## 1 Introduction  
The low-pressure and electronegative radio frequency plasma sources are widely used in the Si-based material etching process and functional thin film deposition [1; 2]. In general, the capacitive [3] and inductive radio frequency sources are applied, and the inductively coupled plasma [4; 5] (abbreviated as ICP) is characterized by its low-pressure discharge, high plasma density, simple device, etc. Due to the interference of negative ions (anions), the transport process and discharge structure of electronegative and gaseous discharging plasma are quite different from the electropositive plasma. In Ref. [6], based on an ambipolar diffusion of triple species (electron, cation, and anion) in highly electronegative plasma, the parabola discharge theory was established by [PERSON] and [PERSON]. Later in Ref. [7], they built the ellipse theory again for the highly electronegative plasma in the case that the Boltzmann's balance is not reasonable for the anions. In Ref. [8], they still found internal sheaths existing in electronegative plasma, and the structure of the non-neutral region varied significantly with the ratios of anion and electron densities and of their temperatures. In addition, the phenomenon of stratification through the electronegative core and electropositive halo in the whole discharge region was recognized in Refs. [6; 7; 8; 9]. Moreover, a double-layer structure was founded by [PERSON] at the interface of the core and halo, and the electronegative plasma was then called double-layer-stratified discharge [10]. Of more interest is that the double layer was accompanied by the oscillation of the electropositive halo. [PERSON] (utilizing the kinetic model) and [PERSON] finally concluding the oscillation was an artifact, respectively [11; 12]. In addition, the negative ion front model was established by [PERSON] at observing the temporal evolution of the electronegative plasma density border in Ref. [13]. The above discharge structure theories of electronegative plasma are based on quasi-direct current discharge, such as ICP sources. When the electronegative plasma oscillates, such as in the CCP source, the famous drift-ambipolar (abbreviated as DA) and striation discharging models were found by [PERSON] [14] and [PERSON] [15], respectively. Besides the above interesting mechanisms constructed in electronegative plasma, our recent works revealed the coagulated structure, such as the comet shape of anions, in the Ar/O\({}_{2}\) ICP source (with low electronegativity) by means of a fluid model [16; 17]. In these references, the self-coagulation idea was for the first time suggested to explain the formation of coagulated structure in the plasma background that is dispersed. In the present article, the self-coagulation theory is formally put forward to interpret the related coagulated structures in general electronegative plasmas, such as the Ar/SF\({}_{6}\) plasma with high electronegativity. Our fluid simulation and theoretic analysis both reveal the significance of ratio of ionic recombination loss in the chemical source, which somehow determines the discharge structure. In particular, if it is neglected, the discharge structure is described by parabola theory. If it is comparative to the generation of cation (ionization), the discharge is described by ellipse theory. Furthermore, if this loss rate is larger than the generation rate, the self-coagulation behavior happens and the coagulated structure is then formed. More of interest is that the coagulated structure, such as a semi-circle in Ar/SF\({}_{6}\) plasma, perhaps collapses at the expelling interaction that is caused by the [PERSON]'s force. The phenomenon of plasma coagulation discovered herein helps correlate again the gaseous discharging plasma in the laboratory and astrophysics plasma in the universe, in addition to the double layer that is used to accelerate the cosmic particle, and meanwhile, it appears in the expanded ICP source [18; 19] and shock (by means of multifluid model and transport theory) [20; 21].