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Some Observations on Disruptions in CY 2007 Run

Some Observations on Disruptions in CY 2007 Run. Stefan Gerhardt. 1720 Discharges From CY07 In Database. Radiated Power: Bolometers Plasma Current: Rogowski Equilibrium: EFIT01. Vertical Motion Flux Difference (EFIT usually bad during quench). Halo Currents

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Some Observations on Disruptions in CY 2007 Run

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  1. Some Observations on Disruptions in CY 2007 Run Stefan Gerhardt

  2. 1720 Discharges From CY07 In Database Radiated Power: Bolometers Plasma Current: Rogowski Equilibrium: EFIT01 Vertical Motion Flux Difference (EFIT usually bad during quench) Halo Currents Two Pearson CTs on buss work to the “McBride” switch…current from inner to outer vessel

  3. Not All Shots “Disrupt” (I) Typical IP Ramp Rate: 107 A/s Non-Disruptive Shots Well Centered At Start of Ramp-Down

  4. Not All Shots “Disrupt” (II) Typical IP Ramp Rate: 107 A/s Halo Currents Reduced for Slower Ramping Shots

  5. Fast Current Quenches (“Disruptions”) Scattered Throughout Campaign or XPs • Previous Data Includes quench on Ramp-Up, or at very low current. • Restrict Analysis to: • Current at Quench > 600 kA • Time of Quench > 150 msec # With Quench Rate >2.5x107 Disruptivity: # of Shots in That XP

  6. XPs have Vastly Different “Disruptivity” 723: Mom. Conf. 711: High q brkdwn. 724: NICD @ high q 704: Ext. Perturb. 727: Stab. Lim. High IN 702: RFA Optimization 728: RWM Stab. 729: n=3/n=1 708: Div. Ht. Flx. Red. 742: SGI 738: Lithium Powder 737: Ion Power Balance 746: ELM Characterization 706: Beta Sup. Alfven Casc. 741: BAAE 744: BEAP

  7. Radiated Power Varies Greatly Among Within and Among XPs Max Prad=Maximum value of Total Radiated Power. Prad at Max(Wtherm)= Total Radiated Power at time of maximum stored energy.

  8. High Radiated Power in Many Cases Before LITER • LITER XP 719 Began on April 20th • First Shot ~123469 Max Prad=Maximum value of Total Radiated Power. Prad at Max(Wtherm)= Total Radiated Power at time of maximum stored energy.

  9. XPs With Highest Radiated Powers 729: n=1/n=3. 718: Li Pellets 737: Ion Power Balance 701: n=1 & 3 Error Fields 702: RFA Optimization 745: ELM Severity and Transport 707: MHD Induced Fast Ion redistribution

  10. Highest Disruptivity Does Not Lead to Highest Radiated Power max(Prad)=Maximum value of Total Radiated Power in a single shot <…>=Average over all shots in an XP

  11. Caveat: Thermal Quench Could More Relevant • Current quench (this presentation) is of concern due to forces (eddy currents, halo currents) • Thermal quench releases the plasma thermal stored energy in ~1msec…often after substantial thermal energy is more slowly lost. • Poorly diagnosed in NSTX…use Wtherm just before disruption. <Stored Energy Before Disruption> <Peak Stored Energy>

  12. Conclusions • Many disruptive XPs related to MHD studies, but not always. • XPs with highest Prad are not the most disruptive. • Additional thermal quench info would be more useful than current quench…Important for disruption studies…we need a fast IR camera.

  13. So If it isn’t Disruptions, what else? • Inner & Outer Gap? • Confinement (correlation with tau from efit)? • Consider only Discharge with >3.5 MW NBI at time of Max Stored Energy

  14. Many Other Items Systematically Vary Among XPs

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