Recent Publications

RF-Specific Tungsten Erosion and Global Transport in ITER under Neon Seeding

Atul Kumar, Dhyanjyoti Nath, Wouter Tierens, Jeremy D. Lore, Andrei Pshenov, Tom Wauters, Andrea Galvan, Davide Curreli, Syun'ichi Shiraiwa, Nicola Bertelli, et al.

Ion cyclotron radio-frequency heating (ICRH) is a key auxiliary heating system in ITER, but high-power RF operation can enhance plasma-material interactions through rectified RF sheath potentials on antenna structures and nearby plasma-facing components. We present the first predictive application of the STRIPE (Simulated Transport of RF Impurity Production and Emission) framework to assess RF sheath-driven tungsten (W) erosion and global impurity transport from the ITER ICRH antenna under ITER-relevant neon-seeded conditions. STRIPE couples SOLPS-ITER plasma backgrounds, full-wave RF sheath calculations, geometry-specific ion energy-angle distributions, sputtering physics, and three-dimensional impurity transport. Simulations predict RF sheath potentials of 1 to 3 kV on antenna limiter sidewalls, increasing gross W erosion by about a factor of 64 relative to thermal sheath conditions and producing a gross source of 3.34e18 W atoms per second. Erosion is governed by RF-modified ion energy-angle distributions together with local plasma flux rather than sheath voltage alone. About 10 percent of sputtered W is locally redeposited, giving a net source of 3.01e18 W atoms per second. The RF-induced antenna source remains about three orders of magnitude smaller than the thermal divertor source and more than two orders of magnitude smaller than the integrated thermal main-chamber source. After 100 ms, about 22 percent of the mobile W inventory resides within the SOLPS-covered confined-plasma region, corresponding to an annular W concentration of 1.70e-6. These results indicate that the ITER ICRH antenna is unlikely to dominate the total W source budget under the conditions considered and demonstrate the need for coupled modeling of RF waves, sheaths, sputtering, redeposition, and global impurity transport.

Electromagnetic analysis of beams for the ITER ECH Upper Launcher

P. Platania, A. Simonetto, J.M. Arroyo, E. Carbonell, N. Casal, M. Choe, D. Farina, G. Garre, M. Henderson, M. Jimenez, et al.

Per-tube parameter characterization and dual-gyrotron operation validation of the CRAFT 170 GHz ECRH test stand

Yu Wang, Zege Wu, Huaichuan Hu, Jingping She, Haoming Chang, Haibiao Zhang, Xiaojie Wang

Helium‑3 minority heating with ion cyclotron range of frequencies (ICRF) in the experimental advanced superconducting tokamak

Yongxin Zhu, Wei Zhang, Yevgen Kazakov, Jinhua Wu, Paola Mantica, Gabriele Cassella, Tao Jin, X. J. Zhang, Lunan Liu, Hua Yang, et al.

During the 2025 campaign, helium-3 ( 3 He) minority heating with waves in the ion cyclotron range of frequencies (ICRF) was investigated for the first time on the Experimental Advanced Superconducting Tokamak (EAST). With the lowest available ICRF frequency of f IC = 27 MHz, experiments were conducted at a high toroidal magnetic field of B t = 2.8 T and plasma current I p = 450 kA. To optimize 3 He minority heating, the variation of 3 He concentration was systematically explored. Real-time feedback control of the 3 He concentration was successfully implemented through spectroscopic measurement and closed-loop regulation of the 3 He gas injection, demonstrating the feasibility of the control system functions. The ICRF heating efficiency reached a maximum at a minority concentration of ∼8-9%, with the core electron temperature increasing from approximately 5.0 to 7.0 keV and the ion temperature from approximately 1.3 to 1.9 keV under 2.9 MW of ICRF power. These results are in good agreement with simulations from the two-dimensional full-wave code TORIC. Experiments further indicate that higher plasma density enhances 3He heating efficiency. We also briefly discuss the strategy for future 3 He ICRF experiments on EAST.

