1. S.V. Shchelkunov, J.L Hirshfield, (Yale Univ., Omega-P), T.C. Marshall (Columbia Univ., Omega-P) G. Sotnikov (KIPT, Ukraine, & Omega-P) in collaboration with AWA Team led by Wei Gai (Argonne National Lab.) Two experiments to conduct: 1) Two-channel Coaxial Dielectric –lined Structure Operating in GHz-regime; 2) Diagnostic for charging and Damage of Dielectric Materials Useful in Accelerator applications ACKNOWLEDGMENT: Office of High Energy Physics, U.S. Department of Energy Omega-P Outreach Meeting for the Argonne Wakefield Accelerator Facility, June/5, 2014

2. annular drive bunch dielectric metal test bunch Two-Channel Coaxial Dielectric Lined Structures General conceptMotivations and advantages 1)mm-scale THz coaxial DWA structures can be suitable to deliver 1 GeV/m; 2)high transformer ratio; 3)both drive and accelerated bunches are mostly stable; accelerated bunch has positive focusing. 4)compatible with a ramped bunch train, where all drive bunches will have low instability growth rate; 5)acceleration of witness bunch is not sensitive to azimuthal asymmetries of the drive bunch charge. Challenges 1)need for annular bunches with associated challenges on the bunch transport system outside the DWA itself a CM-scale GHz coaxial structure which is easy to make and operate is to be studied experimentally to investigate how the bunch parameters (emittance, energy spread, transverse and longitudinal distributions) are affected, and demonstrate that the accelerated bunch is indeed stable Proposed project 1.a

3. OD of outer dielectric tube (mm)30.15 ID of outer dielectric tube (mm)27 OD of inner dielectric tube (mm)8 ID of inner dielectric tube (mm)4.8 Length (mm)100 Dielectric constant (Al 2 O 3 )9.8 Acceleration Gradient (MV/m/nC)0.4 Transformer Ratio (1 drive bunch)6.5:1 GHz-scale Structure as Already Available for Experimental Tests Gun Linac & Steering Coils ICT1ICT2 BPM GV Solenoid Spectrometer YAG1 YAG2 YAG5 Slits DUT YAG4PP YAG former location of the experiment before the AWA shutdown for upgrades Design mode is E 02 @ 18.8 GHz at new place the following to be addressed before runs take place: 1) making annular laser profile to excite a suitable drive bunch; 2) beam dynamics optimizations; experiment can be resumed this summer (?) 1.b

4. Diagnostic for charging and Damage of Dielectric Materials Useful in Accelerator applications (starts mid-2015, if funded) Motivation is to study surface charging, plasma formation, and aspects of damage in a dielectric-lined device. For instance, a passing drive bunch may leave transient residues of charge on the dielectric surface which may, as a result of accumulation by many passing bunches, lead to appreciable local fields that can deflect the paths of drive bunches and/or cause degradation of the structure material. Concept/ approach is to study such charging effects by observing the change of Q-factor and/or shift of resonance frequency in a microwave cavity resonator that encloses the dielectric structure, which would be caused by beam electrons either directly (plasma) or indirectly (dielectric degradation). frequency, GHz approximate diameter, mm approximate filling time for Q ~1000 - 10,000, μsec detectable n [cm -3 ] for Q ~1000-10,000 12300.25 – 2.58·10 9 – 0.8·10 9 7500.43 – 4.33·10 9 – 0.3·10 9 1& 1’ – waveguides; 2 & 2’ – coupling apertures for the incident and transmitted RF power; 3 – end walls; 4- vacuum channel for the electron bunch (6) (or bunch train); 7- dielectric tubing; 8- vacuum. Detectable electron density where ξ < 5 Sensitivity can be calibrated using e.g. a plasma discharge in a gas-filled quartz tube 2.a

5. a well known formula shows how the changes in dielectric conductance (∆g d ) and susceptance (∆b d ) are related to the changes in the complex conductivity, ∆σ = ∆σ Re + j∆σ Im. The imaginary part j∆σ Im of ∆σ gives rise to the changes in dielectric susceptance jb d and the shift in cavity resonance; the real part ∆σ Re changes the Q-factor through the conductance g d. (i) Single-shot application of the method is possible to measure fast (few μsec-scale) changes in the susceptance, ∆b d, and the imaginary part of complex conductivity, ∆σ Im, of the dielectric material to do so, one observes the changes in the power transmission ∆(P t /P i ) at one fixed frequency, ω obs, and infers from these the corresponding cavity resonance frequency shift (calibration is required); evaluation suggests that the measured electron density can be 10 9 cm -3 or less. (ii) Multi-shot application of the method to measure changes in the conductance, ∆g d, and the real part of complex conductivity, ∆σ Re, of the dielectric material do to so, one either collects frequency scans to trace a transmission curve near the resonance. depending on how the scans are done, one can capture processes at time-sales > 5 msec (to note, this scheme also may work with single shots), or capture faster processes (1μsec- 1msec); the first implementation will simply require a fast network analyzer working in its usual mode of operation (tracing a transmission curve in a single frequency sweep; the second implementation will require a network analyzer running in a single–frequency (CW) regime, and be triggered by a pulse/delay generator that produces a delayed trigger pulse after receiving a sync signal. This will require at least 200 reproducible shots to gather the required info. The principal schematic of measurements essentially translates to a network analyzer set to work in a CW regime of measurements 2.b