Gyrotrons are widely used in ECRH (Electron Cyclotron Resonance Heating) systems for plasma heating in nuclear fusion experimental devices. Due to the radiation cooling effect of the gyrotron electron gun, the beam current gradually decreases during long-pulse operation, leading to unstable output power. This paper presents a long-pulse gyrotron beam current control method that regulates the beam current by adjusting the filament power supply, thereby stabilizing the gyrotron output power. The method comprises three decoupled modules: data acquisition, feedback control, and filament power control. Data acquisition is implemented via PXI, feedback control adopts a PI (Proportional-Integral) algorithm, and filament power control is realized through SCPI (Standard Commands for Programmable Instruments) over Ethernet. This approach enhances output power stability and is particularly suitable for ECRH systems without pre-installed beam current feedback mechanisms.

To extend the long-pulse operation at higher plasma current and plasma density on Experimental Advanced Superconducting Tokamak (EAST), a new lower hybrid current drive (LHCD) system operating at 4.6 GHz with 4 MW nominal power is being under development. This paper reports the recent advances in lower hybrid technology including the key components of the klystron, launcher, and circulator, which are supported by the Comprehensive Research Facility for Fusion Technology (CRAFT) project. A prototype klystron at 4.6 GHz with one output window has produced 500 kW radio frequency (RF) power with a duration of 1590 s on the test bed with matched load. An active cooling launcher based on the passive-active-multijunction (PAM) concept at 4.6 GHz has been constructed, which is waiting for the plasma experiments on EAST. For the prototype circulator, a full power (namely, forward power = 500 kW) operation over 1135 s with 30% power reflected back to itself has been achieved. These achievements make a large step towards the possible implementation of an LHCD system with the same frequency of 4.6 GHz on China Fusion Engineering Test Reactor (CFETR).

The lower hybrid current drive (LHCD) system plays an important role in EAST experiments. Rapid detection of klystron overcurrent faults is essential for maintaining its operational efficiency. The existing protection system interrupts power but lacks waveform recording capabilities, making fault localization time-consuming. To address this issue, we designed a high-speed data acquisition system specifically for capturing klystron body overcurrent transients. The system employs STM32+FPGA architecture to achieve 20 MSPS sampling across four channels. A QT-based host application allows for threshold configuration, real-time waveform visualization, and data export. Validation tests show the system's capability to record transients with a maximum duration of 20ms. This system enables rapid fault analysis and significantly reduces the diagnostic downtime of the EAST LHCD system.

Interfaces are effective traps for implanted helium (He), and research on the He interactions with interfaces contributes to our comprehension of the role of interface structure in controlling and mitigating the deleterious effects of He. In this study, we investigate He interactions with three types of face-centered cubic (FCC){111}//{111}FCC semi-coherent interfaces: Cu/Ni, Cu/Pd, and Cu/Ag {111} semi-coherent interfaces. Utilizing molecular dynamics simulations, we demonstrate that He atoms exhibit a tendency to segregate at these semi-coherent interfaces. Notably, the presence of new dislocation loops, accompanied by extrinsic stacking faults, is observed at these semi-coherent interfaces as the concentration of He atoms increases continuously. Moreover, this unique structural evolution of interfaces leads to the dissociation of misfit dislocation intersections, thereby significantly augmenting the nucleation sites for He atoms and improving the He managements at these interfaces. These findings provide insights into the interaction between He atoms and FCC{111}//{111}FCC semi-coherent interfaces, enriching our current understanding of He management at such interfaces.

The Experimental Advanced Superconducting Tokamak (EAST) electron cyclotron resonance heating (ECRH) is an important auxiliary heating method, helping EAST achieve 1056 s of super I-mode discharge. There are currently four subsystems with six gyrotrons on EAST. At present, the EAST ECRH system can stably output 3.2-MW radio frequency (RF) power at 140 GHz with long pulses above 100 s (up to 1000 s) and can output 1.3-MW RF power at 105 GHz with long pulses above 100 s. Using ECRH as one of the main heating methods, EAST has made a series of experimental progress in recent years. In April 2023, the steady-state H mode plasma of 403 s was obtained. In the next two years, we plan to develop #5 and #6 systems. After the development, the total RF power can reach 5 MW at 140 GHz. In this article, the composition and operation of the EAST ECRH system were introduced, and the development advances of gyrotrons, transmission lines (TLs), and antennas were discussed. We analyzed the key characteristics related to the long-term operation instability of gyrotrons, which is an important reference for the operation of future gyrotrons.