A trend-aware data-driven approach for short-term prediction of ICRF antenna–plasma coupling

Wentao Geng, Donghui Xia, Qihang Jiang, Yulong Deng, Junjie Wu, Lianghui Yang, Yong Hua Ding

The antenna–plasma coupling plays a critical role in the performance of ion cyclotron range of frequency (ICRF) heating systems and can vary rapidly under changing plasma conditions, posing challenges for conventional impedance matching approaches. In this work, a data-driven method is proposed for short-term prediction of ICRF antenna–plasma coupling based on experimental data from the J-TEXT tokamak. The prediction problem is formulated in a residual manner, and a trend-aware learning strategy is introduced to emphasize dominant low-frequency dynamics while suppressing high-frequency fluctuations. Causal preprocessing is applied to ensure compatibility with real-time applications. Two sequence modelling approaches, temporal convolutional networks (TCN) and long short-term memory (LSTM) networks, are employed for evaluation. Both models achieve consistent improvement over a quasi-static baseline across multiple prediction horizons in terms of averaged RMSE, with the largest improvement observed at intermediate time scales. The results indicate that prediction performance is closely related to the temporal characteristics of the coupling signal, where low-frequency-dominated dynamics are more predictable than rapidly varying perturbations. Overall, the proposed approach improves short-term prediction performance while also revealing intrinsic predictability limitations, providing a useful reference for future real-time matching and control strategies.

Suppression of stochasticity and radial transport by externally driven current in CFQS quasi-axisymmetric stellarator

T. Fu, X. Q. Wang, X. Su, J. Wang, Y. Xu, J. Cheng, H. F. Liu, J. Huang, X. Zhang, H. Liu, et al.

Using the nonlinear 3D equilibrium code HINT, we investigate the suppression of magnetic field stochasticity and stochasticity-induced radial electron heat transport by an externally driven current in the Chinese First Quasi-axisymmetric Stellarator configuration. For β0=3%, a Gaussian-profile driven current with I0 = −12 kA effectively suppresses stochasticity within the confinement region, increasing the normalized volume-averaged β while maintaining a magnetic well depth of 7%. The suppression mechanism is attributed to the current reducing the rotational transform inside the n/m = 2/4 rational surface, which weakens or eliminates coupling among low-order satellite island chains. Radial heat transport is evaluated via Rechester–Rosenbluth theory. The radial thermal conductivity χr in the stochastic region decreases with increasing magnitude of I0. In the low-density case, the χr is reduced from 498 m2/s to below 0.1 m2/s; in the high-density case, it decreases from 44 m2/s to below 0.01 m2/s. These results confirm that externally driven current effectively suppresses stochasticity-driven radial heat transport in quasi-axisymmetric configurations.

Investigation of impurity behaviour in three-ion ICRF scenarios in H-D and D-T plasmas at JET

Agata Chomiczewska, Yevgen Kazakov, Wojciech Gromelski, Irena Ivanova-Stanik, Agnieszka Jardin, Axel Jardin, Ewa Kowalska-Strzęciwilk, Kerry Lawson, Evie Litherland-Smith, Andy Meigs, et al.

This study investigates impurity behaviour during ion cyclotron resonance heating (ICRF) experiments, focusing on the application of two different three-ion heating schemes in H-D and D-T plasmas at JET. In the D-(³He)-H scenario, the phasing of the ICRF antenna straps was varied to modify the launched parallel wave number k||, enabling a systematic study of its effect on fast-ion generation, plasma dynamics and impurity transport. The results indicate dependence of impurity behaviour on antenna phasing, particularly for the nickel (Ni) in the main plasmas and for the beryllium (Be) source. Analysis of sawtooth oscillations using the symmetrised dot pattern method reveals correlations between sawtooth frequency and crash intensity, the applied ICRF power and antenna phasing. The lowest impurity levels are obtained with +90° antenna phasing, corresponding to maximised fast-ion generation. A comparative study of impurity behaviour in D-T plasmas is also presented for the three-ion T-(⁹Be)-D and hydrogen minority heating scenarios. The three-ion scheme produces the largest increases in ion temperature Ti, while hydrogen minority heating yields higher electron temperatures Te and slightly reduced impurity levels. These results suggest that impurity behaviour in three-ion ICRF scenarios depends on the chosen heating optimisation (fast-ion generation versus ion heating) and can be further controlled through appropriate selection of ICRF antenna phasing.

Experimental observation of neoclassical tearing mode stabilization by ICRF drive in EAST

Hua Yang, Wei Zhang, Lunan Liu, Pengjun Sun, tao JIN, Hui-Hui Wang, Liqing Xu, Zhengshuyan Wang, Tonghui Shi, Hailin Zhao, et al.

