Because the beams will cycle on and off many times, thermal shock and fatigue will be a problem. High heat flux impinging on a small area causes a large thermal gradient that results in high stress. GlidCop, a dispersion-strengthened copper, is the desired design material because of its high thermal conductivity and superior mechanical properties as compared to copper and its alloys. GlidCop is not amenable to joining by fusion welding, and brazing requires diligence because of high diffusivity. Brazing procedures were developed using optical and scanning electron microscopy.

A novel, patented technique of encapsulating high thermal conductivity TPG graphite within a structural material has been developed. This macrocomposite, named TC1050, is an ideal thermal core material because of its high thermal conductivity, low mass density, and ability to have an engineered coefficient of thermal expansion. The encapsulation technique permits the decoupling of the thermal and mechanical interdependence of the constituent materials, allowing each to be optimized independently. The thermal and mechanical performance of the TC1050 material system has been demonstrated in SEM-E, VME and custom format thermal core configurations. TC1050 thermal cores are currently in use in high thermal density airborne circuit cards such as power supplies and digital signal processors and provide three times the thermal conductivity of copper at a mass density less than aluminum.

Diamond has a cubic lattice structure and a very wide bandgap, which suggests that this material should exhibit excellent optical properties at wavelengths ranging from the far infrared to the near ultraviolet. Since diamond also exhibits unusually favorable properties in terms of mechanical strength, chemical stability, and thermal conductivity, there is considerable interest in using diamond for optics applications that involve adverse environmental conditions. The purpose of this paper is to provide an updated assessment of some of the issues that arise in connection with the use of chemically vapor- deposited diamond for applications such as missile system windows or domes, and for designing components that must function in the high photon flux of high-power lasers. Specifically, since the flight velocities of future air- intercept missiles are projected to far exceed those of contemporary systems, this raises the issue of how to access the capability of window/dome material candidates in an aero-thermal shock environment.In this context, it can be demonstrated that, compared to other candidate materials, diamond windows promise to deliver superior performances and should be able to meet any foreseeable requirement. Operation at high speeds, however, imposes limits on the tolerable window emittance to prevent 'blinding' the seeker, and this issue leads to the conclusion that diamond is intrinsically unsuitable for operation in the 3- to 5-micrometers spectral band. Concerning high-energy lasers, note that operational systems always include an optical train consisting of mirrors and windows, which must be capable of transporting and directing the beam without seriously degrading the nominal performance of the laser. In this regard, mirror-faceplate material candidates can be ranked on the basis of appropriate applications that require efficient cooling. Finally, we emphasize that the power- handling capability of diamond laser windows must be examined in the light of potential limitations arising from thermal lensing effects induced by unfavorable refractive index characteristics; edge-cooled configurations may operate at CW beam-power levels of up to 0.5 MW, which is substantial but orders of magnitude below earlier predictions.

A helium-cooled porous metal heat exchanger was built and tested, which successfully absorbed heat fluxes exceeding all previously tested gas-cooled designs. Helium-cooled plasma-facing components are being evaluated for fusion applications. Helium is a favorable coolant for fusion devices because it is not a plasma contaminant, it is not easily activated, and it is easily removed from the device in the event of a leak. The main drawback of gas coolants is their relatively poor thermal transport properties. This limitation can be removed through use of a highly efficient heat exchanger design. A low flow resistance porous metal heat exchanger design was developed, based on the requirements of the Faraday shield for the International Thermonuclear Experimental Reactor device. High heat flux tests were conducted on two representative test articles at the Plasma Materials Test Facility at Sandia National Laboratories. Absorbed heat fluxes as high as 40 MW/m² were successfully removed during these tests without failure of the devices. Commercial applications for electronics cooling and other high heat flux applications are being identified.

