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El “sol artificial” chino se estrella récord de fusión nuclear con 1000 segundos del anillo de plasma continuo

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Se conoce el tokamak experimental experimental chino, denominado “Sintético“Ha logrado un nuevo maestro en la investigación de fusión nuclear. El reactor mantuvo un rollo continuo de plasma durante 1066 segundos, excediendo su registro anterior de 403 segundos. Esta penetración, que se informó el 20 de enero de 2025, representa un paso importante para lograr Fusión nuclear como fuente semi -limpieza limitada.

El último maestro del este

como Mencioné A través de la ciencia viva, según los medios del gobierno chino, East actúa como un reactor de encarcelamiento magnético diseñado para mantener el plasma durante largos períodos. El último éxito se logró a través de las promociones al reactor, incluido el sistema de calentamiento mejorado con poca energía. Song Yunino, Director del Instituto Física de plasma en Academia de Ciencias de ChinaDescripción de la experiencia como decisiva para futuras centrales eléctricas. Habló con los medios de comunicación chinos, enfatizó la necesidad de operar plasma estable durante miles de segundos para lograr la generación continua de energía.

Comprender los reactores de fusión

La fusión nuclear imita el sol integrando átomos de luz bajo calor y presión extrema para formar más pesado y liberar energía en este proceso. A diferencia del sol, ya que la tremenda presión ayuda a reaccionar, los reactores basados ​​en el suelo dependen de temperaturas muy altas. A pesar de la promesa de energía abundante y limpia, los reactores de integración actualmente consumen más energía de la que se produce.

Esfuerzos globales en tecnología de fusión

China es participante en el reactor experimental térmico térmico (IterEl programa, una iniciativa multinacional dirigida a progresar la investigación de integración. Se espera que Iter, ubicado en Francia, comience las operaciones en 2039 y pruebe la fusión continua. Los datos admitirán proyectos internacionales este y otros.

El maestro que logró este Se ofrecen signos de progreso en la tecnología de integración, aunque los contratos de investigación aún no sean antes de su aplicación en generación de energía.

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La NASA captura un binario estelar rociando plasma a un cuarto de billón de millas de distancia

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Nuevas fotos de NASAEl Telescopio Espacial Hubble muestra cómo los restos de una estrella que se desvanece están en su mayoría muertos, hasta que una estrella protuberante cercana los revive, una forma de frankenstein.

El legendario observatorio monitoreó un sistema estelar doble ubicado a unos 700 años luz de la Tierra durante más de 30 años, y capturó cómo se atenuaba y brillaba con el tiempo como resultado de fuertes pulsos de la estrella primaria. binario que consiste en Estrella enana blanca y estrella gigante rojatiene una conexión cáustica, disparando corrientes enredadas de gas brillante al universo como un aspersor de césped errático.

Los astrónomos denominaron a este par tóxico en la constelación de Acuario “volcán estelar” por cómo roció corrientes de gas brillante a unos 400 mil millones de kilómetros en el espacio. espacio. En comparación, eso es 24 veces el diámetro de nuestro sistema solar.

La NASA observa las estrellas para estudiar cómo los elementos se reciclan de regreso al universo a través de la energía nuclear.

“¡El plasma se lanza al espacio a más de un millón de millas por hora, lo suficientemente rápido como para viajar de la Tierra a la Luna en 15 minutos!” La NASA dijo en declaración. “Los filamentos brillan en luz visible porque están energizados por la ardiente radiación del sistema binario estelar”.

Una estrella enana blanca oscila cerca de una estrella gigante roja

Cuando una estrella enana blanca se acerca a una estrella gigante roja, aleja el hidrógeno.
Crédito: Ilustración de Goddard de la NASA

el Sistema estelar binarioconocidas colectivamente como R Aquarii, es un tipo especial de estrella doble, llamada estrella simbiótica, y es el par más cercano a la Tierra. En este sistema, una vieja gigante roja, hinchada y moribunda, y una enana blanca, el núcleo encogido de una estrella muerta de tamaño mediano, orbitan entre sí.