Neoclassical tearing modes (NTMs) in high-beta plasmas can degrade confinement and trigger disruptions. Experiments were conducted on EAST to investigate the effects of ion cyclotron range of frequency (ICRF) heating on NTMs through controlled variation of the power deposition location and fast-ion distribution. Using hydrogen minority heating, on-axis and off-axis ICRF heating scenarios were achieved by varying the toroidal magnetic field, together with additional ICRF power modulation. The results show that on-axis ICRF heating effectively suppresses the m/n = 3/2 tearing mode, while off-axis heating tends to enhance the m/n = 4/3 mode. On-axis heating also improves plasma confinement and increases the neutron yield. TROIC-TRANSP simulations confirm the distinct power deposition locations, while ASCOT calculations indicate that the fast-ion energy reaches up to 800 keV during on-axis heating, which is substantially higher than that in the off-axis cases. A modified Rutherford equation incorporating fast-ion effects suggests that the fast-ion-driven uncompensated cross-field current term is responsible for the observed NTM behaviors. These results demonstrate that controlling the ICRF resonance position is a feasible approach for NTM suppression and improved plasma performance.

Evaluation of neutron emission anisotropy by neutral beam injection in ITER deuterium plasmas

Shota Sugiyama, Takeo Nishitani, Hideaki Matsuura, Shuhei Sumida, Kouji Shinohara, Vitaly Krasilnikov, Bruno Coriton

We have investigated neutron emission anisotropy caused by deuterium beam injection in ITER deuterium plasmas. We evaluate the double-differential emission spectrum and emission anisotropy of neutrons produced by the D(d,n)3He reaction, using the energetic deuteron velocity distribution function obtained by following guiding-centre orbits of test particles. We clarify the dependence of neutron emission anisotropy on the electron density and temperature. Anisotropy increases with decreasing electron density and temperature. We examine the effect of neutron emission anisotropy on the neutron incident flux distribution on the first wall. We show that neutron emission anisotropy can affect the measurements of the neutron emission rate and emission profile based on the incident flux distribution, the distribution of neutron emission anisotropy, and the correspondence relationship between the poloidal angular positions and the neutron detectors that are planned to be installed in ITER. It is inevitable to consider neutron emission anisotropy for plasma diagnostics and monitoring of the neutron generation rate in beam-injected deuterium plasmas.

Analysis of neutron emission during NBI–ICRF synergistic heating in EAST high neutron rate high β p discharges

Andong Xu, Mingyuan Xu, Yunhe Li, Tao Yu, Jiayi Zhang, Yubo Zhang, Yongqiang Zhang, Chenyu Pan, Baolong Hao, Pan Li, et al.

This paper reports the analysis of neutron emission characteristics in high poloidal beta (β p ) discharges on the EAST tokamak, where a record fusion neutron rate of S n = 3.9×10 14 s -1 was achieved with β p ∼2.8, β N ∼2.2, and H 98,y2 ∼1.3. Statistical analysis reveals that while ion cyclotron range of frequencies (ICRF) heating significantly boosts both the neutron rate and plasma stored energy, the neutron rate scales sub-linearly with neutral beam injection (NBI) power (S n ∝P NBI 0.92 ). Interpretive TRANSP simulations demonstrate that the NBI--ICRF synergistic effect directly contributes approximately 30% to the total neutron rate through the formation of a high-energy fast-ion tail. However, this enhancement is partially offset by NBI-induced profile degradation, including fuel dilution, impurity accumulation, and core electron temperature reduction. The generation of the fast-ion tail in velocity space is validated by multi-sightline neutron emission spectroscopy. Furthermore, orbit topology analysis using the ORBIT code reveals that the synergistic effect drives suprathermal fast ions into smaller orbits, such as stagnation orbits, leading to a spatial redistribution of fast ions and a consequent peaking of the neutron emissivity profile. These findings provide critical insights into the complex interplay between auxiliary heating, fast-ion behavior, and neutron emission, offering valuable insights for achieving higher beam--thermal fusion rates in future deuterium--deuterium and deuterium--tritium experiments.

Concept of a megawatt power-level G-band planar gyrotron with transverse energy extraction

V. Yu. Zaslavsky, I. V. Zheleznov, M. N. Vilkov, A. S. Sergeev, A. N. Kuftin, N. S. Ginzburg

At present, the novel compact fusion reactors with strong magnetic fields, including the DEMO project, require the development of 220–240 GHz megawatt continuous-wave heating sources. In this paper, gyrotrons of planar geometry of interaction space with a sheet polyhelical electron beam and transverse energy extraction are considered as such sources. An advantage of this design in comparison with the conventional cylindrical gyrotron configuration is the possibility to ensure effective mode selection over the open transverse coordinate in combination with radiation outcoupling. The theoretical analysis and numerical 3D PIC simulations of a 230 GHz megawatt power planar gyrotron operating at the first harmonic of the cyclotron frequency are performed. The paper considers the feasibility of single-mode generation with output power exceeding 1 MW, efficiency of 30%, and Ohmic loads less than 1.5 kW/cm2, which is compatible with the continuous-wave operation regime.

