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Toroidal asymmetry of impurity seeding

Toroidal asymmetry of impurity seeding. 12. 6. 18. in support of ITER divertor gas injection requirements. Proposer: R. A. Pitts (IO), MIT contact: B. LaBombard. Motivation

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Toroidal asymmetry of impurity seeding

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  1. Toroidal asymmetry of impurity seeding 12 6 18 in support of ITER divertor gas injection requirements Proposer: R. A. Pitts (IO), MIT contact: B. LaBombard Motivation ITER currently foresees gas injection under the divertor cassettes for detachment control via impurity seeding (a supplement to C radiation for CFC target and mandatory for W target). Each injection point equipped with independent gas valve box (GVB) allowing H,D,T and impurity (He, N2, Ne, Ar) with mixtures possible and max. time response ~few 100 ms to 63% of max. throughpout

  2. Toroidal asymmetry of impurity seeding 9 12 6 15 3 18 in support of ITER divertor gas injection requirements Proposer: R. A. Pitts (IO), MIT contact: B. LaBombard Motivation A proposal has recently been made to add 3 extra toroidal injection points (ITER Change Control Board 1-21, 4/3/2009)  improve toroidal symmetry of injection, add redundancy for divertor re-attachment protection. Proposal uses spare GVBs freed up as a result of earlier changes to main chamber injection system  (almost) cost neutral Proposal also suggested in-out divertor injection capability (not addressed in this idea) Proposal provisionally rejected CCB1 requested more quantitative evidence that enhanced injection capability justified  request made by the IO for experimental investigation

  3. Toroidal asymmetry of impurity seeding in support of ITER divertor gas injection requirements Proposer: R. A. Pitts (IO), MIT contact: B. LaBombard Experiment B. LaBombard has offered to bring the C-Mod divertor floor puffers back into service (thank you!)  5, equally spaced toroidal locations into the PFR (like ITER – currently has 3) Time response ~70 ms  quite close to the ITER divertor GIS All puff locations fed by the same plenum  only one gas each time Pre-calibrate drive pressures at each injection location to give same flow rate In standard lower null: Test recycling and non recycling gases (N2, Ne) to see asymmetry differences Begin with single injection location closest to divertor bolometry and in successive shots activate increasingly distant capilliaries to check toroidal decay length Test in L-mode and high power H-mode In upper null: Reference test cases (e.g. 1, 3, 5 locations) with lower gas puffs (to simulate ITER gas injection from plasma top with divertor cryopumping)  what differences in divertor plasma dynamics compared to local injection? Requires field inversion.

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