The importance of plasma diagnostics at semiconductor equipment manufacturers has increased steadily over the past decade. The design and procurement of advanced etching tools now require a full host of plasma diagnostics and modeling capability. Examples of these activities at a semiconductor equipment manufacturer will be given, with specifics of significant and useful results. Examples include the development and optimization of an inductive plasma source, trend analysis and hardware effects on ion energy distributions, and mass spectrometry influences on process development. Discussion will focus on plasma diagnostics for in-house development and proliferation in an environment with strong financial justification requirements.
A compact toroid (CT) penetrating into a tokamak discharge is modelled as a conducting solid sphere with an intrinsic magnetic moment. Equations of CT motion in tokamak discharges are derived and used to calculate the trajectory of a CT with parameters pertinent for penetrating the ITER tokamak. The advantage of tangential CT injection and the optimal direction of the initial magnetic moment are discussed.
The use of Langmuir probes for measuring plasma density is subject to uncertainty because the theories commonly used to interpret the data give widely differing results. This is especially troublesome in partially ionized plasmas used, for instance, in the semiconductor industry, since no existing theory adequately treats the case when there are a few collisions between ions and neutral atoms. In this work, plasma densities measured by microwave interferometry and plasma-oscillation probes are compared with those from probe data analyzed with Langmuir's orbital motion limited (OML) theory, the Allen–Boyd–Reynolds (ABR) theory and the Bernstein–Rabinowitz–Laframboise (BRL) theory. It is found that ABR underestimates and BRL overestimates the density, the problems being the neglect of ion orbiting in ABR and the effect of ion-neutral collisions in BRL. The best theory is either OML or the geometric mean between the ABR and BRL results. For thicker probes, other methods are suggested.
Complete one cycle and 1.5 cycle ac operations are performed in the STOR-M tokamak with the plasma current of ∼20 kA using newly developed feedback control and Ohmic heating circuits. Bias voltage adjustment is installed in the plasma position circuit to optimize the plasma position in the second negative plasma current phase for multicycle ac operation. The key to successful, reproducible multicycle ac tokamak operations on STOR-M is to control both the total vertical field by the feedback control system and the plasma position by application of the bias voltage.
Abstract A sequence of magnetized target fusion devices built by General Fusion has compressed magnetically confined deuterium plasmas inside imploding aluminum liners. Here we describe the best-performing compression experiment, PCS-16, which was the fifth of the most recent experiments that compressed a spherical tokamak plasma configuration. In PCS-16, the plasma remained axisymmetric with δBpol/Bpol<20% to a high radial compression factor ( CR>8 ) with significant poloidal flux conservation (77% up to CR= 1.7, and ≈30% up to CR=8.65 ) and a total compression time of 167 μs . Magnetic energy of the plasma increased from 0.96 kJ poloidal and 17 kJ toroidal to a peak of 1.14 kJ poloidal and 29.9 kJ toroidal during the compression, while the thermal energy was in the range of 350 ± 25 J. Plasma equilibrium was a low- β state with βtor≈4% and βpol≈15% . Ingress of impurities from the lithium-coated aluminum wall was not the dominant effect. Neutron yield from D-D fusion increased significantly during compression. Thermodynamics during the early phase of compression ( CR<1.7 ) were consistent with increasing Ohmic heating of the electrons due to a geometric increase in the current density at near-constant resistivity, and with increasing ion cooling that approximately matched ion compression heating power. Ion cooling by electrons was significant because the electrons were much cooler than the ions ( Te=200eV,Ti=600eV ). Magnetohydrodynamic simulations were used to model the emergence of instabilities that increase electron thermal transport in the final phase of compression. Conditions for ideal stability were actively maintained during compression through a current ramp applied to the central shaft and, after this current ramp reached its peak two-thirds of the way through compression, we measured a transition in plasma behavior across multiple diagnostics.
