1. Conceptual design of non-destructive time profile monitor for femtosecond long electron bunches
I. V. Konoplev, A. J. Lancaster, H. Harrison, F. Bakkali Taheri, G. Doucas.
John Adams Institute for Accelerator Science,
Department of Physics, University of Oxford
Denys Wilkinson Building, Keble Road, Oxford, OX1 3RH

2. Overview Introduction
Historical overview: E203 experiment and its limitations
Experiments at LUCX, KEK
Conceptual design of single-shot monitor
Conclusion

3. Motivation
Demand for non-destructive, single shot, accurate, compact and cost effective diagnostics
Many applications: NGLSs, FELs, wakefield driven accelerators; require or generate short fs long electron bunches or modulated beams with fs periodicity.
Understanding of a bunch profile improves understanding of:
wakefield plasma interaction and radiation generation;
beam – beam interactions ….

4. Coherent radiation spectroscopy for beam profile measurements
Coherent Synchrotron radiation
Free Electron Lasers
Coherent Smith-Purcell radiation
(cSPr)
Coherent Diffraction and
Transition radiation

5. Smith-Purcell Radiation
Coherent, polarised radiation emitted from a periodic structure
Induced by a charged bunch travelling above the structure
Radiation has angular dispersion – frequency spectrum can be measured
Longitudinal bunch profile is encoded within the frequency spectrum

6. Experimental set up E203 at FACET, SLAC
E203 set-up consisted of vacuum chamber, (a) carousel with 3 gratings and a flat piece of metal (‘blank’).
Outside the chamber: (b) system of changeable filters, (c) Winston cones and 11 pyroelectric detectors.
Gratings and filters are interchanged during operation.
(a)
(b)
≈20 GeV electrons
x 1010 electrons per bunch
Normalized emittance 60 mm-mrad
Bunches at 10 Hz
(c)
Fined synonym for remotely, arranged along beam line

7. E203 Schematic layout
Θ=140
Remove it
Θ=40

8. fs-Time bunch profile SP-monitor
Current average profile bunch monitor
(20GeV, sub-ps electron bunches at SLAC)
Carousel with 3 gratings and blank
Normalised amplitude
Green markers mm grating
Blue markers – 0.25mm grating
Red markers mm grating
KK technique
References need to be moved to separate slide
Frequency (THz)
The most recent experiments were to study the properties of cSPr:
- polarization
- directionality

9. Phase reconstruction software
Schematic Diagram of PCI Algorithm

10. Phase reconstruction software
Examples of pulse reconstructions
Pulse reconstruction using PCI algorithm (red line) and iterative algorithm (blue line). Original pulse is dotted black line
Normalised amplitude
Pulse reconstruction using experimental data observed at FACET SLAC (E203 experiment)
Move to FACET
PCI algorithm - red line; Iterative algorithm - green line; KK algorithm - blue line
Current (arb. units)

11. Limitations of the E203 monitor
Multi-shot measurements
Requires minimum 4 sets of measurements:
Three different gratings on a carousel
One “blank” measurement
Mechanically complex:
Carousel rotation
Carousel translation
Changing filters
Components must be λ-independent
Solutions:
Use polarization of cSPr for background separation
Use directionality of cSPr to avoid cross-talk

12. 1/ Coherent SP radiation studies at LUCX, KEK to confirm proposed solutions 2/ Conceptual design of single shot cSPr monitor

13. Numerical predictions of cSPr at LUCX
≈8 MeV electrons
50 pC or 1.0 x 108 electrons per bunch
Normalized emittance ~100 mm-mrad
Number of micro-bunches per train 4
Repetition rate 12Hz

14. LUCX cSPr experimental layout
Electron beam
To cover the same frequency range at LUCX as it was at FACET 10MeV beam should be 0.1mm away to generate radiation at 10THz
LUCX vacuum chamber with gratings installed
Vacuum chamber
Photo will be sent with appropriate grating remove eqs add bullet points about measurements
Beam splitter
Fixed mirror
Parabolic mirror
moving mirror
VDI ZB detector

15. Interferometric frequency measurements
cTr measured to study the detector response
cSPr measured at 90 degree observed from 1mm grating
cSPr measured at 90 degree observed from 1mm grating
The detector frequency range from 290GHz to 420GHz

16. Preliminary polarisation study
Detector and polariser are rotating together
Rotatable polariser
cSPr after interferometer
Rotatable detector
Preliminary estimation of cSPr degree of polarisation:
cSPr ~ 0.9

17. Degree of polarisation of background radiation
Preliminary estimation of background radiation degree of polarisation:
~ 0.14

18. Preliminary conclusion
We can measure cSPr generated by LUCX beam (very different from FACET beam)
The cSPr degree of polarisation agrees with predicted values and can be distinguished from background

19. Conceptual design of a single shot, non-destructive fs-bunch monitor
For the next generation of linear colliders, wake-field accelerators and light sources (X-ray and THz FELs) to understand/control the physics phenomena and machine operation.
1/ Truly single shot monitor (1 bunch = 1 profile)
2/ Compact
3/ Applicable to all fs-particle accelerators including plasma assisted wake-field accelerators

20. Schematic Grating Layout

21. Multi-grating layout
Background radiation is subtracted via polarisation measurements and analysis
Gratings will be longitudinally spaced to avoid geometry problems
Rotated around azimuthal angle to reduce length of the apparatus

22. Femtosecond resolved imaging of e-bunch longitudinal profile
Detector
mirror
polariser
Winston cones
Incoming signal
Vacuum chamber
11 output ports
Beam path
Single grating
Background output window and absorbing material
output port
Consistency with other overheads

23. Femtosecond resolved imaging of e-bunch longitudinal profile
11 output ports
If funds are granted the monitor will be ready in 2017 and installed on CLARA beam line and tested in 2018
Beam path
11 output ports
Consistency with other overheads
11 output ports
1/ Polarisation and frequency resolved
- in the approximate 64cm beam-line footprint system
2/ Spectral coverage from 0.1THz up to 15THz
3/ Single shot, non destructive, fast beam profile monitor

24. Conclusion
Overview of cSPr bunch profile monitor (E203 experiment at FACET, SLAC)
Phase reconstruction algorithm
Limitations of the original monitor
Conceptual design of a single shot monitor
Studies of cSPr radiation
Next step (if funds will be available) is to construct and test the monitor at CLARA (UK) facility by the end 2018.

25. Thank you Acknowledgement: STFC PRD grant (STFC PRD, ST/M003590/1);
Leverhulme Trust Network Grant (IN )

26. References
1/ F. Bakkali Taheri, I. V. Konoplev, et al., Phys. Rev. Accel. And Beams, 19, , 2016.
2/ H. Harrison, et al., I. Konoplev, et al., 6th IPAC 2016: Proceedings, 7-13 May, 2016.
3/ F. Bakkali Taheri, I. V. Konoplev, et al., 6th IPAC 2016: Proceedings , 7-13 May, 2016.
4/ H.L. Andrews, et al., Konoplev, I.V., et al., Phys. Rev. Special Topics - Accelerators and Beams, 17 (5), 2014.
5/ H.L. Andrews, et al., I.V. Konoplev, et al., Nucl. Instrum. Meth. in Phys. Res., A, 740, pp (2014).
6/ N. Fuster-Martínez, et al., I.V. Konoplev et al., 4th IPAC 2013 Proceedings, pp , 2013.
7/ F.B. Taheri, I.V. Konoplev, et al., 4th IPAC 2013 Proceedings, pp , 2013.
8/ I.V. Konoplev, et al., International Conference Proceedings, IRMMW-THz, , 2013.