Argonne Wakefield Accelerator Facility Research Articles

Observation of plasma wakefield acceleration in the underdense regime

Initial experiments which have explored the physics of the underdense (blowout) regime of the plasma wakefield accelerator (PWFA) at the Argonne Wakefield Accelerator facility are reported. In this regime, the relativistic electron beam is denser than the plasma, causing the beam channel to completely rarefy, and leaving a high quality accelerating region which also contains a uniform ion column. This ion column in turn allows the drive and accelerating beams to be well guided over many initial beam beta-function lengths. The results of these experiments, which have taken place over several years, are reviewed. Notable achievements in the course of these studies include the creation and measurement of drive and witness beam generated in an rf photoinjector, as well as previously published studies on drive beam guiding in the underdense regime. In addition, these experiments allowed measurement of both beam energy loss and gain, at a maximum average rate of 25 MeV/m in this regime of the PWFA, which is consistent with a peak acceleration gradient of 62 MeV/m in the excited waves. Difficulties associated with this type of experiment are discussed, as are prospects for mitigating these difficulties and achieving high gradient acceleration in planned future experiments.

Generation and acceleration of high-charge short-electron bunches

We report experimental results on the high peak current electron beam generated at the Argonne Wakefield Accelerator facility for wakefield applications. The facility produces bunch charges in the range 15--100 nC by using a photocathode based RF electron gun. The energy of the beam is 14 MeV. Our measurements show that for bunches of 100 nC, the pulse length can be as short as 30 ps. A detailed systematic study of pulse length versus charge is reported, as well as comparisons with numerical simulations. Dark current beam loading in the high field RF gun is also discussed.