Ellipsoidal Focusing Mirror Research Articles

Conceptual design and analysis of remote steering system for CFETR ECRH system

In order to optimize the operational safety and reliability of the upper launcher for the CFETR ECRH system, a design of the launcher based on the remote steering concept is currently being carried out for comparison with the front steering equivalent. This paper presents the remote steering system's conceptual design and simulation analysis. A Square Corrugated Waveguide (SCW) of 65 × 65 mm has been designed with an optimized length of 9.35 m. By changing the relative length of the waveguide, the transmission efficiency of the SCW is optimized within the range of steering angles ±12°. Different error factors are investigated in detail, and corresponding acceptable error ranges are provided. Considering these error factors and ignoring ohmic losses and thermal effects, the relative transmission efficiency of the SCW is estimated to be >98 % within the steering angle range. A matching steering unit for the SCW is designed, which consists of an ellipsoidal focusing mirror and a steerable flat mirror. The detailed design of the steerable mirror motion trajectory is presented. Also, the influence of the possible beam incident errors caused by the steering unit on the transmission efficiency is analyzed in detail.

Double-focusing geometry for phase correction in neutron resonance spin-echo spectroscopy

Neutron spin phase correction is an essential technique for achieving a high energy resolution in neutron spin-echo experiments. We propose a double-focusing geometry in which two identical ellipsoidal mirrors are arranged in series. This arrangement enables us to correct the path length differences for large divergent beams using a complete ellipsoidal focusing mirror. In this study, we evaluated the effectiveness of this geometry both analytically and numerically. A Fourier time of 1 μs is achievable using this geometry.

Surface processing of PMMA and metal nano-particle resist by sub-micrometer focusing of coherent extreme ultraviolet high-order harmonics pulses.

We demonstrate sub-micrometer processing of two kinds of thin films, polymethyl methacrylate (PMMA) and metal nano-particle resist, by focusing high-order harmonics of near-IR femtosecond laser pulses in the extreme ultraviolet (XUV) wavelength region (27.2-34.3 nm) on the thin film samples using an ellipsoidal focusing mirror. The ablation threshold fluences for the PMMA sample and the metal nano-particle resist per XUV pulse obtained by the accumulation of 200 XUV pulses were determined to be 0.42mJ/cm2 and 0.17mJ/cm2, respectively. The diameters (FWHM) of a hole created by the ablation on the PMMA film at the focus were 0.67 µm and 0.44 µm along the horizontal direction and the vertical direction, respectively. The fluence dependence of the Raman microscope spectra of the processed holes on the PMMA sample showed that the chemical modification, in which C=C double bonds are formed associated with the scission of the PMMA polymer chains, is achieved by the irradiation of the XUV pulses.

New receiving line for the remote-steering antenna of the 140 GHz CTS diagnostics in the FTU Tokamak

A new receiving antenna for collecting signals of the Collective Thomson Scattering (CTS) diagnostics in FTU Tokamak has been recently installed. The squared corrugated section and the precisely defined length make it possible to receive from different directions by remotely steering the receiving mirrors. This type of Remote-Steering (RS) antennas, being studied on FTU for the DEMO Electron Cyclotron Heating (ECH) system launch, is already installed on the W7- X stellarator and will be tested in the next campaign. The transmission of the signal from the antenna in the tokamak hall to the CTS diagnostics hall will be mainly realized by means of oversized circular corrugated waveguides carrying the hybrid HE11 (quasi-gaussian) waveguide mode, with inclusion of a special smooth-waveguide section and a short run of reduced-size square-corrugated waveguide through the tokamak bio-shield. The coupling between different waveguide types is made with ellipsoidal focusing mirrors, using quasi-optical matching formulas between the gaussian-shaped beams in input and output to the waveguides. In this work, after a complete study of feasibility of the overall line, a design for the receiving line will be proposed, in order to realize an executive layout to be used as a guideline for the commissioning phase.

Design of a steerable launcher for the ECH system on KSTAR

105/140Ghz dual frequency gyrotron is used in KSTAR tokamak for an electron cyclotron resonance heating (ECRH). The ECH launcher consists of a fixed mirror, a steering mirror, cooling systems and some mechanical component for a steering mirror. We have designed the fixed ellipsoidal focusing mirror for an efficient heating and localized control. The beam radius using the existing ECH launcher system is about 45 mm at the resonance layer. On the other hand, the modified launcher mirror reduces the beam size at the resonance layer for incident RF beam to 38 mm. The design results showed good agreement compared with the computation and simulation results. Since the distance between the corrugated waveguide and the fixed focusing mirror is fixed, it is difficult to more reduce the beam size. However, reduced beam size is small enough to localize MHD control and heating.

Preliminary Investigation on Design and Fabrication of a Metallic-Ellipsoidal Neutron Focusing Mirror

Neutron beam is a very useful probe for material characterization and non-destructive testing. There are a number of plans to construct neutron instrumens using focusing mirror to improve beam quality with higher intensity and smaller spot size. In this paper, an ellipsoidal mirror made by a metal substrate is proposed. As the metal substrate, electroless nickel is adopted because of its amorphous structure, machinability and relatively large critical angle of neutron reflection. The design of ellipsoidal neutron focusing mirror is made by considering the neutron reflectivity. A mirror is fabricated by ultrahigh precision cutting and 1st polishing process, and the form accuracy of 5 μm P-V with surface roughness of 0.7 nm Ra is obtained. Through this experimental fabrication, the feasibility of the proposed method is verified.

