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One of the keys to successful ion cyclotron range of frequency (ICRF) heating in Experimental Advanced Superconducting Tokamak (EAST) is maximizing the coupled power through evanescent layer in both L-mode and H-mode discharges. Increasing coupling efficiency is critical. To reach high power operation, two newly developed antennas have been tested on EAST. Here, we describe the key design features of the antenna and assess its performance by comparison with old four-strap antenna. The key design features are lower k|| spectrum, two current strap configuration, and field aligned faraday screen. The design for the newly developed antenna is balance between geometrical constraints and physics requirements on EAST. The faraday screen rods are fully aligned with the total magnetic field. To reduce the maximum voltage further in the transmission line, an impedance transformer in the vacuum transmission line was used. With these modifications, the loading is increased by 3 times and the heating efficiency is increased by 2-3 times as compared with old four-strap antenna in both L-mode and H-mode discharges. 4.0MW of the maximum injected power with these two antennas have been achieved at the maximum voltage of 15 kV in the transmission lines. We will report latest experimental results from these two ICRF antennas in the recent campaign of EAST. [ABSTRACT FROM AUTHOR]

This study compares experimental observations on the two challenges of Ion Cyclotron Resonance Heating (ICRH), namely the coupling of waves to the plasma and the enhanced impurity sputtering in EAST and WEST medium size tokamaks. In WEST, Lower Hybrid (LH) power helps improving ICRH coupling. In both machines experiments reveal that fueling from the midplane not only helps to couple waves from nearby antennas like in other devices, but also has an impact on the scrape-off layer (SOL) density in regions that are not magnetically connected to the valves. Localized midplane nozzle valves allow similar (in WEST) or better (in EAST) coupling compared to poloidally distributed valves. Core density control requirements for long-pulse operation, in particular in L-mode regime, however limit the amount of gas that can be injected. During ICRH impurities can contaminate the plasma up to a level detrimental for the operation, e.g. up to 100% of ICRH power can be radiated on WEST in certain high power conditions. In WEST, tungsten (W) production measured by visible spectroscopy increases on all the observed objects during ICRH compared to a reference phase without ICRH. On some components (antenna side limiters, baffle, divertor) the rise is larger than with a similar LH power. The relative contribution of each object and physical process (RF-sheaths, fast ion ripple losses) to core contamination yet remains poorly known. Comparing antenna limiters with W-coating vs low-Z materials would help quantifying the role of these components. In EAST, the core W content, measured by EUV spectroscopy in presence of divertor sources only, is correlated with the total injected power, either from ICRH or LH. Since 2018 the LH guard limiter tiles were W-coated. Their contribution to the core W content appears more important than divertor sources when two-strap ICRH antennas magnetically connected to W components at the midplane is powered, compromising high performance operations. [ABSTRACT FROM AUTHOR]

Radio frequency (RF) power in the ion cyclotron range of frequencies (ICRF) is one of the primary auxiliary heating techniques for Experimental Advanced Superconducting Tokamak (EAST). In this paper, we will present an overview of the main experimental results from recent campaign on EAST. 1) A dedicated experiment for more than 10MW operations has been carried out on EAST. The major aspects linked to the use of the EAST auxiliary heating systems: ICRF,LHCD and NBI are presented with emphasis on ICRF and LH. The challenges for ICRF coupling on EAST will be described at the low densities typically used for long pulse operation with lithium wall conditioning. 2)This paper also summarizes effects of ICRF power on LH coupling and modification of heat loads on EAST. 3) Co-current rotation driven by ICRF are observed in both L-mode and H-mode discharges. Co-current rotation can be generated by ICRF heating in LHCD plasma. Different rotation behavior observed in LHCD discharges. ICRF can also induce counter-current rotation in LHCD L-mode discharges. 4) A high-frequency magnetic probes (HFBs) system has been developed and successfully applied to detect ion cyclotron emission (ICE) in D-NBI injection experiments in the 2018 experimental campaign of EAST. ICE driven by fast D-NBI ions and fusion born ions are observed on EAST.5) In Hydrogen minority in Deuterium plasma, the interaction of fast wave and fast D-NBI ions is detected on EAST. Acceleration of fast D ions is confirmed by increased neutron yield. [ABSTRACT FROM AUTHOR]

