Light sources based on optical-scale accelerators
Gil Travish
Particle Beam Physics Laboratory
UCLA Department of Physics ...
I want to thank the organizers for the opportunity

                                                     Eric             ...
Can you build an iPad
sized light source?
Should you build it?
Optical-scale dielectric-structures promise GeV/m
gradients and naturally short bunches

           + very short pulses
  ...
Basically, an FEL or ICS source has an injector,
accelerator, radiator, and x-ray beamline.
                              ...
The choice of accelerator technology impacts the
possible light source configurations...



                               ...
... the undulator technology has at least as much
impact on the FEL design.



                               PM      Micr...
An example of a soft x-ray FEL-based source
reveals the need for new undulator approaches
  106 electrons; 108 photons    ...
A laser undulator for the 20µm case requires
   guiding or LLNL class lasers
      Magic 20µm laser                       ...
We need to develop four critical technologies to
make the iPad sized Light Source

                     1.Ultra low emitta...
Low charge, high brightness injectors
Conventional RF photoinjectors are a viable source
of low-charge, low-emittance beams


                            At ~1 ...
Electron microscopes achieve the requisite
  emittances, albeit at very low current

                                     ...
Injection into a sub-micron aperture and a sub-ps
bucket is a concern

 IFEL
                                           Fi...
Longitudinal manipulation (bunching) of the beam
on the attosecond level has been shown


                                ...
Integrating the injector and optical scale
accelerator may be the best path
                                              ...
Creating low beta optical-scale structures is hard.
Really hard.

         low ß MAP                                      ...
Optical-scale accelerator structures
Here at SLAC, the E-163 AARD team is producing
a set of laser-driven dielectric micro-accelerators

   PBG

              ...
PBG-fiber-based structures afford large apertures
 and scalability to HEP-length structures




  input port!   X. E. Lin “...
Planar structures offer beam dynamics advantages
as well as ease of coupling power

    MAP             Logpile          G...
The MAP structure consists of a diffractive optic
coupling structure and a partial reflector
The Micro Accelerator Platform (MAP) is undergoing
intense simulation and fabrication study



                           ...
We are planning a ß=1 MAP beam de/acceleration
experiment here at E163




             SBIR collaboration with
The log-pile structure is being fabricated and offers
an intermediate gradient solution




Gradient
   221 MeV/m @ 1.55µm...
The Stanford grating structure is non-resonant and
 might support >10GeV/m

                             Materials near be...
These planar structures are modular and scalable

easy power coupling         “easy” to scale & stage




                ...
Breaking News Alert
The New York Times
Tue, February 23, 2010 -- 3:08 PM ET
-----


Toyota Executive Says Recall Might 'No...
Example: focusing issues in the MAP
                                                Alternating Phase Focusing
           ...
Ultra-short period undulators
RF & Laser based undulators offer advantages but
demand excellent uniformity and are undeveloped


Good:                  ...
A grating based undulator can produce an
intermediate-period device




                                 Plettner and Byer...
Beam powered devices have also been
considered: Image charge undulator (Wakefield)

Issues:
Another beam?
Advantage over RF...
Laser guiding and laser technology
Guiding of the laser reduces the effects of
   diffraction and the Gouy phase shift
ELECTRONS


                          ...
Planar Bragg guiding...
       Claim:
   energy out is
   2 OOM over
    free space,
      but only
 10-6 photons per
    ...
Guiding of the (soft) x-rays is also possible
           Unguided                        Guided               The phase sp...
Conclusions
A soft x-ray light source powered entirely by lasers
and on a laptop scale seems possible

              Parameter        ...
We have the opportunity to develop a suite of on-
 chip particle beam tools
        guns                sub-relativistic s...
Technical development level will
  decide which optical scale
    structure is of interest




 Very low charge is good fo...
prediction
A laser “add-on box” to up-convert to x-rays
 and based on an optical-scale accelerator
         will be availa...
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Light sources based on optical-scale accelerators

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Presented at the 2010 Future Light Sources Workshop, SLAC, Palo Alto, CA. Gives an overview of optical-scale particle accelerator structures as would be used in x-ray light sources.

