Surface wave accelerator based on silicon carbide (SWABSiC) V. - PowerPoint PPT Presentation

Surface wave accelerator based on silicon carbide (SWABSiC) V. Khudik, S. Trendafilov, Kamil B. Alici P.I. Gennady Shvets The University of Texas at Austin V. Yakimenko, M. Babzien, M. Fedurin, K. Kusche BNL/ATF

Laser Beam Damage: Dielectrics vs. Metals vs. Semiconductors From Du and Byer (1999). Most measurements at 0.8-1 micron wavelength (Most) Dielectrics + electron beams = charging Pure semiconductors  few free carriers + full valence band Silicon Carbide: -Can operate at high      2 2 temperature (>1000 ⁰ C) i e  e  ( ) L -Has high electrical breakdown voltage (DC      2 2 i T threshold >300 MV/m) -Is low-loss polaritonic material with e < 0 in (  L = 2 p c/10.3 m m,  T = 2 p c/12.5 m m) mid-IR

Surface-wave accelerator driven by a high-power CO 2 laser Consider vacuum channel • Structure supports two between two thin layers of SiC. modes (  = kc mode)  x can accelerate relativistic SiC e < 0 4 m m particles z • Near field (small gap)  SiC e < 0 attractive ratio E z /E x • Application: injector into laser-plasma accelerator By widely available tunable • Cherenkov diagnostics CO 2 laser SiC /vacuum SPP’s for compressed ATF can be excited beam? Kalmykov, Polomarov, Korobkin, Otwinowski, Power, and Shvets, Phil. Trans. Royal Soc. 364, 725 (2006); AAC’08 Conf. Proc., p.538 (2009).

Electromagnetic modes of the Surface Wave Accelerator Based on SiC (SWABSiC) air air air air Si wafer Si wafer SiC film SiC film Accelerating mode Parasitic transverse @10.708 m m wake @10.708 m m (  L = 2 p c/10.3 m m,  T = 2 p c/12.5 m m) Coupling and propagation challenge: how to couple 10.6 m m radiation into a 4 m m hole  not only the hole small, the mode’s symmetry is not good for coupling!

Si Prism + SiC Film Fabrication • Step 1: cutting Si discs (D=5cm, t=5mm) into 22x12x5 mm “bricks” • Step 2: growth of 1.7 m m SiC in Lyon, France • Step 3: cutting Si “bricks” into prisms (ISP Optics) 28º angle 20 1.78 mm 15º angle mm 10 mm

SWABSiC: two interface SPPs Step 3: Patterning with photoresist Step 1: Grow 1.7 m m of SiC Si “brick” Step 2: LTO deposition Step 4: BOE Etch of 5 µm SiO 2 SiO 2 Step 5: Final Assembly = 6 µm air gap

Longitudinal and Transverse Wakes Si prism Left: schematic Right: target assembly 6 µm air gap Si slab SiC film

Cherenkov diagnostics for compressed (or sliced) ATF beam? • Goal: Pre-bunched electron beam to generate coherent mid-IR Cherenkov radiation. • Application: Diagnostic tool for high-energy electron bunches. - Angular and spectral distribution of the coherent IR radiation can be used to characterize the bunch length and transverse size.

Resonant interaction of beam propagating in channel To avoid scattering, beam can be launched in vacuum channel. It can   / k c excite surface waves there. ||          In this wave, polarization charges are z located on surfaces.          y e  Waves are localized near the channel. 0  2 x    e 2 2 2 How to unlock waves? k k k x y z 2 c Wave front for k y =0 Surface waves with                     (  e 1 / 2 1 ) k y e 1  0 c e 2  1 leak in the second medium Problem: still, these waves cannot leak into vacuum!

