# Presentation: 160746

## Question 15c: 

**FESAC Priorities Panel’s****Fusion Engineering Science Theme**
**Question 15c:**
**Long-pulse Power- and Particle Extraction**

- Peter Mioduszewski
- Oak Ridge National Laboratory

- April 30, 2004

## In a stationary fusion plasma, energy and particles  need to be removed continuously ! 

**Handling high **_**power fluxes**_**:  ****plasma solutions**** - ****engineering solutions**
**  ****plasma solutions**
**  ****e. g. high recycling ; detachment**
**  ****high recyling reduces T****e**** and sheath potential -> sputtering**
**  ****detachment reduces power and particle flux, but... **
**   ****deteriorates core performance: partial detachment acceptable   **
**  ****engineering solutions**
**  ****materials choice: low-Z (T-retention), high-Z (melt-layer), liquid**
**  ****cladding - bonding - substrate:**
**  ****thermal stress issues **
**  ****thick cladding: long erosion life/low power**
**  ****thin cladding : short erosion life/high power**
**  ****plasma/engineering solutions**
**  ****SOL design: e.g. stochastic layers, islands, etc.    **

## Normal operation and off-normal events

**  ****Presently accepted values for ****steady state**** power fluxes are 5 MW/m****2**** **
**   ****with temporary excursions up to 10 MW/m****2**** ****(ITER);***** up to 25 MW/m****2****  **
**   ****(FIRE); **** most reactor designs keep the power flux under 10 MW/m****2**
**  ****CFC and Be would have low Z****eff****, but short erosion life times**
**  ****W would have long erosion life times (excluding melt layer erosion),**
**    ****but needs to be well controlled in the divertor**
** **
**  ****Critical issues for power handling in (future) tokamaks are**
**  **_**Disruptions**_**: 100 MJ/m****2****  in ~1 ms, 100 GW/m****2   ****(ITER=50 x JET);**
**   ****dramatic erosion effects, but ****vapor shield**** will save the day**
**   ****->  losses: ****30 ********m**** of carbon; ****25-75**** ********m for metals**
**  **_**ELMs**_**:  0.4 MJ/m****2**** (CFC) and 0.64 MJ/m****2**** (W) maximum tolerable**
**   ****repetitive pulsed heat load  **
** ***** Today’s ****pulsed**** experiments (t ≤ 10s) can handle ****higher power loads**** - at low duty cycle - **
**   ****through their thermal capacity**** **

## Particle control and exhaust

**1.  A burning fusion plasma needs continuous exhaust of ****helium ash**** **
**     ****to prevent fuel dilution.**
**    ****This requires sufficient particle fluxes into the divertor and **
**    ****corresponding pumping speeds -> ****divertor design; operating regime**
** ****2.  ****Particle (neutrals) control**** is an essential knob for optimizing  **
**      ****plasma performance**
**      ****This is achieved by ****divertor design and operating regime**
** ****3.  Power- and particle control are closely coupled through both  **
**      ****plasma-**** and ****engineering solutions****: divertor regime, materials     **
**      ****choice, geometry, design, etc.  **

## Power- and particle extraction issues:

**High core performance and PFC design is marginal for ITER!**
**	**
**	****Critical issues: ****Disruptions: mitigation, prevention **
**	****	****	****     ****Type I ELMs: type II ELMs, ELM-free scenarios**
**	****	****	****      ****VDEs: ~ 1mm per event on  FW in ITER**
**	**
**Medium term (5 years):**
**	****Find scenarios (experiment & modelling) that simultaneously satisfy safe divertor operations and optimum plasma performance!**
**2.****	****Longer term (10 years):**
** ****	****Need to develop scenarios for power- and particle control with safe margins, low T-inventory, low erosion, low Z****eff****, coupled with optimum plasma performance. ****Need models and codes to support experiments developing integrated divertor and core scenarios****.**