In order to realize the 1000-s long pulse operation of the electron cyclotron resonance heating (ECRH) system on experimental advanced superconducting tokamak (EAST), we developed an ECRH steady-state operation control system. Four working modes were designed, namely, manual restart mode, automatic restart mode, timed alternate operation mode, and protection trigger alternate operation mode. The field-programmable gate array (FPGA)-based NI cRIO was used as the control device, and the LabVIEW was used to write the program. The system has a quick response and accurate timing sequence and can realize the long-pulse steady-state operation of the gyrotrons in EAST ECRH system. The steady-state operation control system has been verified in nearly two rounds of EAST experiments, helping EAST achieve the 1056-s long pulse discharge.

A new method of power feedback control for the lower hybrid wave (LHW) systems on the experimental advanced superconducting tokamak (EAST) is presented. Different methods are applied to control the power of two LHW systems with different frequency at 2.45 GHz and at 4.6 GHz, respectively. The old method is applied to control the 4.6 GHz LHW power through the exciter of klystrons, and the new one is used to control the 2.45 GHz LHW power through the high voltage power supply (HVPS) system. The new method has been applied in EAST and successfully assisted the development of relevant experiments such as loop voltage control, q profile control.

Electron cyclotron resonance heating is an important magnetic confinement fusion heating method. This paper analyzes the relevant signals in detail when protection occurs, which plays an important role in studying the operation law of the gyrotron and ensuring the normal operation of the ECRH system.

With the capability of saving flux consumption in the current ramp up phase, controlling the safety factor (q) profile, providing the required off-axis current drive (CD), a lower hybrid current drive (LHCD) system was eventually determined to be used on the China Fusion Engineering Test Reactor (CFETR). In this paper, a 20 MW/4.6 GHz system composed of 40 units of 500 kW continuous wave (CW) klystron amplifier is preliminarily designed. The feasibility of the frequency choice of 4.6 GHz in the physical aspect is discussed. In order to minimize the transmission loss, a TE01 over-mode of circular waveguide will be used in the transmission system. Although previous calculations indicates that high field side (HFS) launcher location results in waves damping at inner region than low field side (LFS) launcher, which is favorable for plasma stability, HFS launcher will be extremely difficult in engineering due to the limited space. Calculations show that the tritium breeding ratio (TBR) will be decreased by - 1.5% with HFS launcher, while it will be decreased by - 0.22% only with LFS launcher. As a result, the LH power will be coupled to plasma from the top port at LFS. The designed passive active multi-junction (PAM) launcher is arranged in an array of 5 rows and 8 columns with the height of 1181 mm and the width of 794 mm. A shielding block with a thickness of 20 cm will be equipped around the feeding waveguides to protect the feeding waveguides and to prevent neutron leakage. A preliminary scheme of the remote maintenance for the LFS launcher is given. The modeling results shows that the density for optimum coupling is - 1.8 x 1017/m3, lower than the 4.6 GHz cut-off density ne_co = 2.6 x 1017/m3. Around this density, the power directivity (Dp) can be high as 71%.

The quality and life of the injected product are affected by surface quality of curved mold, and reasonable polishing method is the key to obtain the high-quality surface of curved mold. Small polishing tool is controlled by constant displacement polishing in the conventional method of robot polishing. The polishing force is adjusted to affect the surface quality of mold during mold polishing. The shortcomings of traditional control method of robot are investigated by simulation, and the constant force control approach is proposed to maintain stable force, which is achieved by a position-based impedance control algorithm. The polishing experiments of curved mold are conducted by using two control methods with constant displacement control polishing (CDCP) and constant force control polishing (CFCP), respectively. The experimental results show that the CFCP method can maintain polishing force stability and the reduction of surface roughness in the three groups of experiments using CDCP method is much lower than that of CFCP method, respectively. The feasibility of constant force control polishing method (CFCP) is verified.

