Transcript Edge Plasma Energy and Particle Fluxes in Divertor Tokamaks

Update on Thermal Loads during
disruptions and VDEs
A. Loarte
with contributions from M. Sugihara, A. Herrmann,
G. Arnoux, T. Eich, G. Counsell, G. Pautasso,
V.
Riccardo, etc.
Alberto Loarte
10th ITPA Divertor and SOL Physics Group
Avila – Spain
7/10 – 1 – 2007
1
Specification of ITER disruption/VDE Thermal Loads
 New ITER specifications for disruptions and VDEs take into
account latest physics findings
 Pre-disruptive confinement degradation for H-mode
disruptions
 Footprint broadening at thermal quench
 qdiv(t) at thermal quench
 Radiation asymmetries in current quench
 Plasma evolution to thermal quench in VDEs and
broadening of footprint
 Impact geometry of runaway electrons
 etc.
Some issues still poorly understood or restricted database :
asymmetries, runaway power fluxes, thermal quench limiter
disruptions ,etc.  Advice from ITPA required
Alberto Loarte
10th ITPA Divertor and SOL Physics Group
Avila – Spain
7/10 – 1 – 2007
2
Energy Fluxes during disruptions (I)
 Energy degradation before thermal quench for resistive MHD
disruptions (not for ITBs)
 Large broadening of footprint for diverted discharges but small
for limiter discharges (?)
Alberto Loarte
10th ITPA Divertor and SOL Physics Group
Avila – Spain
7/10 – 1 – 2007
3
Effect of background radiation
A. Herrmann
J. Paley, P. Andrew
JET- G. Arnoux
Energy to upper X-point
(DRmp ~ 3.5 cm )
More systematic studies of power flux broadening required
Alberto Loarte
10th ITPA Divertor and SOL Physics Group
Avila – Spain
7/10 – 1 – 2007
4
Energy Fluxes during disruptions (II)
 Timescale (~ R) but large variability (1.0-3.0 ms for ITER)
 Longer timescales in decay phase (> 2 rise phase)
 Toroidal asymmetries (~2) seen in some cases but poor
documentation/statistics
 Systematic study of in/out asymmetries required
Alberto Loarte
10th ITPA Divertor and SOL Physics Group
Avila – Spain
7/10 – 1 – 2007
5
Energy Fluxes during disruptions (III)
Proposed ITER specifications (M. Sugihara/M. Shimada)
Scenario 2 :
unit (MJ/m2)
Energy release at TQ
(1/2-1/3)Wpeak
Wpeak
DE// near separatrix at outer
midplane
DE// near upper ceiling region
(6 cm from 1st separatrix)
DE// near lower baffle region
(6 cm from 1st separatrix)
200 - 70
400 - 200
20 - 50
60 - 100
16 - 40
48 - 80
DE// to divertor plate near 1st
separatrix
280 – 90 (out)
375 – 120 (in)
560 – 280 (out)
750 – 380 (in)
=2.5 cm (left), 5 cm (right) Total energy deposition time
duration = 3-9 ms
Alberto Loarte
10th ITPA Divertor and SOL Physics Group
Avila – Spain
7/10 – 1 – 2007
6
Energy Fluxes during disruptions (IV)
Proposed ITER specifications (M. Sugihara/M. Shimada)
Scenario 4 :
unit (MJ/m2)
Plasma shift caused by beta collapse does
Energy release at TQ
not cause IW contact in ITER unlike JET
experiments (P. Andrew)
Wpeak (325 MJ)
DE// near separatrix at outer midplane
510 - 255
DE// near upper ceiling region
(5 cm from 1st separatrix)
DE// near lower baffle region
(5 cm from 1st separatrix)
DE// to divertor plate near 1st separatrix
120 - 160
95 - 130
730 – 365 (out)
375 – 120 (in)
=2.5 cm (left), 5 cm (right) Total energy deposition time
duration = 3-9 ms
Alberto Loarte
10th ITPA Divertor and SOL Physics Group
Avila – Spain
7/10 – 1 – 2007
7
Energy Fluxes during VDEs (I)
ITER
W
TQ a t q = 1 . 5
peak
JET
DW
2
DW
W