La megaestrella es 400 veces más grande que la megaestrella. sol Su brillo varía mucho durante 400 días. En su apogeo, la gigante roja es 5.000 veces más brillante que el Sol. Al igual que la gran estrella R Aquarii, se espera que el Sol se convierta en una gigante roja en unos 5 mil millones de años.

Velocidad de la luz triturable

A medida que la enana blanca R Aquarii se acerca a su masiva compañera a lo largo de su órbita de 44 años, la estrella muerta roba material estelar por gravedad, causando Gas hidrógeno para apilar En su fría superficie, este proceso hace que el cadáver resurja de entre los muertos, por así decirlo, y finalmente se calienta y se enciende como una bomba.

La NASA y la Agencia Espacial Europea crearon el vídeo de la línea de tiempo anterior de R Aquarii utilizando imágenes del Hubble que abarcan desde 2014 hasta 2023.

Esta explosión termonuclear se llama “nova” y no debe confundirse con una explosión termonuclear. supernovadestruyendo una estrella masiva antes de que colapse en una Agujero negro o Estrella de neutrones. La nova no destruye la enana blanca, sino que la explosión expulsa al espacio más elementos, como carbono, nitrógeno, oxígeno y hierro.

Este año los científicos estaban al borde de sus asientos, esperando que apareciera una supernova. T Corona Borealo T CrB, es un sistema estelar binario a unos 3.000 años luz de distancia en la Vía Láctea. Esta nova en particular, que debería ser visible a simple vista, es interesante porque experimenta explosiones periódicas. Los expertos han determinado que explota aproximadamente cada 80 años.

Hace unos meses, los expertos pensaban que la enana blanca se convertiría en nova en algún momento antes de septiembre. Es extraño que este repentino brillo no haya ocurrido todavía.

“Las novas recurrentes son impredecibles y paradójicas”, dijo Koji Mukai, astrofísico de la NASA. comunicado de junio. “Justo cuando crees que no puede haber ninguna razón para que sigan un determinado patrón, lo hacen, y tan pronto como empiezas a confiar en que repitan el mismo patrón, se desvían de él por completo”.

Es muy importante comprender estos eventos debido a lo importantes que son para generar y distribuir los ingredientes necesarios para dar lugar a nuevas estrellas, planetas y vida. y esto es todo Lo que quiso decir el astrónomo Carl Sagan Cuando dijo que los humanos estamos hechos de “material estelar”, el mismo material que forma nuestros cuerpos se formó literalmente dentro de los núcleos de las estrellas y luego se disparó por todo el universo cuando las estrellas explotaron.

El R Aquaii dispara chorros brillantes que giran en espiral hacia arriba y hacia afuera a raíz de poderosos campos magnéticos. El plasma parece girar sobre sí mismo, tejiendo una enorme espiral.



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La Voyager 2 de la NASA apaga el Plasma Science Instrument para conservar energía

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NASA Uno de los instrumentos científicos de la Voyager 2 ha sido apagado para preservar la energía restante durante su viaje a través del espacio interestelar. Lanzada el 20 de agosto de 1977, la nave espacial se encuentra actualmente a 12,8 mil millones de millas de la Tierra y explora más allá del sistema solar. Desde que abandonó la heliosfera el 5 de noviembre de 2018, viajero 2 Estudió el entorno interestelar utilizando cuatro instrumentos científicos activos. Sin embargo, a medida que el suministro de energía de la sonda disminuyó gradualmente, la NASA se vio obligada a tomar la difícil decisión de desactivar otro instrumento.

Gestionar la disminución del suministro de energía

Voyager 2 con su contraparte viajero 1funciona con plutonio en descomposición, lo que reduce la energía disponible en unos 4 vatios cada año. Para prolongar su vida operativa, la NASA ha ido desmantelando gradualmente sistemas no esenciales y algunos instrumentos. Hasta ahora, se han desactivado seis de los diez instrumentos originales de la nave espacial. El 26 de septiembre de 2024 se tomó la decisión de desmantelar el Plasma Science Instrument, que había resultado dañado. Yo jugué Un papel fundamental a la hora de confirmar la salida de la sonda de la atmósfera solar mediante el seguimiento del descenso de partículas solares.

