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![Page 1: R. Wenninger 1 (35) Sat. Workshop to EPS on Fuelling 16 th June 2008 Status of ELM trigger investigations on JET and AUG R. Wenninger IPP Garching, EFDA.](https://reader031.fdocuments.us/reader031/viewer/2022012919/5697bfd61a28abf838cae1b6/html5/thumbnails/1.jpg)
R. Wenninger 1 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
Status of ELM trigger investigations on JET and AUG
R. WenningerIPP Garching, EFDA JET
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R. Wenninger 2 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
Outline
• Pellet technology at AUG and JET• Pellets – a candidate ELM mitigation method• Observation of pellet triggered ELMs in H-
mode regimes• Direct pellet driven MHD• Careful considerations towards trigger
mechanism• Pellet impact on tokamak (ITER) operation• Summary
![Page 3: R. Wenninger 1 (35) Sat. Workshop to EPS on Fuelling 16 th June 2008 Status of ELM trigger investigations on JET and AUG R. Wenninger IPP Garching, EFDA.](https://reader031.fdocuments.us/reader031/viewer/2022012919/5697bfd61a28abf838cae1b6/html5/thumbnails/3.jpg)
R. Wenninger 3 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
Outline
• Pellet technology at AUG and JET• Pellets – a candidate ELM mitigation method• Observation of pellet triggered ELMs in H-
mode regimes• Direct pellet driven MHD• Careful considerations towards trigger
mechanism• Pellet impact on tokamak (ITER) operation• Summary
![Page 4: R. Wenninger 1 (35) Sat. Workshop to EPS on Fuelling 16 th June 2008 Status of ELM trigger investigations on JET and AUG R. Wenninger IPP Garching, EFDA.](https://reader031.fdocuments.us/reader031/viewer/2022012919/5697bfd61a28abf838cae1b6/html5/thumbnails/4.jpg)
R. Wenninger 4 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
AUG Pellet Centrifuge
AUG fuelling systemVolume to freeze and compress ice
Extrusion nozzel Extrusion arm (s=0.25mm)
Cutter
VHFS
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R. Wenninger 5 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
AUG Blower Gun
• • High frequency: Up to 143Hz
• 2nd injection line for tangential transfer through edge plasma close in or outside separatrix
AUG pacing system
![Page 6: R. Wenninger 1 (35) Sat. Workshop to EPS on Fuelling 16 th June 2008 Status of ELM trigger investigations on JET and AUG R. Wenninger IPP Garching, EFDA.](https://reader031.fdocuments.us/reader031/viewer/2022012919/5697bfd61a28abf838cae1b6/html5/thumbnails/6.jpg)
R. Wenninger 6 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
AUG Injection Capabilities
Centrifuge Blower Gun
Species H2, D2, doped D2
Frequency Up to 83Hz Up to 143Hz
Pellet speed240 - 1200 m/s
(limited by looping to 1000m/s)
100 – 350m/s
Pellet size/mass (D2)
~ 2.8 – 7.2 mm3
(1.7 - 4.3 1020 atoms)
~ 1.7 mm3
(1020 atoms)
Reliability 95% 95%
Injection line VHFS LFS (Invest. line)
![Page 7: R. Wenninger 1 (35) Sat. Workshop to EPS on Fuelling 16 th June 2008 Status of ELM trigger investigations on JET and AUG R. Wenninger IPP Garching, EFDA.](https://reader031.fdocuments.us/reader031/viewer/2022012919/5697bfd61a28abf838cae1b6/html5/thumbnails/7.jpg)
R. Wenninger 7 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
JET – High Frequency Pellet Injector
High Frequency Pellet Injector (HFPI): • Worldwide 1st system fully optimised for ELM
pacing• Deep fuelling also possible
PELIN pellet injector
![Page 8: R. Wenninger 1 (35) Sat. Workshop to EPS on Fuelling 16 th June 2008 Status of ELM trigger investigations on JET and AUG R. Wenninger IPP Garching, EFDA.](https://reader031.fdocuments.us/reader031/viewer/2022012919/5697bfd61a28abf838cae1b6/html5/thumbnails/8.jpg)
R. Wenninger 8 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
JET – Overall Pellet system
Pellet Injection Locations
• Injection from 3 poloidal locations
• Centrifuge – Future option for parallel fuelling and pacing
V
LH
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R. Wenninger 9 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
Fuelling ELM pacing
Species H2, D2 H2, D2
Frequency ≤15 Hz ≤60 Hz
Pellet speed 150-600 m/s 50-200 m/s
Pellet size/mass (D2)
