R. McAdams
A high pumping speed is required in neutral beam injectors to minimise re-ionisation of the neutral beams. The neutral beam injectors on MAST use titanium sublimation pumps. These pumps do not have a constant pumping speed; their pumping speed depends on the gettering surface history and on both the integrated and applied gas load. In this paper we…
Preprint PublishedR. Mcadams
In the development of magnetically confined fusion as an economically sustainable power source, International Tokamak Experimental Reactor (ITER) is currently under construction. Beyond ITER is the demonstration fusion reactor (DEMO) programme in which the physics and engineering aspects of a future fusion power plant will be demonstrated. DEMO wil…
PublishedMarthe Bacal Roy Mcadams Elizabeth Surrey
This paper discusses the possibility that there is an enhancement of volume production due to gettering of atomic hydrogen by the caesium deposited on the walls, which reduces the negative ion destruction by associative and non-associative detachment. Such an enhancement would take place for all plasma grid bias voltages. Furthermore at plasma grid…
PublishedRachel Mcadams H R Wilson I T Chapman
A model system of equations has been derived to describe a toroidally rotating tokamak plasma, unstable to Resistive Wall Modes (RWMs) and metastable to Neoclassical Tearing Modes (NTMs), using a linear RWM model and a nonlinear NTM model. If no wall is present, the NTM growth shows the typical threshold/saturation island widths, whereas a linearly…
PublishedD. B. King A. J. T. Holmes R. Mcadams E. Surrey
A one dimensional model of the sheath between the plasma and the wall in a negative ion source has been expanded to include the effects of a variable wall surface work function and fast positive ion species. The plasma consists of positive ions, electrons and negative ions. The model also includes the emission of negative ions from the wall into th…
PublishedR. Mcadams D. B. King A. J. T. Holmes E. Surrey
In fusion negative ion sources, the negative ions are formed on the caesiated plasma grid predominantly by hydrogen atoms from the plasma. The space charge of the negative ions leaving the wall is not fully compensated by incoming positive ions and at high enough emission a virtual cathode is formed. This virtual cathode limits the flux of negative…
PublishedM. Bacal R. Mcadams B. Lepetit
The knowledge of the mean free path (mfp) of the negative ions is important for many purposes, e.g. evaluating the distance from which the ions can be extracted, or understanding the significance of experimental results. We will present the mfp for similar conditions in volume and caesium seeded sources. It appears that the mfp is longer in the cae…
Published