1

2

3
TQ
Presently proposed ITER specifications
En e rg y lo ss p h ase
based on JET based extrapolations 
d u rin g q d e crea se
Fa st e n erg y lo ss p h a se
input from other tokamaks needed
a fter tra n sition
 DW2 = 20-55 MJ
H -L tra n sitio n
 2 = JET/L-modeJET (0.03-0.09)*L-modeITER
Sta rt of lim iter co n fig .
 DW3 = W(2)-dW/dt|L-mode*3
Alberto Loarte
10th ITPA Divertor and SOL Physics Group
Avila – Spain
7/10 – 1 – 2007
8
3
Energy Fluxes during VDEs (II)
100
VDE_downward
(a)
15
3
(b)
0
-100
(c)
Z
-2
(d)
2
16
(c)
Z (cm)
10
14
4
(a)
0
(b)
15
Current (MA)
- Heat load on lower
Be wall & W baffle
2
20
Z (m)
Downward VDE with
fast CQ
- EM load on BM /
DIV by eddy
(+halo) current
Ip
-200
1
17
(d)
-4
5
-400
pol
halo
I
0
640
650
660
670
680
-6
690
-500
300
400
500
Alberto Loarte
500
VDE_upward
700
800
900
9
8
10
6
Ip
(b)
Z
(c)
10
11
4
Z (cm)
Current (MA)
15
(d)
7
400
Z (m)
- Heat load on upper
Be wall during
VDE and TQ
8
20
(a)
600
R (cm)
Time (ms)
Upward VDE with
fast CQ
- EM load on BM by
eddy (+halo)
18
-300
300
6
200
5
100
4
12
(c)
(b)
(d)
2
5
(a)
pol
Ihalo
0
860
880
900
920
Time (ms)
10th ITPA Divertor and SOL Physics Group
940
0
0
300
3
400
500
600
700
800
R (cm)
Avila – Spain
7/10 – 1 – 2007
9
Energy Fluxes during VDEs (III)
 Indications of broadening of power footprint at VDE thermal
quench
JET-Arnoux
AUG-Herrmann
∫q(r
omp)dr
Power width =
Alberto Loarte
10th ITPA Divertor and SOL Physics Group
Avila – Spain
qmax
7/10 – 1 – 2007
10
Energy Fluxes during current quench (I)
During current quench plasma magnetic energy is lost
1
R
 3
Wm agnetic Lplasm aI 2p with Lplasm a  0 R0 (ln( 8 0 )  2  i   p )
2
a
4 4
Part of Wmag transferred to conductors  Wohmic = Wmag-Wconductors  plasma heating
JET-Pulse No. 69787
JET-Paley-PhD Thesis 2006
JET-P. Andrew JNM 2007
 Most tokamaks/disruptions Wohmic lost by Prad (except high Bf/high Z Alcator C-mod)
Alberto Loarte
10th ITPA Divertor and SOL Physics Group
Avila – Spain
7/10 – 1 – 2007
11
Energy Fluxes during current quench (II)
JET (A. Huber)
#69787
During current quench the radiation distribution is poloidally asymmetric
Alberto Loarte
10th ITPA Divertor and SOL Physics Group
Avila – Spain
7/10 – 1 – 2007
12
Radiation during current quench (II)
JET (A. Huber)
Pwall(MW/m2)
3.5
3.0
2.5
Power deposited on the Wall
t=66.861s
t=66.869s
t=66.872s
2.0
1.5
1.0
0.5
Radiation peaking
3.0
2.5
t=66.869s
t=66.872s
2.0
1.5
1.0
0.5
But deposited power on the wall has
Poloidal distance along wall (m)
0.0
a peaking factor of only 2
0 Group 2
4 Avila –6Spain 87/10 – 1 – 10
Alberto Loarte
10th ITPA Divertor and SOL Physics
2007
13
Runaway electron fluxes on PFCs (I)
Predicted runaway current
Energy spectrum of electrons (E0 for exp(-E/E0))
Inclined angle
Total energy deposition due to runaway current
Average energy density deposition
Duration of the average energy density deposition
Maximum energy density deposition (end of the
plasma termination)
Duration of the maximum energy deposition
Number of event
10 (MA)
12.5 MeV
1 - 1.5
20 MJ
1.5 MJ/m2
100 ms
25 MJ/m2
10 ms
Every major
disruption
 These specifications are generally reasonable but physics basis is
weak (very poor experimental input)
 Largest concern energy load by drifted electrons due to
formation of X-point
Alberto Loarte
10th ITPA Divertor and SOL Physics Group
Avila – Spain
7/10 – 1 – 2007
14
Runaway electron fluxes on PFCs (II)
Current profile during runaway discharge peaks (seen at JET)
 X-point formation in Scenario 2
Smith PoP 2006
EFIT reconstruction by S. Gerasimov
Alberto Loarte
10th ITPA Divertor and SOL Physics Group
Avila – Spain
7/10 – 1 – 2007
15
Runaway electron fluxes on PFCs (III)
 Significant drift of runaways near upper X-point due to
poloidal field null [f(E) = 1/E0exp(-E/E0) with E0 = 12.5 MeV]
 Angle of impact of runaways on drift orbits at upper X-point <
1.5o but impact direction mainly toroidal
Alberto Loarte
10th ITPA Divertor and SOL Physics Group
Avila – Spain
7/10 – 1 – 2007
16
Conclusions
 PID specifications for PFC loads during disruptions and VDEs
in ITER being updated following ITER Design Review
Process
 Key issues for further refinement of disruption thermal quench
loads are timescales, broadening, asymmetries and
dependence on pre-disruptive plasma conditions
For current quench level  distribution of radiative and
conducted loads to be studied systematically
 Specifications for VDEs are now based on real H-mode plasma
observations but more multi-machine data is required
 Dedicated studies on runaway loads during disruptions are
required to provide a firmer base of ITER specifications
Alberto Loarte
10th ITPA Divertor and SOL Physics Group
Avila – Spain
7/10 – 1 – 2007
17
Energy Fluxes during disruptions (V)
Major disruptions during limiter phase :
(M. Sugihara/M. Shimada)
Most severe assumption :
No broadening of deposition width
Ip (MA)
4.5
6.5
Wpeak (MJ)
 10
 20
P ; peak energy
density (MJ/m2)
 7.7
 15
(Kobayashi NF 07)
2 limiter case
If there is no broadening energy fluxes on limiter for disruptions can be
similar or larger than for the divertor disruptions in scenario 2
Alberto Loarte
10th ITPA Divertor and SOL Physics Group
Avila – Spain
7/10 – 1 – 2007
18