Intensified Charge Coupled Device Imaging Research Articles

Atmospheric pressure plasma jet impinging on fiber arrays: Penetration pattern determined by fiber spacing

Atmospheric pressure cold plasmas have great potential for surface functionalization, and the interaction between the plasmas and fibers is essential to understand the underlying physics. In this Letter, the penetration pattern and mechanism of an atmospheric pressure plasma jet (APPJ) interacting with different spacing fiber scaffolds were studied by both experiment and modeling. The intensified charge coupled device images showed that APPJ induced a radial surface streamer on the windward side of the scaffold and another axial forward streamer on the opposite side. Propagation distance of both the radial and axial streamers diminished as the spacing decreased. Similar trends were predicted by a 2D fluid model. The simulation results indicated that the high electrical field carried by the streamer head in APPJ was allowed to pass through the gap for large spacing scaffold, while it was blocked by high intensity charges at small spacing. Instead, one axial streamer was generated in the latter case. The physical insight on the penetration mechanism of plasma jet interacting with fiber array in this Letter may contribute to improve treatment uniformity of plasma technology.

Transmission and multiple reflection mechanisms of guided streamers propagating through grounded annular electrode and interacting with grounded surface electrode

The repeatable dynamics and the reversal propagation of guided streamers remains a major question of fundamental physics. In this article, trains of positive guided streamers are generated within an atmospheric pressure plasma jet supplied in helium and polarized by a high-voltage nanosecond pulse generator. The device is completed by two distant targets: a grounded annular electrode (GAEL) coaxially centered around the capillary through which guided streamers can propagate, and a grounded surface electrode (GSEL) on which they can interact. The resulting transmitted and multiple reflected guided streamers are measured combining optical characterization (fast intensified charge-coupled device (ICCD) imaging) and electrical characterization (high voltage probe and current monitors). While the electrical approach provides information on the capacitive/conductive nature of the current peaks as well as on their positive/negative value, fast ICCD imaging distinguishes whether the guided streamers are incident, reflected or transmitted. Combining these two techniques allow us to demonstrate experimentally that the reflected streamers are negative contrarily to the others. Besides, four types of reflections have been highlighted: a reflection (r) at the outlet of the capillary, a reflection on the GSEL (R) and two reflections (r′ and r″) observed when an incident guided streamer passes through the GAEL. The two techniques agree that the characteristic propagation times are always shorter for reflected negative streamers than for the positive ones propagating forward. Hence, for a GAEL placed 3 cm away from the high voltage electrode, propagation time is 80 ns for reflection versus 250 ns for transmission. These characteristic propagation times are even shorter when the annular electrode is brought closer to the surface electrode with velocities typically higher than 300 km s−1. In addition, the intensity ratios of reflected/incident guided currents drop sharply, typically losing one decade over a counter-propagation length of only 3–5 cm. Finally, all these experimental data are utilized to build an equivalent electrical model that allow to better understand the dynamics of the guided streamers and explain their transmission and reflection modes upon their interaction with the two distant grounded electrodes.

Comparison of laser induced breakdown spectroscopy and fast ICCD imaging for spatial and time resolved measurements of atmospheric pressure helium plasma jet

In this paper we compared the fast Intensified Charge Coupled Device (ICCD) imaging with the newly developed diagnostic method that utilizes laser induced breakdown in plasma jet. Our helium plasma jet was powered by an 80 kHz high-voltage sine wave and propagated into the ambient air. Pulsed laser beam 1064 nm (4 ns pulse duration and 5 Hz repetition rate) was focused with the lens into the plasma jet at energy below breakdown threshold in helium. Laser pulses and the jet powering signal were synchronized. Laser induced plasma is highly dependent on the concentration of seed electrons and other charged particles in the plasma jet channel. We compared the radial profiles of the plasma jet obtained with these two methods. For laser induced breakdown it was ±0.5 mm and for ICCD measurement it was ±1.75 mm, while the ionization wave velocities obtained with these two methods were 15 km s−1 and 20 km s−1 respectively. Electrical characteristics of the plasma jet were also presented and one can see a large hysteresis effect when the applied power to the plasma jet was reducing. We show that the laser induced breakdown spectroscopy can be used as a complementary diagnostics technique with ICCD measurements.

