1. WP4 – Potential FEL Output Performance Enhancements
Accelerators in a new light
Brian McNeil & Neil Thompson
UK XFEL Kick Off Meeting
WP4 – Potential FEL Output Performance Enhancements

2. Workpackage Aim
The aim of this WP is to conduct research that will significantly improve the output qualities of future XFEL designs over those of existing XFELs.
In all tasks the current ‘FEL landscape’ will be reviewed
Methods will be developed that push desirable XFEL output qualities towards their theoretical limits - pulse duration, coherence, power, wavelength...
Some methods identified to have high potential impact for users will be tested on the CLARA FEL test facility
Other methods will be considered based on results of their proof-of-principle demonstration or application at other facilities
Ultimately we will identify the best solutions for inclusion in a UK XFEL, to both
meet the needs of the current science case and
give UK scientists first future access to unexplored physical regimes.

3. FEL Landscape – how it looked in 2013
CLARA Conceptual Design Report 2013

4. Recent Updates – Review of Sources and Science
June 2017: Accepted for publication in Reports on Progress in Physics

5. Recent Updates: Review of FEL Schemes
Main themes which are the basis of the Workpackage: 4.1 Stability
4.2 Flexible Pulse Structures 4.3 Ultrashort Pulses 4.4 Transform Limited Pulses 4.5 Other Enhancements

6. Task 4.1: Stability
Task 4.1 Achieve the best output stability shot-to-shot (ASTeC, CI)
Task Guide to FEL instability [M1-4]
Task Design sensitivity tests [M5-6]
Task Update guide [M7-48]
Achieving the best photon output stability shot-to-shot depends on the stability of the electron beam, which relies on work in each of the other WPs.
There is also a contribution from microscopic electron bunch variations (shot noise) which several FEL techniques aim to overcome (mainly those described in Task 4.4).
WP4 will guide the other WP’s by describing the mapping from macroscopic electron beam instability to photon beam instability.
Reviewing of existing research and areas requiring further research to be identified.
Dependencies of the different FEL methods will be produced by developing and utilising a set of standard sensitivity tests

7. Task 4.2: Flexible Output Pulse Structures
Task 4.2 Generate Flexible Output Pulse Structures (ASTeC, CI, DLS)
Task Review of Current Methods [M1 – M6]
Task Multi-Colour Output [M7-M21]
Task Multi-Pulse Output [M22-M36]
Task Variable Pulse Separation [M37-M48]
Task Flexible Pulse Structures [M37-M48]
Investigation and comparison of possible methods for generating flexible FEL pulses, including methods for generating multi-colour output, multi-pulse output and variable pulse separation.
The leading schemes will be studied to establish likely performance on a UK XFEL, and where possible for demonstration on CLARA.
The analysis will include an assessment of the sensitivity to various input parameters via WP4.1 and identify any potential show-stoppers due to e.g. beam quality limitations.

8. Task 4.3: Ultra-short Pulses
Task 4.3 Generate ultra-short photon pulses (ASTeC, CI, DLS)
Task Update review [M1-3 + periodic updates]
Task Develop new short pulse methods [M4-36]
Task Simulation capabilities [M4-9]
Task Assess techniques in simulations [M7-21 and M28-42]
Task Assess techniques experimentally [M22-27 and M43-48]
Ultra-short photon pulse generation for FELs is a challenge to minimise the number of cycles per pulse.
At hard X-ray this ranges from the shortest experimentally demonstrated values of a few femtoseconds down to less than a single attosecond in proposed ‘few-cycle’ methods.
Other properties, such as peak powers and pulse timing, are also important parameters for users.
This task will research and help determine the leading design options for a UK XFEL by advanced simulations and CLARA experiments and via dialogue with potential users.

9. Task 4.4: Transform Limited Output (Temporal Coherence)
Task 4.4 Generation of Transform-Limited Output (ASTeC, CI)
Task Current and proposed methods [M13 – M36]
Task Cavity FEL Methods [M1-M12]
Task Demonstration of High Brightness SASE on CLARA [16 months over M6-M48]
The three main topics are:
review and analysis of current and proposed methods;
investigation of the use of optical cavities – very relevant for MHz UK-XFEL
demonstration of HB-SASE on CLARA.
At the end of the 48 month period we will have a comparison between the different methods and make a recommendation for UK XFEL.

10. Task 4.5: Other Potential Enhancements
Frequency Modulated FEL
Broad Bandwidth Output
Task 4.5 Potential enhancements (peak powers, harmonics, polarisation, etc) (ASTeC, CI)
Task Review of Current Novel Output Methods [M1 – M12]
Task Novel Method Demonstration Opportunities [M13 – M36]
Task Overlap with Other Methods [M37 – M48]
Task In-Depth analysis of Novel Methods [M13 - M48]
FEL methods to generate novel or improved methods continue to develop.
Output containing Frequency Modulation, Orbital Angular Momentum or access to shorter wavelengths via harmonic up-conversion are possible.
Assessment of user impact and feasibility of possible CLARA experiments and UK XFEL designs.
Regular review of such novel output and its potential impact.
This research effort will require computational simulation development necessary to model new methods.

11. Task 4.0: Simulation Capabilities
Coordination is required between the different components of the start-to-end simulation codes (e.g. Task 3.1 Develop strawman layouts ) and with the hardware providers.
This task underpins all the other Tasks
At the beginning of the design process a coordination meeting will be held to:
1) Provide updates of status quo from all parties in the start-to-end simulation process
2) Agree an overall strategy for coordinating the start-to-end modelling
3) Look at the various modelling codes that are currently being used and look forward to what codes may be of future interest
4) Agree on an initial baseline set of codes that are required
5) Discuss and agree on whether a common HPC platform or some other system of machines should be used for start-to-end simulations
6) Consider how access to the required machines is organised and calculate estimates of how much resource is needed

12. Progress to date
Ongoing review of FEL landscape underway – relevant for all Tasks
New review of FEL sources and applications accepted for publication
New ideas in the pipeline
CLARA Test Facility FEL design under final review to ensure correct balance between currently identified R&D and future flexibility
First meeting already held 22 May 2017 to discuss Task 4.0 (Simulation capabilities)
Second ‘working meeting’ scheduled for Wed 19 - Fri 21 July 2017.
DiRAC HPC seedcorn funds have been granted to install & test various simulation codes.
Looking into setting up Collaborative Computational Project (CCP) in Accelerator Science . Such CCPs smooth access to HPC resources and assistance from computer software engineers. We hope the IoP Particle Accelerators and Beams Group (PABG) will be holding a survey of members to seek their view on the need for such a CCP. Please join the PABG if not already a member and participate in this survey.
An informal grouping of academics have recently set up a Ultrafast Science Series of meetings to be held 3 times a year. The next one-day meeting (arranged by ASTeC & BMcN) is pencilled in for 15 Nov 2017 at DL and will focus on short pulse generation in FELs and potential user applications.
We intend the above events to feed into and inform the Light Sources theme of the on-going STFC Accelerator Strategic Review.

13. CLARA Capability
PRIORITISED SCHEMES
FEASIBLE SCHEMES

14. Accelerators in a new light
THANK YOU