# Presentation: 597790

## High Gradients in Dielectric Loaded Wakefield Structures 

***Manoel Conde***
***High Energy Physics Division***
***Argonne National Laboratory***

*AAC 08 – Santa Cruz, CA*

## AWA & wakefield generation
High gradient excitation
Upgrades and future goals
Wakefield excitation in SLAC / KEK X-band structure

- High gradient excitation
- Upgrades and future goals
- Wakefield excitation in SLAC / KEK X-band structure

***Outline***

## Accelerator R&D at Argonne National LaboratoryHigh Energy Physics DivisionAWA Group

- Wei Gai
- Sergey Antipov
- Manoel Conde
- Felipe Franchini
- Feng Gao

- Chunguang Jing
- Richard Konecny
- Wanming Liu
- Marwan Rihaoui
- John Power
- Zikri Yusof

***External Users / Collaborators:***

-  Euclid TechLabs
-  U.Chicago
-  NIU
-  Fermilab

-  U.Md.
-  IIT
-  APS
-  Yale / Omega-P

## Research at the AWA Facility

- :
- Advanced Accelerating Structures
- 	Current effort has lead to comprehensive knowledge on construction and testing of dielectric based accelerating structures.
- High Power Electron Beam (~ GW) and RF Power Generation
- 	Operating a unique facility to study high current electron beam generation and propagation for efficient beam driven schemes, and high power RF generation.
- Fundamental Beam Physics and Advanced Diagnostics
- 	High brightness beam generation and propagation, phase space measurements, emittance exchange schemes.

## Electron Beam Driven Dielectric Wakefield Accelerator

- A high current relativistic electron beam passing through a dielectric structure can generate high gradient field,  high power microwaves instantaneously.  A new way to power accelerating structures by transporting the power in the electron beam.
- Justifications for looking at dielectric structures:
- Comparable accelerating properties as metal structures.
- More material options; possibly higher gradients.
- Simpler geometry, simpler construction and HOM damping.
- Applications:
- Collinear wakefield acceleration
- Two-beam acceleration

**Notes:**
People have thought that gradient question for NLC had been solved, but it turned that a lot questions come out.  

## Wakefields in Dielectric Structures (a short Gaussian beam)

-      Drive beam is king!
*Energy ***
*Charge ***
*Bunch length ***
*Emittance ***

## AWA Drive Beamline

- 	Single bunch operation
- Q = 1-100 nC (reached 150 nC)
- 15 MeV, 2 mm bunch length (rms), emittance < 200 mm mrad (at 100 nC)
- High Current:  ~10 kA
- 	Bunch train operation
- 4 bunches x 25 nC    or    16 bunches x 5 nC  (present)
- 16 - 64 bunches x 50 - 100 nC  10 - 50 ns long  (future)

## The Argonne Wakefield Accelerator (AWA)

***The Argonne Wakefield Accelerator (AWA)***

**~ 1 meter**

**rf-gun**

**magnetic ****lenses**

**8 MeV**

**15 MeV**

**Laser In**
**λ**** =248nm**

**Linac**

**Quads**

**Spectrometer**

**Faraday**
**cup**

**YAG2**

**YAG1**

**Direction of beam propagation **

**Experimental Area**

## Experimental Setup for High Gradient Tests

- WF signal

- RF field probe (- 60 dB)

- Monitor for breakdown

- Infer Gradients from MAFIA

- 

- Q

- Cu

- Goal:
- Test breakdown thresholds of dielectric structures under short RF pulses.

**Notes:**
Cordierite  = Magnesium Aluminum Silicate

## Dielectric Loaded Structures Tested

| SW  Structure | #1  C10-102 | #2  C10-23 | #3  C5.5-28 |  #4  Q3.8-25.4 |
| --- | --- | --- | --- | --- |
| Material | Cordierite | Cordierite | Cordierite | Quartz |
| Dielectric constant | 4.76 | 4.76 | 4.76 | 3.75 |
| Freq. of TM01n | 14.1 GHz | 14.1 GHz | 9.4 GHz | 8.6 GHz |
| Inner radius | 5 mm | 5 mm | 2.75 mm | 1.9 mm |
| Outer radius | 7.49 mm | 7.49 mm | 7.49 mm | 7.49 mm |
| Length | 102 mm | 23 mm | 28 mm | 25.4 mm |
| Wakefield Gradient | 0.45 MV/m/nC | 0.5 MV/m/nC | 0.91 MV/m/nC | 1.33 MV/m/nC |

## Wakefield Measurements: Structure #1  (C10-102)

- 46 nC → 21 MV/m

## MAFIA Simulation of Structure #1 (C10-102) 

- Snapshots of wakefield amplitude

## Wakefield Measurements: Structure #2 (C10-23)

- Measurement

- Simulation

- Measurement

- Simulation

- TM013 (14.1GHz)

- TM014 (16.2GHz)

- TM012 (13GHz)

- HEM111 (12.4GHz)

- HEM111 (12.2GHz)

- TM012 (13GHz)

- TM013 (14.3GHz)

- TM014 (16GHz)

- HEM112 (14.7GHz)

- HEM112 (14.7GHz)

- Freq (GHz)

- Freq (GHz)

- 86 nC → 43 MV/m

*Measured and simulated E**r** probe signals*

## Wakefield Measurements: Structure #3 (C5.5-28)

- TM013

- 86 nC → 78 MV/m

## MAFIA Simulation of Structure #3 (C5.5-28)

- E-field pattern

- Wz (V/m)