~ 64 mm3 (4 1021 atoms )
~ 1.5 mm3 (9 1019 atoms )
Reliability 98% 98%
JET – HFPI Injection capabilities
Values from HFPI specification
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R. Wenninger 10 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
Outline
• Pellet technology at AUG and JET• Pellets – a candidate ELM mitigation method• Observation of pellet triggered ELMs in H-
mode regimes• Direct pellet driven MHD• Careful considerations towards trigger
mechanism• Pellet impact on tokamak (ITER) operation• Summary
![Page 11: R. Wenninger 1 (35) Sat. Workshop to EPS on Fuelling 16 th June 2008 Status of ELM trigger investigations on JET and AUG R. Wenninger IPP Garching, EFDA.](https://reader031.fdocuments.us/reader031/viewer/2022012919/5697bfd61a28abf838cae1b6/html5/thumbnails/11.jpg)
R. Wenninger 11 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
ELM control – a necessary requirementAcceptable ELM size for ITER:
• Target plate erosion negligible at 0.5MJ/m2 for CFC and W (Zhitlukhin 2007)
• Assume strong asymmetry of deposition on inner/outer targets: Pout/Pin = 1 : 2
• Tolerable energy deposition on target plates per ELM: WELM,target=0.5MJ/m2
1.3m2 (1+1/2) 1MJ (Polevoi EPS 2008)
F. Federici et al PPCF 45 (2003)
Reliable ELM control technology mandatory for ITER
• WELM,target fELM = Psep, = 0.2 – 0.4
(Herrmann 2002) fELM = 20 – 40Hz (spont. ~ 2 - 4Hz)
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R. Wenninger 12 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
ELM control technologies
• Edge ergodisation by resonant magnetic perturbation (Y. Liang PRL 98 (2007)) Plasma edge rarefaction without cooling (needs pellet fuelling)
• Magnetic ELM pacing by vertical kicks – accelerating plasma in vertical direction (Sartori et al.)
• Impurity seeding Type III (higher frequency) + higher radiation fraction
• Pellet ELM Pacing (P. Lang NF 2004)
• …
DIIID
None of these technologies is yet proven to work at ITER
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R. Wenninger 13 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
Pellet ELM Pacing – Proof of Principle at AUG
AUG
JE
T
• fELM ≥ fPEL fELM more than doubled at AUG
• WELMfELM=const at const. Pheat confirmed for pellet triggered ELMs (Lang NF 2002)
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R. Wenninger 14 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
Scaling aspects: size, magnitude, location of required perturbation?
• Local perturbation imposed by pellet particle deposition is strong enough for triggering ELMs at AUG and JET (Until now every pellet injected into ELMy regime triggered an ELM)
• But does this still hold at ITER size? • More physics understanding necessary!• Threshold might be defined by
– local (e.g =T, n, p, j,...) and– relative extension (e.g. x/R)
Readjustment might be possible but at the expense of again stronger fuelling (and pumping) and hence convective losses.
x
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R. Wenninger 15 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
Outline
• Pellet technology at AUG and JET• Pellets – a candidate ELM mitigation method• Observation of pellet triggered ELMs in H-
mode regimes• Direct pellet driven MHD• Careful considerations towards trigger
mechanism• Pellet impact on tokamak (ITER) operation• Summary
![Page 16: R. Wenninger 1 (35) Sat. Workshop to EPS on Fuelling 16 th June 2008 Status of ELM trigger investigations on JET and AUG R. Wenninger IPP Garching, EFDA.](https://reader031.fdocuments.us/reader031/viewer/2022012919/5697bfd61a28abf838cae1b6/html5/thumbnails/16.jpg)
R. Wenninger 16 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
Pellet can trigger an ELM at any time between Type-I ELMs
AUG
• ELMs triggered by with feff up to 350Hz (temporal resolution problem in higher frequency)
•Triggered ELM: 50s delay between pellet causes perturbation and ELM
G. Kocsis
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R. Wenninger 17 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
Quiescent H-Mode: Pellets don’t trigger ELMs in any H-mode regime
• QH: Obtained by counter injection
• Good confinement (H98y~1)
• High pedestal and core ion temp.