Ion fluxes and memory effects in an Ar–O2 modulated radiofrequency-driven atmospheric pressure plasma jet

In this work we used molecular beam mass spectrometry to characterize ion fluxes produced by a modulated radiofrequency (RF)-driven atmospheric pressure plasma jet operating in a homogeneous gas environment (Ar + 1% O2). The influence of the RF modulation frequency (100 Hz to 20 kHz) on the ion fluxes was investigated by time-resolved measurements, and the lifetimes of the dominant ions, O2 +, NO+, O−, O2 − and O3 −, were found to be 28 ± 2, 117 ± 8, 7.3 ± 0.4, 17 ± 1 and 23 ± 2 μs, respectively. The absolute ion densities in the near afterglow region were found to be of the order of 1011 cm−3. Significant differences in the dynamics of the positive and negative ions were found; these are explained by the presence of electrons at similar densities in the afterglow produced by electron detachment reactions from negative ions due to the large concentrations of atomic oxygen and singlet delta oxygen. Transitions in ion flux dynamics for different modulation frequencies and at the startup of the plasma were analyzed together with intensified charge coupled device images recording the plasma propagation in order to assess the dynamics of plasma plume propagation and how it is impacted by ‘memory effects’. Quantitative measurements of the ion densities enabling these memory effects are reported. The results in this paper highlight the tremendous impact of memory effects on plasma propagation and the corresponding pre-ionization.

Plasma-surface interaction: dynamic evolution of interfacial pattern modes during transformation process from dielectric to metallic substrate

Plasma–surface interaction is a complex system involving the codependency between the plasma and the substrate, especially for substrate’s with different permittivities. Therefore, a better understanding of the dynamic evolution of interactions with different substrates is essential for optimizing the required changes of specific substrates. In this work, we report two modes of interfacial pattern formation by a pulsed helium plasma jet interacting with indium tin oxide (ITO) glass and a metal substrate, and we mainly focus on the dynamic evolution process for interfacial pattern modes during a transformation process from ITO glass to metal substrate. Pattern morphology, current–voltage characteristics, intensified charge coupled device images, and reactive species distribution are used to examine the evolution mechanism of the plasma-jet–substrate interaction. Results show that, for the ITO glass substrate, a circular interfacial pattern with plenty of streamer channels is generated while, for the metal substrate, a constricted solid spot interfacial pattern is formed; these two pattern mode transformations are realized from the glass dielectric to the metal substrate. Furthermore, during the transformation process from the dielectric to metal substrate, the pattern area is gradually decreased, while the discharge intensity, emission intensity, and local electric field gradually become stronger. Importantly, by observing the dynamic behavior of the interfacial pattern, the ionization wave on the substrate surface is stopped from spreading toward the metal direction and a bright touch point appears at the interface between the dielectric and the metal, while the surface ionization wave still spreads and has no influence on the other direction besides the metal direction. Additionally, the evolution mechanism of pattern mode transformation is discussed, which may be attributed to the difference in the substrate conductivity leading to the different distribution of the local electric field. This study is beneficial to deep insights into the nature of the plasma–surface interaction.

Caudal autotomy and regeneration of arc in a 3D gliding arc discharge plasma

To gain a better understanding of the mechanism governing arc dynamics in 3D gliding arc discharge (GAD) plasma, the spatio-temporal evolution of GAD was investigated in a reverse vortex flow by a novel reactor with ring (powered electrode, PE) and truncated cone (ground electrode, GE) electrodes. A newly underlying mechanism governing arc evolution in 3D GAD was gained with combination of flow field simulation, synchronous electrical characteristics, intensified charge coupled device images and high-speed photos. The spatio-temporal analysis indicates that, being different from the well-known ignition–gliding–extinction mechanism occurring in traditional GAD, the PE arc root glides continuously in the 3D GAD, but the GE arc root features jumps from the end of the gliding path to the beginning of the next one. By means of the jumping, the arc auto-sheds the caudal part of the arc and a new arc tail is simultaneously generated, rather than rebuilding a new arc channel back to the shortest electrode gap. With this special behavior of caudal autotomy and regeneration, the main part of the arc remains for each jump. This new insight improves the understanding of the discharge mechanism governing arc evolution in 3D GAD and provides a reference for optimization design of gliding arc plasma in a vortex flow.