Datos clave del Plasma Science Instrument

El instrumento científico de plasma incluye cuatro “tazas” para medir partículas cargadas, tres de las cuales están dirigidas hacia el sol y para monitorear el viento solar mientras está dentro de la heliosfera. Después de que la nave espacial pasó la heliosfera, estas copas dejaron de recopilar datos, dejando solo una copa en funcionamiento. Esta copa restante proporcionó datos útiles a intervalos a medida que la Voyager 2 realizaba su rotación periódica de 360 ​​grados.

El futuro de la Voyager 2

El Laboratorio de Propulsión a Chorro de la NASA confirmó que el dispositivo de plasma se apagó sin complicaciones y la nave espacial continúa funcionando con normalidad. Mientras los instrumentos restantes recopilan datos valiosos, los ingenieros continuarán monitoreando las reservas de energía de la sonda para determinar cuándo serán necesarios más apagados, lo que permitirá que la misión continúe el mayor tiempo posible.

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A high-density and high-confinement tokamak plasma regime for fusion energy

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Fusion energy is the ultimate energy source for humanity16. A promising approach is a steady-state fusion reactor using magnetic confinement in the tokamak configuration17,18. With a deeper understanding of tokamak plasma physics and the development of reactor-relevant technologies, many fusion reactor designs have been proposed3,4,5,6,7,8,9,10. When the ion temperature is above 13 keV (1.5 × 108 K) in D–T fusion reactions, the thermonuclear power density19 Pfus = nfuel2σvE/4 is proportional to the fuel density (nfuel) squared, as the change of normalized reaction rate σv with temperature is relatively small. Here, E is the fusion energy released per reaction. Detailed definitions of all variables mentioned in this paper can be found in Extended Data Table 1. Therefore, to achieve attractive fusion goals, most of the recent fusion pilot plant (FPP) designs require very high plasma densities, higher than the empirical edge density limit known as the Greenwald density11 (nGr), in tokamak high-confinement mode (H-mode) plasmas13. The energy confinement quality, represented by the H-factor20 (for example, H98y2), is believed to be the highest leverage parameter for fusion capital cost8. H98y2 is usually required to exceed the standard H-mode level (H98y2 = 1.0) for good fusion economy. FPP designs3,4,5,6,7,8,9,10 simultaneously require 1 ≤ Greenwald fraction (fGr) ≤ 1.3 and 1 ≤ H98y2 ≤ 1.65. However, such a tokamak operating regime is an uncharted area that has never been verified in experiments.

The empirical nGr is a density limit for the pedestal density in an H-mode plasma21,22. The pedestal is a narrow region of plasma at the edge with suppressed turbulent transport and a steep pressure gradient. When approaching nGr at the pedestal, various unfavourable phenomena can be observed in experiments. These cause a strong decrease of the confinement quality or even a sudden, complete loss of plasma energy (disruption)22. A peaked core density profile is, therefore, required to achieve a line-averaged density above the pedestal density limit. Possible approaches include relying on the natural peaking at low collisionality23 and the potential inward particle pinch24. The previous DIII-D experiment24 can achieve a transient fGr of about 1.4 with D2 gas puffing. A large pinch velocity has been measured. H98y2 in this case is around 1. ASDEX Upgrade experiments took a different approach by using pellet injection to improve the core fuelling. The experimental results show a transient fGr ≈ 1.5 with pellet injection25,26. However, the H98y2 values in those discharges were less than 1. More examples with H98y2 < 1 at high density are well documented22. As no tokamak experiment has yet attained a sustained fGr above 1 and H98y2 well above 1 (for example, 1.5) at the same time, experimentally verifying the desired operating regime in FPP designs is a great challenge for the magnetic confinement fusion community.

Another challenge with H-mode reactor plasmas is the very high transient heat load produced by quasi-periodic edge magnetohydrodynamic (MHD) instabilities known as type-I edge-localized-modes (ELMs). Without control, ELMs in a reactor can severely damage plasma-facing-components, for example, the first wall27,28. ELM control is an active research area and various approaches have been proposed29,30,31,32,33. However, compatibility among small/no ELM solutions, high density (above nGr) and high confinement quality (H98y2 well above 1, for example, 1.5) has not been demonstrated in experiments.

