# Presentation: 169161

## Linac Coherent Light Source Update

***Eric A. Rohlfing***
***BESAC Meeting***
***February 26, 2001***

***Office of Basic Energy Sciences***
***Office of Science, U.S. Department of Energy***

**Notes:**
Every BESAC meeting must have a discussion of the LCLS – so here I am again!

## Scientific Case for the LCLS

**  ****Reviews**
- Presented to and discussed by BESAC in October
- Unanimous vote to recommend that BES approve CD0,  ***contingent***** **upon positive external peer review
- External peer review completed in November - 13 reviews (out of 20 contacted)

-   ** “****LCLS:  The First Experiments”**
- Scientific case directly tied to decision on proceeding with LCLS construction (Critical Decision 0 - Conceptual Design)
- Aimed at defining (in some detail) the first classes of experiments that would be mounted on the LCLS
- Basis for experimental requirements for the LCLS CDR
- Assembled through the LCLS Scientific Advisory Committee

**Notes:**
Remind them of where we are with respect to the scientific case.  Document describing first sets of experiments delivered to BES in September, presented and reviewed by BESAC in Oct. and reviewed by ext. panel.  BESAC vote with contingency and review completed.  Now discuss in general terms the review comments.

## Reviewers Comments

** ****Specific Areas:**
- (1) Atomic Physics
- 	Agreed that these studies are basis for understanding intense x-ray-matter interactions
- 	Criticized for not being innovative; concern about lack of impact on field
- 	Concern over interpretation of nonlinear processes with spiked temporal structure (lack of longitudinal coherence) in LCLS pulses

* ***General**
- Very similar to BESAC comments and generally positive
- Several reviewers noted significant improvement over earlier efforts
- Tendency for reviewers to favor science outside their area of expertise

**Notes:**
General – very similar to BESAC and positive.  Noted improvements but (somewhat similar to BESAC) – most impressed outside of field (a concern).
Specific areas – now go through each section of document with comments that are representative of “consensus” (I.e., mentioned by more than one reviewer).
Atomic Physics – buy underpinning argument but not impressed with innovation; not at forefront of field with clear impact; technical detail – spiked pulse structure of LCLS will make nonlinear effects hard to interpret.

## Reviewers Comments

** ****Specific Areas:**
- (2) Plasma and Warm Dense Matter
- 	Clear niche role for LCLS, particularly as a pump source to create WDM
- 	Concern over broader impact and relevancy to BES, but noted clear relevancy to DOE Defense Programs

- (3) Structural Studies on Single Particles and Biomolecules
- 	Most positive set of comments; clearly at forefront of field with huge potential impact
- 	But, some skepticism, not concerning damage model, but whether there would be sufficient signal-to-background to extract molecular structure information

**Notes:**
WDM – clearly a good niche, particularly LCLS as unique pump source to create WDM; broader impact questioned and relevancy to BES (clear DP winner).
Single Bio. – most excited (although again excitement largest for those outside of field) and recognized huge potential impact; but skepticism by some on whether proposed expers. Can really work (and not because of damage!)

## Reviewers Comments

** ****Specific Areas:**
- (4) Femtochemistry
- 	Weakest set of reviews from those most directly associated with ultrafast dynamics (stronger from those outside)
- 	Concerns with synchronization between laser pump and LCLS probe
- 	Clear need for shorter pulses in order to have real impact in dynamics, particularly in the gas phase

- (5) Studies of Nanoscale Dynamics in Condensed Matter Physics
- 	Few review comments (little thin on reviewers)
- 	Not clear that LCLS parameters are ideally suited to experiments; damage calculations for XPCS look marginal

**Notes:**
Femto. – clearly the weakest (although again got high praise from those outside commun.); synchronization a big issue and clear need for shorter pulses to have impact (hear about this in next talk?)
Nano. – few comments (my fault – short on reviewers); not clear that these experiments best suited for LCLS

## Reviewers Comments

** ****Specific Areas:**
- (6) X-ray Laser Physics
- 	Few comments (again a bit thin on reviewers)
- 	Strongly endorsed attempts to shorten LCLS pulse based on scientific needs, particularly for Femotchemistry

**Notes:**
X-ray laser – again thin on reviewers but generally very positive outlook toward any attempts to shorten pulse, which is required by other applications.

## Path Forward

* *** ****BES has delayed approval of CD0**
- Strong support for the LCLS project, but....
- Scientific case and level of “community” support not yet sufficient

** ****BES Workshop on Scientific Applications of Ultrafast, Intense, Coherent X-Rays**
**Organizers:**  Eric Rohlfing and Pedro Montano, BES
**Focus:**  scientific applications of source with LCLS specifications with emphasis on ultrafast dynamics, nonlinear optics, x-ray imaging
**Participants:**  20-25 scientists; LCLS “veterans” with newcomers
**Logistics:**  May 4-5, 2001; Wardman Park Marriott, Washington, DC
**Output:**  report that complements and broadens LCLS scientific case

**Notes:**
Where we stand now and where we’re going (Path Forward in management speak).  We have delayed CD0 decision – the project retains strong support in BES but we’re not convinced that the scientific case for the LCLS is strong enough yet.  This is clearly an evolutionary process that was started years ago, has produced many workshops and meetings and will continue to evolve until machine turns on (and after).  So, to hasten that evolution we will (guess what?) have another workshop!  What’s different about this one – we’re doing it – we know what we want (and are more likely to be happy with our own efforts!).  Focus on areas that need strengthening (and areas not chosen for the initial set of experiments).  Small group combining veterans and newcomers with different viewpoints.  Logistics...  Output (goal) is to complement and broaden existing case (certainly not starting over).  This brings into it elements of the larger scientific case for coherent x-rays using a variety of sources.

## BES Vision for the LCLS

* *** ****LCLS is partly an accelerator/FEL R&D project, but it must also be..**

**  ****A stand-alone scientific user facility**

**  ****The LCLS is not a step along a predetermined path toward a larger XFEL facility**

**Notes:**
Important to understand how we now see the LCLS.  Clearly this is partly relatively high-risk accel/FEL R&D project (science of the LCLS) but it must also be a user facility (science with the LCLS).  Not like the step from 2nd to 3rd gen. Synchrotrons – clearly more uncertainty in producing the photons.  This makes it even more important to clearly justify the impact of such a light source!  Final point – we do not view this as a step along a predetermined path toward a large XFEL facility.  It is too early to tell what the x-ray light sources following the LCLS will look like.