# Presentation: 497670

## E163: Results of the First Experiments

- R. L. Byer*, *E. R. Colby*†, B. Cowan, R. J. England, R. Ischebeck, C. McGuinness, J. L. Nelson^, R. J. Noble, T. Plettner*,             C. M. S. Sears, R. H. Siemann, J. Spencer, D. Walz
- * Stanford University
- Advanced Accelerator Research Department, SLAC
- ^ Test Facilities Department, SLAC

**†** ecolby@slac.stanford.edu

- AAC 2008, Santa Cruz, CA July 27-August 2

- August 1, 2008

## E-163: “Direct” Laser Acceleration

**Motivation**
**High gradient** (>0.5 GeV/m) and high wall-plug power efficiency are possible
** ********  ****HIGH ENERGY PHYSICS**
- Short wavelength acceleration naturally leads to **attosecond bunches** and point-like radiation sources
****** ****BASIC ENERGY SCIENCES**
- Lasers are a **large-market technology** with rapid R&D by industry (DPSS lasers: ↑0.22 B$/yr vs. ↓0.060B$/yr for microwave power tubes)
- Structure Fabrication is by **inexpensive mass-scale** industrial manufacturing methods
-  **COMMERCIAL DEVICES**

**Luminosity** from a laser-driven linear collider must come from **high bunch repetition rate** and **smaller spot sizes, **which naturally follow from the small emittances required

**Beam pulse format is (for example)**
**(193 microbunches of 3.8x10****4 ****e****- **** in 1 psec)**** x 15MHz**
- Storage-ring like beam format  *reduced event pileup*
- High beam rep rate=> *high bandwidth position **	**              stabilization is possible*

- AAC 2008, Santa Cruz, CA July 27-August 2

- August 1, 2008

## ESA

- ESB &
- NLCTA

- AAC 2008, Santa Cruz, CA July 27-August 2

- August 1, 2008

## Slide 4

- AAC 2008, Santa Cruz, CA July 27-August 2

- August 1, 2008

## E-163: Laser Acceleration at the NLCTA

- Brief History
- Endorsed by EPAC and approved by the SLAC director in July 2002
- Director’s and DOE Site Office approval to begin operations granted March 1st, 2007
- E163 Beamline commissioning begun March 8th, 2007, completed March 16th, 2008.

- Scientific Goal: Investigate physical and technical issues of “direct” laser acceleration using dielectric structures by:
- Demonstrating stable production of optically bunched beams suitable for injection into a laser-driven accelerator,
- Demonstrating staging of laser-driven accelerators, and
- Testing candidate microstructures for gradient, coupling efficiency and emittance preservation
- Build a test facility with high-quality electron and laser beams for advanced accelerator R&D

**Energy**

- Ce:YAG Crystal Scintillator Glass graticule (mm)         ICCD 256x1024 camera

- AAC 2008, Santa Cruz, CA July 27-August 2

- August 1, 2008

## Attosecond Bunching Experiment Schematic

- Experimental Parameters:
- Electron beam
-  γ=127
-  Q~5-10 pC
-  Δγ/=0.05%
-  Energy Collimated
-  εN=1.5 
- IFEL:
- 1⁄4+3+1⁄4 period
- 0.3 mJ/pulse laser
- 100 micron focus
- z0=10 cm (after center of und.)
- 2 ps FWHM
- Gap 8mm
- Chicane 20 cm after undulator
- Pellicle (Al on mylar) COTR foil

- AAC 2008, Santa Cruz, CA July 27-August 2

- August 1, 2008

## Attosecond Bunch Train Generation 

- Attosecond Bunch Train Generation

**First- and Second-Harmonic COTR Output as a function of           Energy Modulation Depth (“bunching voltage”)**

- Left: First- and Second-Harmonic COTR output as a function of temporal dispersion (R56)

- C. M. Sears, * et al*, “Production and Characterization of  Attosecond Electron Bunch Trains“, *Phys. Rev. ST-AB*, **11**, 061301, (2008).

