A confident source of hard X-rays: radiation from a tokamak applicable for runaway electrons diagnosis

2016 ◽  
Vol 23 (5) ◽  
pp. 1227-1231 ◽  
Author(s):  
M. Kafi ◽  
A. Salar Elahi ◽  
M. Ghoranneviss ◽  
M. R. Ghanbari ◽  
M. K. Salem
Keyword(s):  
Magnetic Field ◽  
Electric Field ◽  
High Energy ◽  
Toroidal Magnetic Field ◽  
Vacuum Vessel ◽  
X Rays ◽  
Runaway Electrons ◽  
High Energy Electrons ◽  
High Loop ◽  
The Mean

In a tokamak with a toroidal electric field, electrons that exceed the critical velocity are freely accelerated and can reach very high energies. These so-called `runaway electrons' can cause severe damage to the vacuum vessel and are a dangerous source of hard X-rays. Here the effect of toroidal electric and magnetic field changes on the characteristics of runaway electrons is reported. A possible technique for runaways diagnosis is the detection of hard X-ray radiation; for this purpose, a scintillator (NaI) was used. Because of the high loop voltage at the beginning of a plasma, this investigation was carried out on toroidal electric field changes in the first 5 ms interval from the beginning of the plasma. In addition, the toroidal magnetic field was monitored for the whole discharge time. The results indicate that with increasing toroidal electric field the mean energy of runaway electrons rises, and also an increase in the toroidal magnetic field can result in a decrease in intensity of magnetohydrodynamic oscillations which means that for both conditions more of these high-energy electrons will be generated.

scholarly journals Fast magnetic energy dissipation in relativistic plasma induced by high order laser modes

2016 ◽  
Vol 4 ◽  
Author(s):  
Y. J. Gu ◽  
Q. Yu ◽  
O. Klimo ◽  
T. Zh. Esirkepov ◽  
S. V. Bulanov ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Electric Field ◽  
Magnetic Energy ◽  
Collisionless Plasma ◽  
High Energy ◽  
Field Energy ◽  
Displacement Current ◽  
Particle In Cell ◽  
Magnetic Field Energy ◽  
High Energy Electrons

Fast magnetic field annihilation in a collisionless plasma is induced by using TEM(1,0) laser pulse. The magnetic quadrupole structure formation, expansion and annihilation stages are demonstrated with 2.5-dimensional particle-in-cell simulations. The magnetic field energy is converted to the electric field and accelerate the particles inside the annihilation plane. A bunch of high energy electrons moving backwards is detected in the current sheet. The strong displacement current is the dominant contribution which induces the longitudinal inductive electric field.

Development of a novel spiral antenna system for low loop voltage current start up atSteady State Superconducting Tokamak(SST-1).

2021 ◽  
Author(s):  
Debjyoti Basu ◽  
D Raju ◽  
Raj Singh ◽  
Aparajita Mukherjee ◽  
Manoj Patel ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Electric Field ◽  
Antenna System ◽  
Toroidal Magnetic Field ◽  
Vacuum Vessel ◽  
Plasma Current ◽  
Test Results ◽  
Spiral Antenna ◽  
Start Up ◽  
Superconducting Tokamak

Abstract In general, superconducting tokamaks require low loop voltage current start up for the safety purpose of its poloidal field coils. The loop voltage inside the vacuum vessel of Steady-state Superconducting Tokamak (SST-1) is low in nature since its central solenoid is located outside the cryostat. The low loop voltage current start up of the SST-1 is routinely performed by Electron Cyclotron Resonance (ECR) method at the toroidal magnetic field Bt=1.5T(first harmonic) and 0.75T(second harmonic). Recently, an alternative RF based plasma current start up system had been planned for operating the machine specially for higher toroidal magnetic field regime 1.5T ≤ Bt ≤3T. The system is already developed based on an antenna system, made of series combinations of two at spiral antenna, to assist plasma current start up at lower inductive electric field. It is already tested and installed in SST-1 chamber. The system testing had been performed without background magnetic field within frequency regime 35-60MHz at present. The test results show that it can produce electron density ne ≈1016m-3 measured by the Langmuir probe in expense of 500W RF power. The spectroscopy results indicate that its capability to produce plasma density higher than 1013 m-3 and electron temperature Te = 2 -6eV. In addition, it also shows that the presence of turbulent electric field of the order of 106V/m at antenna center and finite anomalous temperature of neutral particles. Calculations show that the obtained density is enough for SST-1 low loop voltage plasma breakdown. The antenna system is also capable to produce plasma at higher frequencies. This article will discuss the development of the prototype and the installed antenna system along with their test results in detail.

