Window Assembly Research Articles

High power 170 GHz gyrotron with synthetic diamond window

A large sized synthetic diamond window assembly was installed on a 170 GHz gyrotron. An aperture and a thickness of the window are 83 and 2.23 mm, respectively, whose edge was directly cooled by water. Gyrotron performances of 520 kW at 6.2 s and 450 kW at 8 s were attained. A temperature increase of the window stabilized after ∼5 s, whereas the power had been limited to below 170 kW with conventional windows. This drastic improvement of a deliverable power was obtained from the outstanding properties of the diamond, that is, an extremely high thermal conductivity (∼1800 W/mK) and a low value of loss tangent (tan δ<1.3×10−4). The gyrotron was inspected after the ∼1300 times operation at 520 kW (>1 s), but no damage nor trouble was found both on the gyrotron and the diamond window. These results give a prospect for a multimegawatt power output from the gyrotron, i.e., the diamond window gives a solution for the window problem which has been regarded as the most serious issue on the development of high power long pulse gyrotron.

Heat Transfer Analysis and Modeling of a Cryogenic Laser Radiometer

This study investigates the laser optimized cryogenic radiometer (LOCR) recently acquired by the National Institute of Standards and Technology in Boulder, Colorado, to calibrate laser power meters and detectors. The objectives are to evaluate potentially significant sources of uncertainty in the radiometric measurements and to develop transient models that efficiently and accurately predict the behavior of this radiometer. The analysis suggests that radiation from the Brewster window assembly may cause the total power entering the radiometer to drift more than 130 nW for a room temperature variation of 0.2 K. Steady-state modeling of the LOCR with finite element analysis software indicates a relative inequivalence between optical and electrical heating of 4 × 10 -6 at the 1-mW power level. A new tbermal model has been developed to simplify transient predictions by combining lumped parameter and one-dimensional elements. This model outperforms single-time-constant exponential models and can be expanded to simulate the complete radiometer system.

Chemical vapor deposition diamond window for high-power and long pulse millimeter wave transmission

To satisfy the electrical and thermomechanical requirements for a continuous wave millimeter wave beam transmission, a window assembly using a large size synthesized diamond disk has been developed. Such window systems are needed as a vacuum barrier and tritium shielding in future electron cyclotron heating systems for fusion plasma heating and noninductive electron cyclotron current drive. The diamond used in this study was manufactured by chemical vapor deposition (CVD) and consists of a polycrystalline diamond disk 96 mm in diameter and 2.23 mm thick. The disk was built into an assembly in which two Inconel tubes were bonded on both sides of the plate to provide vacuum shielding and water cooling to the edge of the disk, leaving an effective window aperture of 83 mm. It will be shown that, as a result of the high thermal conductivity and low dielectric loss exhibited by this grade of CVD diamond, the temperature increase of the window due to the absorption of high-power millimeter wave radiation could be minimized by simple water edge cooling at room temperature. During transmission of a focused Gaussian beam of 170 GHz, 110 kW, 10 s, the temperature increase at the center of the window reached a steady state condition at a value of approximately 40 K, in good agreement with calculated values. Water-edge-cooled CVD diamond windows promise to provide a practical technical solution for the transmission of continuous millimeter wave transmission in excess of 1 MW.

Glazing edge-seal using foamglass as spacer and frameless window design

This article presents a new design for the edge-seal of multiple-glazings with spacers made of foamglass and a new concept for frameless windows to reduce the heat loss through windows significantly. Thus the energy demand for heating is reduced or covered by solar energy gains through the window to a higher extent. The thermal performance of window assemblies with foamglass spacers and with and without frames is compared with that of the common window design. For the calculations of the heat flux a finite element analysis computer program has been used to account for the 2D-effects in the glazing, edge-seal and frame heat transfer patterns. The total heat transfer through an example window with a glazing 1 m×1 m is reduced by 45% using the window design presented. The objective of this article is not only to quantify the heat fluxes for different combinations of glazing, edge-seal and frame. The major part of the article focuses on practical aspects that are important for the durability of edge-seals, such as mechanical stress within the materials, water vapour and gas tightness, as well as on new design concepts of window–wall joints. A frameless window construction is an important aspect to enhance the thermal performance of windows. The costs for this kind of frameless windows are estimated to be less than or equal to windows commonly used now.

High power 170 GHz test of CVD diamond for ECH window

In order to check the usability of large-size CVD (Chemical Vapor Deposition) diamond disks for high power millimeter wave vacuum barrier windows at room temperature (T = 293 K) a first series of experiments, using a 170 GHz, 0.4 MW, 0.2 s JAERI/Toshiba gyrotron1), have been performed. The dielectric loss tangent at a frequency of 170 GHz has been determined to be tan δ = 1.3·10−4. By comparing the experimental results to numerical simulations the thermal conductivity was estimated to be about k ≈ 1800 W/mK. This preliminary results indicate that a single-disk CVD diamond window assembly using a water-edge cooling could fulfill the requirements for a continuous wave (CW) transmission of millimeter wave power in the megawatt range. This is needed for the Electron Cyclotron Heating (ECH) on the International Thermonuclear Experimental Reactor (ITER).