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  • Light sources based on optical-scale accelerators

    1. 1. Light sources based on optical-scale accelerators Gil Travish Particle Beam Physics Laboratory UCLA Department of Physics & Astronomy Input from... Claudio Pellegrini, Sven Reiche, Chris Seers, Chris McGuinness, Eric Colby, Joel England, Josh McNeur Material stolen from... lots of people including C. Brau, J. Jarvis, T. Plettner
    2. 2. I want to thank the organizers for the opportunity Eric Bruce Me HC-1060 < 10 days la se r lig 10 ht el ec tro n be am talk length = ƒ(t) Make a light non-functional source! technology
    3. 3. Can you build an iPad sized light source?
    4. 4. Should you build it?
    5. 5. Optical-scale dielectric-structures promise GeV/m gradients and naturally short bunches + very short pulses + very high repetition rate +/- low charge - no track record - limited R&D work ! The red-headed stepchild of AA Tolerances: Gradients x10-x100 metal PWFA: ~300nm Structural control of fields LWFA: ~30nm Many possible geometries MAP: ~10nm Scalable fabrication
    6. 6. Basically, an FEL or ICS source has an injector, accelerator, radiator, and x-ray beamline. 1 1 ,% # f a ( 2 I / 3 != .' u c w * 1 2" -& 2$ ) IA+ x+ y 0 !u Lg = 4 3"# mc 2 Psat = 1.6 ! Pbeam = 1.6 !" I e SLAC- LCLS Energy spread limit Space charge limit !" 4! I << # kp = << 2ku #" " "I A A DESY
    7. 7. The choice of accelerator technology impacts the possible light source configurations... McGuinness RF Optical Gradient 10-100 MeV/m 1-10 GeV/m Energy gain per period 1 MeV 1 keV Repetition Rate 100 Hz 10-100 MHz Charge per Bunch 0.1 - 1+ nC 0.01-1 pC Bunch Length 1-100 ps 1-100 fs key: charge and time scale; not gradient
    8. 8. ... the undulator technology has at least as much impact on the FEL design. PM Micro/Pulsed RF Optical Period >1 cm 0.1 - 1 mm 0.1-1 cm 1-20µm Parameter 1-10 <1 ~1 ~1 Gap 5 mm 1 mm 1+ cm 20-100µm? Status Mature some SC work stalled paper Focusing is an addition issue: # n 4% !opt " 3 L $ & g
    9. 9. An example of a soft x-ray FEL-based source reveals the need for new undulator approaches 106 electrons; 108 photons Parameter Value Wavelength 6 nm Beam energy 25.5 MeV Energy spread 10-4 Emittance (norm.) 0.06 µm (doh!) Charge 1 pC (whew!) Peak current 750 A Undulator parameter 1 Lcoop/σL<1: 1-2 spikes Undulator period 20 µm Focusing betafunction ~ 3 mm Gain length 500 µm FEL parameter ~3 x 10-3 Saturation length 6 mm (LOL) x-ray flux per bunch ~5 x 108 Pellegrini and Travish
    10. 10. A laser undulator for the 20µm case requires guiding or LLNL class lasers Magic 20µm laser Beating lasers (similar for 10µm case) 800 nm + 1µm for au=1 for au=1 need need EL= 35J EL= 8J x 2 PL ~ 1TW PL < 1TW 2 πw ZR = ; 2LU = 12mm 0 λL w0 ~ 330 µm w0 ~ 70 µm A hard x-ray FEL source using optical period undulator would be too low energy to function well An ICS-based hard x-ray source could produce tolerable fluxes if laser guiding works
    11. 11. We need to develop four critical technologies to make the iPad sized Light Source 1.Ultra low emittance injectors 2. Optical-scale accelerators PSI 3. Micron-period undulators 4. Laser guiding LBNL Kyoto Teramobile
    12. 12. Low charge, high brightness injectors
    13. 13. Conventional RF photoinjectors are a viable source of low-charge, low-emittance beams At ~1 pC, we need <0.01µm (10 nm) emittances LCLS injector What’s the problem? Preservation of nm emittances @ 20 pC Laser technology achieved (MHz repetition rates) 0.13µm emittance Injection into optical structures
    14. 14. Electron microscopes achieve the requisite emittances, albeit at very low current Field and photo-assisted field emission work well Brau & Jarvis Needle cathode work is showing the way
