1. Summary Session October 10, 2008 The Joint Meeting of 4th IAEA Technical Meeting on Spherical Tori and 14th International Workshop on Spherical Torus

2. In order to approach Fusion Nuclear Science (M. Peng) What is required from physics? Plasma-Wall,Steady State,Start-up Plasma-Wall interaction (more critical than in conventional tokamaks) * In/Out Asymmetry of Divertor * Closed Divertor with Cryopumps * Super Extended Divertor Compatible with Stabilizing Shell? * Use of Litium to broaden T e profiles The Joint Meeting of 4th IAEA Technical Meeting on Spherical Tori and 14th International Workshop on Spherical Torus

3. Plasma-Wall interaction (more critical than in conventional tokamaks) * Diagnostics of edge plasma (TS at edge) * Problems with internal electrodes/ Coaxial Helicity Injectors, physics of Open Field Lines * Control of ELMs (or L-mode?) The Joint Meeting of 4th IAEA Technical Meeting on Spherical Tori and 14th International Workshop on Spherical Torus

4. In order to approach Fusion Nuclear Science (M. Peng) Steady state * Control of q and j easied by low A? less critical than in conventional tokamaks? Provocative question: After many years of operational experience do experimentalist still maintain that self- organization in ST is higher and helps with respect to conventional tokamaks? The Joint Meeting of 4th IAEA Technical Meeting on Spherical Tori and 14th International Workshop on Spherical Torus

5. Steady state *Current density measurements more difficult than in conventional tokamaks? *Current Drive: NBI, EBW, LHCD, … more difficult than in conventional tokamaks * Bootstrap Current, even more relevant than in conventional tokamaks, but still to be demonstrated with same success as in conventional tokamak (JT-60U) The Joint Meeting of 4th IAEA Technical Meeting on Spherical Tori and 14th International Workshop on Spherical Torus

6. Steady state *Avoidance of Sawteeth, or even q min >2? more critical than in conventional tokamaks? *Avoidance of Disruptions less critical than in conventional tokamaks? Continuous Fueling Supersonic Gas Injection Continuous Pellet Injection Compact Toroid Injection (in NSTX?) The Joint Meeting of 4th IAEA Technical Meeting on Spherical Tori and 14th International Workshop on Spherical Torus

7. Steady state * Control of ELMs (again) *Higher BT Single/Multiple return of toroidal magnet Cryogenic/Superconducting toroidal magnet Provocative question (not limited to STs): The present progress of technology is such that a continuous (>10 6 s) high power NBI and/or RF system is realistic? The Joint Meeting of 4th IAEA Technical Meeting on Spherical Tori and 14th International Workshop on Spherical Torus

8. In order to approach Fusion Nuclear Science (M. Peng) Startup Inductive Methods * Small retractable solenoid (Seems most feasible option) * Ferromagnetic core (Further Experiments?) * Induction by external coils (M/C : internal coils, DNM: UTST, MASTU?) Effect of Stabilizing Shell? The Joint Meeting of 4th IAEA Technical Meeting on Spherical Tori and 14th International Workshop on Spherical Torus

9. Startup Noninductive Methods RF startup Can the very encouraging results of small experiments be brought to full fruition on larger STs? The Joint Meeting of 4th IAEA Technical Meeting on Spherical Tori and 14th International Workshop on Spherical Torus

10. Startup Noninductive Methods Helicity Injection Problems with Internal Electrodes/Injectors on a Component Test Facility? Current Ramp-up Still to be fully demonstrated (MAST, NSTX) Requires hot and dense initial target plasma to couple NBI The Joint Meeting of 4th IAEA Technical Meeting on Spherical Tori and 14th International Workshop on Spherical Torus

11. General provocative question: It is not very clear at this moment if ST are an alternative line or a support line with respect to conventional tokamaks (ITER/DEMO) In my opinion STs should re-establish stronger connections with Compact Torus Experiments (in present TM/ST Workshop only few papers: FRC and PROTO-SPHERA deal with non- canonical ST configurations) The Joint Meeting of 4th IAEA Technical Meeting on Spherical Tori and 14th International Workshop on Spherical Torus