Temperature peaking at beginning of breakdown in 2.45 GHz pulsed off-resonance electron cyclotron resonance ion source hydrogen plasma

Abstract

An experimental study of temperature and density evolution during breakdown in off-resonance ECR hydrogen plasma is presented. Under square 2.45 GHz microwave excitation pulses with a frequency of 50 Hz and relative high microwave power, unexpected transient temperature peaks that reach 18 eV during 20 μs are reported at very beginning of plasma breakdown. Decays of such peaks reach final stable temperatures of 5 eV at flat top microwave excitation pulse. Evidence of interplay between incoming power and duty cycle giving different kind of plasma parameters evolutions engaged to microwave coupling times is observed. Under relative high power conditions where short microwave coupling times are recorded, high temperature peaks are measured. However, for lower incoming powers and longer coupling times, temperature evolves gradually to a higher final temperature without peaking. On the other hand, the early instant where temperature peaks are observed also suggest a possible connection with preglow processes during breakdown in ECRIS plasmas.

Bimodal ion energy distribution functions in a hydrogen magnetized plasma

“…The values are typically 0.1 eV during the steadystate stage, showing peaks at the beginning of the pulse between 0.6 eV and 0.9 eV. The observation of this peaking behavior agrees with previous measurements of time-resolved electron temperatures [24]. Another lower and wider peak is observed during the pulse decay and may be associated with the well known 'afterglow' phenomenon in ECR ion sources [25].…”

Breakdown transient study of plasma distributions in a 2.45 GHz hydrogen discharge

“…Extensive research on this subject has been conducted with time resolved electrical probes, emission spectroscopy and bremsstrahlung radiation diagnostics under a wide range of parameters for different plasmas [3][4][5]. Understanding the plasma processes involved during the breakdown is beneficial for monocharged beam current optimization as well as the improvement of multiple charged ion production efficiency [6][7][8].…”

Time evolution of the electron energy distribution function in pulsed microwave magnetoplasma in H2

“…A detailed description is given in Ref. 3 where the synchronization system for the Langmuir probe measurements is also explained. Each point of the I-V characteristic is averaged on 20 data acquisitions performed at the same time in different consecutive plasma pulses.…”

“…This first step until 40 ls corresponds to the change of plasma coupling at the beginning of the plasma formation 9 and can be correlated to the temperature peaking already observed at low times after the plasma ignition. 3 The steady state is typically obtained 40 ls after the ignition. As shown in Figures 7 and 8, the EEDF is composed of two components, which can be fitted using the generalized Maxwell distribution form [32][33][34][35] f e e ð Þ ¼ C ffiffiffiffi e e p exp À e e a k !…”

“…have been conducted mainly by means of electrical probes or emission spectroscopy to characterise the plasma parameters at the steady state and to understand or to act on the plasma chemistry. [3][4][5][6][7][8] In recent works, transient phenomena have been studied by means of several complementary investigation methods (directional coupler for incident and reflected power measurements, VUV (vacuum-ultraviolet) spectroscopy, and Langmuir probe) to investigate the plasma breakdown dynamic in ECR plasma sustained in hydrogen on a microsecond scale. [9][10][11] The purpose of the present work is to complete these previous studies and to investigate the change of the Electron Energy Distribution Function (EEDF) on the same microsecond scale.…”