Significant progress has recently been made on EAST in the 2014 campaign, including the enhanced CW H&CD system over 20MW heating power (LHCD, ICRH and NBI), more than 70 diagnostics, ITER-like W-monoblock on upper divertor, two inner cryo-pumps and RMP coils, enabling EAST to investigate long pulse H mode operation with dominant electron heating and low torque to address the critical issues for ITER. H-mode plasmas were achieved by new H&CD system or 4.6GHz LHCD alone for the first time. Long pulse high performance H mode has been obtained by LHCD alone up to 28s at H98~1.2 or by combing of ICRH and LHCD, no or small ELM was found in RF plasmas, which is essential for steady state operation in the future Tokamak. Plasma operation in low collision regimes were implemented by new 4.6GHz LHCD with core Te~4.5keV. The non-inductive scenarios with high performance at high bootstrap current fraction have been demonstrated in RF dominated regimes for long pulse operation. Near full noninductive CD discharges have been achieved. In addition, effective heating and decoupling method under multitransmitter for ICRF system were developed in this campaign, etc. EAST could be in operation with over 30MW CW heating and current drive power (LHCD ICRH NBI and ECRH), enhanced diagnostic capabilities and full activelycooled metal wall from 2015. It will therefore allow to access new confinement regimes and to extend these regimes towards to steady state operation. [ABSTRACT FROM AUTHOR]

An ICRF system with power up to 6.0 MW and a LHCD system up to 4MW have been applied for heating and current drive experiments on EAST. Intensive lithium wall coating was intensively used to reduce particle recycling and Hydrogen concentration in Deuterium plasma, which is needed for effective ICRF and LHCD power absorption in high density plasmas. Significant progress has been made with ICRF heating and LHW current drive for realizing the H-mode plasma operation in EAST. In 2010, H-mode was generated and sustained by LHCD alone, where lithium coating and gas puffing launcher mouth were applied to improve the LHCD power coupling and penetration into the core plasmas at high density of H-modes. During the last two experimental campaigns, ICRF Heating experiments were carried out at the fixed frequency of 27MHz, achieving effective ions and electrons heating with the H Minority Heating (H-MH) mode, where electrons are predominantly heated by collisions with high energy minority ions. The H-MH mode gave the best plasma performance, and realized H-mode alone in 2012. Combination of ICRF and LHW power injection generated the H-mode plasmas with various ELMy characteristics. The first successful application of the ICRF Heating in the D (He3) plasma was also achieved. The progress on ICRF heating, LHCD experiments and their application in achieving H-mode operation from last two years will be discussed in this report. [ABSTRACT FROM AUTHOR]

A new type of toroidal long Radiation Stripline Antenna (RSA) is presented, which can effectively improve antenna radiation, leading in reduction of max voltage on transmission line and decrease of the sensitivity to ELM?'s of the ICRF system at some frequencies. Based on the new concept, a 4-straps RSA is proposed for EAST device. Using 3- D computing simulator code (HFSS), RF current distribution, S-parameters and electromagnetic field distribution on and near the RSA ICRF antenna are analyzed and compared with present ICRF antenna on EAST. [ABSTRACT FROM AUTHOR]

Research on HT-7 tokamak focuses on exploiting the IBW-heated plasmas mainly to understand heating, active control of profiles and the synergetic interaction with LHCD. Both on-axis and off-axis electron heating with global peaked and localize steep electron pressure profile were realized. The operation of IBW and LHCD synergetic discharges were obtained and optimized through moving the IBW resonant layer to maximize the plasma performance and to avoid MHD activity. Experimental Advanced Superconducting Tokamak (EAST) has been built to perform advanced tokamak research in high performance regime and to explore methods for achieving a steady-state operation for a tokamak fusion reactor at ASIPP. This talk reports an overview of ICRF wall conditioning in HT-7 and EAST during recent campaigns. [ABSTRACT FROM AUTHOR]