AE19. Spokesperson: Thomas. C. Marshall (Columbia University), and Jay L. Hirshfield (Omega-P, Inc.)

Fundamentals of Dielectric Wake Field Acceleration

    We report on the experimental demonstration of a novel acceleration technique [1], proposed in 1999, which might deliver high acceleration gradients as required by future linear colliders. This technique utilizes constructive superposition of wake-fields produced in a dielectric-lined waveguide by short (psec) drive bunches which excite a broadband frequency spectrum [1][2] having more than a hundred eigenmodes and thereby synthesize a high-amplitude accelerating field. This experiment is compared with a related experiment by a group at the Argonne National Laboratory where the wake field consisted of a few tens of eigenmodes. We find that the axial accelerating electric field has a sharply- peaked profile with very narrow footprint as desired, and we demonstrate that fields of two bunches have been successfully superimposed. Our observational technique has two important advantages: a) the wake field period can be established with excellent accuracy; b) agreement between theory and experiment can be verified when the bunch spacing is different from the wake field period. The experimental data obtained in the course of this study can be found here.
    We report the development of a nondestructive technique [3] to measure bunch rms-length in the psec range and below, by measuring the high- frequency spectrum of wake field radiation which is caused by the passage of a relativistic electron bunch through a channel surrounded by a dielectric. We demonstrate both experimentally and numerically that the generated spectrum is determined by and sensitive to the bunch rms-length, whereas it is insensitive to the axial and longitudinal charge distribution. Measurement of the millimeter-wave spectrum determines the bunch rms-length in the psec range, and this has been done using a series of calibrated mesh filters. We have developed the analysis of the factors crucial for achieving good accuracy in this measurement, and find the experimental data are fully understood by the theory. We point out that this technique also may be used for measuring fsec bunch lengths, using a prepared planar wake field microstructure. Further details can be found here [see ref.3].
    We also report on the theoretical and numerical investigation of the quantitative behavior of the dielectric wake field accelerator performance (such as the efficiency, accelerating gradient, and energy spread) vs. the dielectric wake field accelerator parameters (e.g. the inner and outer radii, the dielectric constant, the longitudinal shape of a drive/test bunch, the bunch rms- length, etc) for the case of the cylindrical multimode monolayer dielectric wake-field accelerator. Having analyzed over 2,000 cases we reach conclusions about the quantitative behavior of the MM- DWA performance, affected by changes in the structure and/or bunch dimensions, as well as the dielectric material. In particular, we have found an important scaling law that provides a straightforward way to connect changes in the DWA performance with changes in the DWA parameters. Further details can be found here.

REFERENCES

[1] “The Stimulated Dielectric Wake-Field Accelerator: A Structure with Novel Properties”, by T.C. Marshall, T-B. Zang, and J.L. Hirshfield, AIP Conf. Proc., 472, 27, (1999), edited by W. Lawson, C. Bellamy, and D. Brosius

[2] “Theory of Wakefields in a Dielectric- Lined Waveguide”, by S.Y. Park and J.L. Hirshfield, Phys. Rev. E 62, 1266- 1283, (2000)

[3] “A Nondestructive Method for Measuring the RMS Length of Charge Bunches Using the Wake Field Radiation Spectrum”, by S.V. Shchelkunov, T. C. Marshall, J.L. Hirshfield, and M.A. LaPointe, The 11th AAC Workshop 2004 at Stony Brook, New York, June 21-26, 2004, (to be published in AIP Conf. Proc.)

[4] “An Experimental Test Of the Theory Of the Stimulated Dielectric Wake-Field Accelerator”, by J-M. Fang, T.C. Marshall, J.L. Hirshfield, M.A. LaPointe, T-B. Zhang, and X.J. Wang, Proc. of the 1999 Particle Accelerator Conf, p. 3627, (1999)

[5] Thomas C. Marshall, Columbia University

For information please contact: Thomas C. Marshall (tcm2@columbia.edu), Jay L. Hirshfield (jay.hirshfield@yale.edu), or Sergey V. Shchelkunov (shchelkunov@bnl.gov)