An absorbing medium is prepared using nanosize carbon black (CB) blended with nanosize silicon carbide (SiC). The medium improves the wave absorption properties and the wave band of the single CB absorbent. The microstructure, conductivity, dielectric property, and microwave absorption of the material are studied by means of field emission scanning electron microscopy, trielectrode method, and vector network analyzer respectively. The results show that SiC can reduce the percolation threshold of CB/epoxide resin composite. Addition of certain mass of SiC can improve the microwave absorption of the composite. When 5 wt.% carbon black is blended with 50 wt.% SiC to fabricate a composite with a 2 mm thickness, the maximum reflection loss becomes −41 dB at 9 GHz, and the −10 dB bandwidth reaches 6 GHz. Thus, the prepared composite has the potential for use in electromagnetic absorption.

Absorption properties of carbon black/silicon carbide microwave absorbers

Basic principles of heterodyne techniques are introduced and the various components of a heterodyne system are summarized. Special applications in ECE, interferometry and reflectometry are discussed after introducing the diagnostic principles. Realized systems as described in the literature are briefly outlined. Ordering principles are radiometer types in the case of ECE, mixing scheme and generation and stabilization of local oscillator and intermediate frequency signals in the case of interferometry and reflectometry. Special techniques and their impact on the performance of the diagnostic instruments are discussed.

https://iopscience.iop.org/article/10.1088/0741-3335/39/11/001/pdf

Heterodyne methods in millimetre wave plasma diagnostics with applications to ECE, interferometry and reflectometry

The technological development in the field of high brightness linear accelerators and high energy/high quality lasers enables today designing high brilliance Compton-X and Gamma-photon beams suitable for a wide range of applications in the innovative field of nuclear photonics. The challenging requirements of this kind of source comprise: tunable energy (1–20 MeV), very narrow bandwidth (0.3%), and high spectral density (104 photons/s/eV). We present here a study focused on the design and the optimization of an electron Linac aimed to meet the source specifications of the European Extreme Light Infrastructure—Nuclear Physics project, currently funded and seeking for an innovative machine design in order to outperform state-of-the-art facilities. We show that the phase space density of the electron beam, at the collision point against the laser pulse, is the main quality factor characterizing the Linac.

/pdf/electron-linac-design-to-drive-bright-compton-back-3cf9v87ptw.pdf

Electron Linac design to drive bright Compton back-scattering gamma-ray sources

In the thermal barrier tandem mirror GAMMA 10, the scaling law governing the enhancement of the ion confining potential, c, resulting from thermal barrier formation, is obtained experimentally, and is consistently interpreted in terms of the weak and strong ECH theories set up by Cohen and co-workers The scaling law on the axial particle confinement time, τp||, related to this c formation, is also demonstrated in detail; it is in good agreement with the Pastukhov theory as modified by Cohen and co-workers This scaling is verified at any radial position in the core plasma region and at any time through the various stages of a discharge; this indicates a scaling with drastic improvement of τp||, due to the potential formation in the tandem mirror plasma

http://iopscience.iop.org/article/10.1088/0029-5515/28/12/008/pdf

Observation of scaling laws of ion confining potential versus thermal barrier depth and of axial particle confinement time in the tandem mirror GAMMA 10

We report on the small vertical emittance achieved at the 2.4 GeV Swiss Light Source (SLS). A method utilizing vertically polarized synchrotron radiation (SR), in the visible to ultra-violet (vis–UV) range, has been implemented to determine the vertical electron beam size. The paper describes in detail the beam size measurement method and discusses possible error contributions when deducing the corresponding emittance value. The smallest vertical rms beam size determined to date is σ ey =(6.4±0.5) μm. For a low emittance tuning, the vertical rms beam emittance at the monitor was determined to be e y =(3.2±0.7) pmrad over a period of several days in 400 mA multi-bunch (0.98 nC/bunch) user top-up operation mode. The corresponding emittance ratio was g =(0.05±0.02)%. The minimization of the vertical emittance was also demonstrated to be of a global nature.

