Experimental investigation of plasma instabilities by Fourier analysis in an electron cyclotron resonance ion source

Sarvesh Kumar,Devendra Sharma,Shatendra Sharma,Prashant Sharma,Jyotsna Sharma,Yaduvansh Mathur,Manish K Kashyap

doi:10.1103/physrevaccelbeams.21.093402

Abstract

The plasma instabilities play an important role in an electron cyclotron resonance (ECR) ion source for the production of intense heavy ion beams in high charge states for particle accelerators. The geometrical and operational constraints of ECR sources hinder the trapping of ions for a sufficient time to get fully ionized with maximum efficiency. This problem is looked at in detail by studying the plasma instabilities in ECR ion sources. The ECR environment is full of complex rearrangements of various electric and magnetic fields to define a sustainable trap for the ions. The maximum frequency of plasma instability has been observed to be of 122.5 kHz under a set of sustainable plasma parameters. However, this limit may be pushed further if the plasma is overdriven in terms of source parameters. The instabilities cover a full regime of few tens of Hz to few hundreds of kHz under various operating conditions of radio frequency (rf), negative bias voltage, rf power and injection gas pressure. The rigorous details of frequencies and amplitudes of plasma instabilities are being reported by studying the Fourier spectrum of extracted and analyzed beam intensity. The plasma instabilities are attributed as drift waves in an inhomogeneous ECR plasma generated by the application of radio-frequency fields.

Highlights

Electron cyclotron resonance (ECR) ion sources [1,2] are one of the best sources to boost the performance as well as the efficiency of modern particle accelerators and colliders in different fields of physics, especially fundamental research on heavy ions such as nuclear and atomic physics, etc
The plasma instabilities play an important role in an electron cyclotron resonance (ECR) ion source for the production of intense heavy ion beams in high charge states for particle accelerators
Being capable of producing high beam currents and high charges states of heavy ions, the ECR sources are the main injectors for heavy ion accelerators

Summary

INTRODUCTION

Electron cyclotron resonance (ECR) ion sources [1,2] are one of the best sources to boost the performance as well as the efficiency of modern particle accelerators and colliders in different fields of physics, especially fundamental research on heavy ions such as nuclear and atomic physics, etc. Sharma et al [17] calculated the excitation of electrostatic ion-cyclotron waves by an ion beam in a twoion component plasma and found that the unstable wave frequencies of both the light and heavy positive ion modes increase with the magnetic fields in accordance with the experimental observations of Suszcynsky et al [18]. They calculated the excitation of lower hybrid waves [19] by a gyrating ion beam in a negative ion plasma and found the similar observation

EXPERIMENTAL DETAIL AND OBSERVATIONS

TRENDS OF INSTABILITY FREQUENCY

THEORETICAL JUSTIFICATION

PLASMA INSTABILITIES AT HIGHER RF POWER AND CONFINEMENT FIELDS

Findings

CONCLUSION