Accelerator/Radiation-Source Structure Solution: use Si-prism!       15 , 17 . Wave front for k y =0: wedge front Radiation is incident almost          normally to air-prism          e 1  interface! 0 e 2  1 Beam is slowly decelerating. Laser Remember the accelerator configuration: m 1 . 7 m          m 6 . 0 m          Burton Neuner III, Dmitriy Korobkin, e 1  m 0 1 . 7 m Gabriel Ferro, and Gennady Shvets, e 2  1 Phys. Rev. ST Accel. Beams (2012) 5 . 0 mm

Dispersion Equation for waves in SiC Structure. Do the simple case, the electric field in thick SiC SiC          plates. Make inverse Fourier transform:   2   a      p 2  ( ) z a ( )  k i e k  4          i qe     e  i k r i t || || z  ( , ) 0 E r t d k e || || SiC p ||  2 2 z ( 2 ) ( , ) k D k y || ||  m 3 a m  0 . z E In this mode, is symmetric with respect to the plane x x   ||  Main contribution is from poles where ( , ) 0 D k    e  2 2 2 1 / 2 ( / ) , k c ||    e    e    k a k a   ( , ) ( / ) ( / ) 0 , D k e y k e y k    , k v || y y ||      2 2 i    e  e ( ) LO k Solve dispersion equation and find       2 2 * y i TO   0 . 596   k y  / 2  m 1  m m 1 m

Dispersion Equation for Waves in Si-SiC Structure II.  m 1  m m 1 m   m    1  1 30 . k m The second plot tells us that radiation occurs at y out

Intensity vs. wavevector of the waves entering Si plate Wave front for  m Si k y =0 3 a m SiC  m          4 . 7 d m 2 d 2 a          e 1  0 SiC e  11 . 7 e 2  Si 1 Si  x 1  x   ~ 50 Pulse length of the generated radiation  Im( ) / c   m    1  The radiation occurs at 0 . 6 18 . k m y out

Refraction at the prism (Fresnel formulas).       , e s n k Unit vectors n                 e e k , , e e k e e k , p t s t k , p r s r p s  2       2 2 2   k k k       2                2 ( ), 2 , , k r k n n k t x t z y ( ) [ ( )] , 2 k t k n n k n k n n k c 2 c            2( n k ) 2 ( n k )         ( ) ( ) E E e E e        e   e  t s p - 1/2 1/2 ( n k ) ( n k ) ( n k ) ( n k ) t t In vacuum propagation possible for   m 1 0 . 6 k y m

Dependence of Emission on various parameters • Radiation into Si-plate: • Radiation into vacuum: • Beam shape:   Final output:

Lower and upper estimates of radiation energy Coherent radiation of the point charge:   2 2 L x - 1cm – length of the structure 2 FF q k x L x ~ W k x - 0.6 m m – x-component of wavenumber of the radiation pe 4 0 q - charge FF ~ 0.01/3 - form factor   3 Radiation energy for 100pC (coherent) 2 * 10 W J   7 Radiation energy for 1pC (coherent) 2 * 10 W J e – electron charge Incoherent radiation   2 2 2 FF e k L q x x ~ W pe 4 e 0   12 Radiation energy for 100pC (incoherent) 3 . 5 * 10 W J   14 Radiation energy for 1pC (incoherent) 3 . 5 * 10 W J

CAD preparation

Status of the experiments

Status of the experiments • Electron beam was aligned and tested. - σ x , σ y ~ 430um • 1D motorized stage, alignment target, Cassegrain objective were installed • The objective was aligned to the external camera with ~ 3.9um resolution. • The triplet was placed and aligned - σ x , σ y of the microbeam at the focus ~ 6um x 12um • A compact sample holder for SWABSiC was designed and machined. • All the opto-mechanics and SWABSiC were vented in vacuum oven. • A motorized two axes mirror mount was added to the chamber • With a second HeNe laser and pellicle beam splitter first iteration for the placement of flat and parabolic mirrors inside the chamber was completed, IR trasparent window was added • Fine alignment of the SWABSiC channel to the beam line (ongoing)