1. UK-XFEL WP1 – Electron Injector Development
B.L. Militsyn, STFC ASTeC

2. WP Objectives
The performance of the linear accelerator driven Free Electron Laser is defined by the brightness of the driving beam. The last has also severe impact on the cost of the machine. The driver brightness is essentially limited by the brightness of the electron source.
The goal of these WP is:
To deliver design of the high brightness highly stable electron source
To develop critical technologies which are necessary to achieve the required brightness and stability
To provide specifications for the surrounding subsystems – RF, Laser, Power Supplies etc.
To investigate the factors which limits stability of the source
B.L. Militsyn, UK XFEL kick-off meeting, Daresbury,
4 July 2017

3. Where the world is: Electron injectors
Electron emission
Thermionic
Photoemitters
Metal
Amorphous semiconductor
Crystalline semiconductors
Out of the gun photocathode preparation and exchange with a Load-Lock system
Electron acceleration
DC high voltage – CW electron injectors
Radiofrequency acceleration (GHz frequency range)
Normal conductive acceleration – pulsed/train-pulsed electron injectors
Superconductive acceleration – CW electron injector
VHF field acceleration (hundreds MHz frequency range)
Normal conductive acceleration – CW electron injectors
Superconductive acceleration – CW electron injectors
B.L. Militsyn, UK XFEL kick-off meeting, Daresbury,
4 July 2017

4. Where the world is: Photocathode Materials
Class
Material QE
Response time
Intrinsic
Energy
Wave
Length
Gun
Application
Normally conducting metals
Cu, Mg
10’s fs
100’s mV – 1’s V UV
NC-RF,
VHF
Low rep rate FELs
Super conducting metals
Nb,Pb
SC-RF
High rep rate FELs
Positive e- affinity Te-based
Cs2Te
ps’s
100’s mV
NC-RF, SC-RF DC
Positive e- affinity Sb-based
Cs3Sb etc
Visible
VHF,
SCRF(?)
NCRF(???)
ERLs, High rep rate FELs
Negative e- affinity semiconductor
GaAs, etc
1’s ps – 100’s ps
10’s mV – 100’s mV
IR- Visible
DC (XHV)
Polarized sources, ERLs
B.L. Militsyn, UK XFEL kick-off meeting, Daresbury,
4 July 2017

5. Where we are: CLARA High Repetition Rate injector
Mo photocathode plug of the HRRG
May be used as electron source itself
Different metal thin films can be deposited in search for minimum beam emittance
Te- and Sb- based high QE semiconductor layers can be deposited
RF cavity of the CLARA High Repetition Rate Gun (HRRG)
B.L. Militsyn, UK XFEL kick-off meeting, Daresbury,
4 July 2017

6. Where we are: Metal Photocathode Preparation Facility (MPPF)
Replaced vacuum seals to all metal to accommodate UHV requirements
Replaced pumping system with high performance turbomolecular pumps to reach vacuum of mbar
Original loading chamber replaced with a new cleaning/deposition chamber
UV laser installed for QE characterisation
B.L. Militsyn, UK XFEL kick-off meeting, Daresbury,
4 July 2017

7. Where we are: CLARA photoinjector
Units
Operating mode
Beam Repetition Rate
100 Hz
400 Hz
Frequency
GHz
2.9985
RF peak power MW
<10
RF average power kW 10
Gun electric field
MV/m
120
100/80
Bunch charge pC
20-250
250
Pulsed/Train pulsed
Pulsed
RF feedback
Required
B.L. Militsyn, UK XFEL kick-off meeting, Daresbury,
4 July 2017

8. Where we are: CLARA injector commissioning
RF commissioning
RF power delivered to the photoinjector
Characterisation of the amplitude and phase stability
Mo/Cu photocathode commissioning
Photocathode preparation
Photocathode characterisation off-line and in the gun
Laser system development and commissioning
Development of laser stacking and transverse shaping
Characterisation of the longitudinal and transverse laser shape
Beam commissioning
Characterisation of the transverse and longitudinal beam parameters
B.L. Militsyn, UK XFEL kick-off meeting, Daresbury,
4 July 2017

9. Where we are: DC photoinjector
Photocathode gun
ALICE photocathode gun
Operation voltage – 350 kV
Operation beam mode train/pulsed
Photoemitter – GaAs
Photocathode mode – replaceable with gun ventilation
Photocathode
preparation facility
500 kV power
supply
ALICE photoinjector upgrade
(GaAs option)
B.L. Militsyn, UK XFEL kick-off meeting, Daresbury,
4 July 2017

