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Dott. ClaudioVerona Dip. Ingegneria Meccanica Università di Roma “Tor Vergata” , Italy E-mail: claudio.verona@uniroma2. - PowerPoint PPT Presentation


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CVD single crystal diamond photodetectors for UV plasma diagnostic at JET tokamak. Dott. ClaudioVerona Dip. Ingegneria Meccanica Università di Roma “Tor Vergata” , Italy E-mail: claudio.verona@uniroma2.it. Outline. Motivation SCD V-UV detectors Device characterization Results at JET

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slide1

CVD single crystal diamond photodetectors for UV plasma diagnostic at JET tokamak

Dott. ClaudioVerona

Dip. Ingegneria Meccanica

Università di Roma “Tor Vergata” , Italy

E-mail: claudio.verona@uniroma2.it

slide2

Outline

  • Motivation
  • SCD V-UV detectors
  • Device characterization
  • Results at JET
  • Conclusions
slide3

Magnetic Confinement Nuclear Fusion

Joint European Torus (JET)

Culham (UK)

  • Plasma temperature: (T) 100-200 million Kelvin
  • Central density in plasma: (n) 1-2 x 1020 particles m-3
  • Most relevant emissions for plasma diagnostic in extreme-UV / soft-X ray spectral range
slide4

E-UV diagnostic at JET

  • temperature
  • density
  • particle and energy confinement timescale
  • impurities dynamics
  • atomic collision rates
  • plasma-wall interaction
  • plasma dynamics
  • characterization of the electron fluid
  • atomic structure of highly ionized atoms

Required features:

  • Radiation hardness
  • Low sensitivity to neutrons and  rays

Diamond detectors

  • Fast response
  • Visible blind
  • Good sensitivity in the EUV/soft-X spectral range
single crystal diamond deposition
Single crystal diamond deposition

Typical growth parameters

Plasma composition H2-CH4

Temperature 650 - 750 °C

Microwave power 500 - 700 W

Pressure 100 - 150 mbar

Gas flow rate 1- 100 sccm

Thickness rate 1μm/h

  • Substrates
  • (100) HPHT type Ib(Element 6, Sumitomo, others)
slide6

Single Crystal Diamond UV detector

UV

+ Vbias

Cr/Al contact electrode is grid-shaped

CVD intrinsic

Ag contact

CVD B-dopd

A

Grid-shaped Cr/Al electrode

The detector active area is about 6 mm2

HPHT substrate

  • The diamond photodetector operated in transversal configuration.
  • The detector can work with no applied bias voltage (photovoltaic regime).
  • The photocurrent is measured between the p-type diamond layer and ground. No signal due to secondary electrons.
slide7

Devices characterization

Experimental Setup 1

Experimental Setup 2

Stepper motor

  • EUV toroidal grating vacuum monochromator, with 5Å wavelength resolution
  • 10 - 100 nm spectral range
  • DC He and He/Ne gas discharge radiation sources
  • Tunable laser source (210 – 2400 nm)
  • 5 ns pulses
slide9

Devices characterization: I-V curve

The device shows a photocurrent response even at zero voltage bias, exploiting the internal junction electric field

The best signal to dark current ratio (SDR) performance is obtained at zero bias voltage

slide11

Devices characterization: linearity

He UV

He II and He I

Vbias =0Volt

slide12

Devices characterization

He and He-Ne spectra measured by the SCD detector

  • All spectral lines are clearly observed with high signal to noise ratios, demonstrating the good photodetection capabilities of CVD single crystal diamond in the extreme UV spectral region.
  • the low intensity lines of the He spectrum in the wavelength range 22 – 27 nm are easily resolved.
slide13

Devices characterization

The spectral response shows a visible/UV rejection ratio of about 6 orders of magnitude

Iph = qFo η μ E τ /d = qFo η G

R= Iph /Popt

EQE = 1240•R/ λ[nm]

slide14

Measurements at JET

One of those CVD diamond detectors was permanently installed at JET and connected to the main on-line data acquisition system

They are continuously recording every JET shot

VUV broadband spectroscopy

  • Det. n. 1

Feb. 2008 – broadband VUV

KS6

KT2

slide15

Measurements at JET

The detector has been installed inside the KS6 vacuum chamber

Diamond photodetector

40 m vacuum pipe to the reaction chamber

2 mm diameter collimator was placed in front of the detector

The electronic used consist in a variable-gain low-noise current amplifier FEMTO model DLPCA-200 and a 500Hz sampling rate ADC

slide16

Measurements at JET

JET shot #72428: Ne Blips

The detectors inside KT2 is a multi channel plate based on phosforus. The primary function of it is to monitor the impurity content of the JET plasma. Practically every impurity (intrinsic or extrinsic) in the plasma produces some spectral line emission in the KT2 wavelength range (approximately 100 - 1100Å).

slide17

Measurements at JET

Shot #72273: Nickel ablation experiment

slide18

Measurements at JET

Neutron insensitivity

JET shot acquired by keeping closed the UV entrance shutter

Shot #71898

Shot #71902

SCD Neutron monitor

slide19

Conclusions

  • CVD single crystal diamond UV detectors are fabricated in our University laboratory in a p-type/intrinsic/metal layered structure.
  • Our detectors can operate at zero bias voltage and show fast response time with no memory effect (priming) and good signal to noise ratio.
  • One of those detectors was permanently installed at Joint European Torus and connected to the main on-line data acquisition system.
  • First data acquired at JET have evidenced fast response time, good sensitivity and extremely low sensitivity to the neutron background.
  • Two plasma physics research groups at JET are currently using our device in order to measure the dynamic of impurities in the plasma.
slide20

Contributors

Università di Roma “Tor Vergata”, Italy

S. Almaviva

M. Marinelli

E. Milani

G. Prestopino

A. Tucciarone

G. Verona Rinati

EFDA-JET, Culham, UK

I. Coffey

A. Murari

Ass. EURATOM/ENEA, Frascati, Italy

M. Angelone

M. Pillon