Systematic investigation of the pulsed barrier discharges in flowing and stationary gas: From differences to similarities

Pulsed dielectric barrier discharges in flowing and stationary helium at atmospheric pressure are comparatively studied. The discharges are generated in plane-parallel configuration and driven by positive voltage pulses. The intensified charge coupled device imaging and electrical measurements are used for temporally, spatially, and spectrally resolved discharge emission. The populations of excited states are investigated by optical emission and absorption spectroscopy. The discharge operating in flowing helium is characterized by a single current pulse per each voltage flank and a “residual current peak.” In stationary helium or in flowing helium with low velocity (<10 cm/s), multiple current pulses are observed. The appearance of the subsequent current pulse(s) is related to the disappearance of the “residual current peak.” Besides these differences between the two discharge regimes, some similarities are also registered. The maximum emission intensity is reached at the cathode, even for the subsequent current pulses formed in stationary helium, confirming the generation of the glow and multi-glow discharges. Also, the most important similarities between the discharges working in stationary helium and in flowing gas mixture, in relation to flowing helium mode, are discussed. Finally, the subsequent current pulses formed in multi-glow discharges are due to re-ignition of the discharge dominantly by direct electronic excitation and ionization processes, not by Penning ionization, because of the decrease in metastable atoms density and their lifetime. In addition, the metastable lifetime reaches a critical value, for which the discharge transits from glow to multi-glow mode, when the gas velocity or its composition changes.

Discharge characteristics of argon brush plasma plume operated at atmospheric pressure

Atmospheric pressure non-equilibrium low-temperature plasma has been widely used in biomedicine, surface treatment and other fields, which has attracted the attention of researchers extensively. As one of the important methods to generate such a plasma, the plasma jet has become a popular method, which can generate a remote plasma plume at the nozzle through introducing a rare gas flow. However, plasma plume has a small diameter, which results in deficiency for the large-scale surface treatment. A dielectric barrier discharge device with three electrodes is utilized to produce a large brush-shaped plasma plume (50.0 mm × 40.0 mm) downstream of flowing argon under the combined excitation of an alternate current (AC) voltage and a negative bias voltage, thereby increasing the plume scale. The results show that the luminescence intensity of the plasma plume increases with AC peak voltage increasing. By fast photography implemented with an intensified charge coupled device (ICCD), it is found that the plasma plume is composed of temporally superposed branched-streamers. The ICCD images also reveal that the number of branches increases with AC peak voltage increasing. Moreover, the waveforms of AC voltage and light emission signal recorded simultaneously indicate that the plasma plume initiates once per AC voltage cycle, which occurs in the positive half cycle of the applied voltage. With AC peak voltage increasing, the duration and intensity of discharge pulse increase, which results from more branches of the branched streamer. Besides, optical emission spectrum in a range from 300 nm to 850 nm mainly includes OH (A<sup>2</sup>Σ<sup>+</sup>–X<sup>2</sup>Π) peaked at 308.0 nm, the second positive system of N<sub>2</sub> (C<sup>3</sup>Π<sub>u</sub>–B<sup>3</sup>Π<sub>g</sub>), Ar I (4p–4s), and O I (3p<sup>3</sup> P–3s<sup>3</sup> S) at 844.6 nm. Based on the optical emission spectrum, the plasma parameters such as vibrational temperature and intensity ratio of spectral lines (correlated with electron density and electron temperature) are investigated. Besides, the variation of concentration of oxygen atoms in the plasma plume with experimental parameters is investigated by optical actinometry. The results indicate that the concentration of oxygen atoms first increases and then decreases with the distance increasing along the argon flow direction or with oxygen content of the working gas increasing. In addition, the concentration of oxygen atoms increases with AC peak voltage increasing. All these results are discussed qualitatively. These results are of great importance in modifying the plasma surface on a large scale.

