Спектральные и амплитудно-временные характеристики излучения Черенкова при возбуждении прозрачных материалов пучком электронов
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2021-01-01 |
| Journal | Оптика и спектроскопия |
| Authors | В. Ф. Тарасенко, Е. Х. Бакшт, М. В. Ерофеев, А. Г. Бураченко |
| Citations | 1 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This research focuses on characterizing Cherenkov Radiation (CR) and Impulse Cathodoluminescence (ICL) in transparent materials excited by pulsed electron beams (tens to hundreds of keV). The primary motivation is the development of robust detectors for Runaway Electrons (REs) in Tokamak fusion devices.
- Core Achievement: Successful registration and differentiation of CR from ICL in the UV/Visible spectrum (240-400 nm) using standard spectrometers and high-speed photodiodes.
- Optimal Materials: High-purity synthetic diamond (Type Ia, CVD) and quartz glass (KU-1) were identified as the most promising CR radiator materials due to their high UV transparency and high CR intensity relative to ICL.
- CR Characteristics: CR exhibits a near-inertialess response, with pulse durations matching the electron beam pulse (as short as ~100 ps), confirming its suitability for high-speed diagnostics.
- Energy Dependence: CR intensity increases significantly with electron energy and is concentrated in the short-wavelength (UV) region, consistent with theoretical predictions (dE/dλ ~ 1/λ3).
- Material Limitations: PMMA (Plexiglas) is challenging for CR detection due to a strong ICL background, low CR threshold (178 keV), and rapid degradation via electrical streamer discharges at high energy densities (> 0.01 J/cm2).
- ICL Dominance: For electron energies less than 200-300 keV, ICL generally dominates the total light output in most transparent materials, complicating CR-based measurements.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Electron Energy (Range) | 40 - 420 | keV | Pulsed Accelerators (GIN, SLEP, RADAN) |
| Pulse Duration (T0.5) | 0.1 - 12 | ns | Electron Beam Current |
| Beam Current Density (Max) | 230 | A/cm2 | SLEP-150M Accelerator |
| CR Threshold Energy (Diamond, n=2.42) | 50 | keV | Theoretical minimum for CR |
| CR Threshold Energy (Quartz, n=1.46) | 190 | keV | Theoretical minimum for CR |
| CR Threshold Energy (MgF2, n=1.38) | 230 | keV | Highest threshold tested |
| CR Spectral Range (Observed) | 240 - 400 | nm | UV/Visible region |
| Diamond Exciton Peak (C5) | 235 | nm | High-intensity ICL peak |
| Diamond Exciton Decay Time | ~80 | ns | Slow component of light emission |
| PMMA Breakdown Threshold | 0.01 | J/cm2 | Energy density leading to streamer discharge |
| Spectrometer Resolution | 3 - 9 | Angstrom | HR2000+ES, AvaSpec-3648 |
| Photodiode Rise Time | ~80 | ps | Photek PD025 (used for high-speed CR detection) |
Key Methodologies
Section titled “Key Methodologies”The study employed a combination of high-power pulsed electron accelerators and advanced optical diagnostics to characterize the light emission from various transparent materials.
- Pulsed Electron Beam Excitation: Sub-nanosecond (0.1 ns) and nanosecond (up to 12 ns) electron beams (40-420 keV) were generated using accelerators (GIN-500, SLEP-150M, RADAN-220). Beam parameters (energy spectrum, current density) were varied by adjusting the gas pressure and type in the diode.
- Sample Geometry Control: Samples (e.g., diamond, quartz glass, sapphire) were mounted in a vacuum or gas-filled diode and oriented perpendicular to the electron beam path. The angle (ψ) between the sample surface and the beam direction was varied (e.g., 45° to 70°) to optimize the extraction of the directional CR cone into the detector.
- Spectral Analysis: Light emission spectra (190-1100 nm) were measured using fiber-coupled spectrometers (Ocean Optics HR2000+ES, AvaSpec-3648). Spectra were compared against calculated CR spectra, which accounted for material dispersion and electron energy distribution.
- Time-Resolved Analysis: Amplitude-time characteristics were measured using high-speed photodiodes (Photek PD025, ~80 ps rise time) and fast photomultipliers (FEU-97, H7732-10). Optical filters (UFS-1/UFS-2) were used to isolate the fast UV CR component from the slower ICL background.
- CR Identification Criteria: CR was positively identified when the measured light pulse duration matched the short duration of the electron beam pulse, the intensity increased monotonically toward the UV, and the emission showed a strong dependence on the Cherenkov angle (directional emission).
- Degradation Testing (PMMA): PMMA samples were subjected to high-flux multi-pulse irradiation to determine the energy density threshold (> 0.01 J/cm2) at which internal electrical breakdown (streamer discharges) occurs, rendering the material unsuitable for high-dose applications.
Commercial Applications
Section titled “Commercial Applications”The findings are highly relevant to high-energy physics, radiation detection, and fusion energy research, particularly where high-speed, low-inertia particle detection is critical.
- Fusion Energy Diagnostics: Development of robust Cherenkov detectors for Runaway Electrons (REs) in magnetic confinement devices (Tokamaks, e.g., ITER), requiring materials (like synthetic diamond) that withstand high radiation doses and high temperatures.
- High-Energy Particle Physics: Use of transparent materials (e.g., quartz, sapphire) as CR radiators in particle identification detectors (RICH detectors) due to the directional and speed-dependent nature of CR.
- High-Speed Radiation Sensing: Utilizing the near-inertialess response of CR for ultra-fast diagnostics of pulsed electron beams and gamma radiation sources (e.g., in flash X-ray systems).
- Medical Dosimetry: Improving the accuracy of plastic fiber-optic dosimeters (often PMMA-based) by understanding and mitigating the ICL and CR components (stem effect) generated by high-energy therapeutic beams.
- UV/VUV Optics and Windows: Selection of materials (e.g., MgF2, Ga2O3) based on their UV transparency and low ICL background for use in specialized optical systems exposed to ionizing radiation.
View Original Abstract
Interest in the study of the characteristics of the Vavilov-Cherenkov (VCR) radiation has increased in connection with the work on the creation of runaway electron (RE) detectors for TOKAMAK-type installations. This review presents the results of studies of the spectral, amplitude-temporal, and spatial characteristics of VCR, obtained mainly in recent years when transparent substances are excited by an electron flux with energies of tens to hundreds of keV. The VCR spectra in diamond (natural and synthetic), quartz glass, sapphire, leucosapphire are given, and the VCR registration in MgF2, Ga2O3 and other transparent samples is reported. A comparison of the spectra and amplitude-time characteristics of the VCR and pulsed cathodoluminescence (PCL) at various electron energies is carried out. For a number of samples, the VCR spectra were calculated taking into account the dispersion of the refractive index, as well as the energy distribution of the beam electrons and the decrease in the electron energy during their deceleration in the sample material. The emission spectrum of polymethyl methacrylate (PMMA), which is used as a material for radiators in Cherenkov detectors and optical fibers transmitting radiation in scintillation dosimeters, as well as a plastic base in organic scintillators, has been investigated.