    15. 15. Injection into a sub-micron aperture and a sub-ps bucket is a concern IFEL Final focus type Asymmetric emittances IFEL pre-bunching Dielectric Injector E. Colby Flat beam εy ≈ 50 εx D. Edwards, et al., XX Linac Conference, (2000)
    16. 16. Longitudinal manipulation (bunching) of the beam on the attosecond level has been shown velocity bunching ~5% of total Chicane IFEL Lower Energy Higher Energy bunch’o math C. Sears
    17. 17. Integrating the injector and optical scale accelerator may be the best path laser light electron beam Ultrafast Electron Pulses from a Tungsten Tip Triggered by Low-Power Femtosecond Laser Pulses Peter Hommelhoff, Catherine Kealhofer, and Mark A. Kasevich PRL 97, 247402 (2006)
    18. 18. Creating low beta optical-scale structures is hard. Really hard. low ß MAP 100 MeV/m @ 30nm from grating !"#$%&'"() *+) ,-'&./#0)1-2+() John Breuer, Christopher M. S. Sears, Tomas Plettner, and Peter Hommelhoff !"#"$% &'()*+%,-./% !"# 0(1+*%,-./% $%"# 23+'$(3#% All dielectric design needs work &"# $%"# %'"# $""# %'"# $("# %'"# $")# %'"# $*"# %'"# )!#
    19. 19. Optical-scale accelerator structures
    20. 20. Here at SLAC, the E-163 AARD team is producing a set of laser-driven dielectric micro-accelerators PBG HC-1060 Fiber 10 µm Woodpile 4 Layer Structure (10/08) 2 Layer Structure (6/08)
    21. 21. PBG-fiber-based structures afford large apertures and scalability to HEP-length structures input port! X. E. Lin “Photonic bandgap fiber accelerator,” PRSTAB 4, 051301 (2001) Efficient coupling to the accelerating mode of a PBG fiber is absorbing boundary! complicated by various issues: ~2.5 GV/m ➡overmoded: coupling to other modes drains away input power ➡extra modes are lossy and difficult to simulate ➡initial simulation results from overlap with accelerating mode: ~ 12% HFSS: custom dielectric waveguide coupler
    22. 22. Planar structures offer beam dynamics advantages as well as ease of coupling power MAP Logpile Grating Flat beam LS: modes? coherence? undulator?
    23. 23. The MAP structure consists of a diffractive optic coupling structure and a partial reflector
    24. 24. The Micro Accelerator Platform (MAP) is undergoing intense simulation and fabrication study relativistic structure nearing fabrication-ready design !"#"$% &'()*+%,-./% 0(1+*%,-./% 23+'$(3#% !""# $%&# &""# $%&# '""# $&"# e- '""# $("# '""# $")# '""# $!"# '""# $")#
    25. 25. We are planning a ß=1 MAP beam de/acceleration experiment here at E163 SBIR collaboration with
    26. 26. The log-pile structure is being fabricated and offers an intermediate gradient solution Gradient 221 MeV/m @ 1.55µm Fabrication Amenable to higher damage thresholds Tunability Coupling Impedence C. McGuinness
    27. 27. The Stanford grating structure is non-resonant and might support >10GeV/m Materials near beam = easy to make the fields; bad for wakefields Non resonant = 10 fs pulses; but complex coupling and synchronization Plettner, et al., PAC 2007
    28. 28. These planar structures are modular and scalable easy power coupling “easy” to scale & stage flat beams low wakefields >50µm //
    29. 29. Breaking News Alert The New York Times Tue, February 23, 2010 -- 3:08 PM ET ----- Toyota Executive Says Recall Might 'Not Totally' Solve Accelerator Problems He doesn’t know the half of it!
    30. 30. Example: focusing issues in the MAP Alternating Phase Focusing periodically modulating the position of the coupling slot Initial analysis bucket depth is *+',-!.//012$'/0! 34/502!!60127! "#$%&$'()! "08)! !"#$%&$'()! -9:;! -<=;! ->>9! >-?;! impossibly limited -9:;! -9:;! -<=! -<@;! -:! -AB! ??-;! @@-?! -9:;! -<@! ?-?! BB-?! -9;! -<=;! ->:! >-9! -:! -<=;! -9B! :-9;! -:;! -<=;! -9:! ??! -A! -<=;! -:B! ?=!
    31. 31. Ultra-short period undulators