High Resolution 3-D Imaging of Mesospheric Sodium (Na) Layer Utilizing a Novel Multilayer ICCD Imager and a Na Lidar

Equipped with a 1-meter Cassegrain telescope with 6.2 meter focal length and an electronically gated Intensified Charge-Coupled Device (ICCD), a multilayer Na imager is designed and developed at Wuhan in China. This novel instrument has successfully achieved the first preliminary 3-D image of the mesospheric Sodium (Na) layer when running alongside a Na lidar. The vertical Na layer profile is measured by the lidar, while the horizontal structure of the layer at different altitudes is measured by the ICCD imaging with a horizontal resolution of ~3.7 urad. In this experiment, controlled by the delay and width of the ICCD gating signal, the images of the layer are taken with three-second temporal resolution for every 5 km. The results show highly variable structures in both the vertical and horizontal directions within the Na layer. Horizontal images of the Na layer at different altitudes near both the permanent layer (80–100 km) and a sporadic Na layer at 117.5 km are obtained simultaneously for the first time. The Na number density profiles measured by the lidar and those derived from this imaging technique show excellent agreement, demonstrating the success of this observational technique and the first 3-D imaging of the mesospheric Na layer.

Ionization wave propagation in a He plasma jet in a controlled gas environment

Characterizing ionization wave propagation in low temperature plasma jets is critical to predicting production of reactive species and plasma–surface interactions for biomedical applications and surface functionalization. In this paper, results from optical emission and laser induced fluorescence measurements of the ionization wave in a He plasma jet operating in a controlled gas environment are discussed and used for comparison with numerical modeling. The ionization wave was observed using ICCD (Intensified Charge Coupled Device) imaging and characterized by time and spatially resolved electron density measurements using laser-collision-induced fluorescence. The plasma jet was initially characterized using pure He (nominally at 200 Torr), while varying pressure and voltage. When operating in pure He, the ionization wave broadly expands exiting the plasma tube. Increasing the operating pressure reduces the speed and isotropic expansion of the ionization wave. The jet operated with a humid He shroud was also studied. The humid He shroud results in the electron density increasing and having an annular profile due to the lower ionization potential of H2O compared to He and localized photoionization in the mixing region. Numerical modeling highlighted the importance of resonance radiation emitted by excited states of He, photoelectron emission from the quartz tube, and the kinetic behavior of the electrons produced by photoionization ahead of the ionization front.

Size and electron density of open-air plasmas diagnosed by optical imaging

A method for accurate measurements of the size and electron density of open-air plasmas by optical imaging is developed. The plasma size is determined by the intensified charge coupled device (ICCD) imaging and is related to the plasma inductance. The plasma density is then derived from the plasma inductance in open air. The electron densities measured by the ICCD imaging agree well with the reliable Stark broadening method, in stark contrast with the commonly used current–voltage I– method. These shortcomings of the I– method arise because of its heavy reliance on electron mobility values which are uncertain in complex gas mixtures such as air. This work thus presents a new way of using the ICCD imaging to determine the plasma size and electron density and as such contributes to the development of next-generation plasma diagnostic methods.

Characterization of a nitrogen gliding arc plasmatron using optical emission spectroscopy and high-speed camera

A gliding arc plasmatron (GAP), which is very promising for purification and gas conversion, is characterized in nitrogen using optical emission spectroscopy and high-speed photography, because the cross sections of electron impact excitation of N2 are well known. The gas temperature (of about 5500 K), the electron density (up to 1.5 × 1015 cm−3) and the reduced electric field (of about 37 Td) are determined using an absolutely calibrated intensified charge-coupled device (ICCD) camera, equipped with an in-house made optical arrangement for simultaneous two-wavelength diagnostics, adapted to the transient behavior of a GA channel in turbulent gas flow. The intensities of nitrogen molecular emission bands, N2(C–B,0–0) as well as (B–X,0–0), are measured simultaneously. The electron density and the reduced electric field are determined at a spatial resolution of 30 µm, using numerical simulation and measured emission intensities, applying the Abel inversion of the ICCD images. The temporal behavior of the GA plasma channel and the formation of plasma plumes are studied using a high-speed camera. Based on the determined plasma parameters, we suggest that the plasma plume formation is due to the magnetization of electrons in the plasma channel of the GAP by an axial magnetic field in the plasma vortex.

