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1.
工业X光二极管型单焦点高重复频率闪光X光机在科学研究、工业检测等领域具有重要应用前景。基于光导开关脉冲驱动源开展了金属阴极工业X光二极管重复频率运行实验, 采用烘烤处理方法研究阴极表面吸附特性对重复频率发射特性的影响;以二极管阻抗模型为理论基础, 通过重复频率实验获得的二极管电压维持时间和阻抗特性分析等离子体扩散过程。研究表明:对于高阻抗结构工业X光二极管, 金属阴极为表面吸附杂质或气体解吸附形成等离子体发射机制, 一次放电后阴极表面对气体的再吸附过程限制了其在高重复频率条件下的电流发射能力, 同时由于阴极等离子体扩散过程变慢使得二极管电压脉宽变长。具有高重复频率电流发射能力的阴极是发展单焦点重复频率X光机的基础。 相似文献
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G. Denninger V. Dose H. Scheidt 《Applied Physics A: Materials Science & Processing》1979,18(4):375-380
A vacuum ultraviolet isochromat spectrometer employing an energy selective Geiger-Müller photon counter is described. The
mean energy of the spectrometer is 9.7 eV with a standard deviation of ±0.23 eV. Together with the thermal energy distribution
of the electrons emitted from a directly heated tungsten cathode, an overall resolution of ±0.33 eV is obtained. Pulsed operation
of the x-ray tube avoids additional broadening due to the voltage drop across the filament. Further, pulsed operation of the
accelerating voltage is employed to avoid counting losses due to the relatively large dead time of the radiation detector.
Operating frequencies of up to 2 kHz are possible. With sensitivities of typically 107 pulses per Coulomb, the anode currents are in the range of 100–200 μA. These attractive properties suggest to employ the
method to study surface electronic properties of solids. 相似文献
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Detailed calibration of the PI-LCX:1300 high performance single photon counting hard x-ray CCD camera 下载免费PDF全文
X-ray charge-coupled-device(CCD) camera working in single photon counting mode is a type of x-ray spectrometer with high-sensitivity and superior signal-to-noise performance. In this study, two single photon counting CCD cameras with the same mode(model: PI-LCX: 1300) are calibrated with quasi-monochromatic x-rays from radioactive sources and a conventional x-ray tube. The details of the CCD response to x-rays are analyzed by using a computer program of multi-pixel analyzing and event-distinguishing capability. The detection efficiency, energy resolution, fraction of multi-pixel events each as a function of x-ray energy, and consistence of two CCD cameras are obtained. The calibrated detection efficiency is consistent with the detection efficiency from Monte Carlo calculations with XOP program. When the multi-pixel event analysis is applied, the CCDs may be used to measure x-rays up to 60 ke V with good energy resolution(E /?E ≈ 100 at60 ke V). The difference in detection efficiency between two CCD cameras is small(5.6% at 5.89 ke V), but the difference in fraction of the single pixel event between them is much larger(25% at 8.04 ke V). The obtained small relative error of detection efficiency(2.4% at 5.89 ke V) makes the high accurate measurement of x-ray yield possible in the laser plasma interaction studies. Based on the discrete calibration results, the calculated detection efficiency with XOP can be used for the whole range of 5 ke V–30 ke V. 相似文献
6.
Temporal, spatial and spectral characteristics of a multi-keV monochromatic point x-ray source based on vacuum diode with
laser-produced plasma as cathode are presented. Electrons from a laser-produced aluminium plasma were accelerated towards
a conical point tip titanium anode to generate K-shell x-ray radiation. Approximately 1010 photons/pulse were generated in x-ray pulses of ∼18 to ∼28 ns duration from a source of ∼300 μm diameter, athυ = 4.51 keV (K
α emission of titanium), with a brightness of ∼1020 photons/cm2/s/sr. This was sufficient to record single-shot x-ray radiographs of physical objects on a DEF-5 x-ray film kept at a distance
of up to ∼10 cm. 相似文献
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A new type of x-ray lens composed of multi-square polycapillary slices(ASPXRL)used in focusing parallel x-ray beam was presented in this paper.Compared with conventional x-ray polycapillary lens,ASPXRL can provide smaller and brighter focus.The effects of the manufacturing imperfections on focusing quality of ASPXRL were evaluated with the values of transmission efficiency and discussed.It is suggested that ASPXRL has application prospects as a condenser lens for x-ray microscopy and flux collectors for x-ray analytical instruments. 相似文献
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Influence of tube voltage and current on in-line phase contrast imaging using a microfocus x-ray source 下载免费PDF全文
In-line x-ray phase contrast imaging has attracted much attention due
to two major advantages: its effectiveness in imaging weakly
absorbing materials, and the simplicity of its facilities. In this
paper a comprehensive theory based on Wigner distribution developed
by Wu and Liu [Med. Phys. 31 2378-2384 (2004)] is reviewed. The
influence of x-ray source and detector on the image is discussed.
