Magnetic field-enhanced beam monitor for ionizing radiation

Abstract

For the microwave cavity resonance spectroscopy based non-destructive beam monitor for ionizing radiation, an addition—which adapts the approach to conditions where only little ionization takes place due to, e.g., small ionization cross sections, low gas pressures, and low photon fluxes—is presented and demonstrated. In this experiment, a magnetic field with a strength of 57 ± 1 mT was used to extend the lifetime of the afterglow of an extreme ultraviolet-induced plasma by a factor of ∼5. Magnetic trapping is expected to be most successful in preventing the decay of ephemeral free electrons created by low-energy photons. Good agreement has been found between the experimental results and the decay rates calculated based on the ambipolar and classical collision diffusion models.

Influence of a magnetic field on an extreme ultraviolet photon-induced plasma afterglow

“…Due to logarithmic plotting in figure 4(a), these apparent negative n e are not visible. Although these negative shifts have been investigated in prior works [9,16], a conclusive explanation of negative shifts of such an extent is absent. Since the effect is beyond the scope of the current study, which focuses on the decay in the higher n e regimes.…”

“…These measurements also confirmed that the magnetic field magnitude at the position of the cavity is uniform, taking into account the measurement accuracy. These simulations and measurements were also used in [16]. In the cavity, the magnetic field pointed towards the EUV source as is indicated by the direction of 'B' in figure 1.…”

“…A schematic of the data acquisition system is presented in figure 1. The system was similar to the ones used in prior studies [11,16,32]. The data acquisition system consisted of the following: a Stanford Research Systems SG386 microwave generator produced a sinusoidal signal with a frequency, f, and power, P in .…”

“…For pressures exceeding the transition value, p > p trans , additional collisions occur and ambipolar diffusion governs the electron density decay in phase II (see figure 3). The ambipolar diffusion decay time τ amb is [16]…”

“…The newest development [16] in this field utilizes a static magnetic field to confine an EUV-induced plasma to extend its lifetime and thus increase the operational range [17] of the MCRS technique. Besides the improvement of the MCRS method, studying the governing diffusion processes is intriguing from a fundamental point of view, since not all diffusion models remain valid in the applied gas pressure range [18][19][20][21][22][23].…”