Performance analysis of the commissioning filter and window assembly for insertion device beamlines at the Advanced Photon Source

Although the Advanced Photon Source (APS) undulator beamlines are designed for windowless operation, a special window assembly will be used during the commissioning phase of the beamlines until sufficient operational experience is gained with the powerful undulator A photon beam. This assembly is called a ‘‘commissioning window.’’ The commissioning window assembly as designed consists of a 300-μm-thick filter (made of graphite), a fixed mask (made of Glidcop), a multipurpose transmitting filter/BPM disk (made of 127-μm-thick CVD diamond), and set of a double windows (made of 250-μm-thick beryllium). Due to the high total power and power density, the filter/window assembly must be carefully designed to guarantee longevity and satisfactory performance throughout its service. Hence extensive analytical work has been conducted on various thermal and structural aspects of the commissioning window assembly. This paper summarizes the analytical results and presents the expected performance characteristics of the as-designed commissioning window.

Thermal buckling parametric analysis for a diamond disk for a x-ray beamline at the Advanced Photon Source

A thermal buckling analysis for a diamond disk in the commissioning window assembly designed for x-ray beamlines at the Advanced Photon Source is presented. The analytical solution together with associated numerical analysis help to predict the critical temperature of the diamond disk before a thermal buckle occurs.

Hyperthermia induces ultrastructural changes in mouse pial microvessels.

Pial microvessels' responses to local hyperthermia revealed the development of in vivo spontaneous thrombosis. The cellular and subcellular changes which contribute to such events remained unexplored. Therefore, the effect of regional hyperthermia (43 degrees C) on mouse pial microvessels was studied at the ultrastructural level. A simple cranial window assembly, including an artificial cerebrospinal fluid delivery and heating system to ensure a precise brain regional temperature, was used. The animal core body temperature was maintained at 37 degrees C. Topical and transvessel bimodal fixation of microvessels was done with a phosphate buffered mixture of glutaraldehyde and paraformaldehyde, followed by a standard electron microscopy procedure. When the pial microvessels of control (37 degrees C) animals were examined, no evidence of cellular damage was discerned. Endothelial cells including luminal membrane were unchanged. Degranulated platelets or platelet aggregates were not seen. However, numerous platelets in association with scattered red blood cells and occasional white blood cells could be observed in a close proximity, but not adhered, to the endothelial wall of hyperthermic (43 degrees C) brains. Platelets displayed a variety of forms consistent with the onset of platelet activation. Discoid platelets containing granules and spheroid degranulated platelets and those with large pseudopodia were recognized. The venular endothelial surface revealed conspicuous endothelial change, with the presence of endothelial denudation. The site of platelet aggregation in both venules and arterioles was accompanied by focal endothelial lucency and denudation vacuole formation, luminal membrane rupture, and swelling of the nuclear envelope. These findings demonstrate the extent of damage to the pial microvasculature in response to a local hyperthermic exposure. The results emphasize that changes in the endothelium may represent the earliest signs of oncoming vascular pathology.

A radiation accident at an industrial accelerator facility.

On 11 December 1991, a radiation overexposure occurred at an industrial radiation facility in Maryland. The radiation source was a 3-MV potential drop accelerator designed to produce high electron beam currents for materials-processing applications. This accelerator is capable of producing a 25 milliampere swept electron beam that is scanned over a width of 112.5 cm and which emerges from the accelerator vacuum system through a titanium double window assembly. During maintenance on the lower window pressure plate, an operator placed his hands, head, and feet in the beam. This was done with the filament voltage of the electron source turned "off," but with the full accelerating potential on the high voltage terminal. The operator's body, especially his extremities and head, were exposed to electron dark current. In an attempt to reconstruct the accident, radiochromic film and alanine measurements were made with the accelerator operated at two beam currents. Measured dose rates ranged from approximately 40 cGy s-1 inside the victim's shoe to 1,300 cGy s-1 at the hand position. Approximately 3 mo after the accident, it was necessary to amputate the four digits of the victim's right hand and most of the four digits of his left hand. Electron paramagnetic resonance spectrometry, which measures the concentration of radiation-induced paramagnetic centers in calcified tissues, was used to estimate the dose to the victim's extremities. A mean dose estimate of 55.0 +/- 3.5 Gy (95% confidence level) averaged over the mass of the bone was obtained for the victim's left middle finger (middle phalanx).

