Design of the polarization preserving optics system for motional - - PowerPoint PPT Presentation

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Design of the polarization preserving optics system for motional - - PowerPoint PPT Presentation

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Design of the polarization preserving optics system for motional Stark effect diagnostics Jinseok Ko a , Jinil Chung a , and Maarten De Bock b a National Fusion Research Institute, Daejeon, Korea b Eindhoven University of Technology, Eindhoven,

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SLIDE 1

Design of the polarization‐ preserving optics system for motional Stark effect diagnostics

20140225tu, j ko – kstar conf, jeongseon, korea 1

Jinseok Koa, Jinil Chunga, and Maarten De Bockb

aNational Fusion Research Institute, Daejeon, Korea bEindhoven University of Technology, Eindhoven, The

Netherlands Tue 25 Feb 2014, KSTAR Conference, Jeongseon, Korea

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SLIDE 2

20140225tu, j ko – kstar conf, jeongseon, korea 2

  • Control of a burning plasma
  • Non‐inductive steady state operation
  • Plasma wall interactions
  • First wall materials and divertor heat flux
  • Radiation‐resistant structural materials
  • Tritium breeding and fuel cycle

Challenges for commercial fusion plants – Info on internal B comes in

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SLIDE 3

20140225tu, j ko – kstar conf, jeongseon, korea 3

  • Control of a burning plasma
  • Non‐inductive steady state operation
  • Plasma wall interactions
  • First wall materials and divertor heat flux
  • Radiation‐resistant structural materials
  • Tritium breeding and fuel cycle

Challenges for commercial fusion plants – Info on internal B comes in

slide-4
SLIDE 4

20140225tu, j ko – kstar conf, jeongseon, korea 4

  • Control of plasma properties (temperature, density, current etc)

and their profiles is essential for plasma equilibrium and stability.

  • Control of a burning plasma
  • Non‐inductive steady state operation
  • Plasma wall interactions
  • First wall materials and divertor heat flux
  • Radiation‐resistant structural materials
  • Tritium breeding and fuel cycle

Challenges for commercial fusion plants – Info on internal B comes in

slide-5
SLIDE 5

20140225tu, j ko – kstar conf, jeongseon, korea 5

  • Control of plasma properties (temperature, density, current etc)

and their profiles is essential for plasma equilibrium and stability.

  • Control of a burning plasma
  • Non‐inductive steady state operation
  • Plasma wall interactions
  • First wall materials and divertor heat flux
  • Radiation‐resistant structural materials
  • Tritium breeding and fuel cycle
  • Magnetic field profile is one of the most important (and hardest‐to‐measure) quantities

and a direct measure of the equilibrium and stability.

Challenges for commercial fusion plants – Info on internal B comes in

slide-6
SLIDE 6

20140225tu, j ko – kstar conf, jeongseon, korea 6

  • Control of plasma properties (temperature, density, current etc)

and their profiles is essential for plasma equilibrium and stability.

  • Control of a burning plasma
  • Non‐inductive steady state operation
  • Plasma wall interactions
  • First wall materials and divertor heat flux
  • Radiation‐resistant structural materials
  • Tritium breeding and fuel cycle
  • Magnetic field profile is one of the most important (and hardest‐to‐measure) quantities

and a direct measure of the equilibrium and stability.

Challenges for commercial fusion plants – Info on internal B comes in

  • MSE (Motional Stark Effect) diagnostic is under development at KSTAR for this purpose.
slide-7
SLIDE 7

20140225tu, j ko – kstar conf, jeongseon, korea 7

  • Control of plasma properties (temperature, density, current etc)

and their profiles is essential for plasma equilibrium and stability.

  • Control of a burning plasma
  • Non‐inductive steady state operation
  • Plasma wall interactions
  • First wall materials and divertor heat flux
  • Radiation‐resistant structural materials
  • Tritium breeding and fuel cycle
  • Magnetic field profile is one of the most important (and hardest‐to‐measure) quantities

and a direct measure of the equilibrium and stability.

Challenges for commercial fusion plants – Info on internal B comes in

  • MSE (Motional Stark Effect) diagnostic is under development at KSTAR for this purpose.
  • Today’s talks focus on the design of the front optics and filters:
  • Diagnostic principles / development timeline
  • Spatial / temporal resolutions
  • Front optics (etendue, polarization preservation)
  • Bandpass filter design and selection
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SLIDE 8

20140225tu, j ko – kstar conf, jeongseon, korea 8

n = 3 n = 2

E = v  B

Motional Stark effect: Doppler‐shifted polarized light gives local field information

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SLIDE 9

20140225tu, j ko – kstar conf, jeongseon, korea 9

n = 3 n = 2

E = v  B

Motional Stark effect: Doppler‐shifted polarized light gives local field information

