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 temperature (>1000⁰C)

• Has high electrical breakdown voltage (DC

threshold >300 MV/m)

• Is low-loss polaritonic material with e < 0 in

mid-IR

      e e i i

T L

     

2 2 2 2

) (

(L = 2p c/10.3 mm, T = 2p c/12.5 mm)

Surface-wave accelerator driven by a high-power CO2 laser

x z

• Structure supports two

modes ( = kc mode)  can accelerate relativistic particles

• Near field (small gap) 

attractive ratio Ez/Ex

• Application: injector into

laser-plasma accelerator

• Cherenkov diagnostics

for compressed ATF beam? By widely available tunable CO2 laser SiC/vacuum SPP’s can be excited

4 mm

SiC e < 0 SiC e < 0

Kalmykov, Polomarov, Korobkin, Otwinowski, Power, and Shvets, Phil. Trans. Royal Soc. 364, 725 (2006); AAC’08 Conf. Proc., p.538 (2009).

Consider vacuum channel between two thin layers of SiC.

Electromagnetic modes of the Surface Wave Accelerator Based on SiC (SWABSiC)

Coupling and propagation challenge: how to couple 10.6 mm radiation into a 4 mm hole  not only the hole small, the mode’s symmetry is not good for coupling!

Accelerating mode @10.708 mm Parasitic transverse wake @10.708 mm Si wafer Si wafer SiC film SiC film air air air air

(L = 2p c/10.3 mm, T = 2p c/12.5 mm)

Si Prism + SiC Film Fabrication

• Step 1: cutting Si discs (D=5cm, t=5mm) into 22x12x5 mm “bricks”
• Step 2: growth of 1.7 mm SiC in Lyon, France
• Step 3: cutting Si “bricks” into prisms (ISP Optics)

28º angle 15º angle 1.78 mm 10 mm 20 mm

SWABSiC: two interface SPPs

Si “brick” Step 1: Grow 1.7 mm of SiC SiO2 Step 2: LTO deposition

• f 5 µm SiO2

Step 3: Patterning with photoresist Step 4: BOE Etch Step 5: Final Assembly 6 µm air gap

=

Longitudinal and Transverse Wakes

6 µm air gap Si slab Si prism SiC film Left: schematic Right: target assembly

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 excite surface waves there.

In this wave, polarization charges are located on surfaces. Waves are localized near the channel.

z

y

x

How to unlock waves?

c k /

||

 

e 

2 2 2 2 2

c k k k

z y x

  

Surface waves with leak in the second medium

2 / 1

) 1 (   e  c ky

Problem: still, these waves cannot leak into vacuum!

 e

                 

1

e 1

2 

e

Wave front for ky=0

                 

Accelerator/Radiation-Source Structure

Radiation is incident almost normally to air-prism interface! Beam is slowly decelerating.

1

e

        

1

2 

e

Wave front for ky=0: Solution: use Si-prism!

1

e

                 

1

2 

e

        

Laser

Remember the accelerator configuration:

Burton Neuner III, Dmitriy Korobkin, Gabriel Ferro, and Gennady Shvets,

• Phys. Rev. ST Accel. Beams (2012)

. 17 , 15

 

 

front wedge

 

mm m m m . 5 7 . 1 . 6 7 . 1 m m m

Dispersion Equation for waves in SiC Structure.

 e

                 

Do the simple case, the electric field in thick SiC

• plates. Make inverse Fourier transform:

2 || 2 || || || ) ( || 2

) ( ) , ( 4 ) 2 ( ) , (

|| ||

k k e i k k D qe e k d i t r E

z a z t i r k i

     

 

 

  



  p p

 

a 2

, ) / ( ) / ( ) , (

||

    

 y a k y a k

k e k e k D

y y

 e  e  

z

y

x

      e e  e  i i v k c k

TO LO

        

 2 2 2 2 || 2 / 1 2 2 2 ||

, , ) / (  

Solve dispersion equation and find

) (

* y

k   

Main contribution is from poles where

) , (

|| 

k D  

2 / 

596 . 

 

y

k



1 

m m

1 

m m

m a m 3 

SiC SiC In this mode, is symmetric with respect to the plane

x

E

.  z

Dispersion Equation for Waves in Si-SiC Structure II.

1 

m m

1 

m m

The second plot tells us that radiation occurs at

. 30 1

1 

  



• ut

y

m k  m

Intensity vs. wavevector of the waves entering Si plate

a 2

1

e 1

2 

e

Wave front for ky=0                  

d 2 m d m 7 . 4  m a m 3  7 . 11 

Si

e

Si SiC SiC Si

x 

Pulse length of the generated radiation

  50 ~ / ) Im( 1 c x  

The radiation occurs at

. 18 6 .

1 

  



• ut

y

m k  m

n 

Refraction at the prism (Fresnel formulas).

k 

, k e e

s p

    

Unit vectors

) ( ) k n ( ) k n ( ) k n ( 2 ) ( ) k n ( ) k n ( ) k n 2(

t 1/2 1/2

• t

p s t

e E e E E                              e e , k n es     

t s t p

k e e     

,

,

, r s r p

k e e     

), ( 2 k n n k kr        

, )] ( [ ) (

2 2 2

k n n k c n k n n k kt                  

1

6 .



 m ky m

In vacuum propagation possible for

2 2 2 2 , 2 , y z t x t

k c k k    

• Radiation into Si-plate:
• Radiation into vacuum:
• Beam shape:

Dependence of Emission on various parameters  

Final output:

Lower and upper estimates of radiation energy

Radiation energy for 100pC (coherent)

J W

3

10 * 2





Radiation energy for 1pC (coherent)

J W

7

10 * 2





2 2

4 2 ~ pe

x x L

k q FF W  

Coherent radiation of the point charge: Lx - 1cm – length of the structure kx - 0.6mm – x-component of wavenumber of the radiation q - charge FF ~ 0.01/3 - form factor Incoherent radiation

e q L k e FF W

x x 2 2

4 2 ~ pe  

e – electron charge Radiation energy for 100pC (incoherent)

J W

12

10 * 5 . 3





Radiation energy for 1pC (incoherent)

J W

14

10 * 5 . 3





CAD preparation

Status of the experiments

Status of the experiments

• Electron beam was aligned and tested.
• σx , σy ~ 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
• σx , σy 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)