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1.
The accelerator-generating 6.13~MeV pulsed Gamma by
19F(p, αγ )160 reaction usually synchronizes
with an intense bremsstrahlung x-ray which has a maximum energy of
1~MeV. This paper proposes a new method, named the scattering and
absorbing method, to diagnose the 6.13~MeV Gamma. This method
includes two parts: the detector and a scatterer placed in front of
the detector. The detector converts the Gamma to electrons and then
collects the electrons by a scintillator. In order to restrain the
interference of the low-energy background, the scintillator collects the
electrons at a small angle. The scintillator is wrapped with
electro-absorbing material to absorb the low-energy electrons
generated by background x-rays. The theoretical sensitivity ratio of
6.13~MeV Gamma to 1~MeV x-rays is greater than 150. The scatterer is a
pretreatment tool to scatter some background x-rays away from the
radial beam before they enter the detector. By varying the length,
the scatterer can reduce the background x-rays to an acceptable level for
the detector. 相似文献
2.
The transport of runaway electrons in a high-temperature plasma is
relatively easy to measure in a steady state experiment and a perturbation
experiment, which provides runaway electron diffusion coefficient
Dr. This diffusion coefficient is
determined by internal magnetic fluctuations, so it can be
interpreted in terms of a magnetic fluctuation level. The internal magnetic
fluctuation level ($\tilde {b}r/BT is estimated
to be about (2--4)×-4 in the HL-1M plasma. The
results presented here demonstrate the effectiveness of using runaway
electron transport techniques to determine internal magnetic
fluctuations. A profile of magnetic fluctuation level in the
HL-1M plasma can be estimated from Dr. 相似文献
3.
4.
利用硬X射线探测系统监测HT-7托卡马克装置中逃逸电子轰击到装置第一壁材料时所产生的高能硬X射线,研究了在放电平顶阶段提高等离子体密度对逃逸电子行为的影响。实验结果表明,通过提高放电平顶阶段等离子体密度,HXR强度迅速降到很低的水平,这意味着能有效减少这个阶段形成的逃逸电子的数目及能量。 相似文献
5.
This paper presents a model to describe alternating current (AC) conductivity of DNA sequences, in which DNA is considered as a one-dimensional (1D) disordered system, and electrons transport via hopping between localized states. It finds that AC conductivity in DNA sequences increases as the frequency of the external electric field rises, and it takes the form of σac (ω)~ω 2\ln 2(1/ω). Also AC conductivity of DNA sequences increases with the increase of temperature, this phenomenon presents characteristics of weak temperature-dependence. Meanwhile, the AC conductivity in an off-diagonally correlated case is much larger than that in the uncorrelated case of the Anderson limit in
low temperatures, which indicates that the off-diagonal correlations in DNA sequences have a great effect on the AC conductivity, while at high temperature the off-diagonal correlations no longer play a vital role in electric transport. In addition, the proportion of nucleotide pairs p also plays an important role in AC electron
transport of DNA sequences. For p < 0.5, the conductivity of DNA sequence decreases with the increase of p, while for p ≥ 0.5, the conductivity increases with the increase of p. 相似文献
6.
Martín-Solís JR Esposito B Sánchez R Poli FM Panaccione L 《Physical review letters》2006,97(16):165002
We report on the observation of a large production of runaway electrons during a disruptive termination of discharges heated with lower-hybrid waves at the Frascati Tokamak Upgrade. The runaway current plateaus, which can carry up to 80% of the predisruptive current, are observed more often than in normal Ohmic disruptions. The largest runaway currents correspond to the slowest plasma current decay rates. This trend is opposite to what is observed in most tokamaks. We attribute this anomalous behavior to the acceleration of the preexistent wave-resonant suprathermal electrons during the disruption decay phase. These results could be relevant for the operation of the ITER tokamak whenever a sizeable amount of lower-hybrid power is made available. 相似文献
7.
Signals of ultracold plasma are observed by two-photon
ionization of laser-cooled caesium atoms in a magneto-optical trap.