We report a new experimental approach for achieving a line-averaged density above nGr. It exploits an operating regime recently established in the DIII-D tokamak that allows simultaneous fGr > 1.0, H98y2 ≈ 1.5 and small ELMs and could support many existing designs for future reactors3,4,5,6,7,8,9,10. The approach elevates the plasma density in the core while keeping the pedestal fraction of the Greenwald density at moderate levels (for example, fGr,ped ≈ 0.7), thus not violating the empirical density limit. It does so by exploiting self-organized internal transport barriers (ITBs) at large minor radius in the high poloidal-beta (βP) scenario15,34,35,36. More information about the high-βP research can be found in Methods. In experiments, the on-axis fraction of the Greenwald density (fGr,0) can reach up to 1.7, resulting in a line-averaged fGr of 1.3. ITBs in the density and temperature profiles also greatly improve the energy confinement quality (H98y2 up to 1.8), compared to the standard H mode (H98y2 = 1) at the same engineering and operating parameters.

Figure 1 shows a plot of the DIII-D database and illustrates the progress made in extending the plasma operating space towards high fGr and high H98y2. The 2019 high-βP experiments with impurity injection15 have simultaneously achieved fGr > 1.0 and H98y2 > 1.0. However, in these experiments, too much impurity injection also increases the radiative energy loss in the plasma core, limiting H98y2 at high density. Of the violet diamonds in Fig. 1, some have H98y2 ≤ 1.2 when fGr ≥ 1.15. However, these results are not good enough for FPP designs. A major improvement in the 2022 DIII-D high-βP experiment used additional D2 gas puffing (Fig. 2) instead of impurity injection. This approach effectively reduces the core radiation and improves H98y2, as shown in Fig. 1 (blue squares). Thus, this paper reports a clear experimental demonstration of an accessible operating point in an existing tokamak that can meet a few of the FPP requirements, including simultaneous fGr > 1 and H98y2 ≈ 1.5. For comparison, other scenarios presented run on DIII-D have not achieved such simultaneous normalized performance (yellow circles).

Fig. 1: Database of H98y2 and fGr for DIII-D discharges.
figure 1

More than 3,600 discharges are included. Violet diamonds show high-βP experiments performed in 2019 with impurity injection. Blue squares are the new high-βP experiments performed in 2022 without impurity injection. Yellow circles represent all other experiments performed in 2019–2022. The area shaded in orange indicates the parameter space for attractive FPP designs. Vertical and horizontal dashed lines show fGr = 1.0 and H98y2 = 1.0, respectively.

Fig. 2: Time history of experimental parameters and plasma profiles of DIII-D 190904.
figure 2

a, fGr in blue and H98y2 in green. b, βN in blue, βP in green and q95 in violet. c, D2 gas puffing in feedback control in black and dedicated feedforward D2 gas puffing in vermillion. d, Peak pedestal electron density gradient in blue and pedestal total pressure in vermillion. e, Separatrix electron density in green and ratio between pedestal electron density and separatrix electron density in violet. fi, Profiles of electron temperature (f), ion temperature (g), electron density (h) and carbon density (i) at the time slices shown in the vertical dashed lines in a. Dots with error bars are measurements. jl, Dα data for the three periods shown in the shaded area in d. a.u., arbitrary units. mo, Total pressure profiles at the time slices of the vermillion dots in d.