scholarly journals Long-Lived Banana Orbit Formation of Suprathermal Electrons During MHD Spikes in Runaway Tokamak Discharges

2019 ◽  
Keyword(s):  
Magnetic Field ◽  
Electric Field ◽  
Thermal Plasma ◽  
Large Scale ◽  
High Energy ◽  
Runaway Electrons ◽  
Trapped Electrons ◽  
Knock Out ◽  
Coulomb Collisions ◽  
Suprathermal Electrons

The secondary runaway electrons generation is the process in which already existing high energy runaway electrons knock out thermal plasma electrons directly into the runaway region by close Coulomb collisions. Such knocked-on electrons are immediately accelerated to ultrarelativistic velocities, since in the runaway region the toroidal electric field force overcomes the collisional friction force with thermal plasma particles. The avalanche of runaway electrons with mega-electron-volt energy emerges, hit of which with the construction elements of large-scale tokamaks and future international tokamak ITER can lead to catastrophic consequences. Due to its importance, this phenomenon is being actively studied both theoretically and experimentally in leading thermonuclear fusion centers. It is known that during secondary generation, the value of the transversal component of knocked-on electrons momentum with respect to the confining magnetic field may be significantly higher than the longitudinal one: p⊥ >> p∥. Thus, conditions for knocked-on electron trapping in a non-uniform tokamak magnetic field occur (banana orbits). Such electrons can no longer be accelerated by the inducted toroidal electric field to high energies, avalanche formation is partially suppressed. The question is how long this population of knocked-on and trapped electrons exists. In the presented paper, it is shown the additional possibility of formation and existence of such long-lived banana orbits of suprathermal electrons under conditions of plasma MHD activity when MHD instability spikes induced the strong burst of the toroidal electric field that results in the abrupt growth in these knocked-on and trapped electrons. This phenomenon is considered for the recent low-density EAST (Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, China) tokamak quasistationary runaway discharges. Long-lived trapped electrons (p⊥ >> p∥) also have an influence on the intensity of ECE emission. The considered phenomenon is important for correct interpretation of the runaway experiments on present-day tokamaks.

Dependence of Reliability of Ultrathin Mos Gate Oxides on the Fermi Level Positions at Gate and Substrate

1997 ◽  
Vol 473 ◽  
Author(s):  
Tien-Chun Yang ◽  
Navakanta Bhat ◽  
Krishna C. Saraswat
Keyword(s):  
Electric Field ◽  
Fermi Level ◽  
Breakdown Strength ◽  
Gate Oxide ◽  
High Energy ◽  
Constant Current ◽  
Oxide Breakdown ◽  
Mos Devices ◽  
High Energy Electrons ◽  
Substrate Doping

ABSTRACTWe demonstrate that the reliability of ultrathin (< 10 nm) gate oxide in MOS devices depends on the Fermi level position at the gate, and not on the position at the substrate for constant current gate injection (Vg-). The oxide breakdown strength (Qbd) is less for p+ poly-Si gate than for n+ poly-Si gate, but, it is independent of the substrate doping type. The degradation of oxides is closely related to the electric field across the gate oxide, which is influenced by the cathode Fermi level. P+ poly-Si gate has higher barrier height for tunneled electrons, therefore, the cathode electric field must be higher to give the same injection current density. A higher electric field gives more high energy electrons at the anode, and therefore the damage is more at the substrate interface. Different substrate types cause no effect on the oxide electric field, and as a result, they do not influence the degradation.

scholarly journals Very High-Energy Emission from the Direct Vicinity of Rapidly Rotating Black Holes

Galaxies ◽  
2018 ◽  
Vol 6 (4) ◽  
pp. 122 ◽  
Author(s):  
Kouichi Hirotani
Keyword(s):  
Magnetic Field ◽  
Black Holes ◽  
Black Hole ◽  
Electric Field ◽  
Gamma Rays ◽  
Accretion Rate ◽  
High Energy ◽  
Relativistic Electrons ◽  
Field Lines ◽  
The Magnetic Field

