Recent Euclid Wakefield Experiments @ AWA

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

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

4. + r (z) W - W z d d d To Enhance the TR Scheme I---Single Triangular Bunch Reference: Bane et. al., IEEE Trans. Nucl. Sci. NS-32, 3524 (1985) Scheme II---Ramped Bunch Train Reference: Schutt et. al., Nor Ambred, Armenia, (1989) RBT: d=(1+1/2)λ, acceleration for the second bunch, Q1=3Q0, W+=(3-1)W0+=2W0+,W0-=(3-2)W0- =W0-, R=2R0 Rn= nR0~2*n for the large number of bunches

5. The previous experiment by joint effort from Euclid Techlabs and AWA (2006)* Measured Enhancement factor of R2/R1=1.31 Inferred R2=2.3 * Funded by DoE SBIR Phase II

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

8. Measurement • Direct measurement of the wakefield transformer ratio for a single bunch: Normalized selfwake R1=1.94 Normalized wake behind • Tune spacing and charge ratio to achieve: R2=3.4 • Direct measurement of the wakefield transformer ratio Enhancement after the 2nd bunch: Wake behind the 1st bunch R2/R1=1.75 Wake behind the 2nd bunch

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

10. 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. Bench Test Ferroelectric layer Ceramic layer

12. Wakefield Experiment 26.2cm 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.

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. 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.