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At least 271 records · Page 15

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DOE OSTI2026

Fokker-Planck simulations of fast ion ICRF and electron EC heating in a mirror plasma using CQL3D-m

The CQL3D-m continuum bounce-average Fokker-Planck code is adapted for magnetic mirror plasmas [1] and is now routinely used in no-free-parameter classical integrated modeling of mirror devices [2, 3]. In the present effort, we report on two RF methods of plasma heating in mirror machine. The fast ions (FI) are heated by Fast waves at 2nd-4th harmonic, where FIs originate from neutral beam injection at 45 degrees to the magnetic field. The scenario shows an efficient ion heating near the FI bouncing point. The electrons are heated by X-mode launched from the high magnetic field side towards the resonance. Different from the tokamak applications, CQL3D-m provides an evolving self-consistent ambipolar parallel electric field, which determines the shape of the loss cone and hence an accurate confinement time of both ions and electrons. Also, it includes a description of ion and electron sources and sinks (related to charge exchange and impact ionization) which are updated at every time step. CQL3D-m utilizes a fully nonlinear Coulomb collision operator that is important for the significantly non-Maxwellian ion distributions typically established in mirror plasmas.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2024

Final burst of the moving mirror is unrelated to the partner mode of analog Hawking radiation

Flying mirrors with appropriate trajectories have been recognized as an analog system that mimics black hole Hawking evaporation and have been widely investigated. It has recently been suggested that the partner mode of the analog Hawking radiation emitted from a moving mirror would manifest itself through a final burst when the mirror executes a sudden stop. Here, in this study, we argue the opposite via the partner formula for the moving mirror model. By expanding the theoretical foundation of the partner formula and augmenting it with numerical analysis, we demonstrate that the supposed final burst is induced by a shock that requires the input of external energy, whereas the Hawking radiation partner mode, which is associated with the zero-point vacuum fluctuations, is not responsible for the burst.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2026

Two-mirror resonator for next-generation Compton gamma-ray source

The next-generation Compton gamma-ray sources (CGSs) based on storage rings require a high-power, well-focused laser beam as a photon driver, which can be realized using a Fabry-Perot cavity (FPC). In this work, we reexamine the behavior and performance of a two-mirror, nearly concentric resonator by introducing a new figure of merit representing the cavity’s proximity to instability. This figure of merit is used to analyze various aspects of the cavity design, including misalignment, beam coupling limitations, and beam size scaling. We then examine several factors affecting the gamma-ray flux, such as the interaction area, crossing angle for collision, frequency matching between the electron and laser beams, and intrabeam scattering effects. Using an example CGS, we demonstrate how to make improved design choices for a two-mirror resonator to enhance the gamma-ray beam flux. This work shows that simple two-mirror Fabry-Perot cavities are well suited as the laser driver for the next-generation storage ring-based CGS, while offering superior advantages in gamma-ray beam polarization control compared to more complex four-mirror, nonplanar resonators.

Delooze, Will↗

NASA NTRS1966

Mount enables precision adjustment of optical-instrumentation mirror

Mirror mount assembly allows the plane of a mirror to be adjusted through small angles about two orthogonal axes. The assembly, which has a mirror mount with two independently adjustable flexure joints, allows independent precise adjustment of the mirror mount with respect to each axis.

Source record↗

NASA NTRS1973

Thermal correction of deformations in a telescope mirror

Orbiting astronomical observatories have the potential for making observations far superior to those from earth-based mirrors. In order for this performance to be realized, the contour of the primary mirror must be very accurately controlled. A preliminary investigation of the use of thermally induced elastic strains for correcting axisymmetric deformations in space telescope mirrors has been presented. The relation between axial deformation and thermal inputs was determined by a finite difference solution of the equations for thin elastic shells. The use of this technique was demonstrated analytically on a beryllium paraboloid. This mirror had 10 equally spaced thermal inputs and results are presented which show the nature of the temperature distribution required to correct deformations due to an acceleration-type loading.