    32. 32. RF & Laser based undulators offer advantages but demand excellent uniformity and are undeveloped Good: Bad: Ugly: large aperture betatron motion δ aU high fields power loss along waveguide << ρ smooth bore (wakefields) modes and cutoffs aU tunable Beating can create larger periods RF waveguide undulators can work Issues: 800nm + 1µm = 20µm Readily available laser technology Efficient path to longer periods Better than OPO/OPA? Ripples ok?
    33. 33. A grating based undulator can produce an intermediate-period device Plettner and Byer, Phys. Rev. ST Accel. Beams 11, 030704 (2008) Barriers: Smith Purcell parasitic radiation Attosecond pulses and synchronization Low fields? Period limit? (300µm)
    34. 34. Beam powered devices have also been considered: Image charge undulator (Wakefield) Issues: Another beam? Advantage over RF? Energy loss? Acronym challenged (ICU) Y. Zhang et al., NIM A 507 (2003) 459–463
    35. 35. Laser guiding and laser technology
    36. 36. Guiding of the laser reduces the effects of diffraction and the Gouy phase shift ELECTRONS LASER 2Rg ! 2w0 In practice, the fiber (waveguide) will be overmoded L Rg ? λ ≈ 1µ m On the other hand, a very small bore is required to Propagating the electron beam through the obtain significant enhancement from guiding. We take tube is necessary: ε nβ ε nL 2Rg = 20 µm σ= = γ γ The naive flux enhancement factor is simply 2  2w  Electron beam transmission will be very  0  =4 challenging at low energies. There are many  2R   g additional considerations such as vacuum, breakdown, plasma formation, etc. The brightness is enhanced further as the bandwidth may be reduced.
    37. 37. Planar Bragg guiding... Claim: energy out is 2 OOM over free space, but only 10-6 photons per electron Vadim Karagodsky, David Schieber, and Levi Schächter PRL 104, 024801 (2010) Bragg waveguide setup. The electrons interact with a counterpropagating laser and emit x-ray radiation. The laser mode of interest has a TEM form inside the vacuum core. The mode is confined to a submicron cross section, enabling strong interaction not at the expense of interaction length.
    38. 38. Guiding of the (soft) x-rays is also possible Unguided Guided The phase space ! ! reduction factor is !c L !c L 2 2θ c L θc L 1 = = 4θ c Rg 2Rg N zz 2! c r 2! c r Guiding in optical 2Rg 2Rg accelerator driven ICS is Equivalent phase space area: interesting: For the guided source, the 2 phase space is at most short pulse = higher 2θ L c 2θ c 2Rg damage threshold assuming high rep rate = less θ c L ? 2Rg laser energy per pulse (smallest ellipse is fields in guide ~ fields at least x2 bigger) in accelerator
    39. 39. Conclusions
    40. 40. A soft x-ray light source powered entirely by lasers and on a laptop scale seems possible Parameter Value Wavelength 6 nm Beam energy 25.5 MeV Emittance (norm.) 0.06 µm (doh!) Charge 1 pC (whew!) Undulator parameter 1 Undulator period 20 µm FEL parameter ~3 x 10-3 Saturation length 6 mm (LOL) x-ray flux per bunch ~5 x 108 Pellegrini and Travish
    41. 41. We have the opportunity to develop a suite of on- chip particle beam tools guns sub-relativistic structures undulators monolithic structures muons, protons, ions coherent THz/x-ray sources IFEL accelerator deflecting cavities focusing ultra-fast sources ICS Gamma-Ray Source all using laser-driven dielectric structure
    42. 42. Technical development level will decide which optical scale structure is of interest Very low charge is good for very short time scales Killer app for optical structure based light source still needs to be identified
    43. 43. prediction A laser “add-on box” to up-convert to x-rays and based on an optical-scale accelerator will be available in 10 years

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