Working Group Report for
Dielectric based accelerator
S. Antipov, M. Conde, V. Dolgashev , C.
Jing, A. Kanareykin, J. Power, G. Travish,
J. Rosenzweig
March 19, 2010
Charge
• 1. The first product of the discussions should be a list of
ideas/topics that summarize the next generation of
experiments needed to advance the field. Please note
the ones where the capabilities of FACET have strong
overlap.
•
• 2. The second product would be a list of capabilities
that would allow the FACET facility to enable
experiments along these lines. These capabilities can
be ones already included in the design or suggested
additions. Beam parameters, diagnostics, physical
infrastructure are all appropriate to list.
Presentations
•
•
•
•
•
•
A. Kanareykin
W. Gai
G. Travish,
C. Jing
J. Rosenzweig
Discussions
Experiments
1. Continue the basic physics breakdown studies,
materials, …
2. Many different structures geometries, cylinders,
SLABS, PBGs.
3. Extend acceleration distance, Emittance
Preservations:
– Drive beam BBU control. Use permanent magnets to
control the bbu, it could be made to mm size and
Tesla field.
– Beam shaping for high transformer ratio
experiments. (require a good witness beam).
Materials for the Dielectric-Based Accelerator

2b 2a
Materials
Q
Cu
Low-loss high breakdown strength ceramic for the DLA
material
BST+MgO

350-500
tan, X-band
510-3
/, 4 V/m
1.30
Nonlinear ceramic material for the tunable DLA structure
material
TiN, AlN

tan , X-band
9.8
3 10-3
thermoconductivity
180 W/m/0 K

tan 
(f = 9,4 GHz)
(f = 9.4 GHz)
Cordierite
4.50.2
 210-4
Forsterite
6.30.3
 210-4
Alumina
9.80.3
 110-4
D-10
9.70.2
 1.510-4
D-13
13.00.5
 210-4
D-14
14.00.5
 0.610-4
D-16
16.00.5
 210-4
MCT-18
18.03%
 110-4
MCT-20
20.05%
 1.510-4
V-20
20.05%
 310-4
V-37
37.05%
 310-4
Coating,TiN, AlN
What FACET can bring to the DLA studies: diamond structures
with dielectric claddings – short pulse, THz, > 10 GV/m
A. Kanareykin, Euclid Techlabs LLC, FACET Workshop’10
Why is Diamond?
CVD DIAMOND PROPERTIES FOR DLA:
- RF BREAKDOWN THRESHOLD OF ~ 2 GV/m
- LOSS FACTOR DOWN TO 5x10-5 AT 30-140 GHz
- HIGHEST THERMAL CONDUCTIVITY
- MULTIPACTING CAN BE SUPPRESSED ,
CVD diamond conductivity can be
controlled and adjusted during deposition
process.
Planar is easy to fabricate, single crystal is
available commercially
A. Kanareykin, Euclid Techlabs LLC, FACET Workshop’10
THz Planar Diamond Based DLA
w= 300 μm
a= 40 μm, 2a=80 μm
b= 70 μm
b-a= 30 μm
(diamond thickness)

2b
Q
2a
~10 GV/m
LE  modes
5
110
4
510
3
3
MV/m
w
2
Ez, MV/m
4
0
1
0
1 THz
510
3
110
f GHz
4
1.510
 510
3
 110
4
4
LE modes
510
0
Gradient
A. Kanareykin, Euclid Techlabs LLC, FACET Workshop’10
3
z-Vt, cm
0.01
Planar or Cylindrical THz DLA ?
BBU comparison

Q
2b
2a
w
Fr
GV/m
Both structures deflect
the beam at ~ 2 cm
12
10
10 GV/m
8
Fy
6
2 GV/m
4
2
offset, 40 μm
40 μm
0
5
10
20
30
35
40
A. Kanareykin, Euclid Techlabs LLC, FACET Workshop’10
5 μm
Dual Layer Diamond-Alumina Structure
(Multimode Dielectric Cladding)
alumina

diamond
Q
2b
2a
diamond
w
600
550
500
450
400
350
300
250
200
150
100
50
0
ID=80 μm (a=40 μm )
diamond thickness= 30 μm
alumina thickness = 446 μm
gradient ?
T-B. Zhang et al,
Phys. Rev. E 1997
1,000
2,000
3,000
frequency, GHz
A. Kanareykin, Euclid Techlabs LLC, FACET Workshop’10
4,000
5,000
J.G. Power et al.
Phys.Rev., ST-AB, 2000.
All-Diamond Planar THz DLA