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SLIDE 10

20140225tu, j ko – kstar conf, jeongseon, korea 10 10

n = 3 n = 2

E = v  B

Motional Stark effect: Doppler‐shifted polarized light gives local field information

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SLIDE 11

20140225tu, j ko – kstar conf, jeongseon, korea 11 11

n = 3 n = 2

E = v  B

Motional Stark effect: Doppler‐shifted polarized light gives local field information

 

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SLIDE 12

20140225tu, j ko – kstar conf, jeongseon, korea 12 12

n = 3 n = 2

Bandpass filtering

E = v  B

Motional Stark effect: Doppler‐shifted polarized light gives local field information

 

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SLIDE 13

20140225tu, j ko – kstar conf, jeongseon, korea 13 13

MSE NBI LiBeam

  • PEM (Photo‐Electric Modulator)‐based MSE (30 channels) under design

phase collaborating with Eindhoven Univ. of Tech (TU/e), The Netherlands.

  • The development path also includes the Li‐beam Zeeman effect

diagnostic for the pedestal region.

  • Design of (polarization‐preserving) front optics

– Sharing the collection optics with the existing CES: Signals will be separated into 550 nm and 650 nm via a dichroic beam splitter. – Low thermal‐birefringence materials will be used to avoid random change in the polarization in thermally harsh environment.

2013 2014 2015

  • Design of bandpass filter module

– Precise characterization of the bandpass filters and development of the filter module prototype. – PC‐based software to control the filter pass band (tilting).

  • Procurement and assembly (after 2014 campaign)
  • Commission
  • Application to the real‐time feedback control of J(r)

2016

(Collection optics layout) (Prototype of filter module)

Overall plan: Commission in 2015

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SLIDE 14

20140225tu, j ko – kstar conf, jeongseon, korea 14 14

Better spatial resolution than ITER

MSE NBI LiBeam

Emission profile (Ion source 1 in NBI1) ‘Center of mass’ of the emission and the central point of the line of sight are different because of the asymmetry in the manner of intersection.

Machine r/a (%) Number of channels min max ITER 2.5 8 20 JET 2 6 25 JT‐60U 8 10 16 DIII‐D 15T 38 23 10 315T 1.5 15 16 195TL 8 11 8 45T, 195TU < 1.5 8 9, 16 NSTX 3 5 12 C‐Mod 10 40 10 MAST 5 5 35 KSTAR 2 8* 30

  • The ITER MSE requirements: r/a  5 % for

reasonable q profiles for NTM feedback (q = 1.5, 2) and reversed shear control.

  • The FWHM of the emission profiles due to the

NBI of the 30 lines of sight with realistic beam emission and intersection geometry is regarded as the ‘radial resolution’

*R = 1.75 m

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SLIDE 15

20140225tu, j ko – kstar conf, jeongseon, korea 15 15

MSE coverage (using ION1)

r = 1 – 3 cm (mostly 1 – 2 cm)

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SLIDE 16

20140225tu, j ko – kstar conf, jeongseon, korea 16 16

t = 10 – 50 msec seem to accommodate the various characteristic time scales

  • Theoretical limit: PEM fundamental frequencies  20

kHz

  • Practical limit: the amount of photons from the beam

emission  tens of msec

  • The typical H‐mode energy confinement time in KSTAR

 100 msec

  • The current relaxation time in KSTAR

 1.4a2Te 1.5 (keV)/Zeff  1.4  (0.5)2  1.8  2 1.5 / 2  1 sec

  • The real time equilibrium reconstruction planned for

KSTAR discharges can tolerate as low as 50 Hz.

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SLIDE 17

20140225tu, j ko – kstar conf, jeongseon, korea 17 17

Space challenge: optics should reside in the M‐port cassette

Bt Ip

1

“cassette”

  • Very small and narrow space to accommodate the necessary optical elements.
  • Faraday effect vs thermal birefringence?

– Faraday effect: static and systematic (SFL6 glass materials; unacceptably high thermal birefringence constants) – Thermal birefringence: random and varying in time (NSSK5 and NSF15 glass materials; high Verdet constants)

  • Keep toroidal components of the lens surface normal vectors as low as possible.
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SLIDE 18

20140225tu, j ko – kstar conf, jeongseon, korea 18 18

Sharing challenge: collection optics will be shared with CES

  • Do not degrade the current etendue of the CES diagnostic.
  • Dichroic beam splitter is under consideration to separate the CES (~ 550 nm)

and MSE (~ 650 nm) signals.

  • Need to be custom‐made with a large aperture.

