helium elmy h-modes in alcator c-mod in support of iter … · 2015. 11. 19. · elmy discharges -...
TRANSCRIPT
C. E. Kessel1, S. M. Wolfe2, M. L. Reinke3, M. A. Chilenski2, J. W. Hughes2, Y. Lin2, S. Wukitch2 and the C-Mod Team2
1Princeton Plasma Physics Laboratory 2Plasma Science and Fusion Center/MIT 3Oak Ridge National Laboratory (ORISE)
APS-DPP, Savannah, GA, November 16-20, 2015
Helium ELMy H-modes in Alcator C-Mod in Support of ITER Helium Operating Phases
Helium/Hydrogen discharges are the first phases of ITER operations
He/H discharges will be used to prepare for DT operations on ITER
IOS-2.1 joint experiment: characterize He ITER-like discharges and compare with D
q95 ~ 3-4
Access to H-modeAccess to high performance ELMy regimes (Type I)W transport H-mode characteristics: Pped, H98, ELM behavior, ELM controlRadiative divertor operationH-L transition
Alcator C-Mod Expts: ELMy H-modes
We did not match ITER plasma parameters for these discharges (q95, shape, bN, n/nGr, H98,….)
Ip = 0.9 MA, BT = 5.4 T
n = 1.6-3.0 x 1020 /m3, nGrflattop ~ 5.9x1020 /m3
PICRF = 1.75 – 4.0 MW (1st harmonic H-minority)
ELMs were accessed, at varying density, with limited power variation
q95 = 3.65-3.9
= 1.55dU = 0.2, dL = 0.7-0.72
Comparing to similar Deuterium ELMy H-modes from 1090914 and 1120815 Plasma shape used to access ELMy
H-modes
ELMy He Discharge on C-mod 1150716
H-mode H-modeH-mode established with ~ 2.3 MW of ICRF
ELMs begin ~ 20 ms later
ELMs evident on ICRF waveform (coupling), normally not present for EDA
Neutron rate is lower than deuterium discharge when Helium is present
Strong He puff and resulting disruption in rampdown was used to keep He fraction higher
ELMy D discharge on C-Mod, 1090914
ELMy D discharge on C-Mod, 1120815
Good ELMy regimes and Infrequent ELM regimes
H-m
od
e
H-m
od
e
H-m
od
e
L-mo
de
L-mo
de
Lower densities led to good ELMy regimes, while higher density lead to large infrequent ELMs and H-L-
H transitions
Note time frames
Dt = 20 ms Dt = 200 ms
Good ELMy H-mode regime H-L-H… regime
H-mode
L-mode
The He discharge at high and low density
The best ELMy regimes were accessed for H-mode nline ave < 2.0x1020 /m3
Large infrequent ELMs with H-L-H behavior were obtained for H-mode nline ave > 2.6x1020 /m3
Pedestal n and T, and collisionality may be a good variable for separating these regimes
For nline ave ~ 2.0-2.5x1020 /m3 clusters of ELMy phases occur between no-ELM phases…appear to be ELM-free for He, need to examine for any fluctuations
In deuterium this transition has been described as transitioning to EDA H-modes from ELMy H-modes, with ELMs + EDA between
Quantifying the Deuterium and Helium Levels
He fraction in the C-Mod discharges, neutron rate is significantly lower for He
Fitting the Te(R) and ne(R) to calculate the neutron rate and infer D density
Te(R-Ro) = To [ (1-fT,edge) {1-(r/a)2)aT} + fT,edge]ne(R-Ro) = nDD[ (1-fn,edge) {1-(r/a)2)an} + fn,edge]
Use 20 zones in minor radiusBosch-Hale reactivity formulationAssumed flux geometry based on EFIT
Ti(R) = Te(R) , taken from ECE/TS data Deriving Ti from HIREXnDD determined to match neutron rate measurements (fast He3 data)
fn,edge = nped/no fT,edge = Tped/To
Preliminary analysis of neutron data show that He discharges significantly reduced nD
line ave / nline ave
D
D
L-H Threshold in He and D Discharges
L-H threshold power
Net or loss power to enter the H-mode indicates the He discharges are near/or in the low density regime (rising Pthr), limited available power likely made the higher density cases poor ELMydischarges
The 1090914 D discharges indicate the low density regime for L-H transition is at lower densities than reached, and the power to enter the H-modes was lower than He
The 1120815 D discharges show that all cases entered the H-mode at the same density, with a wide spread in power to enter the H-mode
No mass dependence applied
Ploss *Pnet 0
Ploss +Pnet X
Ploss BPnet A
Ploss #Pnet X
nline ave, /m3 x1020
See J. W. Hughes, poster on D threshold sensitivity
Mass dependence in energy confinement scaling IPB98(y,2) and L-H threshold formulations
derived for deuterium plasmas, mass dependence inferred from hydrogen experiments…..no He experiments used
t98(y,2) =0.0562 Ip0.93 B0.15 nL
0.41 R1.970.78 e0.58 P-0.69 (Mi/2)0.19
derived for deuterium plasmas, mass dependence inferred from hydrogen having ~ 2x threshold of D, and tritium experiments
PL-H,thr = 0.0488 nL0.72 B0.84 S0.96 (2/Mi)
There is a Z dependence that affects the ion density at fixed electron density, and mass effects should be separate from this……since the source of these mass factors is not from He expts, evaluations have not accounted for mass, using t98(y,2)
D and PL-H,thrD
ELM Frequency for He and D Discharges
Comparing ELM Frequency for He and D Discharges
Deuterium ELMy discharges from 1120815 and 1090914
The power variations are small, so density provides the more significant variation
As the density increases the ELM frequency decreases, both for D and He
1120815 has high radiated power, and may be in a high freq ELM regime due to Pnet/Pthr proximity??
