Workshop on Transients
byC.M. Greenfield

Presented to the Fusion Energy Sciences Advisory Committee

March 12, 20150

Transients Workshop: Background• Focus on disruptions and ELMs
– Can have deleterious effects on tokamak plasmas and havepotential to cause damage– Generally tolerated in present devices– More severe impacts on ITER
– Even more severe impacts on post-ITER devices (?)– “It is critical to develop the means to minimize these events andtheir consequences when they do occur.”• Build on previous studies, including– ReNeW (2009) – Thrust 2• Same scope, but the present workshop will:– Consider five more years of progress– Have more depth (this was 1/18 of the output of ReNeW)– FESAC Strategic Planning Panel report (2014) – identifies this ashigh priority initiative– USBPO Disruption Task Group1

Greenfield | FESAC 3/12/15

Transients Workshop: Objective

Building on the ReNeW effort, other workshop results, and the ongoing USBPO
disruptions task force plans, this workshop will:
1. Review recent progress
2. Identify the remaining science and technology challenges that must be
addressed to demonstrate that magnetically confined tokamak plasmas
with the characteristics desired for a fusion power plant can be robustly
produced, sustained, and controlled without deleterious effects on thedevice’s materials and structure
3. Based on thorough understanding of the remaining science and technology
challenges, the workshop will identify specific research opportunities that
can address these challenges in the next decade–

These may include both domestic research and international partnerships, andwill be informed by the requirements of ITER and future burning plasma devices

Our deliverable is a report to FES due June 30
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Workshop	  Panels	  Sub-­‐panels	  Workshop	  on	  Transients	  Chair:	  C.	  Greenﬁeld	  (GA)	  Co-­‐chair:	  R.	  Nazikian	  (PPPL)	  Preven1ng	  device	  damage	  from	  disrup1ons	  Lead:	  C.	  Greenﬁeld	  (GA)	  Co-­‐lead*:	  Dylan	  Brennan	  (Princeton	  U)	  Avoiding	  deleterious	  eﬀects	  of	  ELMs	  in	  high	  performance	  plasmas	  Lead:	  R.	  Nazikian	  (PPPL)	  Co-­‐lead*:	  J.	  Canik	  (ORNL)	  Disrup1on	  Predic1on	  	  Lead:	  S.	  Sabbagh	  (Columbia)	  Co-­‐lead:	  C.	  Hegna	  (Wisconsin)	  ELM	  suppression	  or	  mi1ga1on	  with	  resonant	  magne1c	  perturba1ons	  Lead:	  M.	  Fenstermacher	  (LLNL)	  Co-­‐lead:	  O.	  Schmitz	  (Wisconsin)	  Disrup1on	  Avoidance	  	  Lead:	  E.	  Strait	  (GA)	  Co-­‐lead:	  D.	  Gates	  (PPPL)	  Naturally	  ELM-­‐free	  opera1ng	  scenarios	  Lead:	  J.	  Hughes	  (MIT)	  Co-­‐lead:	  W.	  Solomon	  (PPPL)	  Disrup1on	  Mi1ga1on	  Lead:	  V.	  Izzo	  (UCSD)	  Co-­‐lead:	  R.	  Granetz	  (MIT)	  (USBPO	  DisrupQon	  Task	  Group)	  ELM	  pacing	  	  Lead:	  L.	  Baylor	  (ORNL)	  Co-­‐lead:	  G.	  Jackson	  (GA)	  * Disrup'on	  and	  ELM	  panel	  co-­‐leads	  are	  joint	  appointments	  with	  Modeling	  and	  PMI	  workshops	  respec'vely	  Additional members
from ITER Organization
are under discussion

Transients	  Workshop:	  Schedule	  Date

Activity

Participants

Immediate

Organize panels

Workshop and sub-panel leads

February 20

Sub-panel kickoff
videoconference

Workshop and sub-panel leads and coleads

February, March

Sub-panel organization andconference calls as needed

Sub-panel leaders and members

March 30-April 2

Virtual workshop to gather
community input

Community (submits 2-page white papers
and give short presentations)

