1. 1 Blobs in the divertor region R. J. Maqueda (Nova Photonics) Although some understanding is emerging on the generation and evolution of blobs from the edge pedestal near the midplane and away from the X-point regions (Myra, Lodestar Inc., et al.), very little is known about the evolution of these filaments near the X-point. Physics Meeting Oct. 8, 2007 PPPL J.R. Myra et al., PoP 13, 092509 (2006) Blob size Collisionality

2. 2 X-point geometry effects Flux tube stretching near X-point may cause the blob (turbulence) scale length to be less than ion gyro-radius (R. Cohen, D. Ryutov, et al.): - “x-point disconnection” - possibility of inducing turbulence below the X-point, without degrading midplane (R. Cohen, NF 37, p. 621, 1997). Is intermittency (i.e. blobs) seen in the divertor region? What is the relation to midplane turbulence/blobs?

3. 3 Midplane blobs -Characteristic size: 3-4 cm -Move outward and predominantly down (ion grad-B drift) Midplane GPI Deuterium puff D  filter 24 cm S. Zweben, NF 44, p. 134, 2004 H-mode 900 kA, 4.5 kG ~DN 6 MW NBI (very) high  29 MB separatrix antenna limiter shadow

4. 4 Mapping to divertor target plates Ro=149.5 cm, Zo=8.8 cmRo=152.5 cm, Zo=8.85 cm Some  t -Circular flux tube (3 cm diam.) mapped to bottom divertor target plates. -As midplane blob moves out, footprint “creeps” toroidally. -As midplane blob moves downward, footprint “rotates” toroidally (CCW). Midplane GPI

5. 5 Bottom divertor footprint Top view of bottom divertor LiI filter Bay E -Movement of footprint agrees with that expected for midplane blobs. 22 MB

6. 6 Good correlation between midplane intermittency and divertor intermittency Image intensity (a.u.) Time (s) 124819 -Correlation coefficient ~0.76. -Extended region of good correlation. -Location of best correlation close to where expected. Midplane GPI Lower divertor Correlation to midplane

7. 7 Mapping to divertor region, R-Z plane Circular flux tubeElliptical flux tube Ro=147.1 cm, Zo=18.0 cm Ro=148.6 cm, Zo=18.0 cm Some  t -As midplane blob moves out, cross-section in divertor region moves along its inclination, “outward in minor radius”. Lower divertor tangential view

8. 8 Intermittency in the bottom divertor (tangential view) -Movement intermittent structures agrees with that expected from midplane blobs. -Dimension of “divertor blobs” consistent with elliptical midplane blob. D  filter (no puff) H-mode 900 kA, 4.5 kG ~DN 4 MW NBI high  11 MB

9. 9 Summary Intermittency (blobs) seen in lower divertor. Evolution consistent with midplane observations. Poloidal cross-section “shorter” than predicted by circular midplane blobs. Current measurements do not extend to field lines affected by “flux tube stretching”. For FY08 run: - gas puff located tangentially on field of view. - top imaging with extended coverage away from Bay E. 5.6 MB

10. 10 Ro=152.5 cm Zo=8.85 cm