Negative surface streamers propagating on TiO2 and γ-Al2O3-supported Ag catalysts: ICCD imaging and modeling study

Surface streamers propagating on the surface of titanium dioxide (TiO2) and alumina (γ-Al2O3) were studied in negative polarity using intensified charge coupled device (ICCD) imaging and numerical simulation. Detailed time-resolved ICCD images of cathode-directed streamers (CDSs) emanating from a ground electrode are first presented in this report. Instead of primary streamers in positive polarity, only a glow-like discharge appeared in the early stage at the cathode under negative polarity. After this discharge disappeared, a counter-propagating CDS initiated from the ground electrode (anode). Numerical simulation indicated that strong electric fields at the pellet-anode and the formation of positive ion rich local spots were the main reason for the CDS formation near the ground electrode. The maximum velocity was 750 km s−1 for Ag-supported γ-Al2O3 and 550 km s−1 for Ag-supported TiO2, respectively. In contrast to the CDS in the gas-phase with a positive polarity, the CDS in a catalyst packed-bed under negative polarity showed more branching and a larger number of streamers in the presence of oxygen than in pure N2.

The discharge characteristics in nitrogen helicon plasma

Discharge characteristics of helicon plasma in nitrogen and argon-nitrogen mixtures were investigated experimentally by using a Langmuir probe, a B-dot probe, and an optical emission spectrum. Helicon wave discharge is confirmed by the changes of electron density and electromagnetic signal amplitude with the increasing RF power, which shows three discharge stages in nitrogen, corresponding to E-mode, H-mode, and W-mode discharges in helicon plasma, respectively. Discharge images in the radial cross section at different discharge modes through an intensified charge coupled device (ICCD) show a rapid increase in luminous intensity along with the RF power. When the nitrogen discharge is in the W-mode, the images show that the strongest luminance locates near the plasma boundary and no blue core appears in the axial center of tube, which is always observed in argon W-mode discharge. The “big blue” or blue core is a special character in helicon plasma, but it has not been observed in nitrogen helicon plasma. In nitrogen-argon mixtures, a weak blue core is observed in ICCD images since the nitrogen content is increased. The electric field turns to the periphery in the distribution of the radial field and the electron temperature decreases with the increasing nitrogen content, especially when the blue core disappears. The different behaviors of the electron impact and the energy consumption in nitrogen helicon plasma are suggested to be responsible for the decrease in electron energy and the change in the electric field distribution.

A Denoising Method for Randomly Clustered Noise in ICCD Sensing Images Based on Hypergraph Cut and Down Sampling.

Intensified charge-coupled device (ICCD) images are captured by ICCD sensors in extremely low-light conditions. They often contains spatially clustered noises and general filtering methods do not work well. We find that the scale of the clustered noise in ICCD sensing images is often much smaller than that of the true structural information. Then the clustered noise can be identified by properly down-sampling and then up-sampling the ICCD sensing image and comparing it to the noisy image. Based on this finding, we present a denoising algorithm to remove the randomly clustered noise in ICCD images. First, we over-segment the ICCD image into a set of flat patches, and each patch contains very little structural information. Second, we classify the patches into noisy patches and noise-free patches based on the hypergraph cut method. Then the noise-free patches are easily recovered by the general block-matching and 3D filtering (BM3D) algorithm, since they often do not contain the clustered noise. The noisy patches are recovered by subtracting the identified clustered noise from the noisy patches. After that, we could get the whole recovered ICCD image. Finally, the quality of the recovered ICCD image is further improved by diminishing the remaining sparse noise with robust principal component analysis. Experiments are conducted on a set of ICCD images and compared with four existing denoising algorithms, which shows that the proposed algorithm removes well the randomly clustered noise and preserves the true textural information in the ICCD sensing images.