Experiments using a microfocus x-ray source and a CCD detector are
conducted, which show the role of two key factors on imaging: the
tube voltage and tube current. High tube current and moderate tube
voltage are suggested for imaging. 相似文献
10.
The transition of a low-current discharge with a self-heated hollow cathode to a high-current discharge is studied, and stability conditions for the latter in the pulsed–periodic mode with a current of 0.1–1.0 kA, pulse width of 0.1–1.0 ms, and a pulse repetition rate of 0.1–1.0 kHz are determined. The thermal conditions of the hollow cathode are analyzed, and the conclusion is drawn that the emission current high density is due to pulsed self-heating of the cathode’s surface layer. Conditions for stable emission from a plasma cathode with a grid acting as a plasma boundary using such a discharge are found at low accelerating voltage (100–200 eV) and a gas pressure of 0.1–0.4 Pa. The density of the ion current from a plasma generated by a pulsed beam with a current of 100 A is found to reach 0.1 A/cm2. Probe diagnostics data for the emitting and beam plasmas in the electron source are presented, and a mechanism behind the instability of electron emission from the plasma is suggested on their basis. 相似文献
11.
Experimental study on imploding characteristics of wire-array Z pinches on Qiangguang-1 facility 总被引:1,自引:0,他引:1 下载免费PDF全文
To investigate the imploding characteristics of cylindrical wire
array, experiments with load current varying from 1.5\,MA to 1.7\,MA
were carried out on the Qiangguang-1 facility. The complicated
temporal-spatial distribution of x-ray radiation was measured by the
one-dimensional (1D) x-ray imaging system. Other diagnostic
equipments including the x-ray power meter (XRPM) and the
time-integrated pinhole camera were used to record time-resolved
x-ray power pulse and pinhole x-ray images. Analysis shows that the
fast leading edge of the local x-ray radiation pulse is of primary
importance in sharpening x-ray power pulse rather than the temporal
synchrony and the spatial uniformity of implosion. Experimental
results indicated that the better axial imploding synchrony, the
faster the increase of x-ray power for an array consisting of 32
tungsten wires of 5\mum diameter than for the others, and the
higher the x-ray radiation power with maximal convergence ratio
(r_0/r_1) of 10.5. A `zipper-like' effect of x-ray radiation
extending from the anode to the cathode was also observed. 相似文献
12.
Flow actuation by a continuous/pulsed, direct-current (DC) surface glow discharge is explored. The discharge comprises an array of pin electrode pairs flush mounted on a dielectric actuator surface that lies adjacent to stagnant air. Strong electrostatic fields produced in the cathode sheath region of the discharge provides a motive force on the ions which in turn drag the background gas resulting in directed air flow from the anode to the cathode. The induced flow velocity is estimated by particle image velocimetry (PIV) at 10 Hz with TiO2 seeding. For a pulsed DC discharge with peak power of 5 W per electrode pair, the induced flow velocity reaches peak values of about 1.7 m/s which is comparable to dielectric-barrier discharge (DBD) or corona discharge actuators. The actuation effect quantified by the magnitude of induced velocity increases as the pulse frequency increases from 0 to 1 kHz. The actuation effect decreases for further increase in frequency above 1 kHz. Decreased actuation effect at high frequency is accompanied by structural change in the discharge. At fixed frequency of 1 kHz, flow actuation effect is highest for a square wave pulse with a duty cycle of 50% indicating that pulsed DC discharges produces better actuation than continuous DC with a corresponding reduction in energy consumption. 相似文献
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V. Dubrovsky I. G. Gazaryan V. A. Gribkov Yu. P. Ivanov O. A. Kost M. A. Orlova N. N. Troshina 《Journal of Russian Laser Research》2003,24(4):289-300
Classical radiation biology, radiation treatment of patients, and pulsed radiation chemistry usually deal with weak beams of radiation and operate in terms of dose (D). In this case, only the absolute number of ionizing particles or photons interacting with the object independently of one another is important. In this work, we resume our previous investigations of enzyme activation/inactivation produced by pulsed ionizing radiation from a dense plasma focus (DPF) device at a very short and intense irradiation process, when the concentrations of spurs and blobs are sufficiently dense to allow the micro-volumes to overlap each other. The time interval is small compared with the corresponding biochemical process. It is shown that the irradiation of biological objects for a few nanoseconds by beams of x-ray photons with a low dose (D 10-6–10-3 Gy) but at a high dose power (D/103–105 Gy/s) may be of a collective nature and result in synergetic effects. In particular, it was found that a remarkable activation/inactivation of enzymes (horseradish peroxidase, angiotensin-converting-enzyme) takes place at low doses in these regimes. The results of irradiating the above-mentioned enzymes in vitro with x-rays of nanosecond pulse duration coming from a dense plasma focus are presented here. Neutrons (2.5 MeV, 103–105 n/cm2 and x-ray photons of different energy ranges (7–9 keV and 20–200 keV) together with dose power factors are analyzed as possible reasons for the activation/inactivation of enzymes in various dose ranges. Our results are compared to those of the same experiments conducted with continuous x-ray sources based on a classical x-ray tube and on a 137Cs-isotope source (D10-3–102 Gy). 相似文献
14.