This paper describes ongoing efforts to design large surface area cooling modules suitable for sustained operation at heat fluxes approaching 50 MW/m². Modules having actively cooled areas of 10 cm² or more are being developed. Cooling is provided by an array of small diameter water jets operating at speeds of 40 to 50 m/s. These jets impinge on the rear side of a metallic faceplate 2 to 3 mm thick from which the heat load is absorbed. Thermal stress in the faceplate is the expected causes of module failure at high flux, owing to stress levels that may exceed yield strength. We describe our design and the performance estimates for these cooling modules. The behavior of cooling jet arrays is summarized, including numerical simulations for our specific case. Analytical and finite element studies of the stresses in candidate faceplate materials are described for typical thermal and mechanical conditions. The effect of faceplate mounting is a particular issue. A design for a thin-film high-flux resistance heater is also discussed; this heater provides the heat load for testing module prototypes. These cooling modules are intended to be useful in a broad range of applications.

Spray cooling has been considered as one of the most efficient alternatives for the removal of high heat fluxes and is currently used in several modern industrial and technological applications to dissipate high amounts of heat from their components such as in electronics, lasers, metallurgical, and nuclear. In many of these applications steady-state high heat fluxes (SSHHF) removal is required. In this research, experiments were conducted to determine parameters that affect the steady-state behavior of high heat fluxes when using spray cooling. The parameters taken in consideration included the mass flow rate, the heated surface roughness, the liquid subcooling temperature, and the spray angle. Water was used as the working fluid in the experiments. An experimental apparatus was built to carry- out the experiments, consisting of a copper heater with a disc shaped surface, an atomizer system that used commercial nozzles, and a data acquisition systems to accurately measure temperatures, heat fluxes, flow rates, and room conditions. The commercial nozzles generated mean droplet diameters ranging from 85 to 100 micrometers and flow rates between 1.48 and 1.9L/hr. Two surface conditions were sued; one polished with 0.25 micrometers liquid solution and the other polished with 600 grit silicon carbide grinding paper. The SSHHF was determined by observing the transient response of the surface temperature and the surface heat flux. Steady- state heat fluxes in the order of 100W/cm² were obtained in most cases. Results indicated that higher SSHHF can be obtained with increasing mass flow rates and it was easier to achieve them with smooth surfaces. Results also showed that subcooling may not be significant when high mass flow rates. Curves indicating maximum SSHHF were generated as function of the parameters investigated.

The surface temperature uniformity of an internally cooled nosetip and window has been characterized in a laboratory environment. The articles under test were conductively heated by an electrical resistance heater and then cooled by circulating a liquid through internal passages. Data was collected before and during the cool-down. Temperatures were derived from the images collected with an InSb MWIR starring focal plane array camera. All of the nosetips and windows tested, performed as designed.

Blind approach in constructing high heat solar collectors with the one-stage light flux concentration is presented. Shown arc diverse multiclement optical configurations that can be built on the basis of a blind-type concept. Their two main versions using the set of concave parabolic reflecting elements arc described. A preliminary estimation of thc flux concentration level for a circle-blind collector shows it reaching up to half of the thennodyna.mic limit. Key words: solar collectors, high-temperature concentrators, blind reflectois.

Internally liquid cooled apertures (windows) installed in a full size forebody have been characterized under high heat flux conditions representative of endoatmospheric flight. Analysis and test data obtained in the laboratory and at arc heater test facilities at Arnold Engineering Development Center and NASA Ames are presented in this paper. Data for several types of laboratory bench tests are presented: transmission interferometry and imaging, coolant pressurization effects on optical quality, and coolant flow rate calibrations for both the window and other internally cooled components. Initially, using heat transfer calibration models identical in shape to the flight test articles, arc heater facility thermal test environments were obtained at several conditions representative of full flight thermal environments. Subsequent runs tested the full-up flight article including nosetip, forebody and aperture for full flight duplication of surface heating rates and exposure ties. Pretest analyses compared will to test measurements. These data demonstrate a very efficient internal liquid cooling design which can be applied to other applications such as cooled mirrors for high heat flux applications.

As part of an on-going upgrade program at the National Synchrotron Light Source, a parametric study of rectangular flat and curved beryllium windows of varying thickness and heights and under varying thermal loading was undertaken. The study consisted of a series of 2D and 3D thermal stress finite elements analyses to determine the relative benefit of various combinations of parameters with respect to the windows' ability to withstand thermal loads.