Beryllium window and acoustic delay line design for x-ray lithography beam lines at the University of Wisconsin Center for X-ray Lithography

X-ray lithography systems require sample chambers that can perform exposures in helium gas at atmospheric pressure. The interface between the experimental chamber and the beamline is critical for x-ray lithography and the storage ring. It must allow a high x-ray flux throughput while providing a vacuum barrier so that helium gas does not leak into the beam line and the storage ring. The beam line must also be designed to have protection in the case that a window does fail in order to minimize adverse effects to the ring and other systems. The details of the design for the vacuum system used on beam lines for the Center for X-ray Lithography at the University of Wisconsin Synchrotron Radiation Center 1-GeV electron storage ring are reported. Curved beryllium windows with a 1×5-cm2 aperture and 13 μm thick that have a leak rate less than 10−10 Torr ℓ/s have been successfully used at the experimental chamber beam-line interface. This thin flat beryllium foil is mounted in a curved housing with a wire seal to minimize helium leakage. The window assembly is designed and has been tested to withstand substantial overpressure before failure. If the beryllium window does fail, the beamline has an acoustic delay line that is designed to delay the incoming shock wave of helium gas so that a fast valve at the end of the beam line will close and minimize leakage of helium into the storage ring. The acoustic delay line is designed with baffles to slow the shock front and a secondary thin window to protect against molecular diffusion into the storage ring. The acoustic delay line has been tested to determine the effect of baffle design on delay of the shock wave. A theoretical model that provides a good description of the acoustic delay has also been developed.

The performance of aluminium building products in bushfires

AbstractA study of the behaviour of aluminium building products in bushfires was carried out to test the validity of assertions that they perform poorly under bushfire conditions. The work was conducted in two parts: an examination of data from bushfire damage surveys and laboratory experiments in which window assemblies were exposed to radiant heat from a furnace. Data from surveys conducted after major bushfires were augmented with information from a questionnaire related specifically to this work. Analysis of these data did not provide any support for the belief that houses incorporating aluminium building products are at greater risk of being destroyed. The laboratory experiments on both timber‐ and aluminium‐framed windows showed their performance under simulated bushfire conditions to be similar. It was found that bending of glass through distortion of the frames was not a factor in crack initiation.

4973511 Composite solar/safety film and laminated window assembly made therefrom: Peter Farmer, Stanley S Ho, Raymond Riek, Floyd E Woodard assigned to Monsanto Company

4973511 Composite solar/safety film and laminated window assembly made therefrom: Peter Farmer, Stanley S Ho, Raymond Riek, Floyd E Woodard assigned to Monsanto Company

Neutral beam emission spectroscopy diagnostic for measurement of density fluctuations on the TFTR tokamak

A multichannel diagnostic for measuring low amplitude, long wavelength (k⊥ρi<0.5) density fluctuations along the outer half of the plasma has been installed on TFTR. It is based on observing fluctuations in the Hα fluorescence of a neutral heating beam due to collisional excitation from the plasma and impurity ions. Both radial and poloidal correlation lengths as short as 2–3 cm can be determined, with the spatial resolution limited primarily by the width and geometry of the three neutral beam sources. Optical fibers transmit the light from a 20-cm-diam vacuum window, reentrant mirror, and lens assembly to 16 interference filter/photomultiplier combinations located outside the radiation area. Initially, the fibers comprise a fixed 55-channel radial array and readily movable 10-channel vertical arrays which can be positioned at 27 radial locations. The filters are designed to accept the Doppler-shifted Hα emission from primary energy component of the neutral beam, and reject background lines and unshifted edge Hα. The measurable fluctuation amplitude (@ S/N=1) is limited to 0.5% over a 100 kHz bandwidth by the photon noise associated with the dc level of the beam emission. The contribution of impurity collisions to the total beam fluorescence will be determined directly by measuring impurity density fluctuations using charge-exchange recombination emission from the n=8–7 CVI line at 5292 Å.

Neutral beam emission spectroscopy diagnostic for measurement of density fluctuations on the TFTR tokamak (abstract)

A multichannel diagnostic for measuring low amplitude, long wavelength (k⊥ρi<0.5) density fluctuations along the outer half of the plasma has been installed on TFTR. It is based on observing fluctuations in the Hα fluorescence of a neutral heating beam due to collisional excitation from the plasma and impurity ions. Both radial and poloidal correlation lengths as short as 2–3 cm can be determined, with the spatial resolution limited primarily by the width and geometry of the three neutral beam sources. Optical fibers transmit the light from a 20-cm-diam vacuum window, reentrant mirror, and lens assembly to 16 interference filter/photomultiplier combinations located outside the radiation area. Initially, the fibers comprise a fixed 55-channel radial array and readily movable 10-channel vertical arrays which can be positioned at 27 radial locations. The filters are designed to accept the Doppler-shifted Hα emission from primary energy component of the neutral beam, and reject background lines and unshifted edge Hα. The measurable fluctuation amplitude (@ S/N=1) is limited to 0.5% over a 100 kHz bandwidth by the photon noise associated with the dc level of the beam emission. The contribution of impurities to the total beam fluorescence will be determined directly by measuring impurity density fluctuations using charge-exchange recombination emission from the n=8−7 C vi line at 5292 Å.