Figure 2 shows detailed data from an example discharge (190904) in 2022. The striking feature in this discharge is the dynamic synergy between energy confinement quality and plasma density. That is, H98y2 increased along with fGr (Fig. 2a) until the ramping down of the heating power (Extended Data Fig. 1e). This is opposite to the common observation of reduced energy confinement quality in higher density H modes22, especially for experiments close to the Greenwald density. The plasma was maintained at fGr > 1.0 and H98y2 > 1.0 for about 2.2 s, which was 2.2 times the current diffusion time (τR) or 24 times the energy confinement time (τE). Thus, the high normalized density and confinement phase was not transient, which is imperative for application in future long-pulse FPPs. A normalized plasma pressure βN ≈ 3.5 and βP ≈ 2.9 was achieved at safety factor q95 ≈ 8.5 (Fig. 2b) with plasma current Ip = 0.73 MA and toroidal magnetic field BT = 1.89 T, and with mixed co- and counter-Ip neutral beam injection (NBI). Note that nGr = 6.7 × 1019 m−3 in this discharge, close to the Greenwald density of the ITER 9 MA steady-state scenario at 7.2 × 1019 m−3. The dedicated D2 gas puffing time trace is shown in vermillion in Fig. 2c. This approach ensures that there is a sufficient source of particles in the plasma, and it pushes the plasma density to a higher level, regardless of the change in the feedback gas (black line in Fig. 2c).

Profiles of the temperature and density for electrons, deuterium (main ion) and carbon (main impurity) are shown in Fig. 2f–i and Extended Data Fig. 2a. The evolution of the on-axis densities for electrons, deuterium and carbon is displayed in Extended Data Fig. 1c. One can see that ITBs developed in all density channels. The increased deuterium density in this experiment suggests the promising application of this scenario in future FPPs, as it can attain a higher fuel density to give a higher fusion power. A related piece of experimental evidence is shown in Extended Data Fig. 1d. It is clear that with increased plasma density and energy confinement, the neutron rate, an indicator of fusion performance, increased substantially (67% higher, from 0.6 × 1015 to 1.0 × 1015 s−1) from 2 to 4.8 s, whereas the injected power (blue line in Extended Data Fig. 1e) was almost constant. Moreover, a very mild increase of the radiated power was observed in the very-high-density phase of the experiment (Extended Data Fig. 1e). The core radiated power as a fraction of the injected power increased from 10% to 20% as fGr increased from 0.7 to 1.1. The edge radiation remained about 25% of the injected power. Note that for either Bremsstrahlung radiation or impurity line emission, the radiated power was roughly proportional to the electron density squared. Therefore, some increase in the radiated power was expected even with the same impurity level, when the plasma density was increased significantly. Regarding the impurity behaviour, one can see a well-developed ITB at large radius in the carbon density profiles (Fig. 2i). Despite the ITB at large radius, the carbon density inside the ITB did not have a significant central peak, which would usually cause a large amount of core radiation and a reduction of core performance. The ratio between carbon density and electron density stayed around 4–5% during the evolution (Extended Data Fig. 2b). This is consistent with the well-controlled radiated power in the phase with fGr > 1.0.

The evolution of the safety factor profile (q-profile) is shown in Extended Data Fig. 2c. The figure shows the self-organized q-profile evolution, which reflects the change of the local bootstrap current density associated with the development of a large-radius ITB. The local minimum q (qmin) in the outer half of the plasma was at ρ ≈ 0.6 for around 2τR. qmin in this discharge stayed above 2.

When a density ITB built up over time and was sustained, the total pedestal pressure at ρ = 0.88 did not change significantly (Fig. 2d). However, other pedestal parameters and the ELM behaviour changed. At fGr < 0.8, typical standard H-mode pressure profiles and typical large type-I ELMs were observed (Fig. 2j,m). At 0.8 ≤ fGr < 1.0, pressure profiles with an ITB and compound ELMs emerged (Fig. 2k,n). Finally, pressure profiles with a large ITB and small ELMs dominated the fGr ≥ 1.0 phase (Fig. 2l,o). During the evolution, a decreased peak pedestal electron density (ne,ped) gradient, increased separatrix electron density (ne,sep) and decreased ratio between ne,ped and ne,sep were observed, as shown in Fig. 2d,e. These parameter evolutions are consistent with the favourable conditions needed to access the small-ELM regime discussed in the literature29. A more detailed modelling analysis of the pedestal for different ELM behaviours will be discussed later in this paper.

