J.S. Hu

Comparison of various wall conditionings on the reduction of H content and particle recycling in EAST

Reductions in H content and particle recycling are important for the improvement of ion cyclotron range of frequency (ICRF) minority heating efficiency and the enhancement of plasma performance of the EAST superconducting tokamak. During recent years several techniques of surface conditioning such as baking, glow discharge cleaning/ICRF discharge cleaning, surface coatings, such as boronization, siliconization and lithium coating, have all been attempted in order to reduce the H/(H+D) ratio and particle recycling in EAST. Even though boronization and siliconization were both reasonably effective methods to improve plasma performance, lithium coatings were observed to reduce the H content and particle recycling to levels low enough to allow the attainment of enhanced plasma parameters and operating modes on EAST. For example, by accomplishing lithium coating using either vacuum evaporation or the real-time injection of fine lithium powder, the H/(H+D) ratio could be routinely decreased to about 5%, which significantly improved ICRF minority heating efficiency during the autumn campaign of 2010. Due to the reduced H/(H+D) ratio and lower particle recycling, and a reduced H-mode power threshold, improved plasma confinement and the first EAST H-mode plasma were obtained. Furthermore, with increasing accumulation of deposited lithium, several new milestones of EAST performance, such as a 6.4 s-long H-mode, a 100 s-long plasma duration and a 1 MA plasma current, were achieved in the 2010 autumn campaign.

The first results of O-ICR experiments to remove re-deposited layers and hydrogen in the HT-7 superconducting tokamak

Oxidation experiments associated with ion cyclotron resonance discharges (O-ICR) have been performed in HT-7 in the presence of a permanent magnetic field of 1.5-2.0 T. The influence of ICRH power and filling pressure on hydrogen and carbon removal rates was analysed. Total numbers of 5.70 x 10 22 H-atoms, 1.6 x 10 22 D-atoms and 2.35 x 10 22 C-atoms had been removed within eight O-ICR cleanings. An ∼20.5 nm co-deposited film on average was removed from the limiters and liners with an area of 12 m 2 . About 1.73 x 10 22 0-atom retention in an O-ICR experiment corresponds to a coverage of 1.44 x 10 16 O cm -2 . The highest removal rates of H, D and C-atoms of up to 2.64 x 10 22 atoms h -1 , 7.76 x 10 21 atoms h -1 and 1.49 x 10 22 atoms h -1 , respectively, were obtained in a 40 kW, 9 x 10 -2 Pa O-ICR cleaning, corresponding to a removal rate of co-deposits of about 317nm/day (7.2g/day for carbon). In a 50min He-ICR cleaning after the O-ICR experiment about 5.39 x 10 21 oxygen retention was removed. Also the influence of the oxidation experiment on the subsequent plasma operation was studied. Normal plasma discharges could be recovered after a few hours of disruptive plasma discharges.

Removal of re-deposited layers and release of trapped hydrogen by He/O-ICR plasma in a HT-7 superconducting tokamak

Oxidation experiments by ion cyclotron resonance discharge in a gas mix of oxygen and helium (He/O-ICR) have been performed in a HT-7 in the presence of a permanent magnetic field of 1.5?2.0?T at wall temperatures of 400 to 470?K. Two kinds of gas mixture ratios of 4?:?1 and 1?:?1 (helium to oxygen) were used. With the same filling rate of oxygen, a higher pressure of He in the He/O-ICR plasma is beneficial for removal of co-deposition and reduces oxygen retention. For the same filling pressure, both the oxygen retention rate and the removal rate of H and C atoms during the He/O-ICR experiment were lower than that in the pure O-ICR experiment. The influence of ICR power and filling pressure on hydrogen and carbon removal rates was analysed. The highest removal rates of H and C atoms up to 5.4 ? 1021?atoms/h and 7.2 ? 1021?atoms/h, respectively, were obtained in 40?kW He/O-ICR cleaning with a ratio of He/O of 4?:?1 at 9.8 ? 10?2?Pa. By He-ICR cleanings and baking in helium gas, most oxygen retained on the wall was sufficiently removed before the subsequent plasma discharge. High power and high pressure He-ICRF cleanings are effective in removing the oxygen retained in the walls. Plasma discharges could be recovered after a few tens of disruptive plasma discharges.