The Protection of Glazing Systems With Dedicated Sprinklers

Water spray is one method of protecting glazing exposed to fire. Research conducted at the National Research Council's National Fire Laboratory indicates that, under ideal con ditions, a window assembly, when protected by special sprinklers, will stay intact, and can obtain a fire resistance rating of 2 hours or longer. Experiments showed that there are several parameters related to sprinkler operation which affect the performance of the glazing assembly under fire exposure. This paper describes the test facility and discuss es the results of investigations conducted to determine the effect of the sprinkler activa tion time and sprinkler water flow rate on the effectiveness of dedicated sprinkler sys tems for protecting large glazing assemblies. The effect of the sprinklers on the average temperature and temperature gradient in the test room is also discussed.

Low-retardance fused-quartz window for real-time optical applications in ultrahigh vacuum

We describe a low-strain, Suprasil quartz window assembly for ultrahigh vacuum applications that require high transmittance and/or low retardance over a wide spectral range. The assembly mounts on a 2 (3)/(4) in. Conflat flange. The window can be heated externally to 400 °C to remove typical molecular-beam-epitaxy growth deposits, thereby eliminating a major source of inaccuracy in optical pyrometry and allowing high-light fluences to be transmitted with minimal attenuation. Retardations at 459 nm (2.5 eV) of four unmounted Bellcore windows ranged from 0.05° to 0.3° while retardations of properly mounted windows were <0.5°. These retardations could be reduced an order of magnitude by applying small counterstresses, thereby allowing highly accurate real-time growth data to be obtained by polarization-sensitive optical techniques such as reflectance-difference spectroscopy or spectroellipsometry.

Beryllium window assembly for the 53-pole wiggler beamline at the Photon Factory

The performance of a beryllium window assembly which is exposed to large heat loads due to intense photon flux form a 53-pole multipole wiggler is described. Six graphite foils were designed to have a thickness of 0.14 mm each in order to reduce the thermal loads at two 0.2-mm-thick beryllium windows so that the beryllium windows could withstand the high thermal stress caused by a peak power density of 3.2 kW/mrad2 from the wiggler. The beryllium windows are located at the downstream side of the graphite foils and transmit x-ray components to an experimental station. The maximum temperature rise measured at the beryllium windows under a total synchrotron radiation power of 7.75 kW at 300 mA of stored beam current was 180 °C. No visual damage was observed.

A heated window assembly for a molecular-beam epitaxy system

First Page

Optical emission in magnetrons: Nonlinear aspects

Optical emission measurements have been made on the plasmas generated in conventional, planar magnetrons used for high-rate sputtering of metals. The measurements were made as a function of distance from the 20-cm-diam cathode for Al, Cu, and Ti cathodes in Ne, Ar, and Kr plasmas. The emission from the plasma was coupled through a movable collimator and window assembly to a monochromator and diode array detector. The emission intensity was strongly peaked near the sheath, a few millimeters from the cathode. The intensity of the emission of the neutral rare-gas atoms was approximately linear with discharge current at low discharge power, and proportional to the square root of current at high power. This is consistent with previously observed gas rarefaction effects caused by heating by the sputtered atoms. The emission intensity from the sputtered atoms depended on discharge current to approximately the second power at low discharge current, falling to the 1.4 power in some cases at high power levels. The emission intensity for the ionized, sputtered atoms was observed to depend on the discharge power to the 2.6–3.0 power. These latter observations are consistent with a simple model of excitation dependent on the species density and the electron density, coupled with predicted changes in the electron density and temperature as a function of increasing discharge power.

Ruggedized alpha radiation detector

An effort was made to develop an alpha-radiation scintillation detector with an entrance window more rugged than that of conventional types. A novel technique for micromachining thin silicon windows has been implemented. Optically clear epoxy is used to couple the scintillator material to a glass light pipe and to give support to thin portions of the silicon window. Tests indicate that overall efficiency is comparable to that obtained with conventional Mylar window detectors. Compared to conventional scintillation detectors, the more rugged alpha-radiation detector is better suited to harsh environments encountered in outdoor surveys, as the silicon window assembly is a solid construction highly resistant to scratches, punctures, water and thermal shock. >