An HIBP for NSTXWhy and How

Paul Schoch, Associate ProfessorDiane Demers, Research Assistant Professor

Kenneth Connor, Professor

Electrical, Computer, and Systems Engineering Department

Rensselaer Polytechnic InstituteTroy, NY

Why-The Heavy Ion Beam Probe - HIBP

• Probe the plasma with energetic, high mass ions– Not confined by magnetic field– Electron impact ionization will produce higher charge state ions –

secondaries– The change of energy of secondary compared to the primary is a

measure of the potential at the point of ionization– Steer the sample location across the plasma and profiles are

obtained.

Why - Data from 500kV HIBP on TEXT

• Time variation of the secondary ion energy is a measure of the fluctuating potential in the plasma, fig (b).

• Time variation of the total signal is a measure of the fluctuation of the electron density, fig (a)

• These signal can be cross correlated to yield the coherence and the phase relation

Power spectra of density fluctuations, potential fluctuations, coherence and phase shift

Why - Two point TEXT data

• TEXT system had 3 detector sets

• Alignment of sample volumes is along primary ion beam, so typically are displaced both radially and poloidally

Power spectra from density fluctuations using two detectors

Why - TEXT data

0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 10

10

20

30

40

50

60

normalized radius (r/a)

frequ

ency

(kHz

)

GAM Frequency

Scaled MHD Frequency

The GAM part of the Zonal Flow as measured in TEXT. It appears as a fluctuation of potential with m=0 mode structure, with little or on corresponding density fluctuation.

Why - TEXT data

2

21

2

2

2

1

2

21*

21

212

)()()(

)()()(),(

ffYfYfX

ffYfYfXffb

0

0.01

0.02

0.03

0.04

0.05

0 100 200 300 400 5000

20

40

60

80

100

Fre

qu

en

cy o

f Po

ten

tial (

kHz)

Figure 5 Cross bicoherence. Data is plotted over a limited range to highlight nonlinear coupling of the 40kHz zonal flow potential fluctuations with broadband density fluctuations. The left axis is frequency of the potential fluctuations. The bottom axis is the frequency of the density fluctuations.

kHzfffkHzf

forplotted

atsignaldensityofTransformFourierfY

atsignalpotentialofTransformFourierfX

)500(5000

:

75.0)(

69.0)(

1211

.

Higher order spectral analysis showed three wave coupling. The narrow band potential fluctuation, GAM, is coupled to the broad band density fluctuations.

Proposed HIBP for NSTX

nn /~

• 500kV accelerator from TEXT – in storage– Maximum operating voltage is 545kV– Sodium as ion of choice, 545keV very useful, 900keV offers greater

plasma coverage• Lithium is too light, (requires too high an energy.)• Potassium allows greater coverage or even possible use of a 300kV

accelerator, but will be strongly attenuated for moderate density plasma• Sodium is best option

– ~0.4% resolution for density fluctuations (0-500kHz)• Limited by predicted signal level and detector electronic noise• Electronic noise is broadband resistor noise

– ~3Vrms resolution for potential fluctuations (0-500kHz)• Also limited by signal level and electronic noise

– Sensitive to the low wavenumbers, k<3cm-1

How - HIBP for NSTX

nn /~

Sample volume (injection point[1.8 0 2.375]. detection point[2.2 0.8 –0.2])

Red is 580kV Na or 345kV for K, BT=0.45T, Blue is 930kV Na, 540kV K

Overlay of EFIT by F. PaolettiShot 105094, t=241msβt = 19.5%BT = 0.35T

Circled stars represent:350kV Na for BT = 0.35T575kV Na for BT = 0.45T345kV K for BT = 0.45TBlue stars represent:550kV Na for BT = 0.35T910kV Na for BT = 0.45T

Primary sweep at 1.8, 0, 2.375Detector at 2.2, 0.8, -0.2-1 -0.5 0 0.5 1 1.5 2 2.5 3

-1

-0.5

0

0.5

1

1.5

2

Ion beam trajectory in x-z plane

x (meters)

z (m

eter

s)

PF1aPF2

PF3

PF4

PF5

Z(m

)

2.50

-1 -0.5 0 0.5 1 1.5 2

-1

-0.5

0

0.5

1

Ion beam trajectory in x-y plane

x (meters)

y (m

eter

s)

-1 -0.5 0 0.5 1 1.5 2 2.5 3

-1

-0.5

0

0.5

1

1.5

2

Ion beam trajectory in x-z plane

x (meters)

z (m

eter

s)

-0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2

-0.1

-0.05

0

0.05

0.1

0.15

0.2Puncture plot through primary port1

x (port coordinates, meters)

y (

port

coo

rdin

ates

, m

eter

s)

-0.25 -0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2 0.25

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

Puncture plot through secondary port1

x (port coordinates, meters)

y (

port

coo

rdin

ates

, m

eter

s)

Fig.29-32 top view, side view of the energy scan for high field and the puncture plots ( injection point [1.8 0 2.375], detection point [2.2 0.8 –0.2])

Same sample locations as previous slide, shows trajectories at ports

Zhang, Schoch, Connor Rev. Sci. Instrum., Vol. 74, No. 3, March 2003

HIBP for NSTX

nn /~

• Attenuation– 1.6m is an the mean free path for 500keV Na+ for a plasma with

ne = 3x1019m-3, and Te=1keV.• This gives a nice balance between sufficient Na+2 production and not

too much.– The mfp for K+ for the same energy and plasma is about 0.53m

• Still useful but not optimal• Allows for greater plasma coverage but reduced sensitivity.

• Frequency range (0-500kHz) and resolution– Frequency range is limited by detector electronics– Noise is dominated by resistor noise in transimpedence amplifiers

HIBP for NSTX

nn /~

• Wavenumber sensitivity– Sample volumes are disk shaped with the size determined by the ion

beam size, the detector slit size and the magnetic geometry.• Predict sample size of about 2cm in the longest direction

– Spacing between samples is determined by the detector entrance slit geometry and the magnetic field.

– Sensitive to the low wave numbers, k<3cm-1

0.9 0.91 0.92 0.93 0.94 0.95 0.96 0.97 0.980.67

0.68

0.69

0.7

0.71

0.72

0.73

0.74

0.75

0.76

0.77Ion beam trajectory projection onto R-z plane

Major radius (m)

Hei

gh

t (m

)

Sample Volumes

Fig. 34 The primary beam and the geometry of the sample volumes ( Eb=350keV, =223º )

1.17 1.18 1.19 1.2 1.21 1.22 1.23 1.24 1.250.13

0.135

0.14

0.145

0.15

0.155

0.16

0.165

0.17

0.175

0.18Ion beam trajectory projection onto R-z plane

Major radius (m)

Hei

ght (

m)

Fig. 36 The primary beam and the geometry of the sample volumes ( Eb=350keV, =225º)

How -HIBP for NSTX

nn /~

• 500kV accelerator from TEXT– Maximum operating voltage is 545kV– Sodium as ion choice

• Potassium would allow greater coverage or even possible use of a 300kV accelerator, but will be strongly attenuated for moderate density plasma

– ~0.4% resolution for density fluctuations (0-500kHz)• Limited by predicted signal level and detector electronic noise• Electronic noise is broadband resistor noise

– ~3Vrms resolution for potential fluctuations (0-500kHz)• Also limited by signal level and electronic noise

– Sensitive to the low wavenumbers, k<3cm-1