Q
2b
2a
2a
w= 300 μm
a= 40 μm, 2a=80 μm
b= 70 μm, 2b=140 μm
Cylindrical structure
w
ID=80 μm (a=40 μm )
diamond thickness= 30 μm
alumina thickness = 446 μm
A. Kanareykin, Euclid Techlabs LLC, FACET Workshop’10
BBU Simulation. Large tube
Field profiles
Structure:
• iR = 120 μ
• oR = 144 μ
E, V/m
• ε = 5.7 (diamond)
Beam:
• 23 GeV energy;
920 MeV spread
• 3 nC; σr = 5 μ;
offset =5 μ
r, cm
• σz = 30 μ;
Wakefields in large tube
3 000 000 000
2 000 000 000
1 000 000 000
Ez ~ 3.25 GV/m
0
-1 000 000 000
-2 000 000 000
-3 000 000 000
0
0,02
0,04
0,06
0,08
0,1
0,12
Distance behind the bunch, cm
0,14
0,16
0,18
60 000 000
40 000 000
F┴ ~ 65 MV/m,
Initial offset 5 μ
20 000 000
0
-20 000 000
-40 000 000
-60 000 000
0
0,02
0,04
0,06
0,08
0,1
0,12
Distance behind the bunch, cm
0,14
0,16
0,18
BBU Simulation. Large tube
side view
Ez = 3.25 GV / m, F┴ = 65 MV / m
The deflecting gradient grows from 65 MV/m (for initial 5 μ offset) as the beam
is deflected.
Beam crashes in ~ 9 cm distance.
Cure
 General, the BBU can be easily controlled by a damping method, namely,
BNS.
 Small periodical focusing elements are required.
 Better alignments……
 Innovative structure design…….
 Shorter beam?......
 ………….
Summary:
Systematic studies of BBU physics and controls at FACET in dielectric channels
are very useful if extended acceleration is needed.
Experiment is ongoing, we just finished 2-bunch
measurement, R=3.4 (preliminary) is achieved.
Making RBT:
Laser stacking:
20
10
0
10
20
23cm
R=3.4
15
Focusing in DWA tubes
J. Rosenzweig
UCLA
Focusing for drive beam
• Need stability for application to e.g. high XFMR ratio
DWA
• Pass aperture
• Control BBU
• Limit on focusing from lowest energy
– Example: 100 MeV residual beam, from 1 GeV initial
energy driver
• AG permanent magnet focusing, period Lp
– Easily attain 600 T/m
– BR=1.6-16 T-m
– K=40-400 m-2
Focusing calculations
• Average focusing beta
   3 / 2 / 2KLp  2 3 / 2 f q
  
• Choose Lp=10 cm, at low energy

  0.27 m
• Stable even at 100 MeV (min stable~ 60 MeV)
 
 

  0.5cos1 cos K L p /2 cosh K L p /2  0.3  

• Equilibrium
beam size, norm. emit. 1 mm-mrad
 
  n /   36 m
Required diagnostics/alignment
• Beam alignments methods (chambers…)
• Beam size monitors (~ 10 microns).
• Optical/THz transport from the experimental
area to outside (non-rad area).
• Deflecting cavity for bunch length
measurements.
• Low emittance operation, to study beam BBU,
a photo-injector at front?
• Allowance for test beam run, flexible
scheduling for quick experiments. (example 1
day simple test).
• Fast beam access. (several time).
• Ability to have short (< week), but many runs.
Summary
A rich physics can be done at FACET on
dielectric/structure based wakefield
experiments, a good team will do the works.
We will address an important aspect of the
wakefield accelerator: extended acceleration
and BBU control.
Results not only good for HEP, but also
applicable to other fields.