Determination of a small vertical electron beam profile and emittance at the Swiss Light Source

Development of a SiC microwave absorber for a damped cavity is presented. The SiC studied has a resistivity of 101–102 Ω cm, which is the expected value to damp higher‐order modes (HOMs) in the cavity and also has high thermal conductivity. The absorber is attached to the cavity as a part of the beam duct. Since the SiC duct receives a large amount of energy from the electron (or positron) stored beam, it is very important to estimate the dissipation power in the SiC duct and to design a cooling mechanism. The heat load problem of the SiC duct is discussed and the results of high power testing of the SiC duct are presented. The damping mechanism for HOMs is based on the power dissipation due to the resistivity of SiC. The fine control of the resistivity of SiC in fabrication is very important. The preliminary results on this problem are also presented.

Characteristics of a sic microwave absorber for a damped cavity

We present a non-destructive and real-time beam profile monitor using Fresnel zone plates (FZPs) and the measurement of an electron-beam size with this monitor in the KEK–Accelerator Test Facility (ATF) damping ring. The monitor system has the structure of a long-distance X-ray microscope, where two FZPs constitute an X-ray imaging optics. The synchrotron radiation from the electron beam at the bending magnet is monochromatized by a crystal monochromator and the transverse electron beam image is twenty times magnified by the two FZPs and detected on an X-ray CCD camera. The expected spatial resolution for the selected photon energy of 3.235 keV is sufficiently high to measure the horizontal and vertical beam sizes of the ATF damping ring. With the beam profile monitor, we succeeded in obtaining a clear electron-beam image and measuring the extremely small beam size less than 10 μm. The measured magnification of the X-ray imaging optics in the monitor system was in good agreement with the design value.

Measurement of an electron-beam size with a beam profile monitor using Fresnel zone plates

Electron cyclotron emission (ECE) measurements on the tandem mirror GAMMA 10 are reported The fifth-harmonic ECE in the thermal barrier region was measured in order to obtain the temporal and spatial evolution of hot electrons produced by electron cyclotron resonance heating for the formation of a thermal barrier potential well The electron temperatures in the central and plug cells were determined using the second-harmonic ECE which was corrected for the hot-electron emission by considering a relativistic shift of resonance layers The results, thus obtained, show strong evidence for the existence of a thermal barrier

Measurement of Electron Cyclotron Emission from the Tandem Mirror GAMMA 10

New damped cavities have been installed in the Photon Factory (PF) storage ring and successfully operated in the last scheduled user run of 1996. The new damped cavity is a simple single-cell cavity with somewhat large beam-duct holes. The part of the beam duct that is attached to the cavity is made of SiC, which works as a microwave absorber and damps the higher-order modes excited in the cavity. Because of its simple structure, the operation of the cavity is very stable and also a high power input of more than 150 kW is possible. No coupled-bunch instabilities due to the new cavity were observed during operation.

Installation of new damped cavities at the Photon Factory storage ring

This paper describes a new 500 MHz cavity which has a simple damped structure for the 2.0 GeV high‐brilliant synchrotron radiation source. The damping of higher‐order modes (HOMs) is achieved by large hole beam ducts, a part of which is made of microwave absorber. We have adopted as the microwave absorber a sintered SiC named CERASIC‐B manufactured by Toshiba Ceramics Co. Ltd. The latest design of the cavity with CERASIC‐B beam ducts is presented in this paper. We have fabricated a prototype model of the cavity. The results of the low power measurement are also reported here. It was confirmed that by using the CERASIC‐B beam ducts the Q values of HOMs were strongly damped.

Tadashi Koseki

Papers

Characteristics of a sic microwave absorber for a damped cavity

Measurement of an electron-beam size with a beam profile monitor using Fresnel zone plates

Measurement of Electron Cyclotron Emission from the Tandem Mirror GAMMA 10

Installation of new damped cavities at the Photon Factory storage ring

Damped‐structure cavity for a high‐brilliant vacuum ultraviolet and soft x‐ray storage ring