Development of highly-mechanically polished metal-substrate for neutron supermirrors

A small-angle neutron scattering instrument using an ellipsoidal focusing mirror has been developed at Hokkaido University and a prototype machine (mfSANS) has been installed at the JRR-3 research reactor at Japan Atomic Energy Agency (JAEA). They are based on an ellipsoidal focusing mirror on a borosilicate glass substrate. It turned out that borosilicate glass was very brittle and difficult to machine or polish it to the required surface-finishing process. In order to improve this situation, we decided to develop a method to create a metal substrate based ellipsoidal focusing mirror. As the first step, test pieces of flat and ellipsoidal surface neutron supermirrors using metal substrates were fabricated. They were first roughly shaped by a conventional numerically controlled (NC) cutting machine and amorphous NiP was plated. They were then machined using an ultrahigh precision cutting (UPC) method and finished by NC polishing techniques. Surface roughness of Ra ≈ 0.78 nm and surface figure error of submicrometer were realized so far.

EUV Hartmann sensor for wavefront measurements at the Free-electron LASer in Hamburg

A compact, self-supporting Hartmann wavefront sensor was developed for the extreme ultraviolet (EUV) and soft x-ray range. The device is adapted to the characteristics of the Free-electron LASer in Hamburg (FLASH). It operates in a wavelength range from 6 to 30 nm with the capability to measure the wavefront quality of individual free-electron laser (FEL) pulses for beam characterization as well as for beamline alignment and monitoring behind user experiments. We report on online-Hartmann wavefront measurements at beamline BL2 with λ13.5 nm/90 accuracy for wavefront rms (wrms). The results were used to align the ellipsoidal focusing mirror at the beamline, decreasing the residual root mean square (rms) wavefront aberrations by more than a factor of 3 to 2.6 nm. The spot size of 31 μm (x) and 27 μm (y) full-width at half-maximum (FWHM) as well as other beam parameters evaluated from wavefront and intensity data are consistent with independent profile measurements in the focal region, employing both a high-resolution EUV camera and poly(methyl metacrylate) (PMMA) imprints.

Design of a compact varied-line space grating monochromator for enhanced flux at MAXLAB

For soft x-ray fluorescence spectroscopy with selective energy excitation, it is desirable to have maximum flux at moderate resolution. A plane grating monochromator with varied line spacing can be used in the convergent beam of an ellipsoidal focusing mirror to provide moderate resolution with a large collection angle and minimum number of reflecting surfaces. We determine the design parameters for a varied-line-space grating monochromator to provide light in the 200–1000 eV range. The results of modeling are discussed with respect to the optimal choices of monochromator for our experimental requirements. A novel mechanical design is proposed for constructing the monochromator in a compact form with the minimum number of moving parts and alignments.

The vacuum ultraviolet scanning photoelectron microscope at MAX-LAB

The performance of a scanning photoelectron microscope at the MAX I storage ring in Lund is presented. The microscope utilizes undulator radiation in the energy range 15–150 eV and is comprised of a plane-grating monochromator with a Kirkpatrick–Baez objective and a gracing incidence ellipsoidal focusing mirror. The instrument with its high photon flux, 109–1010 photons/s, and narrow bandwidth, better than 0.2 eV, is excellently suited for high-resolution core-level spectroscopy and imaging of samples with lateral inhomogeneties in the micrometer range.

ＳＲ転写用ビームラインシステム

A high power X-ray delivery system consisting of a superconducting compact storage ring and a novel beamline is now in use for SR (synchrotron radiation) lithography research at Mitsubishi Electric. The double ellipsoidal focusing mirror optics of the beamline collects and condenses the horizontally diverging SR beam and transports it to the exposure station, a Karl Suss X-ray stepper. The beamline is kept at an ultrahigh vaccum level by the vacuum control system. Furthermore, the vacuum protection of the beamline ensures that a storage ring vacuum of at least 1.33×10-6 Pa is maintained, even when the beamline vacuum is broken down. We have also investigated the effects of the electron beam orbit change on the vacuum performance of the beamline.

Design Optimization of Synchrotron Radiation Lithography Beamline for a Compact Storage Ring

We have developed a novel beamline for SR (synchrotron radiation) lithography using a compact storage ring. The beamline consists of two ellipsoidal focusing mirrors, collecting 34.9 mrad of the horizontal angle of the fan-shaped SR, which delivers X-rays of high intensity onto the wafer. Moreover, an X-ray stepper of Karl Süss, XRS-200, will be attached to the end of the beamline; it offers the exposure field of 25×25 mm2 in the atmospheric environment. An optical design was realized using a sophisticated method which combines a ray-tracing method with a nonlinear optimization method, the Davidon-Fletcher-Powel (DFP) method. This optimized optical design yielded excellent transmission of photon flux throughout the beamline. We will also discuss the spectral and the spatial uniformity of the illumination, and the quality of the printed image.