Recombination of ions and electrons into Rydberg atoms during the
expansion of ultracold plasma is investigated by using
state-selective field ionization spectroscopy. The dependences of
recombination on initial electron temperature (1--70 K) and initial
ion density ($ \sim $10$^{10}$ cm$^{ - 3})$ are investigated. The
measured dependence on initial ion density is $N^{1.547\pm 0.004}$
at a delay time of 5 $\mu $s. The recombination rate rapidly
declines as initial electron temperature increases when delay time
is increased. The distributions of Rydberg atoms on different values
of principal quantum number $n$, i.e. $n=30$--60, at an initial
electron temperature of 3.3 K are also investigated. The main
experimental results are approximately explained by the three-body
recombination theory. 相似文献
8.
Investigation of the transfer ionization process in collisions of partially stripped ions on He 下载免费PDF全文
In this paper a projectile ion-recoil ion coincidence
technique is used to investigate the transfer ionization processes
in collisions of 0.22--6.30~MeV C^{q + } ions and 0.25--6.35~MeV
O^{q + } ions (q=1, 2, 3, 4) with the He atom separately. The cross
section ratio f of transfer ionization to single electron transfer
is measured, and the dependence of f on both charge state q and
energy E of the projectiles is investigated. The
electron-structure and the mechanisms leading to transfer ionization
affect the dependence of f on q and E. Our measurements, along
with other data published previously, suggest a similar dependence
of f on charge state and energy of projectile for partially
stripped ions over a large energy range. The maximum value of f is
approximately 0.17q^{0.60}; the energy corresponding to maximum
f is about 160q^{0.60}~keV/u. 相似文献
9.
This paper mainly investigates plasma characterization on carbon
fiber cathodes with and without cesium iodide (CsI) coating powered
by a ~300~ns, ~ 200~kV accelerating pulse. It was found
that the CsI layers can not only improve the diode voltage, but also
maintain a stable perveance. This indicates a slowly changed diode
gap or a low cathode plasma expansion velocity. By spectroscopic
diagnostics, in the vicinity of the cathode surface the average
plasma density and temperature were found to be ~ 3×
1014~cm-3 and ~ 5~eV, respectively, for an
electron current density of ~ 40~A/cm2. Furthermore, there
exists a multicomponent plasma expansion toward the anode. The
plasma expansion velocity, corresponding to the carbon and hydrogen
ions, is estimated to be ~ 1.5~cm/μ s. Most notably, Cs
spectroscopic line was obtained only at the distance ≤ 0.5~mm
from the cathode surface. Carbon and hydrogen ions are obtained up
to the distance of 2.5~mm from the cathode surface. Cs ions almost
remain at the vicinity of the cathode surface. These results show
that the addition of CsI enables a slow cathode plasma expansion
toward the anode, providing a positive prospect for developing
long-pulse electron beam sources. 相似文献
10.
High energy electron radiation effect on Ni and Ti/4H-SiCSchottky barrier diode at room temperature 下载免费PDF全文
This paper reports that Ni and Ti/4H-SiC Schottky barrier diodes
(SBDs) were fabricated and irradiated with 1~MeV electrons up to a
dose of 3.43×1014~e/cm2. After radiation, the Schottky
barrier height φ B of the Ni/4H-SiC SBD increased from
1.20~eV to 1.21~eV, but decreased from 0.95~eV to 0.94~eV for the
Ti/4H-SiC SBD. The degradation of φ B could be
explained by interface states of changed Schottky contacts. The
on-state resistance RS of both diodes increased with the
dose, which can be ascribed to the radiation defects. The reverse
current of the Ni/4H-SiC SBD slightly increased, but for the Ti/4H-SiC
SBD it basically remained the same. At room temperature,
φ B of the diodes recovered completely after one week,
and the RS partly recovered. 相似文献
11.