Rhodes, M. D.↗

NASA NTRS1972

Research study to determine critical optical/mechanical properties of materials considered for selection as substrates for the primary mirror on a large telescope

An investigation was conducted to evaluate the stability of a specific low expansion glass-ceramic material relative to its use as a large, lightweight mirror substrate for diffraction-limited spaceborne optical applications. These evaluations were made on a segment (0.44 meter diameter by 0.31 meter thick) of a 2 to 3 meter diameter mirror blank. The dimensional stability of this mirror was measured interferometrically before and after lightweighting, as a function of rough machining, etching, thermal environment, and support configuration. A special computer analysis program was used to plot the coefficients corresponding to aberrations with sixfold symmetry (caused by the mirror's self-weight deflection on a three point support). The objective was to enhance the test sensitivity. Results indicate that any such effects due to self-weight deflection are of the order of 0.015 lambda rms. The rms and peak-to-peak figure changes associated with each processing operation are summarized.

Slomba, A. F.↗

NASA NTRS1973

Effects of surface polishing on the microstrain behavior of telescope mirror materials

Rough ground silicic mirror substrate materials were found in previous investigations to exhibit significant surface yield. This effect was removed by surface etching, a procedure not normally employed in the finishing of optical telescope mirrors. The effects of fine grinding and polishing techniques as well as graded etching are investigated. Torsional shear measurements of yield strain versus stress are made on four candidate mirror substrate materials: polycrystalline silicon, ULE silica 7971, CER-VIT 101, and fused silica 7940. Commonly employed fine grinding and polishing practices are shown to remove a major portion of the surface yield found in rough ground mirror substrate materials.

Eul, W. A.↗

NASA NTRS1972

Scanning mirror for infrared sensors

A high resolution, long life angle-encoded scanning mirror, built for application in an infrared attitude sensor, is described. The mirror uses a Moire' fringe type optical encoder and unique torsion bar suspension together with a magnetic drive to meet stringent operational and environmental requirements at a minimum weight and with minimum power consumption. Details of the specifications, design, and construction are presented with an analysis of the mirror suspension that allows accurate prediction of performance. The emphasis is on mechanical design considerations, and brief discussions are included on the encoder and magnetic drive to provide a complete view of the mirror system and its capabilities.

Anderson, R. H.↗

NASA NTRS1973

Evaluation of control laws and actuator locations for control systems applicable to deformable astronomical telescope mirrors

Some of the major difficulties associated with large orbiting astronomical telescopes are the cost of manufacturing the primary mirror to precise tolerances and the maintaining of diffraction-limited tolerances while in orbit. One successfully demonstrated approach for minimizing these problem areas is the technique of actively deforming the primary mirror by applying discrete forces to the rear of the mirror. A modal control technique, as applied to active optics, has previously been developed and analyzed. The modal control technique represents the plant to be controlled in terms of its eigenvalues and eigenfunctions which are estimated via numerical approximation techniques. The report includes an extension of previous work using the modal control technique and also describes an optimal feedback controller. The equations for both control laws are developed in state-space differential form and include such considerations as stability, controllability, and observability. These equations are general and allow the incorporation of various mode-analyzer designs; two design approaches are presented. The report also includes a technique for placing actuator and sensor locations at points on the mirror based upon the flexibility matrix of the uncontrolled or unobserved modes of the structure. The locations selected by this technique are used in the computer runs which are described. The results are based upon three different initial error distributions, two mode-analyzer designs, and both the modal and optimal control laws.

Ostroff, A. J.↗

NASA NTRS1974

Method and apparatus for optically monitoring the angular position of a rotating mirror

An optical system monitors the angular position of a rotating scanning mirror to indicate the effective start and end of each scan. At a certain angular position, a ray of energy transmitted to the mirror is reflected a plurality of times between the reflectors associated with the optical system and the line on the mirror parallel to the axis, and then to a detector to sense that angular position. A single optical system may be arranged to sense a plurality of different angular positions for each revolution of the mirror.