Although addressing the transient heat load is crucial, mitigating the stationary heat load is equally important for an FPP. Divertor detachment is widely considered to be a necessary solution for realizing an acceptable stationary heat load in the operation of future FPPs. Even without detachment-oriented impurity seeding, Extended Data Fig. 3 shows that the electron temperature at the divertor plates (Te,div) clearly reduced from over 35 eV (before 1.8 s) to 20–25 eV (1.8–2.8 s) and finally to 10–15 eV (after 2.8 s) in the fGr > 1.0 and H98y2 ≈ 1.5 phase, and there were small ELMs. The lowest Te,div phase is consistent with the existence of an ITB at large radius. Although Te,div ≤ 15 eV is not yet considered as divertor detachment (usually Te,div < 10 eV), it already suggests that there would be mitigation of tungsten erosion under the experimental stationary heat load, if a tungsten wall had been used. Note that although the integration of full divertor detachment and high-confinement core has been achieved in previous DIII-D high-βP experiments and reported15,37, the experimental approach and the operating parameter space were both different. The previous results used impurity seeding and fGr ≈ 0.9, which are not sufficient for FPP designs.

Therefore, the analysed typical DIII-D high-βP discharge has demonstrated a sustained, accessible operating point in a present tokamak that integrates high normalized density and confinement quality, small ELMs and reduced divertor electron temperature, thus addressing the key requirements of FPP designs for simultaneous high-performance core and excellent core-edge integration.

To understand the physics that enables high confinement quality at high normalized density, we performed a gyro-fluid transport analysis using the TGLF code38 on the experimental data from the discharge shown in Fig. 2. Figure 3a,b shows the dependence of the normalized electron turbulent heat flux Qe/QGB (where QGB is the Gryo-Bohm heat flux) on the fractional contribution of the density gradient to the pressure gradient (Fp = Tn/p) at mid-minor radius in the plasma. The gyro-fluid modelling indicates that when using either numerical approach to vary Fp (constant T or constant p), the decreasing trend of Qe for increasing Fp is robust. A similar result was obtained for the ion energy transport. These results reveal an important feature in the high-βP scenario, namely that anomalous turbulent transport, which leads to poor global confinement, can be reduced with a high density gradient, that is, a high density in the core with the pedestal density maintained below nGr. This is consistent with the experimental observation of synergy between high confinement quality and high density. If Fp were increased by 30%, the normalized Qe would decrease by a factor of 2 compared with the prediction at the experimental value, when the normalized pressure gradient αMHD (approximately −q2/BT,unit2Rdp/dr) was moderate (1.13), as shown in Fig. 3a. However, the reduction of the transport can be 2–3 orders of magnitude stronger when αMHD is high (2.75) in the experimental equilibrium (Fig. 3b). Note that this finding is also consistent with the previous nonlinear gyro-kinetic theoretical modelling39, which found an extreme reduction in the transport coefficient when high αMHD was combined with moderate density gradients. The underlying physics includes 1) the low drive of the ion-temperature-gradient turbulence at high density gradient (that is, there is a low ratio between the density gradient scale length and the ion temperature scale length (ηi)), and 2) less effective coupling between trapped electrons and the trapped-electron-mode turbulence owing to the much narrower turbulence eigenfunction at high αMHD.

Fig. 3: Transport modelling of the dependence of normalized electron turbulent heat flux on the normalized electron density gradient.
figure 3

a, Moderate αMHD case from the high-βP discharge in Fig. 2. Fp scan with the constant p approach in blue and with the constant T approach in vermillion. The experimental (Exp.) value of Fp is indicated by the black arrow. b, High αMHD case from the high-βP discharge in Fig. 2. Same colour coding as in a. c,d, Temperature (c) and density (d) profiles for the low-q95 H-mode case analysed in e and f. Dashed lines show the radial location for transport analysis. e,f, Two-dimensional scans of normalized electron turbulent heat flux on Fp and local q based on the low-q95 H-mode data shown in c and d. Full experimental βe (e) and half experimental βe (f). The experimental data point from the low-q95 discharge is indicated by a blue star in e.