Integrated modeling study on sustaining high-current reversed magnetic shear configurations in the HL-3 tokamak via combined NBI and ECW

Hai Li, Yijun Zhong, Junbo Zhang, Shoulong Xu, Ziqi Fan, Haozhen Gu, Xinliang Xu, Shuo Wang, Xueyu Gong

Anisotropic Maxwell neural operator for rapid parametric full-wave modelling of ion cyclotron resonance heating

Heng Zhang, Xu Wang, Jiayi Li, Miao Zhang, Jiahui Zhang, Kaihao Wang, Yangdi Yi, Qin Hang, Xinjun Zhang

Full-wave calculations of ion cyclotron resonance heating (ICRH) under different plasma dielectric conditions require repeated assembly and solution of large-scale discretised systems, limiting parameter sweeps and multi-case response analysis. We therefore propose an anisotropic Maxwell neural operator (AMNO) for rapid parametric modelling of ICRH full-wave responses for the Experimental Advanced Superconducting Tokamak (EAST), which learns, within the one-parameter dielectric-field family generated by varying the hydrogen minority fraction X_H over 0.01-0.05 under otherwise fixed settings, a shared solution operator from the spatially varying complex anisotropic dielectric-tensor field to the three-component complex electric field under frequency-domain Maxwell constraints. It represents global spatial coupling through spectral operator layers and local fine-scale responses, and combines sparse reference-field supervision with the frequency-domain Maxwell-equation residual. Comparisons with COMSOL reference solutions for the same EAST frequency-domain Maxwell-dielectric model show that AMNO reconstructs the principal spatial and spectral features and maintains stable accuracy for unseen interpolation test cases. With reference-field points reduced to 7.5% of the dense full-wave set, AMNO reduces the relative L_2 error by 66.1%-89.9% compared with a sparsely supervised Fourier neural operator (FNO-Sparse) under the same supervision and requires about 0.25 s for single-case inference. AMNO thus reduces dependence on dense reference-field supervision while enabling subsecond parametric complex-field inference, providing a physics-constrained and data-efficient surrogate for rapid in-range X_H sweeps and cross-case response analysis within the modelled EAST configuration.

Effect of electron cyclotron waves on plasma with runaway electrons

Pavel Aleynikov, Alexander Franklin Battey, Carlos Paz-Soldan, Eric Matthias Hollmann, Andrey Lvovskiy, Claudio Marini, Daisuke Shiraki, Charles Lasnier

Runaway electrons generated during tokamak disruptions are a major concern for the safe operation of future fusion devices. The interaction of runaway electrons with waves has been proposed as a potential mechanism for their mitigation. This study investigates the effect of electron-cyclotron (EC) waves on post-disruption plasmas containing runaway electrons (REs). O- and X-mode EC waves are routinely used for plasma heating and current drive. However, these modes do not interact directly with relativistic electrons and cannot be injected into plasmas with densities exceeding their respective cutoff densities. In contrast, the internal slow X-mode (sX) can resonate with relativistic electrons and may therefore provide a pathway for their mitigation. We report DIII-D experiments designed to access the internal slow X-mode through O--sX conversion during post-disruption RE plateaus. ECH increased the background-plasma density, doubled the loop voltage, and strongly enhanced the RE synchrotron signal, demonstrating substantial ECH--plasma coupling and increased effective dissipation of the RE channel. Although ECH produced a pronounced response consistent with enhanced RE dissipation, we could not isolate conclusive evidence of resonant sX--RE interaction. Strong heating, ionization, and impurity-redistribution effects appear to dominate the response and may mask a direct wave--particle signature. Nevertheless, the results demonstrate the potential of ECH for RE control through background-plasma modification, with O--sX access offering an additional possibility of direct resonant interaction.

Design of a high-β N operation scenario for the HL-3 tokamak

Guanqi Dong, Guangzhou Hao, Jiaxian Li, Yiren Zhu, Shuo Wang, Yunpeng Zou, Zhuo Wang, Zhengji Li, Hailong Du, Yujie Zhou, et al.

