1. DANE Compton ring for ultra high flux photons in the 100 KeV-10 MeV energy range
D. Alesini
(LNF, INFN Frascati)

2. OUTLINE BASIC IDEA MOTIVATIONS AND APPLICATIONS
FORMULAE FOR PHOTON SOURCE CHARACTERIZATION
ELECTRON beam dynamics PERTURBATION
Results WITH 1 and 10 m LASERS
COST
CONCLUSIONS

3. BASIC IDEA
x/ photons can be generated in DANE using Compton collisions between the electron beam and a high average power laser amplified in a Fabry-Pérot optical resonator.
The very high current storable in the collider rings and the relatively low achievable emittance, allow reaching, in principle, high flux and narrow bandwidth photon beams
We have analyzed the case of a laser wavelength equal to 1 m considering the FP cavity developed and tests at LAL.
30µm

4. MOTIVATION AND APPLICATIONS
The «phase space» in term of photon energy, flux and energy spread in which it is possible to move is relatively large and is function of the machine and laser parameters.
Different working points can be set for the different applications 5%
1012 ph/s
Energy spread
Photon
flux
0.1%
Photon energy
109 ph/s
100 keV
10 MeV

5. FORMULAE FOR PHOTON SOURCE CHARACTERIZATION
The wavelength of the emitted radiation within a small angle of scattering with respect to the propagation axes of the electron beam, is:
(laser=1 m (1.2 eV photons) colliding with the DANE e- beam  5 MeV photons) 
1-the total number of scattered photons per second over the 4 solid angle (Gaussian beams) 
luminosity
2-The rms source bandwidth
e- trajectories 
Collection angle
e- energy spread
LASER PARAMETERS
In NC LINAC, as example, the maximum rep. rate of the collisions cannot overcome few kHz and also the bunch charge cannot overcome few hundred of pC to preserve good beam quality. On the other hand, thanks to the very good beam emittance, it is possible to strongly focalize the beam at the IP.
In a storage ring like DAFNE e- ring, on the contrary, we have a much higher rep. rate (hundred of MHz) higher current per bunch (several nC) but higher emittance that does not allow to strongly focalize the beam at the IP.

6. ELECTRON beam dynamics PERTURBATION
The electrons colliding with the laser emit X/gamma rays with energies proportional to the square of the electron energy, with a typical spectrum and a typical correlation with the angle of emission. This causes a radiation damping and a quantum excitation of the beam.
The final transverse emittance and the energy spread are due to the balance of this effects with those of the storage ring w/o laser. It is straightforward to recognize that the average interval between two consecutive collisions of an electron with a photon is much longer than the damping time of the machine and, as a consequence, the beam dynamics is completely dominated by the dynamics of the electron ring without the laser.
If the emitted gamma ray causes an energy variation of the electron above the energy acceptance of the machine, the electron is lost. Therefore the energy acceptance (RF acceptance and/or dynamic aperture off-energy) has to be larger than the maximum gamma ray energy to avoid a reduction of the beam lifetime.
E=average energy loss of one e- after passing through the laser
Trev=revolution time of the electron beam around the ring
E=electron beam energy
L=wavelength of the laser
c=Compton wavelength of the electron (2.4310-12 m)
m= maximum angular photon frequency (m=42L=82c/L)

7. Results WITH 1 m LASER Stored current I=1.5 A (in 60 bunches mod 2)
Laser wavelength L=1 m
Gamma Photon Energy E=4.966 MeV
x=0.1 mmmrad
IP: 2.5%
Collision angle = 8 deg

8. MAXIMUM ACHIEVABLE ENERGY OF THE x/-BEAM
The energy of the gamma beam can be changed varying the energy of the collision laser or the energy of the electron beam.
To avoid a strong reduction of the beam lifetime, it is important to maintain the maximum energy of the gamma photons within the energy acceptance of the ring.
Typical DANE energy acceptances are <1-1.5% (unless considering very high RF voltages and/or very low momentum compaction factors).
S. Guiducci

9. 10.6 m LASER CW Fabry-Pérot cavities do not exist for two reasons:
This is a regime for mode-locked lasers that up to now has not success with CO2 lasers.
building a high-quality FPC will be difficult as materials and coatings for mirrors in mid-IR have worst qualities if compared to visible and near-IR technology.
BUT ps pulses have been generated with CO2 lasers with other techniques. In this case it is, in principle, possible to generate hundreds of pulses up to the kHz rep. rate with tentative parameters in the following range:
-laser rep rate: 100 Hz-1 kHz -number of pulses per period:
-energy per pulse mJ
-single laser pulse length ps
-laser spot size at the IP µm
-laser pulse distance within the train 5-50 ns
This allows to explore, in principle, a different energy spectrum for the photons

10. Results WITH 10.6 m LASER EDANE=300 MeV Stored current I=500 mA
Laser wavelength L=10.6 m
X rays Photon Energy E=170 keV
x=0.1 mmmrad
IP: 10%
Collision angle = 8 deg

11. COSTS 3 MEuro ISSUES TO BE STUDIED
Machine costs:
1 MEuro: laser/FPC modifications/supports (1m FP CASE)
0.2 MEuro: collimator
1-1.5 Meuro: chambers/magnets
0.5: experimental hall
3 MEuro
Operation costs:
-Mrp OFF
-Wigglers setpoint: 25% power (?)
-Accumulator OFF (?)
60% of reduction with respect to the present DANE power consumption
ISSUES TO BE STUDIED
1- Accelerator Optics at different energies
2-Beam/laser Interaction chamber
2-Impedances/single bunch beam dynamics for 1.5 A - 60 bunches operation has to be done/verified with simulations at 510 MeV and 0.5 A at 300 MeV, as example.
3-Direct injection from LINAC w/o Accumulator
4-CO2 laser operation

12. CONCLUSIONS
A tunable hard X rays/gamma photon source can be implemented in DANE using Compton collisions between the electron beam and a high average power laser pulse at two different wavelengths (1 and 10 µm)
The very high current storable in the collider rings and the relatively low achievable emittance, allow reaching, in principle, high fluxes and narrow bandwidths.
We have shown two cases: 1 m amplified in a FP cavity (photons in the 1-9 MeV range) and CO2 pulsed 10 m (photons in the range keV range)
Perturbation on the DANE transverse and longitudinal beam dynamics seems not to be an issue.
For the 1 m case there is the possibility to use the FPC designed and fabricated at LAL Orsay Laboratory and already tested at ATF.
A preliminary DANE layout to perform experiments with the gamma beam and a first design of a low emittance optics show that the source is feasible.
This is not properly an experiment for DANE as Test Facility but it will convert DANE in an hard X rays/gamma Photon User Facility synergic with the other present (and futures) radiation facilities at LNF based on electrons sources (SPARC_LAB, BTF,
THANK YOU

13. ACKNOWLEDGEMENTS
I. Chaikovska, S. Guiducci, C. Milardi, A. Variola, M. Zobov, F. Zomer, A. Ghigo, O. Blanco, A. Balerna and R. Cimino.
…and Igor Pogorelsky for the very helpfull suggestions on CO2 laser operation and performances…