A scanning soft x-ray microscope with an ellipsoidal focusing mirror

We have developed and brought into operation a new type of scanning soft x-ray microscope which can operate at any photon energy from 20 to 1300 eV. This microscope demagnifies a diaphragm by means of an annular section of an ellipsoidal mirror to a smallest spot size of, at present, about 0.4 μm (FWHM), certainly containing only a small fraction of the total intensity. The sample is scanned across this spot. Between mirror and focus a free space of 30 mm is available for detectors, and particles emitted from a surface at more than 30 ° to the normal can be extracted into a mass or energy analyzer. Transmission, photoemission, luminescence, photostimulated desorption, reflectivity, and other signals may serve for imaging. In addition, a static analysis of very small samples or spots on a sample will become feasible.

Study of different SX-700 monochromator designs for the undulator beamline (BL51) at MAX-lab

Different designs of the SX-700 plane grating monochromator have been investigated for the undulator beamline (51) by using analytical considerations and carrying out ray tracing calculations. The most important modifications of the original design are those where the ellipsoidal focusing mirror has been replaced by a plane elliptical or by a spherical mirror. A significant advantage of the spherical mirror is essentially better figure accuracies (±0.2 arcsec). This is partly compensated by the introduced coma aberration which, however, can be made small with rather long exit arm lengths (5–6 m). If the slope errors of the plane elliptical mirror can be made as small as 0.5 arcsec, the differences in the ultimate resolution are small between the plane elliptical and spherical designs and then the source size is the main factor.

Performance of the high-resolution SX700/II monochromator

This article reports on the high-resolution performance of the grazing-incidence plane grating monochromator SX700/II, installed at BESSY by the Freie Universität Berlin, in the photon energy range from about 40 to 900 eV. The high resolving power up to 10 000 achieved with this monochromator is based on improving the figure error of the ellipsoidal focusing mirror, on reducing the vertical dimension of the beam source, and on employing a 5-μm exit slit. We report on high-resolution gas-phase studies in the double-excitation region of He, as well as at core-excitation thresholds of Ne, Ar, Kr, and Xe in the photon-energy range from ≂45 eV to ≂900 eV. In addition, high-resolution core-excitation spectra at the K thresholds of C, N, and O are presented for gas-phase CO, N2, and O2. In all cases, high-n Rydberg states and/or vibrational sidebands of the electronic excitations were resolved. The various contributions to the present instrumental linewidths are discussed as well as the prospects for further improvements in resolution with this monochromator.

The undulator beamline at the SRS Daresbury

The design and performance of the undulator beamline 5U.1 at the SRS used for soft x-ray spectroscopy is reported and compared with the theoretical expectation of the intensity, resolution, and polarization. The beamline consists of a ten-period permanent magnet variable gap undulator followed by an entrance slitless plane grating monochromator. The energy region covered is from 0.1 to 1 keV. The design is similar to the SX700 but uses a spherical instead of an ellipsoidal focusing mirror. To eliminate the large horizontal beam width at the exit slit the beamline has been modified to include a post-focusing mirror. The spherical focusing mirror has been changed to one with a larger radius resulting in a decreased demagnification, thereby essentially eliminating primary coma. The monochromator contains an ion-etched and lamellar profile 1200-lines/mm plane grating of Pt-coated CVD SiC on a graphite substrate. The high flux of the undulator makes the beam line suitable for SEXAFS studies and for work involving soft x-ray fluorescence detection. The combination of high flux and high resolution is especially advantageous for atomic and molecular spectroscopy and to resolve the quasiatomic structures which are observed in localized 3d transition metal compounds.

Submicrometer-resolution photoelectron-spectroscopy at MAX Lab

The design of a photoemission microprobe beamline at the MAX laboratory is presented. The beamline will utilize the radiation from a 26 period undulator on the 550-MeV MAX storage ring. The beamline will be capable of providing about 1010 photons/s of monochromatized radiation (bandwidth better than 0.25 eV) in the energy range of 20 to 150 eV focused into a submicrometer focal spot. It will be used for scanning photoemission experiments with a lateral resolution better than 1 μm. The optical system is comprised of a plane-grating monochromator with a Kirkpatrick–Baez objective and a specially designed ellipsoidal focusing mirror.

Vertical-viewing electron cyclotron emission diagnostic for the DIII-D tokamak

The vertical-viewing electron cyclotron emission diagnostic on DIII-D will be used to assess the nonthermal electron distributions resulting from electron cyclotron heating and electron cyclotron current drive experiments. Electron cyclotron emission along a vertical chord is collected using an ellipsoidal focusing mirror and retroreflector (the latter to minimize wall reflections). The emission is then transported ∼20 m using a quasioptical transport system composed of eight lenses and three mirrors, and detected between the 2nd and the 10th harmonics by a fast-scanning (40-Hz) Michelson interferometer. The entire system has been aligned using a Gaussian beam simulator and absolutely calibrated in situ using a cold liquid-nitrogen bath. Details of the design, installation, and calibration will be discussed.