Accelerators on a Chip: owards an All- Op/cal Nanostructured Dielectric Accelerator

Transcription

1 Accelerators on a Chip: owards an All- Op/cal Nanostructured Dielectric Accelerator Joshua McNeur, Mar.n Kozák and Peter Hommelhoff Friedrich- Alexander University Erlangen- Nürnberg (FAU), Erlangen J. LDRS McNeur, 2015 LDRS

2 Par3cle accelerators: from RF to op3cal/photonic drive? RF cavity (TESLA, DESY) Based on Conven&onal linear accelerator (RF) (Supercond.) RF caviies Laser- based dielectric accelerator (op&cal) Quartz graing structures Peak field limited by Max. achievable gradients Surface breakdown: 200 MV/m Damage threshold: up to 30 GV/m 50 MeV/m up to 10 GeV/m? - 2 -

3 Proposed dielectric structures Yoder Rosenzweig, 2005 and variants PleRner, Lu, Byer, 2006 Cowan, 2008 Chang, Solgaard, 2014 Goal: generate a mode that allows momentum transfer from laser field to electrons Use first order effect (efficient!) Second order effects (ponderomoive) too inefficient For a review and an extensive list of references, see: R. J. England et al., Dielectric laser accelerators, Rev. Mod. Phys. 86, 1337 (2014) - 3 -

4 Fields Generated by a Single Gra3ng DLA - 4 -

5 GraIng period: 620nm GraIng depth: 450nm Challenge: get close enough (<200nm) to the graing surface without clipping the beam put graing on 20µm high mesa structure GraIng structure electron beam focus Silicon structures made by K. Leedle, H. Deng (Harris & Byer groups, Stanford) to- scale: 2mm length - 5 -

6 Sketch of setup (previous) laser parameters: 350 mw MHz 110 fs In the focus: 8.3 µm beam waist 2.76 GV/m W/cm 2 Details on setup: J. Breuer, R. Graf, A. Apolonski, P. Hommelhoff, Phys. Rev. ST- AB 17, (2014) on laser: S. Naumov, A. Fernandez, R. Graf, P. Dombi, F. Krausz, and A. Apolonski, NJP 7, 216 (2005).

7 Coincidence measurement - 7 -

8 Dielectric laser accelera3on results Max. observed gradient: 25 MeV/m J. Breuer, P. Hommelhoff, Phys. Rev. LeR. 111, (2013)

9 Dual- Gra3ng Structure: Dielectric laser accelera3on of 60 MeV electrons at Stanford/SLAC E. Peralta, Soong, K., England, R. J., Colby, E. R., Wu, Z., Montazeri, B., McGuinness, C., McNeur, J., Leedle, K. J., Walz, D., Sozer, E., Cowan, B., Schwartz, B., Travish, G., Byer R. L., Nature 503, 91 (2013) - 9 -

10 Future Direc3ons Compact MeV electron source Table-top light source cm

11 Future Direc3ons How do we get here? 1) Improve acceleration efficiency new structures, laser sources 2) Demonstrate multi-stage phase-controlled acceleration 3) Demonstrate deflection/focusing

12 Space charge effects: beam envelope equaion Accel. in long. el. field Focusing in radial el. field Focusing in axial magn. field Defocusing due to ang. mom. Defocusing due to norm. emirance Defocusing due to space charge Generalized perveance: measure for space charge effects

13 Space- charge limited current Total charge (0.1 opt. period long pulse): 3 fc, scales with λ 2 J. Breuer, J. McNeur, P. Hommelhoff, J. Phys. B. 47, (2014)

14 EmiRance and space charge Assume emirance limited beam: If perveance term (space charge, treat as perturbaion) is 10% of the emirance term: current limit of transverse focusing with laser field: Demanding a stable beam radius yields: With G = 1 GeV/m and r = 100nm:

15 Are laser- triggered electrons spaially coherent? Carbon nanotube electron beamsplirer 394nm and 405nm (~3.2eV photon energy)

16 Fringes: DC vs. photo- emired DC laser- triggered

17 Extremely low emirance sources: Ip (arrays) With 20pC, 5A from regular RF and DC photocathodes: norm. emir. = 120nm. Ding et al. PRL 2009 Virtual source size ~ a few nanometers EmiRance ~ 0.1nm OpImized source design: Stanford group (Kasevich, PH) Göungen group (Ropers) Nebraska group (Batelaan) PSI group (Tsujino) MIT /DESY group (Kaertner, Berggren) Mustonen,, Tsujino, APL 2011 Hoffrogge et al., J. App. Phys. 115, (2014)

18 OpImized ultralow emirance electron source Few - tens of fs pulse duraion awer accel. to 30 kev, but bunch charge sill an issue J. Hoffrogge et al., J. Appl. Phys. 115, (2014)

19 What s next? Incorporate low-emittance laser-triggered cathode Extend interaction to >2 stages, with both focusing and accelerating elements -requires structure tapering (already demonstrated), pulse front tilting, laser distribution Incorporate novel geometries (e.g. double-sided structures) for more efficient coupling and more spatially uniform fields

20 Michael Förster Chris&an Heide Takuya Higuchi Mar&n Hundhausen Mar&n Kozak Ang Li Joshua McNeur Timo Paschen Jürgen Ristein Ella Schmidt Lisa Seitz Alexander Tafel N. Schönenberger Philipp Weber Peyman Yousefi Robert Zimmermann FAU Erlangen Group Former members: A. Aghajani- Talesh J. Breuer P. Dombi D. Ehberger M. Eisele R. Fröhlich J. Hammer S. Heinrich J. Hoffrogge H. Kaupp M. Krüger A. Liehl L. Maisenbacher F. Najafi H. Ramadas T. SaRler M. Schenk J.- P. Stein H. Strzalka Y.- H. M. Tan S. Thomas Di Zhang Thanks to our DLA partner groups: R. L. Byer, R. J. England, J. Harris et al., Stanford / SLAC I. Hartl, DESY R. Holzwarth, MenloSystems