Non-Inductive Start up of QUEST Plasma by RF Powert

Both start-up and sustainment of plasma were successfully achieved by fully non- inductive current drive using microwave with a frequency of 8.2 GHz. Plasmas current of 15 kA was implemented for 1 s. Magnetic surface reconstruction exhibited a plasma shape with an aspect ratio of below 1.5. The plasma current was dependent significantly on the launched microwave power and vertical magnetic field, while not affected by the mode of launched wave and the toroidal refractive index. Hard X-ray （HXR） emitted from energetic electrons accelerated by the microwave was observed, and the discharge with a plasma current over 4 kA followed the same trend as the number of photons of 10 keV to 12 keV. This suggests that the plasma current may be driven by energetic electrons. Based on the experimental conditions, alternative explanations of how the plasma current could be driven are discussed.

Numerical Simulation of Non-Inductive Current Driven Scenario in EAST Using Neutral Beam Injection

For achieving the scientific mission of long pulse and high performance operation,experimental advanced superconducting tokamak（EAST） applies fully superconducting magnet technology and is equiped with high power auxiliary heating system.Besides RF（Radio Frequency） wave heating,neutral beam injection（NBI） is an effective heating and current drive method in fusion research.NBCD（Neutral Beam Current Drive） as a viable non-inductive current drive source plays an important role in quasi-steady state operating scenario for tokamak.The non-inductive current driven scenario in EAST only by NBI is predicted using the TSC/NUBEAM code.At the condition of low plasma current and moderate plasma density,neutral beam injection heats the plasma effectively and NBCD plus bootstrap current accounts for a large proportion among the total plasma current for the flattop time.

Numerical Sensitivity Studies on Effects of Ice Nucleating Processes on Electrification in Thunderstorms

This study employed numerical simulations to explore the impact of varying ice nucleation processes on the microphysics and electrification within thunderstorm clouds.A two-dimensional cumulus model,incorporating both noninductive and inductive charge separation schemes,was utilized.The findings revealed that the freezing nucleation mechanism significantly influenced the microphysical development,electrification,and charge structure of thunderstorms.Homogeneous freezing generated a large quantity of small ice crystals near the cloud tops,which were primarily responsible for the development of positive charge regions through a non-inductive charging process.Conversely,heterogeneous freezing resulted in larger ice crystals,enhancing graupel formation and leading to a more rapid and intense charge separation rate of around-15°C.Ice crystals formed heterogeneously and charged negatively during the development stage,resulting in an inverted dipole charge structure.When both immersion and homogeneous freezing processes were considered,the competition between these two distinct freezing processes resulted in reduced cloud water content and weaker electrification.Under conditions of low cloud water content at lower storm levels,graupel particles were negatively charged through non-inductive charging,causing the charge structure to quickly revert to a normal dipole structure.

Formation of Low Aspect Ratio Torus Equilibria by ECH in the LATE Device

By ECH under a steady By field, a closed field equilibrium of a low aspect ratio as low as R/a = 1.4 is spontaneously formed in the LATE device. After the spontaneous formation, the plasma current has increased further up to Ip = 7.2 kA by 2.45 GHz, 30 kW and Ip = 11 kA by 5 GHz, 120 kW, by increasing the microwave power with a slow ramp of By for the equilibrium of the plasma loop at larger currents. Both amount to 12% of the total toroidai coil current. ECH/ECCD at 2nd harmonic resonance of EBW supports the plasma. An outline of the theoretical considerations for the formation process is presented.

Formation of ST Plasmas by ECH on LATE

Experiments on formation of spherical tokamak (ST) plasmas by electroncyclotron heating (ECH) alone without a central OH solenoid have been carried out on LATE (LowAspect ratio Torus Experiments). By injecting a 2.45 GHz microwave pulse of 6.3 kW for 4 seconds, aplasma current is initiated and ramped up to I_p approx= 3 kA, and finally maintained for 1 secondby adjusting the external vertical field. Magnetic measurements show that closed flux surfaces areformed and the last closed flux surface has an aspect ratio of A ～ 1.3 and an elongation of κ～1.3. The electron density measured by an interferometer is more than 1.5 x 10^(11) cm^(-3) whichexceeds twice of the plasma cut-off density, suggesting that electron cyclotron heating bymode-converted electron Bernstein waves may take place.

Simulation of ECR Startup and Comparison with Experimental Observations in SUNIST

Transient process of ECR startup in SUNIST is analyzed and simulated in a one- dimensional model. Contributions from the generation, drift, diffusion and loss of electrons are taken into account in the model and estimated from experimental parameters, e.g., toroidal field, vertical field and gas filling pressure. Typical discharges are simulated with the conditions close to the experimental ones. Experimental and simulated results are comparable qualitatively in amplitudes and semi-quantitatively in time. From the results it is confirmed that the transient process of ECR startup ill SUNIST is dominated, as preliminarily deduced from experimental observations, by a pair of exclusive factors, namely the absorption, due to gas ionization, and the reflection of microwave, caused by the shift of over dense plasmas due to outward E x B drift. In addition to these two factors, electron loss along the field line is also very important in determining the character of discharges.

Progress Toward Steady-State Operation on Tore Supra

Important technological and physics issues related to steady-state operationrequired for next step are being examined on Tore Supra, after a major upgrade of internalcomponents in order to increase the heat extraction capability to 25 MW for 1000 s. Here, we showfirst experimental results, where all the plasma facing components were actively cooled duringpulses exceeding four minutes, with reactor-relevant heat load. New physics was observed innon-inductively driven plasmas, including a stationary peaked radial profile of the plasma densitygenerated by an anomalous inward pinch; and a regime characterized by sinusoidal oscillations ofcentral electron temperature, governed by non-linear coupling between heat transport and plasmacurrent analogous to a predator-prey mechanism.

Total Lightning Characteristics and Electric Structure Evolution in a Hailstorm

In this paper, total lightning data observed by SAFIR3000 3-D Lightning Locating System was combined with radar data to analyze characteristics of the lightning activity and electric structure of a hailstorm that occurred in Beijing on 31 May 2005. The results indicated that there were two active periods for the lightning activity during the hailstorm process. The hail shooting was found in the first period. After the end of the hail shooting, lightning frequency decreased suddenly. However, more active lightning activities occurred in the second period with lots of them appearing in the cloud anvil region. The peak of the lightning frequency came about 5 min prior to the hail shooting. Only 6.16% of the total lightning was cloud-to-ground （CG） lightning, among which 20% had positive polarity. This percentage was higher than that in normal thunderstorms. In addition, heavier positive CG lightning discharge occurred before rather than after the hail shooting. In the stage of the hail shooting, the electric structure of the hailstorm was inverted, with the main negative charge region located around the -40℃ level and the main positive charge region around the -15℃ level. In addition, a weak negative charge region existed below the positive charge region transitorily. After the hail shooting, the electric structure underwent fast and persistent adjustments and became a normal tripole, with positive charge in the upper and lower levels and negative charge in the middle levels. However, the electric structure was tilted under the influence of the westerly wind in the middle and upper levels. The lightning activity and electric structure were closely related to the dynamic and microphysical processes of the hailstorm. It was believed that severe storms with stronger updrafts were more conducive to an inverted tripolar electric structure than normal thunderstorms, and the inverted distribution could then facilitate more positive CG lightning in the severe storms.