Investigation of sawtooth heat-pulses arriving on the outer divertor target

1. Proposed by J.L. Terry, B. LaBombard, A. Hubbard, A. White, A. Dominquez Investigation of sawtooth heat-pulses arriving on the outer divertor target • Occasionally we observe small repetitive heat pulses on the outer target. They are well correlated with core sawtooth crashes and sawtooth heat pulses to the pedestal region. • So far these are most pronounced in H-mode plasmas with low-Z impurity seeding. Why is that ? Under what other circumstances does this occur? • Is the heat pulse on to the target consistent with main-plasma kinetic measurements (Te, ne) ? Background: C-Mod Ideas Forum: Jan. 10-12, 2011

2. Teo target surface temp. Investigation of sawtooth heat-pulses arriving on the outer divertor target Te at r= -3.5 cm IR signal from target strike pt. region This shot (and others on this day for which we also observed this) had N2 impurity seeding Te at r= -1.5 cm C-Mod Ideas Forum: Jan. 10-12, 2011

3. Plan: • Investigate whether or not this is seen on other tokamaks (literature search). • Quantify the heatflux on the target arriving in the the sawtooth heat pulse. Attempt to reconcile that value with edge Te & ne measurements. • Examine scaling with systematic variation in the amount of impurity seeding. • Examine the change in footprint shape across the heat pulse. • Examine with higher time resolution (2.6 ms -> 1 ms). Investigation of sawtooth heat-pulses arriving on the outer divertor target - #3 above will require ½ run, the rest can be done piggyback C-Mod Ideas Forum: Jan. 10-12, 2011