《中国物理快报》2016,(11)
Since runaway electrons and magnetohydrodynamics activity can contribute to serious damage and energy losses in tokamaks,the effect of an external electric field on runaway electrons and hard x-ray spectra is investigated.Parameters such as the plasma current,the hard x-ray photons count and the mean energy of runaway electrons are measured.Positive and negative voltages of 300 V are applied at 10 ms after the plasma initiation(while the plasma is forming),at 15ms(while the plasma is stable) and at 20ms(while the plasma is fading away) to attain the most effective time of applying the external electric held.The number of hard x-ray photons has the most changes in the range of 0-200 keV when the external electric fields are applied.Also in the duration of 20-30 ms of plasma the greatest number of hard x-ray spectra is detected.When the external electric fields are applied,the mean energy of runaway electrons reduces significantly,especially at 15ms(while the plasma is stable). 相似文献
12.
The Ni/4H-SiC Schottky barrier diodes (SBDs) and transfer length
method (TLM) test patterns of Ni/4H-SiC Ohmic contacts were
fabricated, and irradiated with 1~MeV electrons up to a dose of
3.43× 1014~e/cm-2. After radiation, the forward
currents of the SBDs at 2~V decreased by about 50%, and the
reverse currents at -200~V increased by less than 30%. Schottky
barrier height (φ B ) of the Ni/4H-SiC SBD increased
from 1.20~eV to 1.21~eV under 0~V irradiation bias, and decreased
from 1.25~eV to 1.19~eV under -30~V irradiation bias. The
degradation of φ B could be explained by the variation
of interface states of Schottky contacts. The on-state resistance
(Rs) and the reverse current increased with the dose, which
can be ascribed to the radiation defects in bulk material. The
specific contact resistance (\rhoc) of the Ni/SiC Ohmic
contact increased from 5.11× 105~Ωega.cm2 to 2.97× 10-4~Ωega.cm2. 相似文献
13.
Self-consistent modeling of the evolution of the plasma current during disruptions in large tokamaks is presented, taking into account both the generation of runaway electrons and their backreaction on the electric field. It is found that the current profile changes dramatically, so that the postdisruption current carried by runaway electrons is much more peaked than the thermal predisruption current. Although only a fraction of the thermal current is converted into runaway electrons, the central current density increases significantly for typical parameters in JET and ITER. It is also shown that the radial runaway profile can easily become filamented in the radial direction. 相似文献
14.
用NaI闪烁体探测器组成的逃逸电子诊断系统和CdTe半导体探测阵列组成的快电子轫致辐射诊断系统,研究了一定等离子体密度条件下低杂波功率和等离子体电流对逃逸产生的影响以及一定低杂波功率下等离子体密度对逃逸电子产生的不同作用效果。根据实验数据计算了HT-7装置等离子体中电子逃逸的阈值电场和一定放电条件下电子逃逸的阈值能量。 相似文献
15.
Density functional theory (DFT) (B3p86) has been used to optimize the structure of the molecule Ta2. The result shows that the ground state of molecule Ta2 is a 7-multiple state and its electronic configuration is ^7∑u^+, which shows the spin polarization effect for molecule Ta2 of transition metal elements for the first time. Meanwhile, spin pollution has not been found because the wavefunction of the ground state does not mix with those of higher states. So, the fact that the ground state of molecule Ta2 is a 7-multiple state indicates a spin polarization effect of molecule Ta2 of the transition metal elements, i.e. there exist 6 parallel spin electrons and the non-conjugated electrons are greatest in number. These electrons occupy different space orbitals so that the energy of molecule Ta2 is minimized. It can be concluded that the effect of parallel spin of the molecule Ta2 is larger than the effect of the conjugated molecule, which is obviously related to the effect of d-electron delocalization. In addition, the Murrell-Sorbie potential functions with parameters for the ground state ^7∑u^+ and other states of the molecule Ta2 are derived. The dissociation energy De, equilibrium bond length Re and vibration frequency we for the ground state of molecule Ta2 are 4.5513eV, 0.2433nm and 173.06cm^-1, respectively. Its force constants f2, f3 and f4 are 1.5965×10^2aJ.nm^-2, -6.4722×10^3aJ·nm^-3 and 29.4851×10^4aJ·nm^-4, respectively. Other spectroscopic data we xe, Be and αe for the ground state of Ta2 are 0.2078cm^-1, 0.0315 cm^-1 and 0.7858×10^-4 cm^-1, respectively. 相似文献
16.
