MPTS Phase 4

Benoit P. LeBlanc

PPPL

19 June 2009

Outline

• Scope of work for Phase 4• Technical issues• Seven unused fiber bundles• Gradient location database• Previous inputs• A partial suggestion

Scope of Phase 4 and More

• Install 10 – possibly 12 -- new radial channels– Use 6-filter polychromator – as in phases 1 & 2

• Install two new alignment channels• Rebuild phase-3 polychromators

– Add 1064-nm filter for Rayleigh noise rejection (unlikely)

• Repair MPTS hardware – three items• Calibrate 40-channel system

– Spectral, fast/slow, gain; before Rayleigh/Raman

• Preparation work for high-Te channels– To be implemented in NSTX-U – 10keV (on the back burner)

Technical Issues

• Plan is to complete more of existing hardware– 7 unused fiber – one bundles sees RF NB– 16 unused sample-and-hold slots– Changes will occur in the polychromator room

• Develop a technique to unglue output end of fiber bundles – tricky but feasible

• Reroute a large number of fiber bundles– Split bundles need to be physical close – order of 6”– Long sequence of activities, which cannot be stopped before

MPTS is back online ≥ 5 months• Upgrade includes the construction of a fourth

polychromator “tower”• All new polychromators and ancillary hardware need to

be ready at the end of FY10 experimental run• Massive calibration work following successful hardware

installation

Polychromator Stacked in Towers

• Current 3 “tower” each house 10 polychromators

• Each polychromator is attached to a movable shelf– Split bundles need to be

next to each other vertically

• The fourth tower will have 12 shelves

Seven fiber bundles remain unused

Seven unused bundles indicated in green R= 31.8, 86.4, 96.3, 104.9, 112.5, 154.6, 157.7 cm

Gradient location database

• 1446 shots from 2008

• Use spline Te and ne profiles to compute the location of maximum gradients, average over times 0.15s – 0.9*max(ts_time)

• Database includes 29 shots suggested by Rajesh Maingi

• Use this data to identify new channel locations

Location of Te vs. location of ne

Distribution plot

Location of Te vs. location of ne

Distribution plot redux

Shots suggested by R. Maingi

Location of Te vs. location of ne

2D histogram plot

Histogram of Te location

3

1 2 split bundle unused

Phase 1Phase 2Phase 3Unused

Histogram of ne location

3

1 2 split bundleunused

Phase 1Phase 2Phase 3Unused

Comments for Team• Rajesh Maingi

– To better resolve the H-mode pedestal gradients, I suggested the spatial resolution be optimized from ~R=141-147cm. Practically this means adding 4-5 channels.

– Shell works best with smaller gap• Jon Menard

– I am concerned about LLD being successful in increasing D pumping– and forcing us to run larger outer gaps to reduce metal influx

– What range of outer gaps would the proposals below support?, i.e.– have good gradient resolution for H-mode for our typical profiles.

– Some of our transport barrier shots are clearly under-resolved in– the core, so this might warrant some additional coverage there.

– Crudely, I tend to think resolving the edge is 2-3x more important– than the core programmatically

• Joel Hosea– Good documentation of pedestal foot, re ELMS

• Ben LeBlanc– The outermost bundle “sees” the BN limiter – antenna was moved inward in 2004– The bundle will not be instrumented at this time.

Use Existing Data to Estimate Error

• Found among 2008 shots six pairs of successive plasmas: (S217 open & S218 open), followed by (S217 open & S218 Shut)

• Check shots for similar time evolution etc.• Took data between 0.05s and 0.5s -- avoid saturation• Compare data with both shutters open – Tef0, dTef0,

nef0 – with data with one shutter closed – Tef1, dTef1, nef1

• Select radial positions with raw signal (S218 shot/open) of 0.3 or 0.5.

Fiber Bundle divided in Two

Fiber Bundle divided in Three

A Suggestion…Revision June 2009

• Propose 10 new channels, but will aim at 12– Cannot fit more channels in the schedule

• One new radial channels at R=154.6 cm (unused FB)• One new radial channels at R=31.8 cm (unused FB)• Four to six(?) new radial channels in “pedestal” region

– Done by splitting instrumented bundles in two• No unused bundles available

– Location of higher-resolution channels to be chosen by team/experts’ recommendation

• 2008 data suggest centering around 141 cm

– How far in before splitting bundles is no longer useful

• Four to six in the core and ITB region– Four unused bundles in the core region

Edge Pedestal Density

Phase 1Phase 2Phase 3Unused

Te ITB Profile

Phase 1Phase 2Phase 3Unused