We also applied the same gyro-fluid transport analysis to a standard H-mode discharge to reveal the requirement for realizing the favourable conditions for low transport at high density. A low-q95 standard H-mode discharge (DIII-D 187019) with strong D2 gas puffing and high density was investigated. Compared with the high-βP discharge discussed above, this discharge had the same heating power (9 MW), comparable line-averaged density (5.0–6.5 × 1019 m−3), slightly lower βN (approximately 2.5), but much lower q95 (4 versus 8.5). This was because of a much higher Ip (1.3 versus 0.73 MA). Typical standard H-mode profiles are shown in Fig. 3c,d, which are different from the ITB profiles in Fig. 2. Figure 3e presents the transport analysis of a two-dimensional scan on Fp and local q at ρ = 0.65. The modelling uses the experimental βe value. As illustrated by the horizontal dashed lines, the figure can be roughly divided into three regimes. At low local q, such as for the standard H-mode experimental data point, the modelling predicts high turbulent transport at high Fp. This is consistent with the experimental observation of decreased H98y2 at high density in this discharge. At medium q, transport is predicted to be almost independent of Fp. Finally, low transport at high Fp can be found in the high-q regime (top right corner of this figure highlighted by the blue dashed line). This example suggests that a minimum of the local q ≈ 4.4 is required to access this regime. Note that the analysed high-βP case has local q ≈ 5.1. However, high local q alone is insufficient to access this regime. Figure 3f indicates the importance of sufficient βe, or the plasma pressure (β). Note that β changes accordingly in the modelling when scanning βe. The range of the two-dimensional scan is the same. However, this scan uses half of the experimental βe in the modelling. As one can see, the results are significantly different. For most of the q values in the scan, high turbulent transport at high Fp is predicted. The favourable low transport at high Fp may still exist but probably requires very high local q, which is less realistic in present tokamak experiments or future machine designs.

In summary, the transport analysis suggests that the standard H-mode could access the favourable low-transport regime at high density, with the following necessary conditions: high local q and high plasma pressure β, which are two key components in the expression of αMHD. Thus, sufficient αMHD is essential for realizing the favourable operating regime. As summarized in the literature15,37,40, α-stabilization is considered as the primary turbulence suppression physics in the high-βP scenario, as it provides a reactor-relevant rotation-independent mechanism for high confinement40. On the other hand, given that βPβNq95, high q95 and high βN lead to high βP. Therefore, the high-βP scenario is naturally an excellent candidate for pursing this goal.

We performed a pedestal analysis to evaluate the pedestal stability and understand the evolution of the ELM behaviour in the high-βP discharge described in Fig. 2. The ELITE calculations41 shown in Fig. 4a predict the stability boundary for peeling–ballooning modes in the pedestal, for each of the three ELM states. In the type-I ELM state, the pedestal lies near the unstable ballooning region. Evolving to the small-ELM state, the experimental point moves along the ballooning boundary towards a lower pedestal pressure gradient and lower pedestal current density. Moving further away from the peeling boundary is consistent with the observation of no giant ELMs in the later phase. Modelling with BOUT++ (refs. 42,43,44) provides details on the instability growth rate in Fig. 4b. The dominant low-n peeling–ballooning mode was identified at n ≈ 10, which agrees with the ELITE result. The predicted low-n growth rate is smallest for small ELMs. BOUT++ modelling also resolves high-n resistive ballooning modes near the separatrix, when considering the plasma resistivity. It is clear that the high-n separatrix modes are dominant in the small-ELM case in contrast to other results in Fig. 4b. The modelling suggests that the high-n separatrix modes played an essential role in the observation of small ELMs in high-βP plasmas.

Fig. 4: Pedestal modelling of the three types of ELM behaviours in DIII-D 190904.
figure 4

a,b, Results for the type-I ELM in blue, the compound ELM in green and the small ELM in violet. a, Pedestal stability versus normalized pedestal current density (y axis) and normalized pressure gradient at the pedestal peak gradient location (x axis). jmax, jsep and j are the maximum pedestal current density, the current density at the separatrix and the average current density in the pedestal region, respectively. Stability boundaries are shown as solid lines. Experimental points are indicated as open squares with error bars. b, Linear mode growth rate (normalized by Alfvén frequency, ωA) at different toroidal mode numbers.

