This paper presents a summary of plasma-material interactions which influence the operation of TFTR with high current (4 2 MA), ohmically heated and high power (~ 10 MW>, n=mtral-beam-heated plasmas. The conditioning procedures which are applied routinely to the first-wall hardware are reviewed. Fueling characteristics during gas, pellet, and neutral beam fueling are described. Recycling near unity are observed for roost gas-fueled discharges. Gas-fueled discharges after helium discharge conditioning of the toroidal bumper limiter and discharges fueled by neutral beams and pellets show R < 1. In the vicinity of the gas-fueled density limit (at n = 5-6 x 10 m ) values of Z-gc are < 1.5. Increases in Z^pf of < 1 have been observed with neutral beam heating of 10 MW. The primary low-Z impurity is carbon with concentrations decreasing from ~ 10% to < 1% with increasing n fi . Oxygen densities tend to increase with n , and at the ohraic plasma density limit oxygen and carbon concentrations are comparable. is the primary and that the wall is a significant of

The PDX divertor configuration has recently been converted from an open to a closed geometry to inhibit the return of neutral gas from the divertor region to the main chamber. Since then, operation in a regime with high energy confinement in neutral beam heated discharges (ASDEX H-mode) has been routine over a wide range of operating conditions. These H-mode discharges are characterized by a sudden drop in divertor density and Hα emission and a spontaneous rise in main chamber plasma density during neutral beam injection. The confinement time is found to scale nearly linearly with plasma current, but can be degraded due either to the presence of edge instabilities or heavy gas puffing. Detailed Thomson scattering temperature profiles show high values of Tc near the plasma edge (∼ 450 eV) with sharp radial gradients (∼ 400 eV/cm) near the separatrix. Density profiles are broad and also exhibit steep gradients close to the separatrix.

The right-hand side of Eq. ( 16) should be in- creased by a factor of 4.In Fq. (17) replace mH by mH and add the rela- tion mH'=mH'+ &~~'.Also, mH should be replaced by m" in Eq. ( 18), the inequality following it in the text, and Eq. ( 19).The phrase" ... three degenerate states ... " preceding Eq. ( 17) should read" ... one charged state ... ,

Results are presented from studies of intensely beam heated plasmas in the PDX and PLT tokamaks. PDX has established that the ion heating quality factor n i = ne δT i /P abs cm -3 keV/MW, where P abs refers to absorbed beam power, is approximately the same for the near perpendicular injection of PDX as for the tangential injection geometry of PLT. The comparison however must be made at similar plasma currents, as n i is found to depend on I p . Electron heating on PDX and a “clean” PLT is quite similar at ~ 0.5 eV/kW for medium densities of ~ 3–4 · 10 13 cm -3 and moderate beam power. We have achieved a poloidal β θ ≈ 1.7 on PDX giving β θ ≈ 0.5 R/a at q(a) = 7.5. Initial results in low-q discharges appear promising, giving β T = 1.3–1.4% with 1.9 MW of absorbed beam power.

Plasma heating by near-perpendicular injection of up to 7.2 MW of neutral-beam power has been studied in the PDX tokamak. Collisionless plasmas with centrla ion temperatures up to 6 keV have been obtained. The total plasma energy, which is dominated by contributions from beam and thermal ions, rises linearly with increasing beam power. The ion heating efficiency in PDX is comparable to the measured in the Princeton Large Torus with tangential injection.

Neutral beam injection experiments on PLT have provided definitive information on ion energy confinement in highly collisionless plasmas. We find that ion thermal conduction is consistent, within a factor of approx. 3, with neoclassical theory, and that anomalous thermal convection of ion energy is a factor of 2-3 less than would be calculated from the INTOR D/sub e/ with a convection loss term of the form 5/2nkTv/sub r/. From our experiments with a shunted TF coil we have found that a single shallow ripple well of 2.5% has a neglible effect on ion energy confinement, even at the lowest collisionality obtainable on PLT. Scrutiny of the analytic theories of ripple induced transport motivated by these experiments, suggests that more theoretical (and perhaps numerical) work is needed in this area.

In the four years of operation of the PLT tokamak (1976–1979), plasma parameters and machine operating conditions have been importantly affected by changes in the choice of limiter material and by the mode of vacuum vessel conditioning. Tungsten, stainless steel, and graphite limiters have been used. The fractional power lost by radiation and the source distribution of the radiation vary strongly with limiter material, wall treatment, and gas programming. With tungsten limiters, radiation from partially ionized tungsten atoms can strongly limit the temperature in the center of the plasma; with graphite limiters, radiation is primarily from carbon and oxygen in the outer cold region and not so much from the center, since in the hot core these atoms are totally ionized. With both tungsten and stainless steel limiters intermediate states exist which have rather uniform radiation source distributions; the characteristics of these distributions are affected by gas programming and by wall conditioning.

PLT discharges are categorized in terms of energy balance into three types: radiation dominated (RD); transport dominated (TD), and an intermediate type (TR). Control of plasma edge conditions is essential for the formation of these types. Measurements and calculations show the relative importance of radiation, transport, and electron-ion coupling in different regions of the discharge. Ion heating for neutral beam injection is found to be effective in all types. Electron heating by neutral beam injection is only consistently obtained for TD discharges.

MEASUREMENTS of the neutron spectra from the PLT tokamak plasma are reported here which provide information on the centre-of-mass velocity of the reacting deuteron pairs. The observation in PLT of no significant directed velocity yields additional evidence that the neuterons are produced by a thermonuclear process. Previous spectral measurements on other fusion devices have often determined that the neutron emission was non-thermonuclear and resulted from a small ‘tail’ component of energetic ions1–3. The neutron spectra indicated a directed velocity of the reacting deuterons and thus non-thermonuclear neutron emission if the injected neutral beam ions were deuterium. In this condition, the neutron spectra were consistent with the expected beam-induced d(d,n) 3He reactions. However, if the heating beam used hydrogen, then the neutron spectra are consistent with a thermonuclear neutron emission resulting from the beam heating of the bulk deuterons in the plasma.

Experimental results from high-power neutral-beam-injection experiments on the Princeton Large Torus tokamak are reported. At the highest beam powers (2.4 MW) and lowest plasma densities [ne(0)=5×1013 cm−3], ion temperatures of 6.5 keV are achieved. The ion collisionality νi∗ drops below 0.1 over much of the radial profile. Electron heating of ΔTeTe≈50% has also been observed, consistent with the gross energy-confinement time of the Ohmically heated plasma, but indicative of enhanced electron-energy confinement in the core of the plasma.Received 1 March 1979DOI:https://doi.org/10.1103/PhysRevLett.43.270©1979 American Physical Society

At the 1968 conference on controlled fusion in Novosibirsk a group from Kurchatov, USSR, led by L. A. Artsimovitch, presented convincing evidence that one conceptually simple method for confining plasmas in a ring showed great promise for future developments. The name for their early machine, the tokamak, has now become the generic name for all such devices. The Russian successes led to a rapid expansion of research with tokamaks, so that while in 1968 there were only nine of them, all in the USSR, there are now more than a hundred; they are in the USSR, the US, Europe, Japan, and elsewhere.