# Presentation: 899074

## Divertor heat flux reduction and detachment in lower ,  LSN plasmas (XP 605)

**V. A. Soukhanovskii**
**NSTX Team XP Review**
**31 January 2006**
**Princeton, NJ**

**Divertor heat flux reduction and detachment in lower ********, ******** LSN plasmas (XP 605)**

## Motivation - understand and control divertor heat and particle fluxes at low aspect ratio

- Understand physics of divertor regimes, including detachment, at low aspect 	ratio
- Basis for CTF divertor scaling and predictive capability
- Contribution to ITER divertor database with high flux expansion divertor
- Study divertor regimes with low recycling surfaces - any surprises? (lithium)
- Unique NSTX contribution in all these topics
- NSTX XP goals: study divertor regimes (heat and particle parallel and perpendicular transport) in NBI-heated H-mode plasmas, determine plasma geometry effects on divertor, develop radiative and/or dissipative divertor scenario with reduced divertor peak heat flux and good core confinement

**Motivation - understand and control divertor heat and particle fluxes at low aspect ratio**

- V. A. Soukhanovskii, XP605 Review, 31 January 2006

## Study heat flux reduction with dissipative divertor in lower  LSN plasmas

-  Multi-institutional experiment - LLNL, ORNL, PPPL, U Washington
-  C. J. Lasnier (LLNL staff at DIII-D) participated in 2005 experiment
-  NSTX results to date (from XP 438, XP 520)
- Inner divertor heat flux < 1 MW/m2, outer divertor heat flux~ 4-7 MW/m2
- OSP does not detach at high densities (*n**e** ~ n**G*) as a result of short *L**||** *and open divertor geometry (?). ISP detaches at low *n**e**, P**in*
- Tried midplane D2 puffing in 2-4 MW NBI L- and H-mode LSN plasmas to raise edge collisionality from 5-20 to 10-80. Result: outer peak heat flux reduced by *2-4*, but no volume recombination signs - no detachment, - radiative divertor?
- Midplane neon puffing - similar result, radiative mantle?
- Lower divertor *semi-steady-state* D2 puffing - got OSP partial detachment (reduced outer peak heat flux *by 4-5*, shift of heat flux profile peak, signs of volume recombination)

**Study heat flux reduction with dissipative divertor in lower ******** LSN plasmas**

- V. A. Soukhanovskii, XP605 Review, 31 January 2006

## Plan is to study routes to detachment with D2 and CD4 puffing

- Study OSP detachment with steady-state divertor D2 puffing (~ 0.5 day)
-  Target plasma - 4 MW H-mode LSN plasma, 4.5-5 kG,
-  δ∼0.45-0.5, κ=1.85-2.0
-  Will use Branch 5 Injector in FLO mode for long continuous gas puffing 		(need to calibrate and test prior to XP execution)
-  Relevant diagnostic set is ready
- Study OSP detachment with extrinsic impurity - CD4 puffing (~ 0.5 day)
- - SOL and divertor temperature in NSTX is too low for neon to radiate
- efficiently, but expect carbon and deuterium to radiate well
- - Have a bottle of CD4 committed to the experiment
- - Study carbon screening
- In both parts focus not only on detachment but also on impurity source
- characterization and core performance

**Plan is to study routes to detachment with D****2**** and CD****4**** puffing**

- V. A. Soukhanovskii, XP605 Review, 31 January 2006

## Detailed shot plan

-  Setup an rt-EFIT-controlled LSN (with PF2L coil) HFS-fueled plasma and perform gas injection rate scan (10 shots)
-  Setup a 0.8-1.0 MA 0.45-0.55 T shot with 2 NBI sources B, C at 90 kV, adjust the X-point height so that the inner strike point remains at 1-2 cm from the inner wall throughout discharge. Example shots: 116485, 116488
-  Vary Branch 5 injector rate from 0 to 250 T l /s, HFS 1200-1300 Torr
-  In one high density discharge, turn off NBI at the time when *n**e* is high (> 5 x 1019 m-3) to obtain high density low input power condition for about 50 ms
-  Greenwald density for *I**p*=0.7 MA is *n**G* = 4.8 x 1019 m-3
-  Use 7-12 min He GDC as appropriate, (conditional) add modulated and full beam A
-  Perform CD4 injection in increasing quantities (0.05 – 0.2 s duration pulses at a rate from 1 to 20 Torr l / s ) into intermediate density two NBI source shot from 1. Monitor radiated power (10 shots).
-  Use Injector 3 for CD4.

- V. A. Soukhanovskii, XP605 Review, 31 January 2006

## Backup slides

- Attempt to change parallel momentum and power balance:

**G. Porter, N. Wolf**

- V. A. Soukhanovskii, XP605 Review, 31 January 2006

## Publications and collaborations

-  Posters at APS 2004, PSI 2004
-  One JNM paper (2005)
-  Oral talk in NSTX session at APS 2005
-  PSI-17 poster abstract accepted
-  Paper in preparation to be submitted to NF
-  IAEA abstract submitted
- Collaboration potential
-  Discussed possible collaboration with DIII-D (through LLNL program)
-  Possible collaboration with MAST

**Publications and collaborations**

- V. A. Soukhanovskii, XP605 Review, 31 January 2006

## NSTX Gas system

- V. A. Soukhanovskii, XP605 Review, 31 January 2006

## NSTX Lower Dome and Branch 5 gas system

**NSTX Lower Dome and Branch 5 gas system**

- V. A. Soukhanovskii, XP605 Review, 31 January 2006