10. Where we are: Photocathode research program
At the moment concentrated on III-V (GaAs type photoacthodes) and metal (Cu) photocathodes
Metal thin film photocathodes
Theoretical modelling of photocathode materials
Alkali (Te- and Sb- based) in preparation/design stage
AFM
LEED
X-ray Gun
Analyser
UHV Vacuum System
TESS – Transverse Energy Spread
Spectrometer
Photocathode surface research facility
B.L. Militsyn, UK XFEL kick-off meeting, Daresbury,
4 July 2017

11. What shall we do:
Task 1.1 Characterisation of the CLARA Photoinjector – M18 (ASTeC, CI, TD)
The low emittance, high repetition rate, gun is installed into VELA beamline which has a dedicated suite of beam diagnostics that will be used for fully characterising the performance of the gun. The goal of this task to investigate ultimate achievable gun parameters like beam momentum, momentum spread, beam projected and slice emittance, bunch length. Consolidation of RF and thermal stabilisation design.
B.L. Militsyn, UK XFEL kick-off meeting, Daresbury,
4 July 2017

12. What shall we do:
Task 1.2 Blue Sky analysis of the recent achievements in the gun development – M12 (ASTeC, TD) 
During design and commissioning of CLARA photoinjector some other achievements have been done in the photoinjector development – new gun is ready for commissioning, new injector concepts have been developed. Great achievements have been done in the development of the gun infrastructure – RF, Lasers, Magnet system, and Thermal stabilisation. The goal of this task is to analyse these achievements and decide which of them may be implemented into the UK XFEL injector design.
B.L. Militsyn, UK XFEL kick-off meeting, Daresbury,
4 July 2017

13. What shall we do:
Task 1.3 Design of the UK XFEL gun - M48 (ASTeC, CI, TD)
The goal of this task is to provide design of the UK XFEL photoinjector and to issue specifications of the RF, Laser, Power Supplies and thermal stabilisation system.
Task 1.4 Telluride Photocathode Trials – M36 (ASTeC, CI, TD) 
The goal of this task is to set-up Cs2Te photocathode technology at DL – it involves design and manufacturing of photocathode deposition system, off-line characterisation and optimisation of the photocathode deposition procedure and commissioning of the Cs2Te photocathodes in CLARA photoinjector.
B.L. Militsyn, UK XFEL kick-off meeting, Daresbury,
4 July 2017

14. What shall we do:
Task 1.5 Development of the laser pulse formation optical system for UK XFEL injector – M36 (ASTeC, TD, CI)
The goal of this task is to develop optical system which would be able to deliver highly stable laser pulse with tuneable transverse and longitudinal shape. The task comprises design of the system, estimation of its achievable parameters, and delivery of commissioned design on CLARA.
B.L. Militsyn, UK XFEL kick-off meeting, Daresbury,
4 July 2017

15. What shall we do:
Task 1.6 Consideration of the CW UK XFEL injector – M48 (ASTeC, CI, TD)
The goal of this task is to deliver design of a CW High Repetition Rate electron injector which will be able to provide high brightness beams in CW regime with a MHz scale repetition rate. The primary goal will be the comparison of the available technologies which can provide this type of beams, the estimation of the achievable beam parameters, to provide design of the electron source, and to propose the injection scheme which will satisfy the required FEL facility operational stability.
B.L. Militsyn, UK XFEL kick-off meeting, Daresbury,
4 July 2017

16. Deliverables and Milestones:
Del 1.1 Report on Blue Sky analysis [M12] 
Del 1.2 Report on measured performance of the 400Hz gun with beam [M18]
Del 1.3 Report on achieved performance of Cs2Te photocathodes [M36]
Del 1.4 Report on design and commissioning of the laser shaping optical system [M36]
Del 1.5 Report on design of UK XFEL injector [M48]
B.L. Militsyn, UK XFEL kick-off meeting, Daresbury,
4 July 2017

17. Resources required RF engineer/scientist Laser scientist
Mechanical engineer
Surface scientist
Magnet designer
Vacuum engineer
Environmental engineer
B.L. Militsyn, UK XFEL kick-off meeting, Daresbury,
4 July 2017

18. Thank you for your attention!