• ELMs replaced by ‘edge harmonic oscillation’ (EHO, ~10kHz) + ‘high frequency oscillation’ (300 – 400kHz)
• Even large pellets do not trigger ELMs
AUG
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R. Wenninger 18 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
Pellet can terminate phase free of spontaneous ELMS
• Pellets trigger first ELM ~0.5s earlier than first spont. ELM occurs in reference shot
• Avoid spontaneous Giant ELM (e.g. 1st after ELM free phase)
• Each pellet triggered an ELM of smaller size, with <20% the loss in energy, than the spontaneous Giant ELM
B. Alper 2002
JET
14MW NBI
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R. Wenninger 19 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
Pellets lead to fastest ELM-growth (I)
Comparison of growth time of MHD signal up to its max. value (ELM rise time):spontaneous Type I pellet driven between Type I
pellet driven between Type III < spontaneous Type III
AUG
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R. Wenninger 20 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
Pellets lead to fastest ELM-growth (II)
Type I
Rad. cooled Type I
Type III
• ELM rise time of pellet driven ELMs const. ( spont. Type I: fastest growth)
• ELM rise time increases from Type I, via rad. cooled Type I to Type III
Correlated e.g. with parallel resistivity at pedestal top
AUG
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R. Wenninger 21 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
Outline
• Pellet technology at AUG and JET• Pellets – a candidate ELM mitigation method• Observation of pellet triggered ELMs in H-
mode regimes• Direct pellet driven MHD• Careful considerations towards trigger
mechanism• Pellet impact on tokamak (ITER) operation• Summary
![Page 22: R. Wenninger 1 (35) Sat. Workshop to EPS on Fuelling 16 th June 2008 Status of ELM trigger investigations on JET and AUG R. Wenninger IPP Garching, EFDA.](https://reader031.fdocuments.us/reader031/viewer/2022012919/5697bfd61a28abf838cae1b6/html5/thumbnails/22.jpg)
R. Wenninger 22 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
Simplistic causal model
Pellet
Perturbation of plasma parameters (n, T, j,...)
Direct pellet driven MHD
ELM
Option 1:
Option 2:
Pellet
Perturbation of plasma parameters (n, T, j,...)
Direct pellet driven MHD
ELM
![Page 23: R. Wenninger 1 (35) Sat. Workshop to EPS on Fuelling 16 th June 2008 Status of ELM trigger investigations on JET and AUG R. Wenninger IPP Garching, EFDA.](https://reader031.fdocuments.us/reader031/viewer/2022012919/5697bfd61a28abf838cae1b6/html5/thumbnails/23.jpg)
R. Wenninger 23 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
Magnitude of required ELM trigger perturbation: Tiny in pellet terms?
JET
Magnetic signal for pellet driven ELMs can be separated in• ELM related MHD• Directly pellet driven part
observed even in L-mode stops abrupt with burn out @ trigger time below resolution Direct pellet driven MHD sufficient, if threshold would be > x100, if option 1
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R. Wenninger 24 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
OH: Direct pellet driven MHD only
≈ 50 µs
AUG
• Ohmic plasma (OH) Only direct pellet driven component
• Faintest pellet provokes stronger MHD than at typical ELM onset
![Page 25: R. Wenninger 1 (35) Sat. Workshop to EPS on Fuelling 16 th June 2008 Status of ELM trigger investigations on JET and AUG R. Wenninger IPP Garching, EFDA.](https://reader031.fdocuments.us/reader031/viewer/2022012919/5697bfd61a28abf838cae1b6/html5/thumbnails/25.jpg)
R. Wenninger 25 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
OH: No sign. Variation of directly pellet driven MHD with pellet parameters
•Repeated use of same stationary scenario
• Averaging of amplitude of dB/dt (MHD) over entire shot for all pellets (about 10)
• MHD clearly correlated to radial position of pellet and thus on local plasma parameters (e.g. p, j, Te, …)
• No significant dependence on pellet parameters (mass, velocity) and thus on ablation / deposition saturation effect?
