ITER  is  an  international  research  project  to  build  an  experimental  fusion  reactor.  The  success of ITER would mark an important step towards creating a sustainable carbon-­free source of fusion energy. A major goal of ITER is to demonstrate the generation of 500 MW of  fusion  power  from  a  50  MW  input.  One  of  the  biggest  challenges  for  ITER  will  be  to  control  the  fusion  plasma.  Fusion  reactions  generate  massive  amounts  of  heat.  The  heat from the fusion reaction in ITER will cause the plasma inside ITER to reach temperatures as hot as the Sun, 150 million degrees Celsius. ITER will use strong magnets to contain the extremely hot plasma yet edge plasma may still interact with the surface of ITER and create a  turbulent  environment  where  edge  plasma  behavior  is  difficult  to  predict  and  control.  Controlling  the  edge  plasma  behavior  is  necessary  to  create  a  sustained,  controlled,  and confined fusion process. Edge plasma behavior is therefore critical to ITER’s success.  

First,  ITER  must  be  able  to  reliably  withstand  the  steady  exhaust  heat  deposited  in  an  extremely  narrow  strip  on  the  divertor  target  plates.  Second,  ITER  edge  plasma  must  be able to access physical conditions that create suitable edge plasma behavior known as the high  confinement  mode  of  operation  (L-­‐H  transition).  Here  the  edge  plasma  supports  confinement  by  forming  a  barrier  called  the  ‘edge  pedestal’.  Third,  instabilities  that periodically destroy the edge plasma pedestal must be avoided or mitigated.  

To optimize the chances for ITER’s success in controlling the high energy edge plasma, this project  supports  computational  simulations  to  understand  edge  plasma  physics  using  highly accurate extreme-­scale edge gyrokinetic code XGC1, developed for this purpose by collaborative SciDAC activities between computer and fusion scientists supported by DOE’s ASCR and FES programs.