April 15

Deadline for submitting white papers

April, May

Sub-panel conference calls asneeded

Sub-panel leaders and members

June 8-10

Workshop on Transientsat General Atomics

Leaders and sub-panel members invited.
Others may attend on a first-come, firstserve basis (limits due to room size andlab attendee administrative limit)

June 11

Report writingat General Atomics

Leaders and writing committee

June 30

Submit completed report to FESLeaders

Greenﬁeld	  |	  FESAC	  3/12/15	  My intention is to welcome community input andparticipation• There are trade-offs– I will do everything I can to make sure everybody has anopportunity to affect our report– But… we actually need to produce a report – broad participation
may not be practical at every step
• Sub-panels are being kept small to preserve working character– Mostly populated by invitation– Members are expected to contribute to written report• Two-page white papers and short presentations:
Virtual workshop week of March 30– Announcement and call for white papers will come today or tomorrow• Transients Workshop: June 8-10 at General Atomics– Attendance may be limited (due to factors I can’t control)• 100 person capacity of conference room
• Legal/bureaucratic limit (DOE $100K/workshop limit è lab/
government employee attendance ≤ ~35)
– Limited remote participation should be possible (need to preserve
working character of meeting)
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For more information• All four community planning workshops will have website either
hosted by the US Burning Plasma Organization or linked fromthe USBPO website
http://burningplasma.org• Direct link:
https://www.burningplasma.org/activities/?article=Transient

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Greenﬁeld	  |	  FESAC	  3/12/15	  Backup slides follow…

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Frequently asked questions (1)• Will the Transients Workshop establish priorities for research in the next
N years?
– No. Due to the laws governing how DOE receives advice from thecommunity, advice on prioritization can only come through aFACA* committee like FESAC**. The tradeoff is that nobody isrecused from participating in these workshops.
– Although we can’t prioritize, I’m sure we will say something about
sequencing (you have to do A before you do B)• What is N?
– Nominally 10 years, but for Transients, I see two time scales
1. What do we have to do to make ITER successful, and what isthe deadline?
2. What do we have to do beyond ITER to make FNSF/DEMO/
Power plant/etc. successful?
• Isn’t the answer just “build a stellarator?”– Our marching orders are to plan solutions specific to the tokamak– FES may revisit stellarators in a future workshop (not this year)* Federal Advisory Committee Act** Fusion Energy Science Advisory Committee
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Frequently asked questions (2)• Can I join a sub-panel?
– You would need to contact the leader of the sub-panel you’reinterested in. Please understand that the subpanel may alreadybe full.
• Do I want to join a sub-panel?
– Do you want to spend hours in conference calls?
– Do you want to write sections of the report?
• If asked, should I join a sub-panel?
– Yes!
• If I can’t join a sub-panel can I still make my voice heard?
– Yes! Write a white paper, give a presentation at the pre-workshop,and/or participate in discussions at the main workshop.
• How can I ensure that I will like everything in the final report?
– You probably won’t like everything. I probably won’t likeeverything. We will do the best job we can, but you can’t – andshouldn’t try to - make everybody happy.
• How will FES use the report we produce?
– This is not entirely clear, but it seems reasonable to assume it will beused in planning future research
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Transients Workshop Organization and Goals• The Transients workshop will be organized in two panels, each withthree sub-panels. Each sub-panel will consider a complete research
program in their area, which in most cases will include elements ofexperiment, theory, and modeling. Since there are obvious overlaps
with the Workshop on Integrated Simulations, where appropriate one
member of each panel or sub-panel can be designated to serve
jointly on an Integrated Modeling panel.
• Our task is largely that of revisiting Thrust 2 in the 2009 ReNeW report,
taking into account the ensuing six years of progress – and discoveryof new issues. The research plan we will develop may go into moredetail than ReNeW, but we are once again being asked to develop aspanning set of research activities rather than prioritizing them.
• All sub-panels should consider two time scales for research. The most
rapid progress is needed to ad-dress areas that will impact safe
operation of ITER. In some cases, additional progress will be needed
beyond ITER in order to be able to safely address transients in moredemanding future devices such as an FNSF or DEMO.
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Panel 1: Preventing Device Damage from Disruptions
Sudden terminations of a fusion grade plasma can be triggeredby either MHD instabilities or hardware failure. Developing anapproach to preventing damage related to the sudden releaseof the plasma’s thermal and magnetic energy content will require
progress in three broad areas. When a disruption is imminent andunavoidable, a mitigation system will be deployed to safely shut
down the discharge. This should be a last resort, with preferenceto efforts to completely avoid the disruption via plasma control.
The decision making – steps to take for avoidance, when toengage the mitigation system, etc. – will require advances inpredictive capabilities.

