Gross particle confinement characteristics by the boundary plasma in the JFT-2 Tokamak

Abstract.I short revie\\. of some features of the edge plasma in limiter tokamaks is given. The limits of thr simple 1-1) SOL model and the relation betw-een the core plasma arc discussed. MARFE phenomcnir and detached plasma are closely connected with the particle and energy balance of the SOL. Their occurrence is bused on the relation of plasma parameters of the edge plasma to those of the core. Important problems of plasma wall interactions are the detection of the irnpurity sources and sinks and the study of the impurity transport and shielding. The non-uniform character of plasma wall interactions and their dependence on the discharge performance still renders difficult any t hc oreticnl forecast of impurity distribution and transport and calls for better diagnost ic.9. Irit rodtietionThe torui(la1 tokaniak scheme proved to be most successful to produce high temperature plasmas of hydrogen isotopes reaching conditions close to the ignition of controlled thermonuclear reactions. For purposes of thermal insulation and stabilization of the plasma (plasma confinement) strong magnetic fields are used, which in the case of a tokamak represent a superposition of an externally produced toroidal field and the magnetic field of the discharge current. Additional fields are applied for stabilization and positioning of the discharge colnmn. This field configuration leads to a pronounced anisotropy of transport processes parallel and perpendicular to the resulting magnetic field. Solid limiters or magnetic divertors are used to control the plasma wall contact as well as the lieat. antl pa.rticle r e m o d .The bounclary between the plasnia. column and the edge plasma is determined by the edge of the limiter or the magnetic separatrix. Radially inside t.he boundary the magnetic surfaces are clusecl, radially outside they intersect the solid surface of the limiter or they are carried away from the niain plasiiia onto the t.arget plates of the tlkertor. In the following only the limiter case is considered. Obviously in t,hc so defined boundary or scrape-off layer (SOL) there is a large parallel loss of particles antl energy to the limiters. The length of the field lines (known as the connection length L ) connecting via the plasnia the surfaces of liniiters, probes and other inner structures of the tolamak play an important rule in determining the plasma conditions. It is mainly this contact of the plasma 1vit.h the limiter or the wall which produces the unir-anted impurities. Incompletely stripped impurity ions niay radiate enough energy to degrade the energy confinement. l ) Invited paper given a t the VIII. ESCAJIPlG, Greifswald, GDR, August 1986.

Section: The Simple Solmentioning

confidence: 99%

Properties of the Tokamak Edge Plasma

Wolff¹

1988

“…The cause of this radial motion can be drift or diffusion. If diffusion processes are assumed a diffusion coefficient of about 7 . lo3 cmZ/s is obtained for the SOL-plasma in the investigated discharges which is close to the Bohm value (6 103 cm2/s).…”

Section: P R O P E R T I E S Of E F F L U X E S F R O M T H E Core Plmentioning

confidence: 99%

Collector Probe Measurements of Impurity Fluxes Injected into the Plasma of the T‐10 Tokamak

Hildebrandt

Grote

Herrmann

et al. 1988

“…Using with a Langmuir probe (single probe) with the electrode diameter a pr = 1.3 mm and the electrode length L=3 mm with molybdenum the electron temperature T e and density profile were measured in the boundary plasma in JFT-2, where JFT-2 is the medium size tokamak with the major radius R = 0.9 m and minor radius a = 0.25 m with the toroidal magnetic filed B t = 1.7 T in JAERI (now JAEA) [1]. Here, the density n is evaluated by the ion saturation current I is = exp (-1/2)env s S, (v s = T e /m i ) is the ion sound velocity, m i is mass of ions and S is probe collecting area.…”

Section: Introductionmentioning

confidence: 99%

“…This equation can be expressed very approximately n=n 0 exp(-r/λ n ) when r/λ n >>1. The perpendicular diffusion coefficient D ⊥ estimated experimentally by the value of λ n as [1].…”

Section: Introductionmentioning

confidence: 99%

Electrostatic Probes for Studying Transport Properties in Tokamak Plasmas

Uehara

Sadamoto

Amemiya

et al. 2010

Electrostatic probes for measuring the boundary plasma in tokamaks are reviewed and presented. Transport properties in JFT-2, the ion temperature and the magnetic surface in JFT-2M and floating potential fluctuations during the strong additional heating in JT-60 are measured by several types of electrostatic probe the abovementioned purposes. The Langmuir probe including the double probe is applied to measure the spatial profile of boundary plasma in JFT-2. The ion sensitive probe, the rotating cylindrical double probe, the asymmetric double probe and the differential double probe are applied to measure the ion temperature and magnetic surface in JFT-2M. The reciprocating Langmuir probe applied to JFT-2M observes the potential and density fluctuations and a new type probe is proposed for the quick diagnostic of core hot plasmas as a development of this probe. The fluctuation observed in JT-60 is identified to be the ion cyclotron instability of the hot plasma caused by the strong anisotropy of the ion distribution function.