Observation of self-organized FRC formation in a collisional-merging experiment

Asai, Tomohiko; Kobayashi, Daiji; Seki, T.; Tamura, Yasuaki; Watanabe, Takeharu; Sahara, Naoto; Takahashi, Tsutomu; Morelli, Jordan; Gota, H.; Roche, T.; Magee, Richard; Binderbauer, Michl; Tajima, T.; Inomoto, Michiaki; Takahashi, Toshiki

doi:10.1088/1741-4326/ac189c

Cited by 17 publications

(9 citation statements)

References 23 publications

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“…During the merging process, the FRCs are compressed in axial and radial directions and a reversedcurrent sheet between the two colliding FRCs is developed during the reconnection. In contrast to a recent experiment reporting that the FRC temporarily lost its reversed magnetic structure during merging [11,20], we show that our FRC retains its structure throughout the merging process.…”

Section: Introductioncontrasting

confidence: 99%

“…Several devices have stated that the collision-merged FRCs have been successfully formed in their experiments, and their experimental evidences were the field reversed structure measured by a one-dimensional (1D) magnetic probe [9,10] or some indirect measurements like ion Doppler spectroscopy [11], interferometry and Thomson scattering measurements [6]. The detailed merging process of two colliding FRCs remains unclear.…”

Section: Introductionmentioning

confidence: 99%

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First direct experimental evidence of the merging of two colliding field reversed configurations

Liao¹,

Hu²,

Li³

et al. 2022

Plasma Phys. Control. Fusion

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The collisional merging of two Alfvénic-speed translated field reversed configurations (FRCs) via magnetic reconnection is presented with a two-dimensional magnetic probe array in the KMAX-FRC experiment. The collision is accompanied by axial compression and radial expansion, resulting in the increase in the FRC’s current density and poloidal flux. A reversed-current sheet is found to form during collision, indicating the occurrence of magnetic reconnection. After merging, the ion and electron temperature are increased. By comparing three different scenarios, i.e., the single-translated FRC, the FRC colliding solely with a stream plasma, and the collisional-merging FRC, we identify that axial compression and magnetic reconnection both contribute the electron heating.

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Section: Introductioncontrasting

confidence: 99%

Section: Introductionmentioning

confidence: 99%

First direct experimental evidence of the merging of two colliding field reversed configurations

Liao¹,

Hu²,

Li³

et al. 2022

Plasma Phys. Control. Fusion

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“…The advantages of FRC as a magnetic confinement of hightemperature plasma include the high averaged beta [2], the linear device geometry, the stability exceeding expectations from the magnetohydrodynamics (MHD) theory [3,4], and the natural divertor structure [5]. Besides these, an FRC plasma can maintain its magnetic structure during the supersonic translation [6,7] and survive the violent collision and merging process [8,9]. FRC is considered a promising candidate for compact fusion reactor due to its simplicity, high power density, and robustness [10].…”

Section: Introductionmentioning

confidence: 99%

MHD simulation on magnetic compression of field reversed configurations with NIMROD

Zhu²,

Ren³

et al. 2023

Nucl. Fusion

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Magnetic compression has long been proposed a promising method for plasma heating in a field reversed configuration (FRC). However, it remains a challenge to fully understand the physical mechanisms underlying the compression process, due to its highly dynamic nature beyond the one-dimensional (1D) adiabatic theory model [R. L. Spencer et al., Phys. Fluids 26, 1564 (1983)]. In this work, magnetohydrodynamics (MHD) simulations on the magnetic compression of FRCs using the NIMROD code [C. R. Sovinec et al., J. Comput. Phys. 195, 355 (2004)] and their comparisons with the 1D theory have been performed. The effects of the assumptions of the theory on the compression process have been explored, and the detailed profiles of the FRC during compression have been investigated. The pressure evolution agrees with the theoretical prediction under various initial conditions. The axial contraction of the FRC can be affected by the initial density profile and the ramping rate of the compression magnetic field, but the theoretical predictions on the FRC's length in general and the relation r s=√2 r o in particular hold approximately well during the whole compression process, where r s is the major radius of FRC separatrix and r o is that of the magnetic axis. The evolutions of the density and temperature can be affected significantly by the initial equilibrium profile and the ramping rate of the compression magnetic field. During the compression, the major radius of the FRC is another parameter that is susceptible to the ramping rate of the compression field. Basically, for the same magnetic compression ratio, the peak density is higher and the FRC's radius r s is smaller than the theoretical predictions.

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“…The features of FRCs include high beta, movability and a simple geometry, as well as a natural divertor formed by its open magnetic field lines in the edge, making it an appealing fusion concept, especially for advanced aneutronic fusion reactions, such as D-He 3 and p-B 11 . Collisional merging (CM) FRCs formed by two single-translated FRCs have gained increasing attention following a series of experiments conducted in the Inductive Plasma Accelerator (IPA) experiment [3], the C-2 series device (C-2, C-2U and C-2W) of TAE Technologies Inc. [4][5][6], and the FAT-CM device at Nihon University [7,8], in which the poloidal flux was amplified and the confinement was improved after merging. The collisional merging process can yield a long-lived FRC, which can benefit the quasi-steady-state operation by neutral beam injection or even the development of FRC-based magnetic inertial fusion [9,10].…”

Section: Introductionmentioning

confidence: 99%

Experimental study of single-translated field-reversed configuration in KMAX

Liao¹,

Hu²,

Li³

et al. 2022

Plasma Sci. Technol.

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For the collisional merging field reversed configurations (FRCs), it is desired to have both FRCs to be tuned approximately same, as well as to optimize each FRC to have high temperature, and high translation speed so as to retain most of the equilibrium flux after traveling a distance to the middle plane for merging. The present study reports the experimental study of a single-translated FRC (field-reversed configuration) in the KMAX-FRC device with various diagnostics, including a triple probe, a bolometer, several magnetic probe arrays, and a novel 2D internal magnetic probe array. According to the measurements conducted in the present study, a maximum toroidal magnetic field equal to ~1/3 of the external magnetic field inside the FRC separatrix radius is observed, and the typical parameters of a single-translated FRC near the device’s mid-plane are n e ~ 2-4×1019 m-3, T e ~ 8 eV, T i ~ 5 eV , R s ~ 0.2 m , l s ~ 0.6 m, and Φ p(RR) ~ 0.2 mWb . The 2D magnetic topology measurement revealed, for the first time, the time evolution of the overall internal magnetic fields of a single-translated FRC, and an optimized operation regime is given in the paper.

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Observation of self-organized FRC formation in a collisional-merging experiment

Cited by 17 publications

References 23 publications

First direct experimental evidence of the merging of two colliding field reversed configurations

First direct experimental evidence of the merging of two colliding field reversed configurations

MHD simulation on magnetic compression of field reversed configurations with NIMROD

Experimental study of single-translated field-reversed configuration in KMAX

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