From thorlabs.com

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SLIDE 19

20140225tu, j ko – kstar conf, jeongseon, korea 19 19

Two challenges are implemented into the final optics design

PEM Mirror Beam splitter

MSE signals go up after beam splitter (reflected) CES signals go straight beam splitter (transmitted)

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SLIDE 20

20140225tu, j ko – kstar conf, jeongseon, korea 20 20

Etendue is well reserved (close to an ideal optics)

 f fo di do df o Fiber Optics Image (or source)

NA = 0.22 (silica) f = 25.4 NA = 0.37 (hard polymer) f = 39

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SLIDE 21

20140225tu, j ko – kstar conf, jeongseon, korea 21 21

Dielectric coating on reflective elements to minimize the change of polarization

Plane‐of‐incidence

Normal reflective surface (Multi‐layer) dielectric‐coated surface

P‐pol S‐pol

  • The phase difference between P‐ and S‐polarizations should be close to 0 or 180.
  • The relative reflectivity between P‐ and S‐polarizations is close to 1.
  • These coating qualities are strongly dependent on angles‐of‐incidence (AOI) and wavelengths:

Very difficult and sophisticated to fabricate

  • The AOI’s at reflective elements are expected to be

– At dielectric mirror: 35 ‐ 55 – At dichroic beam splitter: 40 ‐ 50 for chief rays.

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SLIDE 22

20140225tu, j ko – kstar conf, jeongseon, korea 22 22

Dielectric coating on the mirror

  • MLD Tech (USA) is specialized in extreme

performance optical coating: Already supplied the dielectric‐coated mirrors to PPPL (for C‐Mod MSE)

  • KSTAR MSE mirror has one additional

requirement: high transmission over the CES band (468 – 540 nm)

  • Design performance:

– > 98 % reflectivity over 468 – 674 nm – For MSE band (656 – 674 nm) and AOI = 35 ‐ 55

  • S/P reflectance ratio: 1.000  1%
  • Phase difference:  3

Phase difference (Mirror) S/P reflectance (Mirror)

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SLIDE 23

20140225tu, j ko – kstar conf, jeongseon, korea 23 23

Dielectric coating on the beam splitter

  • Short‐pass type beam splitter (cut‐off

wavelength: 600 nm)

  • Design performance:

– > 95 % transmission over 468 – 540 nm – For MSE band (656 – 664 nm) and AOI = 40 ‐ 50

  • S/P reflectance ratio: 1.000  1%
  • Phase difference: 180  2

Phase difference (Beam splitter) S/P reflectance (Beam splitter)

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SLIDE 24

20140225tu, j ko – kstar conf, jeongseon, korea 24 24

Full characterization of the interference filter performed

  • The comparison between the theory from the filter specification and the

measurements of the filter properties has been made.

  • The measured value of the central wavelength as a function of the tilt angle of

the filter (up to  25) corresponds well to the theory.

  • A maximum difference in the central wavelength: 0.2 nm – this corresponds to

7.5% error.

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SLIDE 25

20140225tu, j ko – kstar conf, jeongseon, korea 25 25

Filter control: Ip = 0.5 – 1.0 MA, Bt = 1.5 – 3.5 T, ENBI (Ion1) = 70 – 100 keV

  • Tuning range: ~ 2 nm towards

shorter wavelengths

  • CWL: Largest wavelength to measure

(red‐shifted pi with V = 100 kV and B = 3.5 T) + a margin (0.5 nm ~ FWHM)

red‐shifted π red‐shifted π blue‐shifted π blue‐shifted π

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SLIDE 26

20140225tu, j ko – kstar conf, jeongseon, korea 26 26

Prototype of the filter assembly with controller established

Detector 60mm cage system cage plates for lens mounts Filter (in holder) Motorized rotation stage Fiber bundle mount (mimicked by iris) Focussing lens Collimating lens Controller rotation stage Custom base plate

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SLIDE 27

27 27

MSE NBI LiBeam

  • PEM (Photo‐Electric Modulator)‐based MSE (30 channels) under design

phase collaborating with Eindhoven Univ. of Tech (TU/e), The Netherlands.

  • The development path also includes the Li‐beam Zeeman effect

diagnostic for the pedestal region.

  • Design of front optics

– Sharing the collection optics with the existing CES: Signals will be separated into 550 nm and 650 nm via a dichroic beam splitter. – Low thermal‐birefringence materials will be used to avoid random change in the polarization in thermally harsh environment.

2013 2014 2015

  • Design of bandpass filter module

– Precise characterization of the bandpass filters and development of the filter module prototype. – PC‐based software to control the filter pass band (tilting).

  • Procurement and assembly (after 2014 campaign)
  • Commission
  • Application to the real‐time feedback control of J(r)

2016

MSE (& ZE): Commission in 2015

20140225tu, j ko – kstar conf, jeongseon, korea