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Panel 1: Preventing Device Damage from Disruptions
Sub-panels

131.

Disruption Prediction

2.

Disruption Avoidance

3.

Disruption Mitigation– There has been significant progress in disruption prediction in individual devices.
Examples include the system devised for NSTX experiments that predicts mostdisruptions with few false positives. Another system has been deployed on JET
that is routinely used to trigger its mitigation system. Advances are needed toimprove the accuracy and reduce the incidence of false positives, and toproduce a “portable” predictor that can be deployed on new devices such as
ITER with some acceptable minimum training set.
– Most disruptions occur when the plasma approaches known stability limits. Achallenge for plasma control is to be able to operate near these limits withoutcrossing them. In some cases, active suppression of instabilities can be done
under plasma control (e.g. ECCD used to “search and suppress” NTMs in DIII-D).
– As a last resort, the plasma must be safely terminated. Mitigation systems
deployed on present-day tokamaks rely on injection of massive quantities ofmaterials to radiate away the plasma’s energy content via gas injection or
shattered pellet injection. Other methods have been proposed but studied inmuch less detail. Several issues remain under study, such as radiation
asymmetries and the generation of a “runaway” electron population that cancause severe, local, damage to in-vessel components. This area is time criticalas the ITER Disruption Mitigation System (DMS) is scheduled to undergo a final
design review in 2017.
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Panel 2: Avoiding deleterious effects of ELMs in high performance plasmas

Edge Localized Modes, or ELMs, are repetitive instabilities that are
effective in flushing impurities from the core of H-mode plasmas
but are also capable of depositing large amounts of heat andparticles in concentrated target areas in the divertor. Several
techniques are currently under study for use in ITER andsubsequent devices for the suppression or mitigation of these
instabilities, and for the development of alternate operational
scenarios that are free of ELMs and meet impurity control
requirements. Since these areas are also related to the physics ofthe H-mode pedestal and boundary physics, there may beconnections (and joint members) with panels within theWorkshop on Plasma-Materials Interactions.

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Panel 2: Avoiding deleterious effects of ELMs in high performance plasmas
Sub-panels

15

4.

ELM Suppression or Mitigation with Resonant Magnetic Perturbations

5.

Naturally ELM-free Operating Scenarios

6.

ELM Pacing– ELM suppression and/or mitigation with magnetic perturbations generated byexternally powered coils has been demonstrated in DIII-D, and subsequently exploredon several de-vices in the US and elsewhere. The promise of this approach led to it’s
becoming the leading method for ELM control in ITER, with the planned addition of
an internal coil set to the ITER baseline design. While the current progress inexperiments is encouraging, the under-standing of the suppression or mitigation
mechanisms in a range of existing devices is still insufficient for robust extrapolation toITER, FNSF or beyond. This panel will address the outstanding issues and researchneeds in experiment, modeling and theory in this area.
– Alternate operational scenarios, such as the QH-mode and I-mode, have been
identified which combine the favorable confinement properties of ELMing H-mode
plasmas with an edge region that is naturally free from ELMs. This panel will address
research needs and identify paths for applying these or similar scenarios to ITER andsubsequent devices.
– Rapid, repetitive injection of pellets of deuterium or lithium have been shown totrigger ELMs, thereby increasing the ELM frequency and decreasing the impulsive
fluxes produced by each individual ELM to a potentially tolerable level. Further
research will explore the parameter space where this technique is capable ofameliorating the negative consequences of ELMs in high performance scenarios andto continue to build a scientific basis for extrapolation to future devices.

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