- 800 nm

- 400 nm

- 400 nm

- 800 nm

******=800 nm**

- AAC 2008, Santa Cruz, CA July 27-August 2

- August 1, 2008

## Inferred Electron Beam Satellite Pulse

- E

- 400 nm

- 800 nm

- Q(t)

- I(t)

- Electron Beam Satellite!

- AAC 2008, Santa Cruz, CA July 27-August 2

- August 1, 2008

## Staged Laser Acceleration Experiment

- Total Mach-Zender Interferometer path length: ~19 feet = 7.2x106  !!
- All-passive stabilization used (high-mass, high-rigidity mounts, protection from air currents)

- Energy Spectrometer

- Buncher

- Accelerator

- 3 feet

- e

- AAC 2008, Santa Cruz, CA July 27-August 2

- August 1, 2008

## Staging Experiment

- 3 feet

- e

- 

- 

**ITR**

**Chicane**

**IFEL**

- AAC 2008, Santa Cruz, CA July 27-August 2

- August 1, 2008

## Demonstration of Staged Laser Acceleration

- The first demonstration of staged particle acceleration with visible light!

- Effective averaged gradient: 6 MeV/m (poor, due to the ITR process used for acceleration stage)

**12 minutes/7000 points**

- Binned 500/events  per point

- Phase of Accelerator (radians)

- Centroid Shift (keV)

- Energy Gain/Loss (keV)

- Energy Gain/Loss (keV)

- C. M. Sears, “Production, Characterization, and Acceleration of Optical Microbunches”, Ph. D. Thesis, Stanford University, June (2008).

- AAC 2008, Santa Cruz, CA July 27-August 2

- August 1, 2008

## First Tests on an Extended Micro-accelerator Structure

- Left: SEM scan of HC-1060 fiber core
- Right: Accelerating Mode fields for
**Test Structure length: 1200******** (1 mm)**

- In Progress Now:
- (Excitation of Resonant Wakefield in a commercial PBG fiber)

- beam envelopes: x (μm) y (μm)

**500 T/m PMQ Triplet**

- AAC 2008, Santa Cruz, CA July 27-August 2

- August 1, 2008

## 2D Photonic Band Gap Structure Designs

- Design fibers to confine vphase = c defect modes within their bandgaps
- Understand how to optimize accelerating mode properties: ZC, vgroup, Eacc/Emax ,...
**Codes:**
- RSOFT – commercial photonic fiber code using Fourier transforms
- CUDOS – Fourier-Bessel expansion from Univ of Sydney

**Accelerating Modes in Photonic Band Gap Fibers**
-  Accelerating modes identified as special type of defect mode called “surface modes” : dispersion relation crosses the vphase=c  line and high field intensity at defect edge.
-  Tunable by changing details of defect boundary.
-  Mode sensitivities with defect radius R, material index n, and lattice spacing a:
-                        dλ/dR = -0.1,  (dλ/λ)/(dn/n) = 2,  dλ/da = 1.
-  Example: For 1% acceleration phase stability over 1000 λ, the relative variation in
-  fiber parameters must be held to: ΔR/R ~ 10-4, Δn/n ~ 5×10-6, Δa/a  ~ 10-5

| Rinner(μm) | λ(μm) | Eacc/Emax  | ZC(Ω) | Loss (db/mm) |
| --- | --- | --- | --- | --- |
| 5.00 | 1.8946 | 0.0493 | 0.136 | 0.227 |
| 5.10 | 1.8872 | 0.0660 | 0.250 | 0.035 |
| 5.20 | 1.8767 | 0.0788 | 0.371 | 0.029 |

- Ez of 1.89 μm accel. mode in Crystal Fibre
- HC-1550-02

***Silica, ************=1053nm, E******z******=790 MV/m***

***Silica, ************=1890nm, E******z******=130 MV/m***

- Large Aperture

- High Efficiency High Gradient

- AAC 2008, Santa Cruz, CA July 27-August 2

- August 1, 2008

## Planar Photonic Accelerator Structures

- Accelerating mode in planar photonic bandgap structure has been located and optimized
- Developed method of optical focusing for particle guiding over ~1m; examined longer-range beam dynamics
- Simulated several coupling techniques
- Numerical Tolerance Studies: Non-resonant nature of structure relaxes tolerances of critical dimensions (CDs) to ~λ/100 or larger

