1. Recent Euclid Wakefield Experiments @ AWA C. Jing, S. Antipov, A. Kanareykin, P. Schoessow, Euclid Techlabs, LLC M. Conde, W. Gai, W. Liu, J. Power, Z. Yusof, HEP, ANL HG Workshop, Feb. 2011

2. 2 I. Experiment on Transformer Ratio Enhancement Using a Ramped Bunch Train

3. 3 Wakefield Transformer Ratio Transformer ratio limited: R≤2 @ a longitudinally symmetric drive bunch, but it can be enhanced greater than 2 using asymmetric bunch. Transformer ratio R = Max energy gain of the witness bunch Max energy loss of the drive bunch Q W - min W + max q Collinear Wakefield Acceleration

4. 4 Scheme I--- Single Triangular Bunch Scheme II--- Ramped Bunch Train Reference: Schutt et. al., Nor Ambred, Armenia, (1989) Reference: Bane et. al., IEEE Trans. Nucl. Sci. NS-32, 3524 (1985) To Enhance the TR RBT: d=(1+1/2)λ, acceleration for the second bunch, Q 1 =3Q 0, W + =(3-1)W 0 + =2W 0 +, W 0 - =(3-2)W 0 - = W 0 -, R=2R 0 R n = nR 0 ~2*n for the large number of bunches

5. 5 The previous experiment by joint effort from Euclid Techlabs and AWA (2006)* Measured Enhancement factor of R 2 /R 1 =1.31 Inferred R 2 =2.3 * Funded by DoE SBIR Phase II

6. 6 The latest experiment by joint effort from Euclid Techlabs and AWA (2010)* What’s the same comparing to the previous experiment? Same Ramped Bunch Train Technique. Same DLA Structure What’s new comparing to the previous experiment? Laser stacking technique to elongate the bunch length of AWA beam. Improved data taking conditions (upgraded LLRF, remotely controlled delay line for the witness bunch, independent controlled shutter for each bunch, etc.) *Results will appear in PRSTAB soon.

7. 7 time (ps) Intensity (arb. unit.) time (ps) Intensity (arb. unit.) 20  10  0 20 7 mm  -BBO 14 mm 2 crystal set Laser stacking for RBT Experiment FWHM~ 24 ps FWHM~8 ps FWHM~24 ps Streak camera measurement Bunchlength=2.7mm from Parmela simulation

8. 8 Measurement Direct measurement of the wakefield transformer ratio for a single bunch: Normalized selfwake Normalized wake behind R 1 =1.94 Tune spacing and charge ratio to achieve: Direct measurement of the wakefield transformer ratio Enhancement after the 2 nd bunch: Wake behind the 1 st bunch R 2 /R 1 =1.75 Wake behind the 2 nd bunch R 2 =3.4

9. 9 II. Experiment on the 1 st Tunable DLA Structure* * Funded by DoE SBIR Phase II

10. 10 Geometric and accelerating parametersvalue Radius: b 0, b 1, b 2 4.79mm, 6.99mm, 7.49 mm, Effective Length101.6mm Dielectric constant: dielectric, ferroelectric6.8, 310 (at room Temp.) Loss tangent: dielectric, ferroelectric2*10 -4, 2*10 -3 Freq. of two dominant wakefield modes7.8GHz, 14.1GHz (at room Temp.) Q of two dominant wakefield modes385, 1250 Peak wakefield by 50nC drive bunch (  z=2.3mm) 16MeV/m Tunable DLA Structure By introducing an extra nonlinear ferroelectric layer which has dielectric constant sensitive to temperature and DC, the frequency of a DLA structure can be tuned on the fly by controlling the temperature or DC voltage.

11. 11 Ferroelectric layer Ceramic layer Bench Test

12. 12 Wakefield Experiment The experiment demonstrated that by varying the temperature of the structure over a 50  C temperature range, the energy of a witness bunch at a fixed delay with respect to the drive beam could be changed by an amount corresponding more than half of the nominal structure wavelength. 26.2cm

13. 13 Bench Test---DC Voltage Although introduction of a high DC voltage to a tunable DLA structure in the vacuum environment appears to be challenging at this moment, this approach is still attractive because of its extremely short response time compared to the temperature control. One can conclude the best solution for the future tunable DLA structures would be a combination of ”coarse” but slow temperature tuning by 100s of MHz and rapid fine tuning with high voltage dc biasing applied.

14. 14 Summary Wakefield transformer ratio of 3.4 has been achieved in the recent experiment at AWA facility with help of the elongated bunch length. A novel low loss BSTM ferroelectric material has been used in dielectric based accelerators as a method of frequency tuning. Wakefield acceleration experiment show an excellent tuning capability through control of either temperature.