# Presentation: 652347

## Divertor Characteristics from Probe Measurements during NBI

**NSTX Results Review **
**26-28 July 2006****PPPL Princeton, NJ**** **

- C.E. Busha, R. Kaitab, P. Roneyb, R. Maingia, E.. Fredricksonb, S. Sabbaghc,
- V. Soukhanovskiid, J.G. Watkinse
*a**Oak Ridge National Laboratory, Oak Ridge, TN USA *
*b**Princeton Plasma Physics Laboratory, Princeton, NJ USA*
*c**Columbia University, NY USA*
*d**Lawrence Livermore National Laboratory, Livermore, CA USA*
*e**Sandia National Laboratories, Albuquerque, New Mexico, USA*

## Outline 

- Initial NSTX Langmuir Probe System is a coarse array
- Sample IV Characteristic data
- Langmuir Probe data obtained for vast majority of shots
- Especially the last 3 campaigns
- Data for many configurations
- Data  for many conditions
- Report Emphasizes a Beam Power Scan
- Also a series of Gas Puff experiments
- Isat, Te reported for a limited set of experiments
- Summary

- Phys of ST

- DPP APS 99

## Backup Slides

- END

- The EFIT equilibrium shows the location of the inner and outer strike-points on the divertor plates of NSTX .  In general the strike-points and measured probe positions are in good agreement.

- Outer Strike-point

- Inner
- Strike-point

- Lower
- Single-null
- Divertor

## Divertor Langmuir Probes

- 1

- 2

- 3

- 4

- 1  R(probe 1) = 1.02 m

- 2  R(probe 2) = 0.91 m

- 3  R(probe 3) = 0.80 m

- 4  R(probe 4) = 0.49 m

- Phys of ST

- DPP APS 99

## Fit to IV Characteristic for Flush Probe

**Fit to IV Characteristic for Flush Probe**

- Sweep voltage ± 50 volts
- Only points V < VLimit included in fit.
- Here VLimit = +15 V
- The relatively flat upper part of curve due to 10 volt limit on digitizer *not *to electron current saturation.
- * Te fit corrected for nonsaturation
- of ion current.
- Te = 6.72 eV
- (12 eV uncorrected).

- Fit to IV data

- Solid lines, data for 2 different sweeps

- Isat(ion)

- Probe sweep voltage

- I

- V

- 0

- I (A)

- IV Characteristic

- 0.04

- -0.04

- 0.08

- 0.12

- -40

- 0

- 40

- V (Volts)

- 14

- Phys of ST

- DPP APS 99

## Outer Divertor Probe Te vs Time, Pb = 4 MW

- Shot  112498
- Pb = 4 MW
- Rprobe = 0.91 m

- Phys of ST

- DPP APS 99

## Heat flux profile becomes more peaked with increasing NBI power

- 0.306 sec

*R. Maingi*

- Peak in Isat occurs near peak heat flux
- In general peak Isat is independent of Pb, heating power

- Isat Probe 3

- IsatProbe 2

**40**

**30**

**20**

**10**

**0**

**50**

**I****sat**** (mA)**

- IsatProbe 1

- Phys of ST

- DPP APS 99

## Isat Does not Depend Strongly on NBI Power

- Isat(A)

- Time (s)

- 0

- 0.2

- 0.6

- 0.4

- 0.8

- Probe 1

- Pb(MW)

- 0

- 3

- 6

- Isat(A)

- Probe 2

- Isat(A)

- Probe 3

- 0.05

- 0.05

- 0.05

- 0.10

- 0

- 0

- 0

- Shots112508112498112499

- Phys of ST

- DPP APS 99

## Isat for Probes - PDD with LDGIS GAS Puff 700 Torr

- 0

- 20

- 40

- 60

- Current (mA)

- 2711

- 2812

- 2913

- 116486

- 0

- 20

- 40

- 60

- 80

- 1307

- 1408

- 1509

- 0.4

- 0.6

- 0.8

- 1.0

- Strike point radius (m)

- Current (mA)

- Phys of ST

- DPP APS 99

## Summary

- NSTX has a coarse probe array
- Radial variation of Isat Outer Divertor similar to that of the heat flux
- Te along divertor surface in range 4 to 20 eV over the beam power scan
- Response to Gas Puff Experiments
- Probes in SOL show correlation with Dα measured at divertor plate (possible ~10 ms lag)
- Signals large in SOL, smaller in private flux region
- Other features

- Phys of ST

- DPP APS 99

## END

- Phys of ST

- DPP APS 99

## Corrected Fit 

- 	Normal IV Characteristic Fit for 3 parameters Isat, Vf, Te
- 	I = Is*[1-exp(e(V-Vf)/kTe)]
- For nonsaturation of I(V) we need a 4th
- 	I=[Is+ I(Vf-V)][1-exp(e(V-Vf)/kTe)]

- Phys of ST

- DPP APS 99

## Isat Does not Depend on NBI Power

- Isat(A)

- Time (s)

- 0

- 0.2

- 0.6

- 0.4

- 0.3

- Probe 3

- D(arb)

- Pb(MW)

- 0

- 3

- 6

- 0

- 2

- 4

- 0

- 0.05

- 0.10

- Phys of ST

- DPP APS 99

## Isat for Probes - Neon GAS Puff 190 Torr, 4Tls

- 0

- 5

- 10

- 15

- Current (mA)

- 2711

- 2812

- 2913

- 116489

- 0 5

- 10

- 15

- 20

- 25

- Current (mA)

- 1307

- 1408

- 1509

- 0.4

- 0.6

- 0.8

- 1.0

- Strike point radius (m)

- Time (s)

- 0.0

- 0.1

- 0.2

- 0.3

- 0.4

**I****sat**

**I****sat**

- Phys of ST

- DPP APS 99

## Histograms of Isat for Outer Divertor Probes

- 0.08

- 0.04

- 0

- 0.04

- 0

- 0.02

- 0.01

- 0

- 0

- 4

- 0

- 400

- 0.9

- 0.7

- 0.0

- 0.2

- 0.4

- Time (s)

- Isat(13) (A)

- Isat(14) (A)

- Isat(15) (A)

- Ip(kA)

- Dα(arb.)

- R(m)

- Phys of ST

- DPP APS 99