XP 737 2007 NSTX Results Review

Beam Modulation Effects on Ion Power Balance

XP 737

P.W.Ross

XP 737 2007 NSTX Results Review

Basics of XP 737• The goal of XP 737 is to study the ion power balance

and the coupling between the injected beam and the thermal ions

• Also goal is to minimize known uncertainties in power balance such as edge charge exchange losses (need edge neutral measurements

Experimental technique for fast ion response● Modulate Beam power, modulate 3->2 beams● Evaluate the fast ion response using the NPA,

SSNPA, FIDA, and SFLIP diagnostics● Compare diagnostics to TRANSP predictions● Understand any differences

XP 737 2007 NSTX Results Review

ENDD Profile and image

XP 737 2007 NSTX Results Review

ENDD shows densities from 1e12-1e14

The Edge Neutral Density Diagnostic measures the neutral density in the edge of the plasma. Typical densities range from 1e12 to about 5e13.

Seperatrix

Preliminary

XP 737 2007 NSTX Results Review

Problems with the ENDD Diagnostic

● ENDD is heavily dependent on Thomson Scattering. This is in the region of low temperature (a few eV).

Slight variations in the temperature causes significant changes in the calculated Neutral Density

ENDD profiles behave erratically with edge TS (large error bars in the edge).

Possibility of lithium coating.● X-rays can cause spikes in the image which

need to be ignored.

XP 737 2007 NSTX Results Review

NPA signal shows lack at certain pitch angles

Rtan=80cm Rtan=120cmRtan=50cm

Beams

Neutrons

NPA 73 keV

NPA 77 keV

NPA 81 keV

XP 737 2007 NSTX Results Review

NPA signal dependent on Beam Timing

● Shot 125331 ● Shot 125332

These shots were very similar. The beam timing on shot 331 was a mistake, but it showed how the beam timing affects the NPA signal.

XP 737 2007 NSTX Results Review

TRANSP shows NPA modulations at all pitch angles

Rtan 125

Rtan 80

Rtan 50

TRANSP shows modulations at all tangency radii that match the beam modulations. This is not seen in the measured NPA signal, particularly for Rtan 80, near the magnetic axis. (The measured NPA signal is not shown)

XP 737 2007 NSTX Results Review

FIDA shows similar behavior to NPA

0 200 400 600 800 1000 1200-0.1

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0.1

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0.3

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0.8sh#125332

t [ms]

signals [a.u.] FIDA

Φn

Shot 125332 showed no distinct signal on the NPA and shows a similar lack of signal on the FIDA diagnostic with the beam modulation (Neutron signal in red, FIDA in black)

This is the overlay of 5 shots with identical beam timing and plasma parameters. Individual shots were too noisy to detect a correlation. When several signals are overlaid from repeated shots, a small modulation is seen. A similar effect may be possible with the NPA and other diagnostics

XP 737 2007 NSTX Results Review

SSNPA and SFLIP Add to the Confusion

SSNPA signal at various energies. No obvious signal matches beam modulation

SFLIP probe shows loss associated with MHD activity, but does not show any activity associated with the beam modulation

XP 737 2007 NSTX Results Review

Conclusions and Further Analysis● The ENDD diagnostic has taken data and initial analysis has

been performed● Firm estimates will be available about the effect of lithium on the

edge neutral density● XP 737 highlighted the lack of understanding of the presence or

absence of a strong NPA signal, particularly as related to beam modulations

● Shots with 3 beams early have a significantly higher absolute NPA signal, but lack the large modulations that are apparent in shots without 3 beams early

● SSNPA, FIDA and SFLIP confirm lack of large modulations in fast ion population, although overlaying several shots/performing a Fourier transform may show low amplitude signals

● We would like to have TRANSP simulate other diagnostics, such as the FIDA and SSNPA, which would assist in understanding their signals.