On HL-2A,two different injections(supersonic molecular beam injection(SMBI)and pellet injection(PI)) are used to mitigate edge localized mode(ELM)-filament convective transport.The changes of their characteristics are studied in this paper.A high spatiotemporal resolution probe shows there are many similar phenomena,and the filament density amplitude and radial velocity are both suppressed.Our statistical results indicate that:the velocity suppression comes from the decrease of filament density and temperature;the transient particle and heat fluxes drop strongly;and long-range correlation along a magnetic flux surface also decreases,when the electron-ion collisionality increases significantly,which may have a role on the filament parallel current during ELM mitigation.
SMBI (supersonic molecular beam injection), as an effective fueling method forfusion plasmas, has been widely used on the HL-2A tokamak and other fusion devices. Twodifferent types of SMBI system are now installed on HL-2A. One is an electromagnetic valveinjector on the low field side (LFS), and the other is a pneumatic valve injector on the high fieldside (HFS). A new electron density record n_e= 4.7×10^(19)m^(-3), which exceeds both the Greenwalddensity limit and the maximum density obtained by gas puffing (GP), was obtained on HL-2Awith single-null-divertor operation. The HFS injection system is still under test, however, itsoutstanding fueling characteristics have already been observed, e.g. it has higher fueling efficiencycompared to the LFS system. This excellent feature is still preserved during the process of ECRH.
In this paper, we describe the behavior of impurity transport in the HL-2A electron cyclotron resonance heating(ECRH) L-mode plasma. The neon as a trace impurity is injected by the supersonic molecular beam injection(SMBI) technique, which is used for the first time to study the impurity transport in HL-2A. The progression of neon ions is monitored by the soft X-ray camera and bolometer arrays with good temporal and spatial resolutions. The convection and diffusion process of the neon ions are investigated with the one-dimensional impurity transport code STRAHL. The results show that the diffusion coefficient D of neon ions is a factor of four larger than the neoclassical value in the central region. The value of D is larger in the outer region of the plasma(ρ > 0.6) than in the central region of the plasma(ρ < 0.6). The convective velocity directs inwards with a value of ~ 1.0 m/s in the Ohmic discharge, but it reverses to direct outwards with a value of ~ 8.0 m/s in the outer region of the plasma when ECRH is applied. The result indicates that the impurity transport is strongly enhanced with ECRH.
Perturbative experiments on electron heat transport have been successfully conducted on the HL-2A tokamak.The pulse propagation of the electron temperature is induced by the supersonic molecular beam injection (SMBI),which has characteristics of good localization and deep deposition.A model based on the electron heat transport in cylindrical geometry has been applied to reconstruct the measured amplitude and phase profiles of the electron temperature perturbation.The results show that the heat transport is significantly reduced near the pedestal region of the H-mode plasma.In the "profile stiffness/resilience" region,similar heat diffusivities have been observed in L-mode and H-mode plasmas,which verifies the gradient-driven transport physics in tokamaks.