When developing a high-heat-flux system, it is important to be able to test the system under relevant thermal conditions and environmental surroundings. Thermal characterization testing is best performed in parallel with analysis and design. This permits test results to impact materials selection and systems design decisions. This paper describes the thermal testing and characterization capabilities of the Laser Hardened Materials Evaluation Laboratory located at Wright-Patterson Air Force Base, Ohio. The facility features high-power carbon dioxide (CO_2$ and neodymium:glass laser systems that can be teamed with vacuum chambers, wind tunnels, mechanical loading machines and/or ambient test sites to create application-specific thermal and environmental conditions local to the material sample or system. Representative results from recently conducted test series are summarized. The test series described demonstrate the successful use of a high power CO₂ laser paired with environment simulation capability to : 1) simulate the expected in-service heat load on a newly developed heat transfer device to ensure its efficient operation prior to design completion, 2) simulate the heat load expected for a laser diode array cooler, 3) produce thermal conditions needed to test a radiator concept designed for space-based operation, and 4) produce thermal conditions experienced by materials use din solid rocket motor nozzles. Test diagnostics systems used to collect thermal and mechanical response data from the test samples are also described.

Transient thermoreflectance techniques, especially the picosecond transient thermoreflectance method (PTTR), provide a means of determining the thermo-physical properties of a thin film and of measuring thin film properties and temperature during manufacturing. In these techniques a pump and probe method is used to heat the sample and to measure the reflectance from it. It has been shown using a plane wave analysis and a 1D thermal analysis based on uniform spatial irradiation that internal reflections caused by the spatial temperature field significantly affect the accuracy of the method in some materials. The internal reflection mechanism alters the temperature field as compared to that predicted without it. Criteria to define the range of importance of the internal reflection mechanism have been developed based on these assumptions. THese results are extended using numerical analysis to investigate the effects of an incident Gaussian beam instead of uniform irradiation. The code includes mechanism to describe the temperature and intensity dependent absorption coefficients and index of refraction. It is found that the 2D effects decrease the 1D normalized reflectance change by 24 percent. A technique for the incorporating the code into the analysis of the PTTR is described.

In order to utilize the full potential of high power wiggler beam lines with heat loads up to several kW and large white beam cross sections, a variety of monochromator crystal designs are in use. Either the crystal is efficiently cooled or the unwanted distortions are compensated by different means which require external control mechanisms. Based on the self-adapting crystal design developed at the Advanced Photon Source, we present a new Si-monochromator crystal and matching support structure. This design makes use of forces inside the crystal which are generated by the heat load hitting the crystal. The heat load induced distortions of the reflecting surface are compensated by these forces. Finite element calculations are the basis for the tested components. The design of the support structure, which provides the necessary mechanical and thermal boundary conditions to the crystal is shown. The present setup allows to measure and adjust the force between crystal and support.

A long undulator installed at a low emittance storage ring, generates quasi-monochromatic beams of high brightness and partial coherence properties; however, this also raises concerns regarding high heat loads on beam line components. There have been intensive research efforts to develop beam line optics to exploit brightness and coherence properties from undulators. These components must withstand high heat loads produced by intense synchrotron radiation beams impinging on their surface which could degrade beam line performance. The effects of high flux undulator radiation on beam line optics for EUV interferometry and photoemission microscopy will be discussed. Specifically, beam line schematics, design considerations of indirectly side cooled mirror and grating assemblies developed at the Center for X- Ray Optics and recent data of performance under undulator radiation load from beam line BL12.0 being commissioned at the ALS will be presented in this study.

A novel, silicon crystal monochromator has been designed and tested for use on undulator and focused wiggler beamlines at third-generation synchrotron sources. The crystal utilizes a thin, partially transmitting diffracting element fabricated within a liquid-nitrogen cooled, monolithic block of silicon. This report summarizes the results from performance tests conducted at the European Synchrotron Radiation Facility (ESRF) using a focused wiggler beam and at the Advanced Photon Source (APS) on an undulator beamline. These experiments indicate that a cryogenic crystal can handle the very high power and power density x-ray beams of modern synchrotrons with sub-arcsec thermal broadening of the rocking curve. The peak power density absorbed on the surface of the crystal at he ESRF exceeded 90 W/mm² with an absorbed power of 166 W, this takes into account the spreading of the beam due to the Bragg angle of 11.4 degrees. At the APS, the peak heat flux incident on the crystal was 1.5 W/mA/mm² with a power of 6.1 W/mA for a 2.0 H X 2.5 V mm² beam at an undulator gap of 11.1 mm and stored current up to 96 mA.