- Vacuum defect
- beam path is into the page

- silicon

- Synchronous (=1) Accelerating Field

- X (m)

- Y (m)

**This “woodpile” structure is made by stacking gratings etched in silicon wafers, then etching away the substrate. **

- S. Y. Lin *et. al*., Nature **394**, 251 (1998)

- AAC 2008, Santa Cruz, CA July 27-August 2

- August 1, 2008

## Fabrication of Woodpile Structures in Silicon

- Silicon woodpile structure produced at Stanford’s Center for Integrated Systems (CIS)

- AAC 2008, Santa Cruz, CA July 27-August 2

- August 1, 2008

## The Transmission Grating Accelerator 

**The Transmission Grating Accelerator **

**Simple Variant: Fast Deflector **

***Silica, ************=800nm, E******z******=830 MV/m***

- AAC 2008, Santa Cruz, CA July 27-August 2

- August 1, 2008

## Additional semi-free space laser-driven particle acceleration experiments

**Additional semi-free space laser-driven particle acceleration experiments**

**Experiment setup and expected dependence on laser crossing angle**

**?**

- M. Xie, Proceedings of the 2003 Particle Accelerator Conference (2003)
- Z. Huang, G. Stupakov and M. Zolotorev , “Calculation and Optimization of Laser Acceleration in Vacuum”, Phys. Rev. Special Topics - Accelerators and Beams, Vol. 7,  011302 (2004)

**Test with different boundaries**

**Reflective**
**Transparent**
**Scattering**
**Black absorbing ***

- AAC 2008, Santa Cruz, CA July 27-August 2

- August 1, 2008

## Laser Acceleration R&D Roadmap

**LEAP**
- Demonstrate the physics of laser acceleration in dielectric structures
- Develop experimental techniques for handling and diagnosing picoCoulomb beams on picosecond timescales
- Develop simple lithographic structures and test with beam
**E163**
**Phase I. ****	****	****Characterize laser/electron energy exchange in vacuum**
**Phase II. ****	****	****Demonstrate optical bunching and acceleration**
**Phase III. ****	****Test multicell lithographically produced structures **
**Now and Future**
- Demonstrate carrier-phase lock of ultrafast lasers
- Continue development of highly efficient DPSS-pumped broadband mode- and carrier-locked lasers
- Devise power-efficient lithographic structures with compact power couplers
- Develop appropriate electron sources and beam transport methods

- Damage Threshold Improvement

**In 3-4 years: Build a 1 GeV demonstration module from the most promising technology**

- AAC 2008, Santa Cruz, CA July 27-August 2

- August 1, 2008

## E163 Beamline Capabilities

- Electron Beam
- 60 MeV, 5 pC, p/p≤10-4, e~1.5x1.5 tpsec
- Beamline & laser pulse optimized for very low energy spread, short pulse operation
- Laser Beams
- 10 GW-class Ti:Sapphire system 	(800nm, 2 mJ)
- KDP/BBO Tripler for photocathode	(266nm, 0.1 mJ)
- Active and passive stabilization techniques
- 5 GW-class Ti:Sapphire system 	(800nm, 1 mJ)
- 100 MW-class OPA 		(1000-3000 nm, 80-20 J)
- Precision Diagnostics
- Picosecond-class direct timing diagnostics
- Femto-second class indirect timing diagnostics
- Picocoulomb-class beam diagnostics
- BPMS, Profile screens, Cerenkov Radiator, Spectrometer
- A range of laser diagnostics, including autocorrelators, crosscorrelators, profilometers, etc.

- AAC 2008, Santa Cruz, CA July 27-August 2

- August 1, 2008