# Presentation: 314278

## Towards the realization on JET of 

**an integrated H-Mode scenario for ITER**

**19th IAEA Fusion Energy Conference**
**14 to 19 October 2002**
**Lyon, France**

**J.Ongena and EFDA-JET work programme contributors**
- Task Force Leader Scenario 1 at JET
- Ecole Royale Militaire / Koninklijke Militaire School
- Association “EURATOM-Belgian State”
- Brussels, Belgium** **

## O U T L I N E

-  ITER Q=10 ELMy H-Mode operational      requirements for high density, confinement and      beta simultaneously realized in JET discharges
-  Towards the realization of acceptable heat loads on          the ITER divertor target plates
-  Summary and Outlook

## High Confinement and high density

**in ELMy H-Mode discharges**

- Obtained in three different ways :
- Plasma Shaping : High triangularity
- Impurity seeding : Low and High  plasmas
- High Field Side pellet injection
- Peaked density profiles can be seen
- Modified confinement scaling taking into account influence of density peaking, triangularity, proximity to Greenwald density

## 1. Plasma Shaping 

**High Confinement and High Density at High ******

- Confinement of high performance         high  discharges :
-  Type I ELMs with indications for     Type II ELMs at high density
-  Simultaneously for ~ 4 sec (~ 9E) :
-  High density n/nGW > 1
-  High N,th > 1.8
-  High Confinement H98(y,2) = 1

## JET Confinement depends on  and ELM Type

-  Degradation versus density    for all triangularities
-  At high  : n/nGW, H98(y,2) and N     for ITER obtained simultaneously
-  Confinement in lower  plasmas     improved by increasing Pin/PL-H
-  Best points :       n/nGW > 1 with H98(y,2) = 1     		        N ~ 1.9

- Black diamonds from new HT3 configuration designed for high current/field operation

**See also J.Pamela, OV/1-4**

## 2. Impurity Seeding combines High Confinement and High Density with Radiating Mantle

- Result of Ar seeding :
-  Increased radiation : Prad/Ptot = 0.65
-  Increased density (f  p )
-  Density up to 1.15 n/nGW    (with H98(y,2) = 0.9 and N,th = 2.1)
-  Effects on ELMs
- Reduction of ELM frequencyHigher D between ELMs
-  Moderate increase of Zeff:    Zeff ~ 0.2 and CAr(0.2) = 0.05%
-  Lack of central heating terminates pulse

## Radiating Mantle and ITG stabilization with Ar Seeding 

**Radiating Mantle and ITG stabilization with Ar Seeding **

-  Radiating Mantle in Plasma Edge

-  Reduction of ITG growth rate Improvement of core confinement

- For both high and low  discharges :

- High  discharges #53149 #53146

- Calculated with Weiland model(I.Voitsekhovitch)

- Larger mantle in high  discharge

- Without Ar

- With Ar

- #53146 #50473

## 3. High Field Side Pellet Injection  

-  Applied to discharges with medium  = 0.32
-  Fast Pellet Sequence to raise density
-  Slow Sequence to keep density and confinement
-  Strongly Peaked Density Profiles: n(0)/nped ~ 2

##  Density Peaking

- Obtained with High Field Side Pellet Injection
- But also without Pellet Injection on JET :
- 	Tuning of gas dosing and heating
- Impurity seeding in low  discharges

## ELM Mitigation Studies

-  New ELM behaviour leading to reduced        ELM losses at high n and high       (inter ELM losses correlated with MHD,  appearance of ELMs similar to Type II ELMs) :

**ELM Mitigation Studies**

**How to reach acceptable heat loads in the ITER divertor ? **

**Loss of Power due to ELMs  : P****ELM**** =**** ****f****ELM**** ******** ********W****ELM**

-  Low n 	                 High n

-  Determined by edge transport, Psep  /  edge parameters
-  Tools :  , D puff, Ar, power

-  Beneficial influence of impurities

**See also A.Loarte, EX/P1-08 **

## Reduction of WELM/Wped at high density and high 

**Reduction of ********W****ELM****/W****ped**** at high density and high ******

-  With increasing density :      Reduction of WELM/Wped       Reduction of (Te/Te)ped      Weak decrease of (ne/ne)ped
-  ‘Minimum’ Type I ELMs found   (at U = 0.5 and reduced L = 0.3)   with (Te/Te)ped = 0 and   WELM/Wped = 4.5%