In this paper, we have extended the operating space of a tokamak plasma towards a regime with simultaneous fGr up to 1.25 and H98y2 ≈ 1.3–1.8, using the high-βP scenario in DIII-D. The achievement of entering this previously uncharted regime provides essential support to many attractive FPP designs all over the world. The increased deuterium density and neutron rate in the experiment confirm the promising application of this scenario for higher fusion performance in future FPPs. Unlike many previous high-density H-mode experiments, the high-βP scenario uniquely features a synergy between high confinement quality and high density, especially around the Greenwald value. We have also elucidated the important role of α-stabilization in this achievement, showing that the favourable regime of low turbulent transport at high density is predicted and achieved only at relatively high local q and high β, namely for sufficient αMHD at high βP. This successful experiment not only addresses a few of the key requirements on FPP core plasma parameters but also suggests a potential solution for core-edge integration by demonstrating sustained small ELMs together with fGr > 1.0 and H98y2 > 1.0. Realizing the small-ELM regime is understood as a combination of the reduced growth rate of low-n modes and the predominance of the high-n resistive ballooning mode near the separatrix because of the decreased peak density gradient in the pedestal, increased separatrix density and high βP. During the natural small-ELM phase with a high normalized density and confinement, the plasma is close to divertor detachment, which is believed to be the most promising solution for achieving steady-state plasma–wall-interactions in FPPs37,45. The natural proximity of detachment conditions shows the potential of a fully integrated scenario with high-performance core and cool edge. As the divertor detachment was not optimized in the discussed experiment, doing so will be important work for future experiments. Note that the compatibility of the high-βP scenario with full divertor detachment has been demonstrated37. So far, neither a significant central peak in the density profile of the impurity (carbon) nor a significant increase in the core radiated power has been observed when the density is above the Greenwald value. Dedicated impurity transport experiments and modelling work are also under consideration for this operating regime. Fast-particle confinement is important for future FPPs. Experiments on the high-βP scenario in DIII-D usually exhibit classical fast-ion transport. More discussion of previous results is presented in ‘DIII-D high-βP experiments’ (Methods).

We fully appreciate that further work is needed to address other critical issues related to FPP compatibility, for example, operating with a metal wall and helium exhaust. On DIII-D, limited experiments with high-βP plasmas operating with a divertor strike point on a (temporary) ring of tungsten tiles have shown promising results, with no significant degradation of core performance. However, to fully address the compatibility with a metal wall, we are collaborating closely with the Experimental Advanced Superconducting Tokamak (EAST) and Korea Superconducting Tokamak Advanced Research programme in the development of high-βP scenarios so that we can exploit their metal wall and long-pulse operation capabilities. Long-pulse operation (over 10 s) will further address the alignment for steady-state q-profiles and pressure profiles with ITB in the high-βP scenario. With regard to the helium exhaust, several review papers give favourable conclusions for high-βP plasmas with ITBs in JT-60U46,47. The results for JT-60U high-βP ITB plasmas show that the helium density in the core was controlled well and that no helium accumulation was observed, even with helium NBI for the core helium source. Moreover, the results also emphasize the importance of helium exhaust techniques, such as pumping, for controlling the helium content in the core.

Furthermore, there has been recent activity on extending the high-βP scenario towards true long-pulse operation, including modelling work for EAST48, ITER49,50 and FPPs under design10. Depending on the design philosophy of each group, the high-βP scenario can be applied in a wide range of FPP designs, from large conventional tokamaks14 to relatively small and compact devices9,10. One example from CAT-DEMO (Case D)9 shows a possible design point of an FPP using the high-βP scenario: R = 4 m, R/a = 3.1, BT = 7 T, Ip = 8.1 MA, q95 = 6.5, fGr = 1.3, fGr,ped = 1.0, βN = 3.6, H98y2 = 1.51, fusion gain Q = 17.3 and output electric power 200 MWe. The experimental achievement and the increased understanding reported in this paper may open a potential avenue to an operating point for producing economically attractive fusion energy.

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