In order to minimize the deformation of cooled x-ray mirrors, it is necessary to understand and to control several parameters: the mirror geometry, the cooling geometry, the power density variation in the beam, the mirror border line effects and the beam end effects. This paper gives an analysis of the influence that these parameters have on the thermal slope error by the use of both an analytical approach, and a finite element approach. A distinction is made between the two basic contributions to the thermal slope: the flexion and the bump. Engineering guidelines are then provided for the designer willing to minimize the thermal slope error.

This paper describes the specifications, design, and fabrication of a 1.2 meter long ultra high vacuum silicon mirror for use as the first optical element on an x-ray beamline at APS. The mirror, which is 1200 mm by 90 mm by 120 mm in size, intercepts the incident x-ray beam at 0.15 degrees. The thermal power incident on the mirror is 1.2 kW with a peak heat flux of 0.38 W/mm². The heat is removed by flowing water through a set of channels configured in the face plate of the mirror. Various aspects of this mirror, including its purpose, utility, expected thermal and structural performance, cooling design, UHV provision, support and mounting, surface figure and finish, bonding of the cooling conduits, and other manufacturing steps are discussed.

For some x-ray experiments, only a fraction of the intense central cone of x-rays generated by high-power undulator sources can be used; the x-ray source emittance is larger than the useful emittance for the experiment. For example with microfocusing optics, or for coherence experiments, x- ray beams with cross sections less than 0.1 mm² are desirable. With such small beams, the total thermal load is small even though the heat flux density is high. Analyses indicate that under these conditions, rather simple crystal cooling techniques can be used. We illustrate the advantages of a small beam monochromator, with a simple x-ray monochromator optimized for x-ray microdiffraction. This monochromator is designed to achieve negligible distortion when subjected to a narrow beam from an APS undulator A operating at 100 mA. It also allows for rapid and repeatable energy scans and rapid cycling between monochromatic and white beam conditions.

This paper describes the design, expected performance, and preliminary test results of a contact-cooled monochromator for use on high heat load x-ray beamlines. The monochromator has a cross section in the shape of the letter U. This monochromator should be suitable for handing heat fluxes up to 5 W/mm². As such, for the present application, it is compatible with the best internally cooled silicon crystal monochromators operating at room temperature. There are three key features in the design of this monochromator. First, it is contact cooled, thereby eliminating fabrication of cooling channels, bonding, an undesirable strains in the monochromator due to coolant-manifold-to-crystal-interface. Second, by illuminating the entire length of the crystal and extracting the central part of the reflected beam, sharp slope changes in the beam profile and thus slope errors are avoided. Last, by selecting appropriate crystal geometry and cooling locations, tangential slope error can be substantially reduced.

The undulator beamline at the storage ring PETRA of the Hamburger Synchrotronstrahlungslabor HASYLAB delivers hard x-ray photons usable up to 300 keV. The total power of the beam is now up to 7.5 kW with closed gap and 60 mA stored particle beam. After a planned upgrade of the undulator, the power can increase to about 15 kW. The vertical white beam slit for the PETRA undulator beamline is located at about 105 m from the source. The worst case for the slit is when all the power is absorbed in one pert of the slit system, which he slits must survive. The paper presents the results from parameter optimization in the worst case. The goal of the optimization is to minimize the maximum temperature of the slits. The geometrical parameters are the cooling hole size, its location from the surface, and the distance between holes. the worst case is found by moving the x-ray beam to all the possible locations. The maximum temperature of an optimized slit that has a two degree angle with the beam is about 192 degrees C. The corresponding thermal stress in the slit is very low. The analysis assumptions, modeling, results, discussion, and conclusion will be given in the paper.

