Development of Dielectric-Based Wakefield Power Extractors Chunguang Jing 1,2, W. Gai 1, A. Kanareykin 2, Igor Syratchev, CERN 1. High Energy Physics Division, ANL 2. Euclid Techlabs LLC April * Now with National Light Source, BNL

2 Contents Introduction 7.8GHz Dielectric-Based Power Extractor--- design, fabrication, and test. 26GHz Dielectric-Based Power Extractor--- design, fabrication, and test. Proposed 12GHz Dielectric-Based Power Extractor (for CLIC) Summary

3 Dielectric-lined Waveguide to Slow the Wave Electric Field Vectors (TM01) Pros: simplicity of fabrication potentially higher breakdown threshold low surface field enhancement Easy deflecting mode damping Cons: Multipactor E r /E z =  a/ Dielectric loaded waveguide can slow the RF wave for acceleration like the conventional disk-loaded waveguide. Low-loss dielectric materials bring promise to this kind of structure.

4 7.8GHz Dielectric-Based Wakefield Power Extractor* Two related journal publications: 1) F. Gao, et al, PR ST-AB, 11, (2008); 2) F. Gao, et al. IEEE Trans. NS, 56, 3, JUNE (2009) *Prototype structure without transverse mode damping. It is to demonstrate the concept.

5 7.8GHz Dielectric-Based Wakefield Power Extractor----design Geometric and accelerating parametersvalue ID / OD of dielectric tube 12.04mm /22.34 mm Dielectric constant4.6 Length of dielectric tubes266 mm Synchronous frequency of TM 01 mode7.8 GHz Group velocity0.23c R/Q of TM 01 mode 6090(  /m ) Q of TM 01 mode Generated rf power (AWA beam:T b =769ps,  z =1.5~2mm) MW/10nC per bunch

6 mode launcher inside DL deceleration waveguide TM 01 -TE 10 coupler rf output port Insertion loss Reflection 7.8GHz Dielectric-Based Wakefield Power Extractor---- fabrication & bench test

7 7.8GHz Dielectric-Based Wakefield Power Extractor---- beam test (I): setup

8 A UV laser pulse is split into two trains, each consisting eight micropulses spaced by 2T. e - bunch train generated: i). 16 bunches, T b = 769ps, q max = 4.8nC ii). 16 bunches, T b = 1.54ns, q max = 4.9nC iii). 4 bunches, T b = 769ps, q max = 26.5nC 7.8GHz Dielectric-Based Wakefield Power Extractor---- beam test (II): e-bunch train generation

9 15ns rf pulse generated, P max = q max = 4.8nC. 7.8GHz Dielectric-Based Wakefield Power Extractor---- beam test (III): 1-16 bunches, Tb=769ps

10 30ns rf pulse generated, P max = q max = 4.9nC. 7.8GHz Dielectric-Based Wakefield Power Extractor---- beam test (IV): 16 bunches, Tb=1.54ns

11 7.5ns rf pulse generated, P max = q max = 26.5nC. 7.8GHz Dielectric-Based Wakefield Power Extractor---- beam test (V): 4 bunches, Tb=769ps 44MW generated 40MW extracted f - GHz t - ns

12 26GHz Dielectric-Based Wakefield Power Extractor ---- by Euclid Techlabs, supported by DoE SBIR program

13 26GHz Dielectric-Based Wakefield Power Extractor----design Geometric and accelerating parametersvalue ID / OD of dielectric tube7 mm /9.068 mm Dielectric constant6.64 Length of dielectric tubes300 mm Synchronous frequency of TM 01 mode26 GHz Group velocity0.25c/0.42c R/Q of TM 01 mode 9788(  /m ) Q of TM 01 mode Generated rf power (AWA Beam) MW/10nC per bunch

14 *20nC, single bunch, bunch length 1.5mm. *16, 20nC bunch train, steady output power of 148 MW and 56 MV/m peak gradient. The energy loss is 5.7 MeV for the last bunch in the bunch train. 26GHz Dielectric-Based Wakefield Power Extractor---- power estimation

15 26GHz Dielectric-Based Wakefield Power Extractor---- fabrication SiC based 26GHz UHV rf load 26GHz UHV rf power detector

16 Load Rf probe LO=14.576GHz GHz BPF ( 228MHz BW ) 16GHz scope 26GHz Dielectric-Based Wakefield Power Extractor---- beam test (I): setup

17 26GHz Dielectric-Based Wakefield Power Extractor---- beam test (II): 16 bunches, Tb=769ps Down-converted rf Trace = GHz SiC based Rf load behaves well.

18 26GHz Dielectric-Based Wakefield Power Extractor---- beam test (III): 4 bunches, Tb=769ps = GHz Background noise to the scope Down-converted rf Trace SiC based Rf load behaves well.

19 Number is the percentage of charge transmission out of the structure, which indicates the BBU appears when charge goes high. Theoretically, 9nC  29.6MW, 24.8MV/m; 17MW was measured (bunch length effect, coupler loss, etc) 26GHz Dielectric-Based Wakefield Power Extractor---- beam test (IV): charge sweeping, 4 bunches, Tb=769ps

20 Transverse Damping---- to improve the high current beam transportation TM01 mode (axial current only) HEM11 mode (azimuthal current included) TM01 mode Ez HEM11 mode Ez SiC Copper Dielectrics Vacuum by Euclid Techlabs, supported by DoE SBIR program

21 Proposed 12GHz Dielectric-Based Wakefield Power Extractor ---- submitted to DoE 2010 SBIR program by Euclid Techlabs In collaboration with CERN ( Igor Syratchev)

22 12GHz Quartz-Based Power Extractor Using CLIC Parameters: σz=1mm, Q=8.4nC, Tb=83ps Freq11.994GHz Effective Length23cm Beam channel23mm Thickness of the dielectric tube2.582mm Dielectric const.3.75(Quartz) Loss tangent Q7318 R/Q 2.171k  /m Vg0.4846c Peak surface GradientE ll =12.65MV/m; E  =18.28MV/m Steady Power142MW

23 -The ceramic part is installed into the separate copper tube. The other compact piece integrates the choke and the matching grove and could be the part of the flange to be connected to the coupler. - Between the two, one can foresee the EB welding or another flange. With this approach the system cab be easily dismantled and the pieces recycled. - For later the slot can be equipped with damping material (for the HOM) and to be used for the vacuum pumping of the entire volume. - By design, the system is rather insensitive to the fabrication/installation errors (slot width, position of ceramic and etc.) - For the fabrication, it looks inexpensive. Preliminary Design of a 12GHz Quartz-Based Power Extractor (by Igor Syratchev)

24 Current Status The 1 st step is to build a GHz version DWPE so that we can high power rf test it at SLAC and explore the possible issues. This work has been applied for 2010 DoE SBIR funding (just funded).

25 SUMMARY Dielectric-based wakefield power extractors have been successfully demonstrated. Two structures, 7.8GHz and 26GHz, were fabricated and tested. 40MW for 7.8GHz and 20MW for 26GHz were measured. X-band DWPE is planned to develop soon.