In recent years, EAST has achieved a 60-s scale steady-state plasma operation (SSO), which is electron dominant heated by the electron cyclotron wave and low hybrid wave. Substantial progresses have been made in the development of long-pulse operation, such as active control of radiative divertor, edge localized mode (ELM) suppression, and He plasma experiment. To further develop the steady-state operation scenario and study the related critical physical issues, the upgrade of EAST has been completed in 2020. The auxiliary heating systems were rearranged and upgraded with a total heating power capability of 33 MW. The 2.45-GHz lower hybrid current drive (LHCD) launcher has been updated from full active multijunction (FAM) to passive active multijunction (PAM) to avoid damage caused by plasma–material interaction. The injection power capability of electron cyclotron resonance heating (ECRH) system is upgraded to 1.4 MW. The upgraded ion cyclotron resonance frequency (ICRF) antenna injects low parallel wavenumber ( $k_{\vert \vert }$ ) spectra with good single pass absorption. The neutral beam injection (NBI) system is moved from F-port to D-port and is reoriented from counterclockwise to clockwise injection. The armor material of lower divertor has been upgraded from graphite to tungsten improving the steady-state heat handling capability from 2 to 10 MW/m2. Based on the upgraded pumping system and improved conductance, the effective pumping speed for $D_{2}$ of the EAST lower divertor increased twice. With all these upgrades, 100-s scale steady-state operation ( $T_{e0} >10$ keV) and 1056-s high-performance operation with 1.73-GJ injection energy were achieved in 2021 campaigns. The experience in high-performance long-pulse operation obtained on EAST will lay a foundation for the ITER and Chinese Fusion Engineering Testing Reactor (CFETR) operation.

为了实现EAST上电子回旋共振加热(ECRH)系统在长脉冲放电下的稳态运行,设计了一套ECRH稳态运行控制系统.该系统通过多种模式切换,运用重新启动和多组回旋管轮流运行的方案提高ECRH系统在EAST装置的400～1000 s长脉冲放电过程中的连续运行能力.本设计采用NI CompactRIO及其组件作为下位机,使用LabVIEW语言编写程序.本系统响应迅速,时序准确,能够实现长脉冲放电下ECRH系统的稳态运行.

This paper proposes a force control strategy based on velocity modulation and impedance control algorithm to address unstable contact problem between the tool and workpiece in machining. In many application scenarios of industrial robots, contact force is required to some extent. Therefore, a force control component guarantees that robot can maintain stable contact force with the predetermined trajectory and react in the rapidly changing environment. The position controller is used to adjust the movement of the robot. During movement, position controller combined with speed-based impedance control can compensate for the uncertainty of controller and robot Meanwhile, the velocity of the robot is controlled in the velocity modulation subspace to reduce the vibration force in contact, thus the contact overshoot decreases and the machining accuracy of the workpiece is improved. Evaluations through non-contact to contact transition experiment indicates that low contact vibration and reliable position/force control can be achieved by this proposed controller.

Since the last IAEA Fusion Energy Conference in 2016, the EAST physics experiments have been developed further in support of high-performance steady-state operation for ITER and CFETR. First demonstration of a >100s time scale long-pulse steady-state scenario with a good plasma performance (H-98(y2) similar to 1.1) and a good control of impurity and heat exhaust with the upper tungsten divertor has been achieved on EAST using the pure radio frequency (RF) power heating and current drive. The EAST operational domain has been significantly extended towards a more ITER and CFETR related high beta steady-state regime (beta(p) similar to 2.5 and beta(N) similar to 1.9 of using RF and NB and beta(p) similar to 1.9 and beta(N) similar to 1.5 of using pure RF). A large bootstrap current fraction up to 47% has been achieved with with q(95) similar to 6.0-7.0. The interaction effect between the electron cyclotron resonant heating and two lower hybrid wave systems has been investigated systematically, and applied for the improvement of current drive efficiency and plasma confinement quality in the steady-state scenario development on EAST. Full edgelocalized mode (ELM) suppression using the n = 2 resonant magnetic perturbations has been achieved in ITER-like standard type-I ELMy H-mode plasmas with a range of the edge safety factor of q(95) approximate to 3.2-3.7 on EAST. Reduction of the peak heat flux on the divertor was demonstrated using the active radiation feedback control. An increase in the total heating power and improvement of the plasma confinement are expected using a OD model prediction for a higher bootstrap fraction. Towards a long-pulse, high bootstrap current fraction operation, a new lower ITER-like tungsten divertor with active water-cooling will be installed, together with further increase and improvement of heating and current drive capability.