A finite element analysis method (FEA) was used to predict the performance of a silicon monochromator for a high- energy-resolution scattering beamline at sector 3 of the Advanced Photon Source. The monochromator is internally cooled through 17 rectangular channels with liquid gallium and is designed to operate at photon energies near 14 keV, under beam from a 2.7 cm period undulator. The atomic planes of the monochromator have a orientation with an asymmetric cut angle of 4.5 degrees. The displacement profile calculated from the structural FEA was used to compute the double-crystal rocking curves tat 14.41 keV. Both the simulations and the experiment show that this monochromator will operate at about 40 mA with rocking-curve broadening of only about 0.5 arcsec. This corresponds to a surface heat flux of 1.2 W.mm² and a total absorbed power of about 86 watts. The monochromator was used for the commissioning of the beamline and to perform the first series of experiments up to 100 mA. In this paper, we give the results of the FEA calculations and diffraction simulations and compare these to the experimental data.

Third-generation synchrotron radiation sources are currently becoming operational. These powerful x-ray radiation sources will be critical in advancing research in key areas of science, engineering, and medicine. Efficient utilization of these sources requires the development of critical beamline optical components which can withstand their very intense beams without significant distortion. In this paper we will discuss the applications of an innovative, low-cost, castable form of SiC as a monolithic cooled mirror substrate for use on high energy synchrotron beamlines. The superior bulk material properties of SiC--excellent thermal conductivity, a very low coefficient of thermal expansion, excellent specific stiffness and non-reactive with typical coolants--are well known. In addition to the superior bulk material properties, this high purity form of SiC has a number of other desirable characteristics which make it particularly well suited for this application: 1) it can be fabricated with complex, internal cooling channels in a monolithic fashion; 2) it has been demonstrated to provide the excellent surface figures and surface finishes required for x-ray optics applications; and 3) the castable SiC can be manufactures in a very low cost manner, particularly in high volumes. Overall, the innovative SiC mirror substrate discussed promises to offer improved performance, significantly reduced cost, and reduced risk compared to present approaches.

This paper reports a thermo-mechanical study of a beamline filter for undulator/wiggler operations.It is deployed in conjunction with the current commissioning window assembly on the APS insertion device (ID) front ends. The beamline filter at the APS will eventually be used in windowless operations also. Hence survival and reasonable life expectancy of the filters under intense ID heat flux are crucial to the beamline operations. To accommodate various user requirements, the filter is configured to be a multi- choice type and 'smart' to a low only those filter combinations that will be safe to operate with a given ring current and beamline insertion device gap. However, this paper addresses only the thermo-mechanical analysis of individual filter integrity and safety in all combinations possible. The current filter design is configured to have four filter frames in a cascade with each frame holding five filters. This allows a potential 625 total filter combinations. Thermal analysis for all of these combinations becomes a mammoth task considering the desired choices for filter materials, filter thicknesses, undulator gaps, and the beam currents. The paper addresses how this difficult task has been reduced to a reasonable effort and computational level. Results from thermo-mechanical analyses of the filter combinations are presented both in tabular and graphical format.

White-beam slits are precision high-heat-load devices used on beamlines of the APS to trim and shape the incoming x- rays beam before the beam is transmitted to other optical components. At the APS, the insertion devices that generate the x-ray are very powerful. For example, the heat flux associated with an x-ray beam generated by undulator A will be on the order of 207 W/mm² at the L5-80 slit location at normal incidence. The total power is about 5.3 kW. The optical slits with micron-level precision are very challenging to design under such heat flux and total power considerations. A novel three-metal composite slit has been designed to meet the diverse thermal, structural, and precision requirements. A closed form solution, and a commercial code, ANSYS, have been used for the analysis of the optimized design for the slit set.