Lansing, J. C., Jr.↗

NASA NTRS1974

Solar simulator mirror refurbishment

Solar simulator mirrors were refurbished. Two different refurbishment methods were employed. In the first, the electroformed mirror replica was removed from the casting and replaced with a new mirror replica. In the second, only the aluminized surface, with its protective overcoat, was removed from the mirror and replaced after cleaning of the nickel surface.

Leverton, W. R.↗

NASA NTRS1974

Solar absorptance of second surface mirrors for high angles of incidence

Recent measurements have indicated an increase rather than a decrease in the solar absorptivity of second surface mirrors at angles of incidence greater than 80 deg. These observations stimulated an analytical effort which revealed that the increase does occur. Using electromagnetic wave theory, the solar absorptance equations for the mirror configurations commonly encountered in application are developed. An increase in mirror solar absorptance has also been deduced from the temperatures of a second surface mirrored radiator being monitored on the Nimbus E microwave spectrometer experiment. Test and calculated results substantiating the solar absorptance increase are presented.

Stultz, J. W.↗

NASA NTRS1975

Structural evaluation of candidate designs for the large space telescope primary mirror

Structural performance analyses were conducted on two candidate designs (Itek and Perkin-Elmer designs) for the large space telescope three-meter mirror. The mirror designs and the finite-element models used in the analyses evaluation are described. The results of the structural analyses for several different types of loading are presented in tabular and graphic forms. Several additional analyses are also reported: the evaluation of a mirror design concept proposed by the Boeing Co., a study of the global effects of local cell plate deflections, and an investigation of the fracture mechanics problems likely to occur with Cervit and ULE. Flexibility matrices were obtained for the Itek and Perkin-Elmer mirrors to be used in active figure control studies. Summary, conclusions, and recommendations are included.

Soosaar, K.↗

NASA NTRS1975

The 100 cm solar telescope primary mirror study

The manufacturing impact of primary mirror configuration on the performance of a 100 cm aperture solar telescope was studied. Three primary mirror configurations were considered: solid, standard lightweight, and mushroom. All of these are of low expansion material. Specifically, the study consisted of evaluating the mirrors with regard to: manufacturing metrology, manufacturing risk factors and ultimate quality assessment. As a result of this evaluation, a performance comparison of the configurations was made, and a recommendation of mirror configuration is the final output. These evaluations, comparisons and recommendations are discussed in detail. Other investigations were completed and are documented in the appendices.

Source record↗

NASA NTRS1977

Torque-while-turnaround scan mirror assembly

A scan mirror assembly which is part of a thematic mapper system is described with emphasis on mechanical aspects of the design. Features of the oscillating scan mirror mechanism include: a low level of structural vibration for the impact energies involved in mirror oscillation and return of energy lost during impact to the mirror by applying torque during the instant of impact.

Starkus, C. J.↗

NASA NTRS1978

Anastigmatic three-mirror telescope

A three-mirror telescope for extraterrestrial observations is described. An ellipsoidal primary mirror, a hyperbolic secondary mirror, and an ellipsoidal tertiary mirror, produce an image in a conveniently located finite plane for viewing.

Korsch, D. G.↗

NASA NTRS1980

Detecting surface faults on solar mirrors

Two quality control tests determine reflectivity and curvature faults of concave solar mirrors. Curvature defects in solar mirrors are easily revealed by photographing mirror surface. Calibrated aperture placed in front of camera lens admits rays reflecting only from acceptable areas of mirror, blocking out diverging rays reflected from defective areas. Defects can pinpoint problems that may exist in production. Same photograph can be obtained using calibrated disk instead of aperture, except that, this time, only defective areas would be exposed.

Argoud, M. J.↗

NASA NTRS1981

Low-cost concentrating mirrors

Parabolic concentrators used in solar-energy systems are constructed from many flat rectangular mirrors. Each mirror is elastically deformed in one dimension. Several such mirrors placed adjacent to each other along parabolic curve form inexpensive mirror suitable for solar application.

Carroll, T. R.↗