• Pellet driven MHD depends mainly on plasma parameters
AUG
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R. Wenninger 26 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
Outline
• Pellet technology at AUG and JET• Pellets – a candidate ELM mitigation method• Observation of pellet triggered ELMs in H-
mode regimes• Direct pellet driven MHD• Careful considerations towards trigger
mechanism• Pellet impact on tokamak (ITER) operation• Summary
![Page 27: R. Wenninger 1 (35) Sat. Workshop to EPS on Fuelling 16 th June 2008 Status of ELM trigger investigations on JET and AUG R. Wenninger IPP Garching, EFDA.](https://reader031.fdocuments.us/reader031/viewer/2022012919/5697bfd61a28abf838cae1b6/html5/thumbnails/27.jpg)
R. Wenninger 27 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
Spont. type I and triggered ELMs – No significant difference on level of density fluctuation
• Reflectometry at fixed frequency mode density fluctuation
• Compare frequency power spectra (Integration: 2.5ms) for
• 3 different densities
• LFS and HFS
• Spontaneous and triggered ELMS
No significant difference between spontaneous type I and triggered ELMs AUG
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R. Wenninger 28 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
Spont. type I and triggered ELMs – No significant difference in target power load pattern
• Infrared Thermography: Observation of type I ELMs reveals non-axissymmetric stripes on divertor targets mapped to filaments (Eich PRL 2003)• For later ELM phase mode structure can be identified
No significant difference in patterns between spontaneous type I and triggered ELM
AUG
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R. Wenninger 29 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
Pellets in the Peeling-Ballooning-Picture
• PB-Theory quantifies ELM dynamics via growth Rate of driving mode
• Type I ELM cycle (Connor 1998)
• Type I ELMs:
Typical av. inter ELM time > ms
• Pellet triggered ELMs:
t(pellet at location – ELM) < 0.1ms
If there is a similarity in the mechanism, pellet must shortcut the type I ELM cycle significantly
J
Stable <C
Instable >C
Transport time scale
Res
istiv
e tim
e sc
ale
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R. Wenninger 30 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
Outline
• Pellet technology at AUG and JET• Pellets – a candidate ELM mitigation method• Observation of pellet triggered ELMs in H-
mode regimes• Direct pellet driven MHD• Careful considerations towards trigger
mechanism• Pellet impact on tokamak (ITER) operation• Summary
![Page 31: R. Wenninger 1 (35) Sat. Workshop to EPS on Fuelling 16 th June 2008 Status of ELM trigger investigations on JET and AUG R. Wenninger IPP Garching, EFDA.](https://reader031.fdocuments.us/reader031/viewer/2022012919/5697bfd61a28abf838cae1b6/html5/thumbnails/31.jpg)
R. Wenninger 31 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
Pellet impact on tokamak (ITER) operation – Penetration depth and required pellet mass
Kocsis 2007
• Cumulative distribution function of trigger locations ~100% at ped. top
Assumption: Pellet penetration to pedestal top is required
• Pellet mass required to reach pedestal top for different scenarios:Reference: width 20cm, Te at top 4keV
Wide pedestal: width 30cm, Te at top 4keV
High pedestal: width 20cm, Te at top 5keV
• Lower speed More mass required but stronger perturbation
• Assumption: Ref. scenario
ITER
K.Gál (Hybrid-LLL-Code)
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R. Wenninger 32 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
Pellet impact on tokamak (ITER) operation – 3 injection scenarios
Option v (m/s) Feasibility PerturbationMin. pellet
massAdditional
fuelling rate
Pessimistic (P)
100 Demonstrated Max 351020D 1401021D/s
Optimistic Standard
(OS)500
JET – HFPI at lower mass
Mid 101020D 401021D/s
Optimistic Advanced
(OA)1000
To be demonstrated
– straight injection line!
Min 11020D 41021D/s
Results from Hybrid-LLL code
Assuming 40Hz pellet frequency
X
?ITER total pumping rate: 40 – 50 1021 D/s
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R. Wenninger 33 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
Pellet impact on tokamak (ITER) operation – Convective power losses due to pellets
• Pellet particles are heated by the plasma up to 75% Tped,ref
• Steady state cond.: Pellet = add. loss
Padd. loss= 3 Pellet kB <T>
• Assuming <T>=3keV (75% Tped,ref)
Padd. loss 200MW (P)
60MW (OS)
6MW (AO)
ITER total heating power: 40MW
Conclusion:1. Self-consistent modeling of the localized particle deposition and
enhanced transport required for more robust figures2. At least OS is needed – better AO
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R. Wenninger 34 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
A new idea – Beryllium pellet injection
• Advanced Optimistic: 1000m/s of 1020D (1.6mm3) extremely challenging
• High speed should be easier for Be pellet (melting point 1278°C, crystal structure)
• Simulation with a C pellet (K.Gál) indicate 1 * 1019 Be (a Ø 500μm sphere) would be sufficient to reach pedestal top
• Fuel dilution: Taking a plasma particle content of 1023e, P=1s, finjection=40Hz :
ΓP ≈ 4 * 1020/s Be, but ≈ 4 * 1021/s expected from wall
Need to demonstrate:
- ELM triggering by a Be pellet
- Pellet transfer through a tube
ITPA Activity
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R. Wenninger 35 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
Summary
• JET-HFPI: Milestone in development of pellet injector technology
• Pellet ELM Pacing: Candidate technique for ITER ELM control
• So far every pellet injected into ELMy regime triggered an ELM – not clear, if this holds for ITER
• Pellet can trigger an ELM at any time between Type-I ELMs
• Pellet triggered ELMs grow as fast as the fastest spontaneous ELMs (Type I)
• Pellet driven MHD depends mainly on plasma parameters
• If there is a similarity in the mechanism, pellet must shortcut the type I ELM cycle significantly
• 500 or 1000m/s injection mandatory for tolerable pump load and additional power losses in ITER
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R. Wenninger 36 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
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R. Wenninger 37 (35) Sat. Workshop to EPS on Fuelling 16th June 2008
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