Brief Review of Microwave Dielectric Accelerators Chunguang Jing May 2017

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

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

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

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

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

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

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

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

RF test at SLAC 2013/ Beam test at AWA 2014

Conceptual design of short pulse collider

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%)

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

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

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

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

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