1. F. Villa Laboratori Nazionali di Frascati - LNF On behalf of Sparc_lab
Generation, measure and FEL radiation of ultrashort electron beams at Sparc_lab
F. Villa
Laboratori Nazionali di Frascati - LNF
On behalf of Sparc_lab

2. Sparc_lab Compton, LWFA THz, diagnostic studies FLAME 300 TW laser FEL
Photoinjector

3. Ultrashort bunch generation: Gun
Laser:
300 fs FWHM,
0.3 mm diameter (flat top)
264 nm central wavelength
Electron bunch charge: 20 pC
Injection phase: 38° (optimizes the energy at the gun exit, 5 MeV)

4. Ultrashort bunch generation: velocity bunching
Emittance compensating solenoids (300G)
Velocity bunching
On crest
Energy: MeV
Energy spread: 0.2 MeV (0.1%)

5. Electron longitudinal phase space
Pixel size = 33.5 um
Pixel value= 22 fs
Beam Energy (MeV)
Energy
Spread (%)
Bunch rms duration (fs)
Charge (pC)
Long. Emit. (keV mm)
(0.01)
0.146 (0.004)
32 (1)
20.00 (0.25)
2.62 (0.09)
Actual peak current: 625 A

6. Compression scan
resolution

7. Electron envelope and emittance

8. FEL: undulators FEL diagnostics: Fiber spectrometer (850-350 nm)
Linac
Electron diagnostics
and matching
5 undulator sections
FEL diagnostics:
Fiber spectrometer ( nm)
In vacuum spectrometer (NIR-UV)

9. FEL radiation: single spike
Central wavelength
𝜆 𝐹𝐸𝐿 = 𝜆 𝑢 2 𝛾 𝐾 2 2
=740 𝑛𝑚
Single spike condition
Fiber spectrometer
In vacuum spectrometer
GENESIS 1.3 simulation
𝐿 𝑒 <2𝜋 𝐿 𝑐 = 𝜆 𝐹𝐸𝐿 𝜌
𝐿 𝑒 =32 𝑓𝑠⋅𝑐; 𝐿 𝑐 =37 𝑓𝑠⋅𝑐
FEL parameter: K = 1.8 ρ =

10. SASE fluctuation Experimental data GENESIS 1.3 simulations
(with e- shot noise only)
Due to other jitters
(Charge, positions,
energy, emittance…)

11. FEL spectrum bandwidth15 20 25 30 35 40 45 50 55
3,5
4,0
4,5
5,0
5,5
6,0
6,5 Dl
(nm)
L(fs)
FEL spectrum bandwidth
Experimental points
GENESIS 1.3 simulation
Analytical formula
𝜎 𝜆 ∝𝜌∝ 𝜎 𝑧 − at saturation

12. Summary Short electron bunch FEL radiation Velocity bunching
Single spike condition
Electron length vs. FEL spectral bandwidth