**See also A.Loarte, EX/P1-08**

## ELM mitigation with impurity seeding

- Without Ar

**Reduced Target Surface Temperature with Ar seeding **** **

- With Ar

- During ELMs in Between ELMs

**Unique feature of impurity seeding : ****Drop in base line target temperature will allow larger temperature ****excursions due to ELMs before reaching ablation limit**

**See also J.Rapp, P.Monier-Garbet, EX/P1-09**

## Scaling of ELM size and extrapolation to ITER 

** ****Raises hope for a possibility of Type I ELMs operation on ITER with****     an acceptable divertor lifetime**
** ****Further work ongoing to determine the correct parameter dependence**

******//****front****  : char. time for****heat front to reach the target**

**Scaling of ELM size and extrapolation to ITER **

**Correlation between ELM size and both ************ped**** and ********//****front****  **** **

**See also A.Loarte, EX/P1-08 and G.Matthews, EX/D1-1**

## Conclusions1. ITER Q=10 ELMy H-Mode Requirements reached on JET with several techniques   

**Conclusions****1. ITER Q=10 ELMy H-Mode Requirements ****reached on JET with several techniques   **

## Conclusions

**2. New results on ELM physics and extrapolation to ITER :**
** ****Decrease of ELM size at high density for ITER ******
** ****Further alleviation of constraints due to ****    ELM heat load possible with impurity seeding**
** ****Hope for a possible window for Type I ELMs operation ****    with an acceptable ITER divertor lifetime**

**JET is an excellent testbed to prepare for ITER operation**

## OUTLOOK

**Continue preparation for  ITER Operation using new ‘tools’ at JET **** **

**New Pellet Track****ITER deep fuelling**

**New ITER relevant Discharge Shapes**

**New very long divertor phase (50s) pulses**

- Near Double Null
- Study of Type II ELMs

- Plasmas with reduced disruptive force
- Study of High Current Plasmas

- Optimisation of pellet fuelling for ITER

- Long time plasma and wall constants

- NEW!

## Slide 17

## Very Long Divertor Phase Pulses On JET 

- Study of Long time constants in wall and plasma parameters

## 2. Impurity Seeding

- Aim :
- Realize an integrated operational scenario combining :
- High density and high confinement
- Acceptable power exhaust
- 	In JET : using Ar seeding in low and high  discharges
- 	Cautious D and Ar dosing

##  3. Pellet Injection from the High Field Side

- In medium triangularity discharges
- Using an optimised pellet cycle
- High densities reached while keeping high confinement
- Peaked density profiles

## Spontaneous Density Peaking

- Stationary peaked profiles : n(0)/nped ~ 1.3

-  Tuning of gas dosing (flux, position) and plasma heating
-  High and stationary  n/nGW = 1, N,th = 2 and H98(y,2) = 1

## Confinement and L-H Threshold Scaling Studies on JET 

-  Influence of plasma shaping, density peaking and proximity to the Greenwald limit                 H98(y,2),corr = H98(y,2) F                  F = 0.46 + 1.35 ln(q95/qcyl) + 0.38(n/nped - 1) - 0.17n/nGW

- BENEFICIAL :
- Plasma Shape and Density Peaking

- DETRIMENTAL :
- Proximity to Greenwald limit

- Effect on Confinement:

-  He plasmas (purity CHe / CD = 85%) show :
-         Isotope scaling : E  M0.19Z-0.59 (from previous H and T data + He database)        L-H Power Threshold in He : same Ip Bt and mass dependence as for D		            		50% higher in absolute value

## Density Peaking with Impurity Seeding 

-  Low  plasmas ( ~ 0.3)
-  High and stationary       n/nGW = 1, N,th = 2 and H98(y,2) = 1
-  Peaked density profiles : n(0)/nped ~ 1.3

## Heat pulse delay of ELMs IR from IR thermographic measurements

**Heat pulse delay of ELMs ********IR**** ****from IR thermographic measurements**

**Indications for non-determining role of *********,ped**