When a black hole accretes plasmas at very low accretion rate, an advection-dominated accretion flow (ADAF) is formed. In an ADAF, relativistic electrons emit soft gamma-rays via Bremsstrahlung. Some MeV photons collide with each other to materialize as electron-positron pairs in the magnetosphere. Such pairs efficiently screen the electric field along the magnetic field lines, when the accretion rate is typically greater than 0.03–0.3% of the Eddington rate. However, when the accretion rate becomes smaller than this value, the number density of the created pairs becomes less than the rotationally induced Goldreich–Julian density. In such a charge-starved magnetosphere, an electric field arises along the magnetic field lines to accelerate charged leptons into ultra-relativistic energies, leading to an efficient TeV emission via an inverse-Compton (IC) process, spending a portion of the extracted hole’s rotational energy. In this review, we summarize the stationary lepton accelerator models in black hole magnetospheres. We apply the model to super-massive black holes and demonstrate that nearby low-luminosity active galactic nuclei are capable of emitting detectable gamma-rays between 0.1 and 30 TeV with the Cherenkov Telescope Array.

scholarly journals Detection of TeV Gamma Rays from SN1006

1998 ◽  
Vol 188 ◽  
pp. 121-124 ◽  
Author(s):  
Toru Tanimori
Keyword(s):  
Magnetic Field ◽  
Cosmic Rays ◽  
Gamma Rays ◽  
High Energy ◽  
Shock Acceleration ◽  
Emission Region ◽  
X Ray ◽  
High Energy Electrons ◽  
Tev Gamma Rays ◽  
The Magnetic Field

In spite of the recent progress of high energy gamma-ray astronomy, there still remains quite unclear and important problem about the origin of cosmic rays. Supernova remnants (SNRs) are the favoured site for cosmic rays up to 1016 eV, as they satisfy the requirements such as an energy input rate. But direct supporting evidence is sparse. Recently intense non-thermal X-ray emission from the rims of the Type Ia SNR SN1006 (G327.6+14.6) has been observed by ASCA (Koyama et al. 1995)and ROSAT (Willingale et al. 1996), which is considered, by attributing the emission to synchrotron radiation, to be strong evidence of shock acceleration of high energy electrons up to ~100 TeV. If so, TeV gamma rays would also be expected from inverse Compton scattering (IC) of low energy photons (mostly attributable to the 2.7 K cosmic background photons) by these electrons. By assuming the magnetic field strength (B) in the emission region of the SNR, several theorists (Pohl 1996; Mastichiadis 1996; Mastichiadis & de Jager 1996; Yoshida & Yanagita 1997) calculated the expected spectra of TeV gamma rays using the observed radio/X-ray spectra. Observation of TeV gamma rays would thus provide not only the further direct evidence of the existence of very high energy electrons but also the another important information such as the strength of the magnetic field and diffusion coefficient of the shock acceleration. With this motivation, SN1006 was observed by the CANGAROO imaging air Cerenkov telescope in 1996 March and June, also 1997 March and April.

Thermoluminescence of irradiated ammonium perchlorate crystals

1976 ◽  
Vol 54 (7) ◽  
pp. 766-770 ◽  
Author(s):  
S. Radhakrishna ◽  
M. Riggin ◽  
P. W. Whippey ◽  
P. W. M. Jacobs
Keyword(s):  
Absorption Spectrum ◽  
Single Crystals ◽  
Heating Rate ◽  
Ammonium Perchlorate ◽  
Uv Light ◽  
High Energy ◽  
X Rays ◽  
Spectroscopic Evidence ◽  
Additional Peak ◽  
High Energy Electrons

The thermoluminescence of single crystals of ammonium perchlorate irradiated with X rays, uv light, or high energy electrons has been measured between 80 and 420 K. With a heating rate of 5 K/min. prominent peaks occur at 95, 113, 134, 246, and 320 K; an additional peak is found at 347 K after longer irradiation times. The absorption spectrum of uv-irradiated ammonium perchlorate has also been measured and shows bands at 300, 360, and 610 nm. A comparison of these data with chemical and spectroscopic evidence obtained by other workers has permitted the probable identification of ClO3−, ClO−, ClO2, and F centres as radiation products. Three thermoluminescent peaks remain unassigned.

Sign in / Sign up

Export Citation Format

Share Document