- Wz > 1MV/m @ 1nC for 10GHz Structure

- 28mm

- 2.5mm

- 7.5mm

***MAFIA Simulation of Structure #3 ******(C5.5-28)***

## Wakefield Measurements: Structure #4 (Q3.8-25.4)

- 75 nC → 100 MV/m

- HEM111

- TM012

- TM013

- TM014

## Gradients Reached:

- Structure #2      43 MV/m
- Structure #3      78 MV/m
- Structure #4    100 MV/m

***Gradients Reached:***

***Where we go from here:***

- Once the upgrade is complete, the goal is to achieve:
- Higher gradient excitation:  ~ 0.5 GV/m in structures ( 3 mm apertures)
- Higher RF power extraction:  ~ 1 GW (10 ns)

- To improve the drive beam, we are currently upgrading the AWA facility:
- A new L-band 1.3 GHz RF station to increase the drive beam energy from 15 to 25 MeV.
- Fabrication of Cesium Telluride high quantum efficiency photocathodes to produce long, high charge bunch trains.
- A second RF gun to restore two-beam-accelerator capability.

## Future AWA Facility  (25 MW + 25 MW = 50 MW)

***Future AWA Facility  (25 MW ******+ 25 MW = 50 MW******)***

- *all distances in cm

**D.U.T.**

**Drive Gun**
**(12 MW)**

**Linac 1**
**(10.5 MW)**

- 0

- 225 cm

- 351.6 cm

- 581.6 cm

- 29.1 cm

- 455 cm

- 650 cm

**Linac 2**
**(10.5 MW)**

**D.U.T.**

- 7.5 MeV

- 15.75 MeV

- 25 MeV

- Single Bunch:  50 - 100 nC
- Bunch Train:   16 – 64, total charge 1 – 2.5 μC

**Notes:**
This means we are spending 44 MW out of 50 MW.  This is overhead.

## Verify that structures can withstand gradients higher than 100 MV/m.
Generation of ~ GW level RF power (25 MeV, 130 Amps, 10 ns, 3 GW beam power).
Demonstrate high gradient, broad bandwidth, low cost structures (power extractors and accelerators).
Typical parameters:
f = 10 – 30 GHz, Vg = 5 – 20%
Required power: 0.5 – 5 GW peak
Example (for dielectric based structure):
21 GHz, a = 3 mm, b = 4 mm, ε=12, Vg=0.112
For Ez=200 MV/m, it requires P= 1 GW
16 ns RF pulse, structure length : 30 cm, fill time = 8.4 ns
Beam loading (fundamental mode):0.75 MV/m/nC

- Verify that structures can withstand gradients higher than 100 MV/m.
- Generation of ~ GW level RF power (25 MeV, 130 Amps, 10 ns, 3 GW beam power).
- Demonstrate high gradient, broad bandwidth, low cost structures (power extractors and accelerators).
- Typical parameters:
- f = 10 – 30 GHz, Vg = 5 – 20%
- Required power: 0.5 – 5 GW peak
- Example (for dielectric based structure):
- 21 GHz, a = 3 mm, b = 4 mm, ε=12, Vg=0.112
- For Ez=200 MV/m, it requires P= 1 GW
- 16 ns RF pulse, structure length : 30 cm, fill time = 8.4 ns
- Beam loading (fundamental mode):0.75 MV/m/nC

## Wakefield Observation on SLAC / KEK X-Band Standing Wave Structure

***Wakefield Observation on SLAC / KEK X-Band Standing Wave Structure***

-  Single bunch charge: up to 80nC.
-  Measurements:
-  Time structure and spectrum of the generated wakefield;
-  Linearity of the voltage-charge curve.

## Dimensions for copper only 3-cell standing wave structure experiment

- Dimensions for **copper only** 3-cell standing wave structure experiment

**t**

**b_conv**

**b_end**

**b1**

**b2**

**a_cpl**

**a_pipe**

**5×Rb**

**Rpipe**

- 5×**ellips_r**

**5×D**

| 2b_end | 23.241249 |  |
| --- | --- | --- |
| 2b1 | 22.968 |  |
| 2b2 | 23.072 |  |
| 2b3 | 22.965 |  |
| 2b_cpl | 22.970 |  |
| 2b_conv | 22.86 | 0.9inch |
| 2a | 11.295 |  |
| 2a_pipe | 12.7 | 0.5inch |

**4×a**

| a_cpl | 5.2715 |  |
| --- | --- | --- |
| D | 13.116 |  |
| Rpipe | 3.00 |  |
| Rb | 1.00 |  |
| t | 4.5980688 |  |
| ellips_r | 3.398573 |  |
|  |  |  |
|  |  |  |

- Dimensions for 20 deg. C

*V.A.Dolgashev, 2 March 07*

**b3**

**b_cpl**

## Measured voltage signal

- 11.427GHz
- 5500

- 9.408GHz
- 4600

- 8.361GHz
- 3600

- 7.783GHz
- Q ≈ 6700

- t -μs

- voltage - Volt

- f – GHz

- voltage spectrum

- 13.711GHz
- 1700

- 13.825GHz
- 3900

- q = 34.6nC

## The wakefield in the ceramic vacuum break for ICT may contribute 

- 11.427GHz

- 9.408GHz

- 8.361GHz

- 7.783GHz

- f – GHz

- voltage spectrum

- 13.711GHz

- 13.825GHz

- f – GHz

- spectrum of the wakefield in the vacuum break for ICT (simulated)

- The wakefield in the ceramic vacuum break for ICT may contribute
- to some of the peaks

- vacuum break

## The 11.4GHz component is filtered out

- 11.427GHz

- f – GHz

- voltage spectrum

- t -μs

- voltage - Volt

- q = 34.6nC

- IFFT

- Q ≈ 5500

- Vmax

- Vmin

##  voltage peak value

- charge q - nC

- For 11.427GHz component: