Externally Heated Hollow Cathode Arc Plasma Source for Experiments in Plasma Wakefield Acceleration

Ryan Roussel,Kunal Sanwalka,Claire Hansel,Eric Wisniewski,James Rosenzweig,River Robles,Gerard Lawler,Gerard Andonian,Walter Lynn,Nathan Majernik

doi:10.3390/instruments3030048

Abstract

An externally heated, hollow cathode arc source was recommissioned at UCLA for use in experiments to drive plasma wakefields with shaped beams at the Argonne Wakefield Accelerator. The hollow cathode arc source provides a robust plasma column with a density in the 10 13 – 10 14 cm − 3 range while external heating of the cathode allows the plasma arc regime to be accessed with applied voltages down to 20 V. Overall source operating principals are described, along with time-resolved plasma current measurements and plasma density characterization with the use of a triple Langumir probe. The results show that relevant plasma densities that match facility beam parameters are readily achievable.

Highlights

The Argonne Wakefield Accelerator (AWA) facility at Argonne National Laboratory provides a unique platform for measuring wakefield dynamics of both dielectric and plasma-based wakefield structures
Ramped beams generated by emittance exchange at AWA are nominally ∼20 ps (6 mm) long, so to achieve high transformer ratios with a drive length l = 2λ p a plasma density target of n p ≈ 1.2 × 1014 cm−3 was set for the hollow cathode arc (HCA) source
This paper describes the hollow cathode arc plasma source developed at UCLA, which is used for plasma wakefield acceleration measurements at the Argonne Wakefield Accelerator

Summary

Introduction

The Argonne Wakefield Accelerator (AWA) facility at Argonne National Laboratory provides a unique platform for measuring wakefield dynamics of both dielectric and plasma-based wakefield structures. Previous experiments using the emittance exchange (EEX) beamline [1] at AWA have studied high transformer ratio wakefield generation using longitudinally ramped beams in dielectric structures [2]. We discuss recommissioning of a hollow cathode arc (HCA) plasma source at UCLA for use in plasma wakefield experiments at AWA, including high transformer ratio and flat beam propagation experiments. High transformer ratio experiments at AWA aim to generate wakefields with a transformer ratio greater than the classical limit for symmetric beams R < 2, using longitudinally asymmetric beams generated by emittance exchange [3]. Ramped beams generated by emittance exchange at AWA are nominally ∼20 ps (6 mm) long, so to achieve high transformer ratios with a drive length l = 2λ p a plasma density target of n p ≈ 1.2 × 1014 cm−3 was set for the HCA source

Hollow Cathode Arc Plasma Source and Characterization

Findings

Conclusions