Introduction

Our community speaks with different voices regarding the scientific value of a burning plasma experiment. At the risk of oversimplifying the situation, some feel a push strongly directed towards an energy milestone is what we should be about. Others feel we have to do things smarter before we do them bigger, and might be convinced that invigorating a broad base program is at least as important as a BP. Still others might have an attraction for the science problems offered by a narrow subset of the fusion science effort, and wonder what investment in a BP means for what their way of pursuing their goals. Creating a common vision for a community with such voices represents a major challenge for the fusion energy sciences.

To this end, a significant opportunity, and deep obligation, resides in developing a clear articulation of the scientific value and goals of a burning plasma experiment. At best, we have done this poorly in the past. Often the value is assumed to be self-evident, but this is not universally accepted. In my view, clear articulation of our scientific goals is a necessary step if we are to develop a program vision that includes a burning plasma and that speaks to the motivations of the various segments of the broader plasma physics community. It is also a requirement if we are to get the required support from the broader scientific community. Articulating this vision is the most significant opportunity presented by the Snowmass meeting.

Beyond a Uniform Technical Assessment

Snowmass has often been described as a venue for performing a uniform technical assessment of the three burning plasma options of ITER-FEAT, IGNITOR, and FIRE. However, the opportunity, and moreover the obligation, runs much deeper than that. The major opportunity of a community get-together such as Snowmass is, in my opinion, the development of a sharper vision and articulation of the science we hope to extract from a burning plasma and from the broader program as a whole.

I agree that a uniform technical assessment ought to be one goal of this activity. Still, in addition to this scientific assessment, there are a couple of points that I think are particularly important. It has been pointed out in the past that, with respect to the NRC and FESAC reviews, Snowmass should provide first a clear articulation of the scientific basis for proceeding with a burning plasma experiment, and second it should identify principal new physics phenomena and requirements for their study.

Building community: flexibility and addressing scientific motivations

At Snowmass, I would put a lot of weight on identifying flexibility requirements. In addition, I think there is indeed a very valid place for discussion at Snowmass of more general physics issues that might be accessible with such tools. It is likely that we can better quantify what we mean by this with the technical assessment exercises. In what follows, my thoughts at times focus on transport as an example, but hopefully it is pretty easy to map them to a concern about any aspect of the physics. Let's consider a physicist truly interested in transport phenomena and nonlinear dynamics as an example. While a BP needs a cadre of flexible tools to optimize the chances for good fusion yield, it becomes a lot more interesting scientifically to this physicist if these tools can also enable a certain class of studies of transport and pressure profile dynamics in a self-heated environment. In this example, if our Snowmass modeling exercises can help quantify what a given amount of flexibility buys us in terms of access to new nonlinear dynamics regimes in each device being discussed, then we begin to develop a way of understanding the different possibilities each concept offers at the scientific level. In addition, and importantly from the point of view of community building, the burning plasma dialogue starts to get a lot more interesting to some who have not been coupled to this dialogue as of yet.

The value of articulating our science

Snowmass provides an opportunity for a much-needed development of a case as to why we find the prospects of a BP scientifically exciting and important. Part of this is the assessment of flexibility requirements for any of the three experiments on the table. More fully, however, I think we have the opportunity and obligation in this meeting to develop the case as to why the integration goal of a BP is scientifically rich and meaningful. Right now, our best words in this regard are generally not meaningful to anyone who is in a position to support us.

Implications of poor articulation

Without such articulation, the Snowmass effort is likely to be wasted. I think the message from our funders, from Capitol Hill, and from those in other sciences has been for some time that a BP proposal will go nowhere if the science mission is not clearly articulated to, and understood and respected by, other scientists. With this as background, the Snowmass activity has to go beyond an assessment of confidence regarding performance. I would like to make sure that we come out of this process with something scientifically grounded with respect to why we find this endeavor exciting and why it is scientifically valuable. Without developing that vocabulary, we are learning how to communicate what we think is best only amongst ourselves. Even there we fail: the community speaks in very different tongues when it comes to the question of why a BP is scientifically interesting. With respect to transport science, the Transport Task Force can help when it comes to identifying these issues, but I don't think it alone can perform this task. Its interests are much broader than learning how to articulate this scientific case. We are working to make the BP dialogue more constructive within the TTF, but this Snowmass meeting is the best near-term opportunity for making significant progress in this matter.

Snowmass should be a venue for sharpening our scientific vision

To me, this speaks to a need to use these uniform assessments to help us articulate our own vision as to what we mean by the oft-cited "integration goal," to clarify what the new physics is, and to help us develop a language for articulating this vision outside of our community. The integration goal is often referred to as the compelling scientific reason to pursue such an experiment. However, one can obtain a wide variety of opinions regarding what this means, and even less clear articulation of how we define our success at integration. By using our technical assessments to identify different classes of physics accessible with only with a BP, we might take an important step towards clarifying to ourselves what we mean by this goal.

What a Snowmass gathering can do that is most positive in this regard is put meat on the bones of the claim that integration is the most exciting scientific aspect of a BP. This is what I heard as the strongest charge coming out of the Austin UFA meeting I attended, as well as from the Snowmass meeting two years ago, but I am not aware of any efforts to follow through on this sentiment. Let me speak again of the transport issue as an example: in the upcoming Snowmass effort, can we identify and quantify what new nonlinear dynamics are revealed in an alpha heating-dominated environment? Is there something that really is fundamentally new and that would be exciting to another scientist interested in nonlinear systems, or is this case weaker than we thought? With this sort of identification and clarification in transport and in other areas, I think we come closer to making the community, beyond what was represented in Austin and San Diego (and it was indeed a slice limited to those who already believe in the mission of the BP, despite the best efforts to be inclusive), attracted to a BP experiment. We also come closer to the succeeding in the essential mission of articulating in a deep manner the intrinsically interesting and important science that a BP has to offer.