Future fusion reactors require high normalized beta ($\beta_N$) operation to achieve economically attractive power density. High-$\beta_N$ operation is also a key objective for the HL-3 tokamak. Designing a stable and robust operational scenario prior to experiments is therefore essential for the successful execution of high-$\beta_N$ campaigns. This study presents the design of an H-mode scenario with $\beta_N > 3$ for HL-3 at a plasma current of $2$~MA and a toroidal magnetic field of $2.2$~T. A multi-level integrated modeling approach is employed, progressing from macroscopic parameter determination and zero-dimensional scans to 1.5-dimensional dynamic scenario construction. Using the OMFIT framework, modules including EFIT, ONETWO, TGYRO, and EPED1-NN are coupled to obtain self-consistent plasma equilibria and radial profiles. Two heating schemes are considered: pure neutral beam injection (NBI, $10$~MW) and NBI combined with electron cyclotron resonance heating (ECRH, $8$~MW + $2$~MW). Both scenarios achieve $\beta_N > 3$, with a plasma stored energy of approximately $2.9$~MJ and a confinement factor $H_{98} \approx 1.8$. A complete discharge waveform is developed, covering null-field breakdown, current ramp-up, and flat-top phases. Divertor heat flux analysis using SOLPS-ITER indicates that without impurity seeding, the heat load on the lower divertor target exceeds the material limit ($7$~MW/m$^2$); neon seeding at $\sim 1\times10^{20}$~s$^{-1}$ can reduce the peak heat flux to below $6$~MW/m$^2$, approaching detachment conditions. Magnetohydrodynamic stability analysis confirms resilience to vertical displacement events (VDEs), resistive wall modes (RWMs), and neoclassical tearing modes (NTMs), though edge localized modes (ELMs) are expected due to peeling-ballooning instability, requiring active mitigation. This work provides a physics foundation and engineering roadmap for high-$\beta_N$ experiments on HL-3.

First Plasma Commissioning and Operational Highlights from India's First Spherical Tokamak at IPR

Kishore Mishra, Aditya Verma, N. Mansoori, Saurabh Verma, Y. Paravastu, M. S. Khan, Arvind Kumar, S. G. Thatipamula, Vishal Verma, M Sheetal, et al.

A compact Spherical Tokamak(ST) is commissioned at Institute for Plasma Research (IPR) to explore low aspect ratio tokamak physics and technologies that complement to the existing high aspect ratio tokamaks namely ADITYA-U and SST-1 by enabling studies on non-inductive startup, current drive in over dense plasmas, and shaped plasma physics on a low cost platform. The device, India's first spherical tokamak has completed major mechanical, magnetic, and electrical integration, and the coil system has been successfully tested with series of integrated commissioning. First plasma experiments have been carried out with a modest Ohmic system assisted by a 2.45GHz microwave system, supported by a centralized control and data acquisition system. An initial diagnostic set comprising visible imaging, spectroscopy, magnetics, and radiation monitors required for machine operation has been installed. This paper presents the integrated commissioning experiences and first plasma experiments of the newly installed machine.

Observation of significant non-collisional ion heating in helical plasmas with dominant electron heating by neutral beam injection on LHD

Kazuo Toi, Shigeru Morita, K Tanaka, Akihiro Shimizu, Masaki Nishiura, Kunihiro Ogawa, Novimir Antoniuk Pablant, Donald A. Spong, Tokihiko Tokuzawa, Ichihiro Yamada, et al.