A long pulse ECRH system with a goal of 140GHz 4MW 100~1000s has been developed to meet the requirement of steady-state operation on EAST. Gycom gyrotrons are employed in the No.1 and No.3 systems, CPI gyrotrons are used in the No.2 and No.4 systems. The development of the two Gycom gyrotron systems has been finished. The first short pulse EC wave injection has been demonstrated successfully during the EAST 2015 Spring campaign. In the commissioning and operation towards steady-state operation, 0.4MW 100s has been injected to plasma successfully by using the No.1 system, 4.7keV 102s L-mode and 102s H-mode plasma have been achieved on EAST with the help of ECRH. Recently, a longest pulse of 0.55MW 1000s has been obtained based on calorimetric dummy load measurements on the No.3 gyrotron. The No.2 gyrotron also has been installed and partially tested, 500kW 80s has been demonstrated in the dummy load. The remaining No.4 gyrotron will be ready to test in 2018 or 2019. The whole 4MW system will be completed within two years. The 400s fully non-inductive H-mode operation would be expected in the next four years in the condition of fully tungsten diverter on EAST.

To satisfy various requirements of different physics experiments, a new power modulation method of the lower hybrid wave (LHW) has been developed in Experimental Advanced Superconducting Tokamak (EAST), including the development of a control source combining software and hardware. Such modulation system is realized by the main positive-intrinsic-negative diode switch located at the oscillator. The LHW modulation system has been installed and tested, demonstrating that the modulation parameters can be controlled flexibly. The maximal modulation frequency is about 10 kHz, which is limited by the hardware circuit speed. The system has been successfully used to study the influence of LHW on the performances of plasma. Under the modulation of LHW, strong mitigation of edge-localized modes (ELMs) has been observed, and ELM pace-making technique has been demonstrated. Further experimental studies with the modulation system will be continued in EAST.

In this paper, an overcurrent protection system is designed to ensure the safety of the gyrotrons in the EAST ECRH system. Two overcurrent protection systems were established, a fast one and a slow one. The fast one uses the current transformers as the current sensors. The models of the current transformers and the superconducting magnet were built to analyze the effect of the environmental magnetic field on the current transformers using FI method. The analysis results show that the magnetic induction at the position near the current transformers must less than 0.002 T, i.e., the current transformers should be placed at a distance greater than 2.2 meters from the magnet center to ensure its normal work. The slow one uses the shunt to monitor the currents. An anti-fuse FPGA and a timer is used to realize the signal processing in the fast protection circuit and the slow protection circuit respectively. The response time of the fast protection circuit is less than 100 ns, and the response time of the slow protection circuit is less than 31 μs.

The gyrotron is the most important device in the ECRH system. The cathode power supply is one of the most important ancillary devices for gyrotron. Some interesting transient phenomena about the cathode voltage and the cathode current was found in the gyrotron operation. In order to explain these phenomena, an equivalent model of the magnetron injection gun was proposed. The equivalent circuit is composed of parallel resistors and capacitors, and it can explain the test results very well.

. China Experimental Fast Reactor (abbr. CEFR) is a pool-type sodium-cooled fast reactor in China Institute of Atomic Energy (abbr. CIAE), with a thermal power of 65MW and an electric power of 20MW. The construction started in 2000 and the first criticality was reached in July 2010. On December 15th 2014, CEFR reached full power for the first time and was successfully operated for 72 hours. During the physical start-up of CEFR, a series of tests were carried out in four aspects, i.e., fuel loading and first criticality, control rod worth measurements, reactivity coefficient measurements, and foil activation measurements. A large amount of experiment data was obtained in the process. In order to compile and reserve the experimental data in a standard and refined form, and to benefit the worldwide fast reactor society on the validation of codes and nuclear data, China Institute of Atomic Energy proposed an IAEA Coordinated Research Project, and got approved preliminarily.

A long pulse electron cyclotron resonance heating (ECRH) system has been developed to meet the requirements of steady-state operation for the EAST superconducting tokamak, and the first EC wave was successfully injected into plasma during the 2015 spring campaign. The system is mainly composed of four 140 GHz gyrotron systems, 4 ITER-Like transmission lines, 4 independent channel launchers and corresponding power supplies, a water cooling, control & inter-lock system etc. Each gyrotron is expected to deliver a maximum power of 1 MW and be operated at 100-1000 s pulse lengths. The No.1 and No.2 gyrotron systems have been installed. In the initial commissioning, a series of parameters of 1 MW 1 s, 900 kW 10 s, 800 kW 95 s and 650 kW 753 s have been demonstrated successfully on the No.1 gyrotron system based on calorimetric dummy load measurements. Significant plasma heating and MHD instability suppression effects were observed in EAST experiments. In addition, high confinement (H-mode) discharges triggered by ECRH were obtained.