Some observations on disruptions in cy 2007 run
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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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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

Two Pearson CTs on buss work to the “McBride” switch…current from inner to outer vessel


Not All Shots “Disrupt” (I)

Typical IP Ramp Rate: 107 A/s

Non-Disruptive Shots Well Centered At Start of Ramp-Down


Not All Shots “Disrupt” (II)

Typical IP Ramp Rate: 107 A/s

Halo Currents Reduced for Slower Ramping Shots


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


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


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.


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.


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


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


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>


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.


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


Many Other Items Systematically Vary Among XPs


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