Helium cooling is an attractive alternative to water cooling for high heat flux components. Helium offers advantages from safety considerations, such as excellent radiation stability and chemical inertness. General Atomics (GA) has considerable expertise in use of helium cooling due to its high temperature gas cooled reactor experience. In order to prove the feasibility of helium cooling at high heat flux levels of above 5 MW/m², GA designed, fabricated, and tested a helium cooled module. The module was sized to have a heat flux surface of 25 mm wide and 80 mm long due to test setup limitations on maximum deposited power. WIth a smooth flow channel, a flow rate of 0.23 kg/s, and a pumping power of 2300 W was required to keep the copper module surface temperature below 500 degrees C at a heat flux level of 10 MW/m². Hence, different techniques were examined to enhance the heat transfer, which in turn reduced the flow and pumping power required. It was concluded that an extended surface was the most practical solution. An optimization study was performed to find the best parameters. The module with an optimized extended surface geometry was estimated to require a flow of about 0.032 kg/s and a pumping power of 50 W to remove 20 kW of power. This is more than an order of magnitude reduction in pumping power required compared to the smooth channel. The module was made from dispersion strengthened copper. The fabricated geometry was slightly different than the optimized design due to constraints of machining. The fabrication was done by electro discharge matching. The testing was carried out at the electron beam test facility of Sandia National Laboratory, Albuquerque. The specifications of the loop and the electron beam testing facility were: 4 MPa pressure, 32 g/s of helium flow, and 30 kW beam power. The testing was carried out during August 1993 and again in December 1994. The testing confirmed the design calculations.

High heat flux testing for the US fusion power program is the primary mission of the Plasma Materials Test Facility (PMTF) located at Sandia National Laboratory. This facility, an official Department of Energy User Facility, has been in operation for over 15 years and has provided much of the high heat flux data used in the design and evaluation of plasma facing components for many of the world's magnetic fusion tokamak experiments. In addition to domestic tokamaks such as Tokamak Fusion Test Reactor at Princeton, the DIII-D tokamak at General Atomics, and Alcator C-Mod at MIT, components for international experiments like TEXTOR, Tore- Supra, and Jet also have been tested at the PMTF. High heat flux testing spans a wide spectrum including thermal shock tests on passively cooled materials, thermal response and thermal fatigue tests on actively cooled components, critical heat flux burnout testes, braze reliability tests, and safety related tests. The program's main focus now is on testing of beryllium and tungsten armor tiles bonded to divertor, limiter, and first wall components for the International Thermonuclear Experimental Reactor (ITER). The ITER project is a collaboration among the US, EU, RF, and Japanese fusion programs. This article provides a brief overview of the high heat flux testing capabilities at the PMTF, and describes some recent test results.

Modifications made to the long trace profiler system at the Advanced Photon Source at Argonne National Laboratory have significantly improved the accuracy and repeatability of the instrument. THe use of a Dove prism in the reference beam path corrects for phasing problems between mechanical errors and thermally-induced system errors. A single reference correction now completely removes both error signals from the measured surface profile. The addition of a precision air conditioner keeps the temperature in the metrology enclosure constant to within +/- 0.1 degree C over a 24 hour period and has significantly improved the stability and repeatability of the system. We illustrate the performance improvements with several sets of measurements. The improved environmental control has reduced thermal drift error to about 0.75 microradian RMS over a 7.5 hour time period. Measurements made in the forward scan direction and the reverse scan direction differ by only about 0.5 microradian RMS over a 500mm trace length. We are now able to put 1- sigma error bar of 0.3 microradian on an average of 10 slope profile measurements over a 500mm long trace length, and we are now able to put a 0.2 microradian error bar on an average of 10 measurements over a 200mm trace length. The corresponding 1-sigma height error bar for this measurement is 1.1 nm.

At CHESS, 2500 W total are absorbed by the first crystal of the double bounce monochromators located on the A2 and F2 wiggler beamlines. In order to dissipate this absorbed power and deliver the highest x-ray flux to an end station, we have explored the technique of internally cooling the silicon first crystals with water channels. This technique brings with it the need for reliable mechanical joints between the silicon diffracting surface and a glass or silicon water manifold. The joint must have structural strength to resist the internal water pressure and the cyclic heat load, be vacuum leak tight for operation in UHV, and not act as a source of residual strain in the crystal lattice of the diffracting surface. We have explored four bonding techniques which have been tested for their suitability to monochromator fabrication: direct silicon to silicon bonding, anodic glass to silicon bonding, a variety of ceramic and die attach adhesives and metallic diffusion bonding/brazing. In this paper, we characterize each method with respect to the requirements of structural integrity, residual strain and vacuum compatibility.