determining pellet penetration depth using video...
TRANSCRIPT
Determining pellet penetration Determining pellet penetration depth using video diagnosticsdepth using video diagnostics
Tamás SzepesiKFKI-RMKI, Budapest, Hungary
21 April 2006
Contents
1. Motivation2. The pellet injector and the video diagnostics systems
3. Penetration depth
• Definitions
• Comparison
4. Future work and outlook
1. Motivation
Plasma edge control by ELM triggering
- ELM: MHD instability at the plasma edge→ fast (~ms) particle and energy loss→ type-I ELM: at strong heating, fELM ~ Pheat
- type-I ELMy H-mode: stable, robust→ WMHD, ne ≈ const.→ stable level impurity concentration ⇒ Prad ≈ const.⇒ candidate for reactor operation modeBUT: fELM · ΔWELM = const. and ΔW scales with machine size→ ITER: max. 5-10 MW / m2 peak load on divertor plates – critical [Lang, Nucl. Fusion 2004]
- ELM control (mitigation) by cryogenic D pellet injection
→ each HFS injected pellet triggers its own type-I ELM
→ sufficiently high injection frequency ⇒ full control over ELMs (no intrinsic ELMs)
→ the empirical formula seems to hold for triggered ELMs as well
[H. Zohm, PPCF 36, 105-128.]
1. Motivation
Aims
- to localize pellet when the ELM is triggered→ determination pellet trajectory (long exp. images)→ time stamps of the trajectory (multiple short exp.)
⇒ location of pellet caused perturbation can be found(ELM onset time from Mirnov signals)
- to study penetration depth and ablation of the pellets
→ extend the presently existing database [Belonohy] of HFS injected pellets (ASDEX Upgrade) with penetration depth calculations from video diagnostics
→ find correction formulae to calculate the „real” penetration from the ablation monitor signal
→ find a scaling of the penetration depth to extrapolate to larger machines e.g. ITER
2. The pellet injector systems
centrifuge system
• pellet speeds:
240, 600, 880 and 1000 m/s
• pellet mass: ~ 1020 D atoms
• max frequency: ~80 Hz
Leidenfrost-gun system
• pellet speed: 80 – 300 m/s
• pellet mass: ~ 1020 D atoms
• max. frequency: 100 Hz (with 90% reliability)
[Lang]
[Cierpka]
Leidenfrost-gun
[Kocsis EPS 2004]
2. The video diagnostics system
- up to 3 fast framing cameras may havethe same view
→ the same pellet can be observedwith different exposure schemes
- typical exposure schemes:
→ long exposure:‘bright’ imagewhole pellet trajectory visibleno time stamps of the path
⇒ penetration, calibration, pellet trajectory
→ multiple short exposure:‘dark’ imageparts of the trajectory visiblecarries temporal information
⇒ pellet speed, trajectory with temporal info
2. The video diagnostics system
side view, long exposure
injection lineinjection line
side view, multiple short exposure
HFS LFS HFS LFS
2. The video diagnostics system
top view, long exposure
injection lineinjection line
top view, multiple short exposure
HFS
LFS
HFS
LFS
3. Penetration depth
Definitions (1)
- penetration depth from the ablation monitor signal (λabl)
→ time-of-flight (TOF) measurement: λabl = vpel · Δt
☺ relatively easy to evaluate
☺ available for all pellets
assumes vp = const.
assumes straight pellet path
no spatial information
difficult to identify fragmentation
Time [s]
Ablation M
onitor [au]
Δt ~ 1 ms
[Belonohy diploma]
3. Penetration depth
injection line
injection tube end
separatrix
separatrix intersection
projected penetration
separatrix penetration
Definitions (2)
- penetration depth fromvideo diagnostics (λv)
complicated calibration → difficult to evaluate
not available to all pellets (max. 5 Hz repetition rate)
assumes no toroidal movement
☺ detailed spatial information on pellet trajectory in real and magnetic coordinates
☺ fragments easier to see (multiple short exp.)
3. Penetration depth
Comparison (1)
- fast pellets (1000 m/s)
→ often fragmented
→ fragmentation usually difficult to recognize (usually not detected)
→ straight trajectory
⇒ TOF measurement tends to give higher values
?
3. Penetration depth
Comparison (2)
- slow pellets (240 m/s)
→ less fragmentation
→ curved trajectory (acceleration!)
⇒ video measurement tends to give higher values (TOF does not account for radial acceleration)
⇒ a correction formula can be defined
projected penetration (+) in good agreement with the TOF measurements
0)()sin(v)(
1)cos(v)(
00
100
=+=
+++= +
ttztz
ta
btRtR a
θφ
φ
[Kálvin]
What is the ‘real’ penetration depth? – a physically relevant quantity should be defined
4. Future work
Pellet trajectory fitting
- to fit parameters of the curved pellet trajectory:
• a, b, φ
⇒ real path length of the pellet can be determined
⇒ to find the dependence of these parameters on the plasma parameters (esp. Te)
0)()sin(v)(
1)cos(v)(
00
100
=+=
+++= +
ttztz
ta
btRtR a
θφ
φ
[Kálvin]
4. Future work
Measurements with the Leidenfrost-gun
- top view very useful, but ~2m distance
→ lower resolution, less bright
⇒ more difficult to calibrate (distortion)
⇒ need compromise in calibration (or maybe optics upgrade)
Thank you for your attention!
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- How much for a beer?
The bartender looks at the neutron and answers: - For you? Free of charge!