531 



4. SUGGESTED AREAS FOR INCREASED COLLABORATION 



Key areas in tokamak physics and devices mostly relevant to each of 

 them are listed in Table 1. Those areas in which the Subgroup 

 believes that increased or new cooperation would be particularly 

 appropriate are: 



4.1 General performances. 



- Pellet injection 



Recent results have shown substantial improvements in the energy 

 confinement times in both ohmic and neutral beam heated regimes, 

 when the plasma is refuelled from the inside by pellet injection. 

 Large machines with long pulse operation require both pellet 

 injection velocity higher than what is available and a high 

 repetition rate sustained for long periods. Such a specific 

 technical development will require sizeable efforts and could lead 

 quite naturally to transfer of hardware between laboratories. 



- Impurity control, exhaust, refuelling 



This important issue will be well covered once the implementing 

 agreement on ASDEX and ASDEX-Upgrade will have been concluded, 

 complementing the TEXTOR agreement already in action. Within the 

 latter, the realization of the advanced pump limiter ALT II is 

 recommended. 



4.2 Additional heating. 



- Neutral beam heating 



Despite progress in RF heating, neutral beam injection remains the 

 reference method for plasma heating in present devices. The reduced 

 efficiency of neutral injection at high particle energy (which is 

 necessary for large devices) can be corrected by two methods: 



a) energy recovery of the non-neutralized beam (in the intermediate 

 energy range) and 



b) negative ion production and acceleration (in the high energy 

 range). 



For practical use, these two methods need to be developed at the 

 megawatt level. This represents a large effort which could 

 profitably be shared between specialized development teams. 



52 



