1. Brief Review of Microwave Dielectric Accelerators
Chunguang Jing
May 2017

2. Brief overview Dielectric Accelerator Time Structures facility content
2001 ~2015
11.4GHz external powered Dielectric accelerators
NRL Magnicon, 20MW, 200ns
Multipactor suppression: different coating techniques, surface geometrical perturbations, external solenoid field, etc.
2005 ~2007
X-band dielectric wakefield structures
AWA 15MeV beamline
Single bunch high charge wakefield excitation. 100MV/m, ~5ns; high transformer ratio collinear; tunable DWA, etc.
2015 ~2017
26GHz short pulse dielectric accelerator
AWA 70MeV beamline
Short pulse TBA, 50MeV/m
2017
11.7GHz short pulse dielectric accelerator (under fabrication)
Short pulse TBA

3. Brief overview Dielectric PETS Time Structures facility content
2006~2008
7.8GHz DPETS
AWA 15MeV beamline
50MW, 10ns
2009
26GHz DPETS
20MW, 10ns
2013
11.4GHz DPETS
SLAC ASTA klystron
40MW, 50ns, 100ns
2014
12GHz DPETS
Transverse wake damping
2016~2017
AWA 70MeV beamline
2017
11.7GHz DPETS (under fabrication)
>200MW, 10ns

4. Example: X-band Traveling Wave DLA
Single piece dielectric tube
Broad band
no field enhancement at surface
Multipactor
Relatively lower Shunt impedance
Alumina
Silver metalization
X-band assembly

5. Example: 26GHz short pulse DLA Structure
parameters
value
ID / OD of dielectric tube
3 mm /5.025 mm
Dielectric constant
9.7
Length of dielectric tubes
105 mm Vg
11.13%c
R/Q
21.98 k/m
Q (loss tan=10^-4)
2295
Shunt impedance
50.44 M/m
Eacc for 316MW input
158 MV/m

6. Cure of Multipactor using Solenoid Field for a Standing Wave DLA (Oct
Bifurcation
Enhancement
Mitigation
Blocking

7. The 26GHz Full Dielectric Short Pulse TBA Test ( Feb.2017)
DPETS
~4MeV deceleration was measured for each drive bunch which is aligned with ~160MW rf power output by a 4x22nC bunch train.
~1.8MeV acceleration of a 230pC witness beam transmitted through the dielectric accelerator, which is eqv. to ~50MV/m gradient.
Note: Gradient is lower than the ideal case due to the combination of RF loss in the waveguide, miss-match of the phase advance, and inefficient rf coupling, etc.
ID=7mm, L=30cm
DLA
ID=3mm, L=10cm

8. Dielectric PETS (CLIC Power Extraction and Transfer Structure)
Using CLIC Beam: σz=1mm, Q=8.4nC, Tb=83ps
Freq
11.994GHz
Effective Length
23cm
Beam channel
23mm
Dielectric wall thickness
2.582mm
Dielectric const.
3.75(Quartz) Q
7318
R/Q
2.171k/m Vg
0.4846c
Peak surface Gradient
Ell=12.65MV/m; E=18.28MV/m
Steady Power
142MW

9. Construction Dielectric loaded waveguide RF output coupler
Impedance matching section
Transverse mode damping
Quartz tube
SiC tube
metalization
3 section of damper
Brazed copper ring
Quartz tube

10. RF test at SLAC 2013/ Beam test at AWA 2014

11. Conceptual design of short pulse collider

12. 3TeV 30MW Beam Argonne Flexible Linear Collider
18km
7.5km linac
7.5km linac
Based on scientifically mature and low cost Dielectric TBA technologies
Short rf pulse (20ns) for high gradient (e+ e- 200MeV/m of effective gradient)
Modular design easily staged
Wall plug efficiency (~10%)

13. Zoom-in for each 150GeV AFLC Module
Drive beam
Stage 2
Stage 1
photons
rf delay m
rf delay 1
rf delay m
rf delay 1
1.3GHz SW Linac
Staging with high quality main beam L L
Main beam
Simplified Staging by manipulating RF instead of high energy drive beam

14. Zoom-in to AFLC Structure Level
Short pulse accelerator
~15cm
Power Extractor
30cm
Gradient needs ~300MV/m
Shorten the rf pulse length ~20ns
Logic: high gradient in structure>short rf pulse>high power>TBA; values are achievable
High group velocity accelerator (10%c) to reduce rf filling time
GW level rf power
TBA
high frequency (26GHz) to high shunt impedance
Dielectric accelerator for low cost

15. AFLC Beam Power for high luminosity:
16ns
5us
100us
200ms 1s #1 #2
#20
#21
#40
#22
#81
#82
#100
In pulse beam current =6.5A
Average current=10.4uA
Average beam power=15.6MW
0.5nC/bunch
Main Beam Structure
3ns
Trf=28ns
Tf=9ns
Tbeam=16ns
Competitive rf-beam efficiency for the short pulse TBA
6.5A
267MV/m
0.3m
1.264GW
16ns
25ns
AFLC RF-to-beam efficiency:
RF Structure

16. AFLC Power and efficiency flow chart
Site Power
~400MW
291MW
AC-rf=55%
Main beam injection, magnets, services, infrastructure, and detector
Power supplies to klystrons gallery
~100MW*
160MW
* Borrowed from the CLIC design
Drive beam acceleration
rf-drive=86%
138MW
total~7.8%
Drive beam Dumps
DPETS
126MW
rf-tran=95%
120MW
rf-main=26%
Main linac
31.2MW
Main beam

17. Improved AFLC Power and efficiency
AC-rf=90% (CLIC/SLAC)
Site Power
~200MW
100MW
AC-rf=55%
Main beam injection, magnets, services, infrastructure, and detector
Power supplies to klystrons gallery
~100MW*
90MW
* Borrowed from the CLIC design
Drive beam acceleration
rf-drive=86%
total~16%
77MW
Drive beam Dumps
DPETS
65MW
rf-tran=95%
rf-main=50% (AWA bunch shaping)
62MW
rf-main=26%
Main linac
31.2MW
Main beam