Upgraded flowing liquid lithium limiter for improving Li coverage uniformity and erosion resistance in EAST device

We report on design and technology improvements for a flowing liquid lithium (FLiLi) limiter inserted into auxiliary heated discharges in the experimental advanced superconducting tokamak device. In order to enhance Li coverage uniformity and erosion resistance, a new liquid Li distributor with homogenous channels was implemented. In addition, two independent electromagnetic pumps and a new horizontal capillary structure contributed to an improvement in the observed Li flow uniformity (from 30% in the previous FLiLi design to >80% in this FLiLi design). To improve limiter surface erosion resistance, hot isostatic press technology was applied, which improved the thermal contact between thin stainless steel protective layers covering the Cu heat sink. The thickness of the stainless steel layer was increased from 0.1 mm to 0.5 mm, which also helped macroscopic erosion resilience. Despite the high auxiliary heating power up to 4.5 MW, no Li bursts were recorded from FLiLi, underscoring the improved performance of this new design.

Medium Bandgap D-A Type Photovoltaic Polymers Based on an Asymmetric Dithienopyran Donor and a Benzotriazole Acceptor

Conjugated polymers based on the donor of an asymmetric 5H-dithieno[3,2-b:2′,3′-d]pyran (DTPa) and the acceptors of benzo[d][1,2,3]triazole (BTA) or di-fluorinated benzo[d][1,2,3]triazole (ffBTA) with thiophene as π-bridge were designed and synthesized. Two asymmetric-building-block-containing polymers (ABC-polymers) possess a strong and broad absorption in the range of 300–750 nm and medium optical bandgap of 1.73 and 1.77 eV for PDTPa-TBTA and PDTPa-TffBTA, respectively. Polymer solar cells using PDTPa-TBTA as donor and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as an acceptor exhibited power conversion efficiencies (PCE) of 2.22% with a Voc of 0.58 V, a Jsc of 6.04 mA/cm2, and an FF of 63.41%. The introduction of fluorine substituents on the BTA unit evidently influenced the optical and photovoltaic properties. Interestingly, although the HOMO energy level indeed decreased, PDTPa-TffBTA showed a decreased Voc of 0.52 V in solar cells. Combined with an obviously enhanced Jsc of 10.23 mA/cm2, and an outstanding FF of 0.64, the PCE of solar cells based on PDTPa-TffBTA was improved by nearly 55%, reached 3.43%. Our results indicate that the BTA unit can be used to construct ABC polymers with a medium bandgap, and the introduction of fluorine on the BTA unit is also effective in improving the photovoltaic performance.

Vacuum operation of first divertor campaign on EAST

Experimental Advanced Superconducting Tokamak is the first whole superconducting tokamak with divertor configuration commissioned in the world. Vacuum system is one of the most important sub-systems of EAST device. Wall conditioning also plays a very important role for the plasma operation. Because Ion Cyclotron Resonance Frequency discharge cleaning could be carried out with a high toroidal magnetic field, it is used often for wall conditioning, especially for boronization, which was done successfully on EAST. This paper describes the vacuum operation of this new device. The first part describes the vacuum system, consisting of pumping, fuelling and wall conditioning related sub-systems. Then the operation of the vacuum system is introduced including leak detecting, pumping, boronization, etc. At last, the plan for the coming campaign is discussed.

Study on a linear compressor with metal-bellow replacing conventional cylinder-piston unit

Publisher Summary This chapter presents the study of a linear compressor of moving-coil type with metal-bellow unit, which is made up of a wavelike thin wall pipe and is used to produce the pressure oscillation. Linear compressor, which acts as a pressure wave generator in regenerative refrigerator system, is an important element converting electric power to acoustic power. And its high efficiency, flexibility, and survivability exhibit multifold advantages over conventional compressors. Due to non-leaking interface between the front and back sides of bellow unit, the working gas is protected from being contaminated by the gas emitted from the coil and lubrication oil inside. Furthermore, it can avoid the friction, precision mechanical technology. Theoretically, it is important for the linear compressor to work resonantly to achieve high efficiency and low electrical power consumption. And its also important to match the acoustic load to the compressor to obtain high efficiency. Furthermore, the phase between current and stroke must be 90° when it works resonantly. The influence of mechanical parameters and acoustic loads is investigated when it works resonantly. Some guidelines are provided for designing an efficient linear compressor with metal-bellow assembly.