Time-and-space resolved measurements of the emission uniformity of carbon fibre cathode in high-current pulsed discharge 下载免费PDF全文
The remaining challenges, confronting high-power microwave
(HPM) sources and pulsed power generators, stimulate the
developments of robust relativistic electron beam sources. This
paper presents a carbon fibre cathode which is tested in a single
pulsed power generator. The distribution and the development of
cathode plasma are observed by time-and-space resolved diagnostics,
and the uniformity of electron beam density is checked by taking
x-ray images. A quasistationary behaviour of cathode plasma
expansion is observed. It is found that the uniformity of the
extracted electron beam is satisfactory in spite of individual
plasma jets on the cathode surface. These results show that carbon
fibre cathodes can provide a positive prospect for developing
a high-quality electron beam. 相似文献
15.
This paper studies the properties of a kind of portable ultra-bright
microfocus x-ray source with the Monte-Carlo method in detail. The new
x-ray source consists of an electron-emission system, an
electrostatic focusing system and a metal target. A crystal
Lanthanum Hexaboride cathode, a Wehnelt grid and an extracted
electrode compose the triode electrode electron-gun system. Two
equal radius cylinder electrodes form the focusing system. The key
factors determining the focus properties of the electron beam such as the
ratio Dw/H, grid bias Vg, and the properties of the
extracted electrode are numerically studied. The calculated results
reveal that when Dw/H, Vg, the length of
the extracted electrode, and the distance between the grid and the extracted
electrode equals 5, --0.6~kV, 10~mm, and 8~mm respectively, the
electron beam focal spot can be concentrated down to 9~μm in
radius and a reasonable focal length about 72.5~mm can be achieved,
at the same time, the cathode emission currents can be as high as
30~mA. 相似文献
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R. Beck 《Applied physics. B, Lasers and optics》1987,42(4):233-236
A new type of CO2-laser with high-power capability is described. It employs fast axial flow driven by a high-frequency radial impeller. Due to the coaxial design which integrates discharge tube, blower, and gas cooler into a single cylindrical housing, a very compact laser unit is realized. The discharge is rf excited (13.56 MHz). With a specific input power of 21 W/cm3 an output of 800 W is generated at an efficiency of 16%. The discharge can easily be operated in a pulsed mode with frequencies up to 10 kHz. 相似文献
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Z-pinch experiments with two arrays consisting, respectively, of 32
4-μm- and 6-μm-diameter tungsten wires have been carried out on
QiangGuang-1 facility with a current rising up to 1.5MA in 80ns. At early
time of implosion, x-ray framing images show that the initial emission comes
from the central part of arrays, and double clear emission rings, drifting
to the anode and the cathode at 5×106cm/s and 2.4×107cm/s respectively, are often produced near the electrodes. Later,
in a 4-μm-diameter tungsten wire array, filamentation caused by ohmic
heating is prominent, and more than ten filaments have been observed. A
radial inward shift of arrays starts at about 30\,ns earlier than the
occurrence of the x-ray peak power for both kinds of arrays, and the
shrinkage rate of emission region is as high as 1.7×107cm/s in
a 4-μm-diameter tungsten wire array, which is two times higher than
that in a 6-μm one. Emission from precursor plasmas is observed in
implosion of 6-μm-diameter tungsten wire arrays, but not in implosion
of a 4-μm-diameter tungsten wire array. Whereas, in a 4-μm-diameter tungsten wire array, the soft x-ray emission shows the growth of
m=1 instability in the plasma column, which is caused by current. The
reasons for the discrepancy between implosions of 4-μm- and 6-μm-diameter tungsten wire arrays are explained. 相似文献
20.
《中国光学快报(英文版)》2016,(7)
The vacuum-sealed miniature modulated x-ray source(VMMXS) with a hot cathode is fabricated via the singlestep brazing process in a vacuum furnace. An experiment following the VMMXS is implemented to present its performances, including the influence of grid electrode potential on x-ray intensities. The modulation type of the grid electrode as a switch is proposed, and its feasibility is successfully demonstrated. It is noteworthy to discover a phenomenon for the first time, to the best of our knowledge, that the high repetition frequency grid pulse of the VMMXS has a significant effect on the x-ray intensity. The probable cause for this new finding is analyzed. 相似文献