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Particle transport in the edge plasma of the IR-T1 tokamak in the presence of a resonant helical field (RHF) and biased limiter have been investigated and analyzed. For this purpose, a limiter biasing system was designed and constructed. The time evolution of the potential fluctuation, the electric field and the turbulent transport have been measured using two arrays of Langmuir probes in both the radial and poloidal directions. The experiments have been carried out in different regimes: as positive and negative limiter biasing, RHF and a combination of the two. The analyses have been done by the fast Fourier transport method. The results show that radial turbulent transport decreases by about 60% after applying positive biasing while it increases by about 40% after negative biasing. The effect of positive biasing on the poloidal turbulent transport displays an increase of about 55%, while negative biasing decreases the poloidal turbulent transport by about 30%. Consequently, confinement is improved and plasma density rises significantly due to applying positive biasing in IR-T1. But the results are inversed when negative biasing is applied. Also, in this work, the results of an applied RHF (with mode L = 3) are compared with biasing results and discussed.

The high-energy current of runaway electrons during a major disruption in tokamak reactors can cause serious damage to the first wall of the reactor and reduce its lifetime. Therefore, it is important to find methods for decreasing the generation of runaway electrons and their energy. Tokamak limiter biasing is one of the methods for controlling the radial electric field and can induce the transition to an improved confinement state. In this paper, the generation of runaway electrons and the energy they can obtain is investigated theoretically. Moreover, in order to apply radial biasing, emissive limiter biasing is utilized. This biasing limiter can apply ?380?V in the cold and hot (emissive) states to the plasma and can result in an increase of negative bias current in the hot state. In fact, in this experiment, the researchers try to decrease the generation of runaway electrons and their energy by using emissive limiter biasing inserted in the IR-T1 tokamak. The mean energy of these electrons was obtained by hard x-ray spectroscopy.

Tokamak limiter biasing is one of the methods for controlling the radial electric field and can induce a transition to an improved confinement state. Moreover, the mean energy of runaway electrons and therefore emitted hard x-rays depends on fluctuations of plasma current and loop voltage, which can be controlled using limiter biasing. In this paper, we studied the effects of a biased limiter on loop voltage and hard x-rays. Hard x-ray emissions are produced by the collision of runaway electrons with limiters. Experiments were done by discharges in the range of a positive 180–380 V biased limiter.

We report here the first results of our movable electrode biasing experiments performed in the IR-T1 tokamak. For this study, a movable electrode biasing system was designed, constructed and installed on the IR-T1 tokamak. A positive voltage was applied to an electrode inserted in the tokamak limiter. The plasma current, poloidal and radial components of the magnetic fields, loop voltage and diamagnetic flux in the absence and presence of the biased electrode were measured. Results of the improvement done to plasma equilibrium behaviour are compared and discussed in this paper.

In this contribution we have measured the horizontal displacement of the plasma column center using two analytical solutions of the Grad–Shafranov equation in the IR-T1 tokamak. In the first technique, four magnetic pickup coils were designed, constructed and installed on the outer surface of the IR-T1 tokamak chamber and then plasma displacement was determined from them. To compare the results obtained using this method, the second analytical solution of the Grad–Shafranov equation based on expansion of free functions as quadratic in the flux function is also experimented on in the IR-T1. The results of the two methods were compared and were found to be in good agreement with each other.

An attempt is made to investigate the time evolution of the energy confinement time, internal inductance and effective edge safety factor on IR-T1 tokamak. For this purpose, four magnetic pickup coils were designed, constructed and installed on the outer surface of the IR-T1 and then the Shafranov parameter (asymmetry factor) was obtained from them. On the other hand, also a diamagnetic loop was designed and installed on IR-T1 and poloidal beta was determined from it. Therefore, the internal inductance and effective edge safety factor were measured. Also, the time evolution of the energy confinement time was measured using the diamagnetic loop. Experimental results on IR-T1 show that the maximum energy confinement time (which corresponds to minimum collisions, minimum microinstabilities and minimum transport) is at low values of the effective edge safety factor (2.5

In this paper, we measured plasma horizontal displacement using two experimental methods in the IR-T1 tokamak. First, two poloidal flux loops were designed and installed on the outer surface of the IR-T1 tokamak and were used to measure the Shafranov shift. Also, modified Rogowski and saddle sine coils based on the multipole moment method were designed, constructed and used. The results from these two methods are compared and are found to be in good agreement.