Examining the power (loss and net) against the threshold to characterize possible regimes (Type III, Type I, etc.)….better to run pedestal stability
Plasma Performance for He and D Discharges
He discharges tend to underperform the best D discharges in terms of energy confinement and
stored energy, in flattop ELMy H-modes
nGr = 5.92 x 1020 /m3nline ave, /m3 x1020
Powers relative to the threshold power in sustained ELMy H-mode phases
DeuteriumHelium
PthrD = 0.0488 nL
0.72 BT0.803 S0.94
Scatter makes deriving trends difficult, but there does appear to be a somewhat higher Pnet required to maintain an H-mode in He than D, which persists over nline ave range
Lines to guide eye
The flattop H-modes indicate that higher Pnet
relative to PthrD is required for He
There is variability in the D discharges in terms of achieved stored energy, or energy confinement, but similar Pnet/Pthr
D
1150716 He
1120815 D
1090914 D
The Power terms are used to characterize the discharges in different run days, both He to D and
D to D
He D
Global W Impurity Transport for He and D Discharges
Tungsten LBO provided global particle confinement times in He discharges
1.05 1.10 1.15 1.20 1.25Time [sec]
0.0
0.2
0.4
0.6
0.8
1.0
No
rma
lize
d W
Brig
htn
ess [A
U]
129
1150716
025
127
11507
16026
146
11
507160
27
123
115071
6030
tZ [ms] =
1.05 1.10 1.15 1.20 1.25Time [sec]
0.0
0.2
0.4
0.6
0.8
1.0
No
rma
lize
d W
Brig
htn
ess [A
U]
1150716
025
H/L Trans.
11507
16028
H/L Trans.
11
507160
29
ELMs provided effective W particle removal
Infrequent ELM regimes show long holdup of W
M. Reinke
tE ~ 33-31 mstE ~ 36-29 mstE ~ 31-43 mstE ~ 27-34 ms
tW* ~ 129 ms
tW* ~ 127 ms
tW* ~ 146 ms
tW* ~ 123 ms
ELMy cases
ELMy
Infrequent ELMs
ELM clusters
tW* / tE ~ 4
Pedestal Comparison of He and D Discharges
The electron pedestal pressures appear similar between He and the D discharges
Based on TS data for electrons
Infrequent large ELMs
ELM crashes
Both the density and temperature of the pedestal appear to be similar for the He and D discharges
Exceptions are the high density He cases which have large infrequent ELMs, and ELM crashes caught by the TS
Tped is presently determined only to 25 eVincrements
Electron pedestal collisionalities ranged from ~ 0.2-1.0 for the majority of He and D discharges
- ped
The He and and higher performing D discharges reach similar electron pressures in similar collisionality regimes
Based on TS data for electrons
Tped is presently determined only to 25 eVincrements
Examining MHD modes in H-mode phases for He to compare to D
High frequency mode between ELMs that occur every ~ 5 ms
Closer examination shows a dropping frequency just before an ELM (S. G. Baek and A. Diallo)
No mode in early H-mode (ELM-free?)High frequency mode appearing between long no-ELM phase
1150716033
High frequency mode over long ELM-less period, is this the QCM?
L-mode
Observations and Future Work
Overall, the He discharges behaved similarly to D discharges
- Similar ELMy regimes were accessed- Similar Tped, nped, ELM freq, etc.- Loss of ELMy regime with rising density, progression
toward infrequent large ELMs is similar
- There may be differences in the transition away from ELMy at increasing density….need to verify
There is variability for the ELMy D discharges evidenced by 1120815 and 1090914
- The underlying differences between these are still unclear, although ELM frequency is much different
Will add more discharges to the comparison between He and D ELMy discharges
- Add 1101027 (other He ELMy data)- Add companion 1101026 D- Add 1101214 D, 1110325 D, 1101117 D (others at 0.9 MA
and 5.3-5.4 T)
Tungsten global particle confinement times from W LBO identify tW
* / tE ~ 4, and that sustained ELMy phases avoid W holdup associated with infrequent ELM regime
- W holdup was seen for the infrequent ELMs
Examine the presence of or lack of “modes” (eg. QCM) between ELMs in the He and D discharges, both frequent ELMy and infrequent ELMs