In LHD, transient but significant increases in the central ion temperature T_io are observed in low density plasmas having a non-monotonic rotational transform profile produced by high energy neutral beam injection (NBI). The T_io-increase realizes T_io ~ T_eo (central electron temperature) on strong electron heating condition. The increase gradually decreases as the line-average electron density increases, and disappears once it exceeds 1×10¹⁹ m⁻³. During the T_io-increase phases, turbulent density fluctuations in the core plasma region are not suppressed but are enhanced slightly. The ion temperature increases are attributed to an addition of non-collisional ion heating, but not confinement improvement due to suppression of turbulent transport. The ion heating power density estimated from the time evolution of T_io is much higher than that of collisional ion heating by NBI. The estimated maximum power density averaged over the plasma volume becomes transiently comparable to or even higher than the volume-averaged total NBI heating power density. The observed amplitude of energetic ion driven geodesic acoustic modes (EGAMs) with a significant value 〖eϕ〗_EGo⁄T_io ~ 1 (ϕ_EGo: peak value of the EGAM amplitude at the plasma centre) decreases clearly during the initial T_io-increase phase but is maintained at a finite level, with some modulation, until the end of the NBI pulse. The EGAM damping rate expected from the observed ion heating power density is much higher than the linear Landau damping rate estimated from the GAM dispersion relation of a helical plasma. Nonlinear ion Landau damping in high-amplitude EGAM is thought to be one of the leading mechanisms for qualitatively explaining the observed significant ion heating. The significant T_io-increases always induced in the upward-sweeping phase of n=1 reversed shear Alfvén eigenmode (RSAE) frequency are suddenly suppressed, when nonlinear wave-wave coupling of EGAM with n=1 RSAEs and n=0 global Alfvén eigenmodes (GAEs) is activated noticeably (n: toroidal mode number) in the latter phase of the upward sweeping and the downward sweeping of the RSAE frequency. This observation shows a potentiality of a new energy channeling scenario based on EGAM in a future fusion plasma.

Beam optics and stripping losses in a full-scale ITER negative ion source: multibeamlet analysis by beam emission spectroscopy

Riccardo Agnello, Marco Barbisan, Roberto Pasqualotto, Antonio Pimazzoni, Emanuele Sartori, Barbara Zaniol, Edgard Zuin

In this work, Beam Emission Spectroscopy (BES) is applied to the investigation of beam divergence and stripping losses in the full-scale ITER negative ion source prototype SPIDER, operating in multibeamlet configuration. A semi-analytical model is developed to simulate the emission spectra produced by overlapping beamlets, accounting for realistic beamlet divergence, aiming, and beam composition along the accelerator and drift regions. The comparison between synthetic and experimental spectra shows that the Doppler broadening measured in multibeamlet operation cannot be interpreted solely in terms of single-beamlet divergence, but results from the combined effects of beamlet overlap, residual magnetic deflections, electrostatic repulsion, and halo contributions. Using beamlet parameters independently obtained from calorimetric diagnostics, the model reproduces a significant fraction of the experimentally measured divergence. Moreover, the possibility of displacing a line-of-sight allows the detection of variations in the populations of particles with different divergences, namely the core and halo components, across the beam. As a phenomenological characterization, stripping losses are systematically quantified over a wide range of operational parameters, showing an approximately linear increase with source pressure and values consistent with previous single-beamlet studies. These results demonstrate the capability of BES, combined with multibeamlet modelling, to support beam optimization and performance assessment in ITER-relevant negative ion sources.

Machine-agnostic Gaussian process-based surrogate model for electron cyclotron heating and current drive

Andrew M. Irvin, Livia Casali, Sebastian De Pascuale, Ehab Hassan

Real-time total ECRH power control for reliable long-pulse operation and density feedback at Wendelstein 7-X

Laurent Krier, Stefan Marsen, Heike Laqua, Heinrich Laqua, Dmitry Moseev, Frank Noke, Hans Oosterbeek, Niklas Simon Polei, Sergiy Ponomarenko, Taurino Reichert, et al.

The Electron Cyclotron Resonance Heating (ECRH) system at the Wendelstein 7-X (W7-X) stellarator is equipped with eleven megawatt-class gyrotrons that operate at a frequency of 140 GHz, designed for pulse durations of up to thirty minutes. For long-pulse detached-divertor plasma experiments at W7-X, a stable total ECRH power delivered to the plasma is crucial, because the radiated power at the plasma edge is preferably close to the heating power. Consequently, the unexpected shutdown of only one gyrotron can cause a premature end of the experiment due to radiation collapse of the plasma. This paper introduces a system-level controller that dynamically redistributes power among gyrotrons to maintain total ECRH power, improving reliability and enabling feedback control. The controller maintains a specified total ECRH power output by adjusting the accelerating voltage of all gyrotrons. First implemented in the operational phase (OP) 2.2, the system contributed to two major milestones of W7-X during OP 2.3: highest long-pulse triple product for 43 s and highest energy turnover of 1.8 GJ during 360 s. In addition to reliability improvements, the controller enables the adjustment of the total ECRH power for other control objectives, such as maintaining a desired line-integrated plasma density to counteract the ECRH pump-out effect in high-performance scenarios. This paper also presents the first proof-of-principle experiments demonstrating an ECRH-based density feedback system.