1. Monocycle Harmonic Generation in FELs
Takashi Tanaka
RIKEN SPring-8 Center
Designing Future X-ray FELs Workshop

2. Principle of Operation
How to Implement in XFELs
Numerical Examples
Summary & Outlook

3. Principle of Operation
How to Implement in XFELs
Numerical Examples
Summary & Outlook

4. Pulse Length of XFEL New Method to Generate a Monocycle Pulse
Electron Beam
Undulator
XFEL
# Microbunches: N
# Periods M(<<N)
Pulse Length: Nlx
New Method to Generate a Monocycle Pulse
Avoid pulse lengthening by slippage, even with N=M≫1
N=1
# Periods M
Pulse Length: Mlx
Pulse Lengthening by Slippage
Pulse Length: lx
N=1
M=1
Designing Future X-ray FELs Workshop

5. Strongly Tapered Undulator
Basic Concept
“Chirped”
Microbunch
Strongly Tapered Undulator
Monocycle Pulse
Necessary Condition
Interval at the n-th microbunch
＝Slippage at the n-th period
Designing Future X-ray FELs Workshop

6. Principle of Operation1 2 3 j 10
Current Profile s E
Radiation Profile at Each Period s
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7. Principle of Operation1 2 3 j 10 s
Resonant Pulse E
After 1st Period s l 1
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8. Principle of Operation1 2 3 j 10 s E
After 2nd Period l2 s
l1+l2
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9. Principle of Operation1 2 3 j 10 s E
After 3rd Period l3 s
l1+l2+l3
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10. Principle of Operation1 2 3 j 10 s E
After 4th Period s
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11. Principle of Operation1 2 3 j 10
High Power Monocycle Pulse s E
After 10th Period s
Designing Future X-ray FELs Workshop

12. Principle of Operation
How to Implement in XFELs
Numerical Examples
Summary & Outlook

13. Accelerator Layout Upconvert the monocycle pulse with l=l0
Pulse (l=l0)
e- bunch
(i)
(ii)
(v)
(iv)
(iii)
Monocycle
Pulse (l=l0/m)
Upconvert the monocycle pulse with l=l0
Monocycle Harmonic Generation (MCHG)
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14. Sec.(i)：Generating a Single Microbunchj E
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15. Sec.(ii)：Generating a Chirped Pulsej E
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16. Sec.(iii)：Applying Fresh Bunchj E
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17. Sec.(iv) : Generating a Chirped Microbunchj E
Designing Future X-ray FELs Workshop

18. Sec.(v)：Generating a Monocycle Pulsej E
Designing Future X-ray FELs Workshop

19. Principle of Operation
How to Implement in XFELs
Numerical Examples
Summary & Outlook

20. Assumed Parameters lu=170mm K=3.13 N=1 R56=15mm lu=27mm K=3,DK=1.5
e- beam
E=2GeV
I=2kA
e=0.4mm
Seed Pulse
P.E.=10mJ
l=60nm
Dt=0.38fs
Designing Future X-ray FELs Workshop

21. Example (m=7, sg/g=5x10-5)
Designing Future X-ray FELs Workshop

22. Example (m=7, sg/g=5x10-5)
Designing Future X-ray FELs Workshop

23. Relation between m and sg/g
DK/K:0.5→0.2
N(iv):2→4
Peak Power Can Be Enhanced at the Expense of Pulse Lengthening

24. Summary & Outlook
This scheme can be repeatedly used to further shorten the wavelength, and thus the pulse length of XFEL.
Note that it has a few difficulties
Complicated accelerator layout
Highly sensitivity to e-spread
An alternative idea has been recently proposed, submitted, & under review

25. Thank you for you attention!
Designing Future X-ray FELs Workshop