Noise in a coupling electromagnetic detecting system for high frequency gravitational waves 下载免费PDF全文
This paper discusses the basic categories of noise in detecting high
frequency gravitational waves in the microwave band (~0.1--10 GHz), which contain shot noise from the laser and the
thermal radiation photons, thermal noise from statistical
fluctuation of the thermal photons and fluctuation of the
temperature, radiation press noise on the fractal membrane, the
noise caused by the scattering of the Gaussian Beam (GB) in the
detecting tube and noise in the microwave radiometers. The analysis
shows that a reasonable signal-to-noise ratio may be achieved for a
detecting device with the fixed power of GB (105 W), only when
the temperature of the environment is no more than T=1 K, and the
optimal length of the microwave radiometers is about 0.3 m. 相似文献
17.
HT-7托卡马克的逃逸电子诊断系统由CdTe,BGO,Na三种探测器组成,可以用来观测逃逸电子撞击托卡马克第一壁材料产生的硬X射线轫致辐射,它的能量响应范围是0.3~1.5 MeV。结合电子回旋辐射、中子等诊断手段,研究了HT-7超导托卡马克在低杂波电流驱动下的逃逸电子行为。实验结果显示:高功率低杂波的关断和低功率低杂波的投入都会增强逃逸电子的产生,但是如果低杂波可以将等离子体环电压降低到逃逸的阈值电场以下,低杂波的投入就可以抑制电子的逃逸。逃逸电子的产生还和低杂波功率有着密切的关系,可以通过控制低杂波的投入和关断的时刻以及改变低杂波功率来抑制逃逸电子的产生。 相似文献
18.
It is shown that electron-positron pair production is expected to occur in post-disruption plasmas in large tokamaks, including JET and JT-60U, where up to about 10(14) positrons may be created in collisions between multi-MeV runaway electrons and thermal particles. If the loop voltage is large enough, they are accelerated and form a beam of long-lived runaway positrons in the direction opposite to that of the electrons; if the loop voltage is smaller, the positrons have a lifetime of a few hundred ms, in which they are slowed down to energies comparable to that of the cool ( less, similar 10 eV) background plasma before being annihilated. 相似文献
19.
This paper reports that the K x-ray spectra of the thin target 47Ag, 48Cd, 49In and 50Sn were measured by an HPGe semi-conductor detector in collisions with 84.5 MeV 6C4+ ions. Our experiment revealed the Kα x-ray energy shifts were not obvious and the Kβ1 x-ray energy shifts were about 90~110 eV. The simple model of Burch et al has been previously used to calculate the K x-ray energy shifts due to an additional vacancy in 2p orbit. The present work extends the model of Burch to calculate the x-ray energy shifts of multiple ionized atoms induced by heavy ions with kinetic energy of MeV/u. In addition to our experimental results, many other experimental results are compared with the calculated values by using the model. 相似文献
20.
An experimental study of runaway electrons in the EAST tokamak has been performed by a recently developed multi‐channel hard x‐ray diagnostics based on NaI(TL) scintillator detectors. It is found that in the current quench phase, the inductive loop voltage plays an important role in the generation of runaway electrons. And the avalanche mechanism was the main mechanism for runaway electrons after the disruptions. The distribution and transportation of runaway electrons were also investigated by multi‐channel hard x‐ray diagnostics. It is also found that the intensity of runaway electrons emission in the core plasma was much higher than those in the downside of the cross‐section, while the emission intensity of runaway electrons in the core plasma was almost the same. Calculated shrinking coefficient of runaway electrons emission after the plasma disruption was about 26 m/s according to the experimental data (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献