Measurement of mean excitation energy by energy loss

ＭｅａｓｕｒｅｍｅｎｔｏｆｍｅａｎｅｘｃｉｔａｔｉｏｎｅｎｅｒｇｙｂｙｅｎｅｒｇｙｌｏｓＬｉｕＣｈａｎｇＳｈｉ（ＢａｓｉｃｓＤｅｐａｒｔｍｅｎｔ，ＸｉｎｊｉａｎｇＰｅｔｒｏｌｅｕｍＣｏｌｅｇｅ，Ｕｒｕｍｑｉ８３００００）ＡｂｓｔｒａｃｔＴｈｅｍｅａ...     

能损法测平均电离激发能

采用电子透过金属箔后的最可几能损测量法，由兰多公式经实验反推Ａｌ，Ｔｉ，Ｆｅ，Ｃｕ及Ｔａ平均电离激发能之实验值，所得结果与已有文献值比较有很好的一致性。实验结果表明这是一种测平均电离激发能的简便、易行且具有较高准确性的方法。     

Fusion energy conversion in magnetically confined plasma reactors

One of the most pressing problems of this century is to solve the energy supply problem and in particular the development of fusion energy technology. Fusion powers the Sun and stars, but on Earth is difficult to achieve in a controlled manner. The International Thermonuclear Experimental Reactor (ITER) is the most technologically advanced machine where net energy from fusion is envisaged to be produced. But this will not be easy, since there are still open issues of plasma confinement, reactor materials, fuel supply, and heat removal. Efficient conversion of fusion energy into the thermal energy in a thermonuclear reactor is, therefore, of great technological relevance and in this paper the energy conversion in magnetically confined plasma reactors is addressed. The chamber wall surrounding the plasma is built from the plasma facing components and from the blanket and divertor modules where the fusion energy is converted into the thermal energy, tritium is produced, and the external components of the chamber are shielded from radiation. The useful materials for building the chamber wall components are low neutron activation steels, refractory metal alloys, and carbon fibre and silicon carbide reinforced composites. The suitable coolants of these components are high pressure helium gas and lithium-based liquid metals and molten salts, where the latter can also serve as tritium breeders. Some of these components will be tested in ITER and eventually may be employed for building demonstration fusion power plants envisaged to become operational during the second half of this century. High performance fusion energy conversion concepts being investigated include: Solid and liquid breeder blankets, separately cooled blankets and tritium breeders, high velocity helium jets for cooling plasma facing components, liquid metals flowing along the solid and through the porous metal walls facing the plasma, liquid metals and molten salts flowing through electrically insulated and non-insulated channels of blankets, and liquid metal heat pipes incorporated into the blankets and divertors for augmenting heat removal and achieving high thermal energy conversion efficiencies. The current fusion-to-thermal energy conversion technologies are, however, in an early stage of development and require reduced-activation, long life operation at high temperatures, resistance to plasma disruptions, and low fusion fuel retention materials, and innovative tritium breeding and heat removal concepts for building simple, reliable, safe, and efficient fusion energy technology.     

Measurement of plasma flows into tile gaps

Particle fluxes falling into narrow gaps are of high interest since international thermonuclear experimental reactor plasma facing components will be castellated. In order to investigate the plasma deposition in gaps between tiles, we have developed a special probe that recreates a gap and that can measure the ion saturation current profiles along its both sides. Measurements were performed in the tokamak Czech Academy of Sciences TORus and are compared with a self-consistent kinetic model. The simulations reproduce well the observed asymmetry of the plasma deposition in both poloidal and toroidal gaps and the intensity of the collected currents is well-estimated. However, the agreement is less perfect for poloidal gaps due to the presence of a positive peak on the negative potential inside the gap. Therefore, the plasma deposition does not decay exponentially like in toroidal gaps. Nevertheless, this unique set of experiments confirms globally the results of our model.     

Measurement of α particle energy loss in biological tissue below 2 MeV

The energy loss of α particles crossing biological tissue at energies between 0.8 and 2.2 MeV has been measured. This energy range is very important for boron neutron capture therapy, based on the ¹⁰B(n,α)⁷Li reaction, which emits α particles with energies of 1.78 and 1.47 MeV. One of the methods used for the measurement of the boron concentration in tissue is based on the deconvolution of the α spectra obtained from neutron irradiation of thin (70 μm) tissue samples. For this technique, a knowledge of the behaviour of the energy loss of the particles in the irradiated tissue is of critical importance. In particular, the curve of the residual energy as a function of the distance travelled in the tissue must be known. In this paper, the results of an experiment carried out with an ²⁴¹Am source and a series of cryostatic sections of rat-lung tissue are presented. The experimental measurements are compared with the results of Monte Carlo calculations performed with the MCNPX code.     

中能核反应的余核测量与分布性质

报道了30Me/Vu^40Ar ^112,124Sn反应中余核的测量方法和结果。对反应中的余核、裂变碎片以及类弹粒子在平行板雪崩计数器的不同响应以及各自的几何探测效率进行了Monte-Carlo模拟。利用平行板雪崩计数器,通过TOF-△E的关联成功地鉴别了余核,并得到了反应的线性动量分布,余核的分布与模拟计算的结果基本一致。     

Evaluation of energy and particle impact on the plasma facing components in DEMO

We analyze the first wall blanket W/EUROFER configuration for DEMO under steady-state normal operation and off-normal conditions, such as vertical displacement events (VDE) and runaway electrons (RE). The main issue is to find the optimal thickness of the W armor which will prevent tungsten surface from evaporation and melting and, on the other hand, will keep EUROFER below the critical thermal stresses. Under steady-state operation heat transfer into the coolant must remain below the critical heat flux (CHF) to avoid the possible severe degradation of the coolant heat removal capability. From the plasma side it is particularly demanding to keep the bulk plasma contamination during the reactor long operational discharges below the fatal level. The possible damage of the FW materials due to the plasma sputtering erosion is estimated. The minimum thickness of the tungsten amour about 3 mm for W/EUROFER sandwich structure will keep the maximum EUROFER temperature below the critical limit for EUROFER steel under steady-state operation and ITER like cooling conditions.     

Measurement of the correlation spectrum of electrostatic potential fluctuations in an ECRH Helimak plasma

Measurements of the length and time scales of turbulent potential fluctuations were carried out on the MIT Versatile Toroidal Facility (VTF). Plasmas were produced by ECRF heating in a novel toroidal configuration which we have termed the Helimak. The configuration consists of a toroidal fieldB of approximately 800 gauss and a vertical fieldB _z of typically 10 gauss, produced by a Helmholtz coil.T _e is approximately 10 eV. The density exhibited a peaked profile havingn _max 2×10¹⁰ cm^–3 and a density gradient scale length of 10 cm. The fluctuation experiments were conducted using a mobile vertical array of eight Langmuir probes. At major radii outside the density peak, the vertical correlation lengths _c of fluctuations were found to be on the order of 5–10 cm for fluctuation frequencies below 3–8 kHz, and on the order of 1–2 cm at higher frequencies. At major radii on the inner slope of the density peak, a new feature appears in the spatial coherence function consisting of a second peak at a probe separation which scales linearly with vertical field. This observation indicates that these fluctuations have a correlation length on the order of 2R ₀600 cm in the direction parallel to the helical magnetic field lines.     

利用轫致辐射能谱测定高频腔体电压

报道了利用轫致辐射能谱测定高频腔体电压的原理、方法及结果分析,并与直接测量法的结果进行比较,说明这种间接测定法的优点。通过实际调束流轨道、能量的测定与计算验证了用能谱法测定腔体电压数值的准确可靠性。