Spatial-temporal evolution of self-organized loop-patterns on a water surface and a diffuse discharge in the gap

Excited by an alternating current voltage, a patterned discharge and a diffuse discharge are generated in a needle to liquid configuration. Using an intensified charge-coupled device (ICCD), temporal evolution of the discharge between the two electrodes is investigated for the diffuse mode and the patterned mode, respectively. For the diffuse mode, the positive discharge is in a glow regime, and the negative discharge is in a Townsend discharge regime. For the patterned mode, the discharge always belongs to the Townsend discharge regime. Moreover, in the patterned mode, various patterns including the single loop, single loop with the surrounding corona, triple loops, and concentric loops with a central spot are observed on the water surface with the increasing positive peak-value of the applied voltage (Upp). Temporally resolved images of the loop-patterns are captured on the water surface. From the electrical measurements and the ICCD imaging, it is found that the loop pattern emerges after the discharge bridges the two electrodes. Then, it begins to evolve and finally degenerates with the decrease in the discharge current. The pattern does not disappear until the discharge quenches. Formation of the loop-patterns is attributed to the role of negative ions.

Luminous phase of nanosecond discharge in deionized water: morphology, propagation velocity and optical emission

We employed the techniques of time-resolved intensified charge-coupled device (ICCD) microscopy and spectroscopy to register basic morphologic and emission fingerprints of micro-discharges produced in deionized water. Fast rise-time positive high-voltage pulses (full width at half maximum of ∼7 ns and amplitude of ∼100 kV) in a point-to-plane electrode geometry produced micro-discharges, either periodically or in a single-pulse regime with the energy of ∼0.1 J dissipated during a single discharge event. Time resolved ICCD images evidence typical streamer-like branched filamentary morphology. Luminous discharge filaments show very fast and approximately linear initial expansion of the length with propagation velocity of ∼2 × 105 m s−1. When the HV pulse reaches its maximum value, the length of the primary luminous filaments reaches ∼1.3 mm. After initial expansion, the length of luminous filaments collapses and can be characterised by velocity of ∼1.9 × 104 m s−1. The first collapse is followed by a second slightly slower expansion, which is driven by the arrival of a reflected HV pulse, and which can be roughly approximated by propagation velocity of ∼1.5 × 105 m s−1. The second collapse (occurring after second expansion) proceeds at a nearly identical velocity compared with the first one. By combining two ICCD based techniques, we have been able to associate, for the first time ever, characteristic emission spectra with the most important phases of the micro-discharge development. The UV–vis-NIR emission spectra show a broad-band continuum evolving during the first expansion and collapse, followed by the well-known HI/OI atomic lines occurring together with continuum emission during the second expansion and collapse. We conclude that bound–free and free–free radiative transitions are basic emission characteristics of the nanosecond discharge initiation mechanism in liquid water which does not involve the formation of vapour bubbles.

Experimental setup for temporally and spatially resolved ICCD imaging of (sub)nanosecond streamer plasma.

Streamer discharges are efficient non-thermal plasmas for air purification and can be generated in wire-cylinder electrode structures (the plasma reactor). When (sub)nanosecond high-voltage pulses are used to generate the plasma, components like a plasma reactor behave as transmission lines, where transmission times and reflections become important. We want to visually study the influence of these transmission-line effects on the streamer development in the reactor. Therefore, we need a unique experimental setup, which allows us to image the streamers with nanosecond time resolution over the entire length of the plasma reactor. This paper describes the setup we developed for this purpose. The setup consists of a large frame in which a specially designed plasma reactor can be mounted and imaged from below by an intensified charge-coupled device (ICCD) camera. This camera is mounted on a platform which can be moved by a stepper motor. A computer automates all the experiments and controls the camera movement, camera settings, and the nanosecond high-voltage pulse source we use for the experiments. With the automated setup, we can make ICCD images of the entire plasma reactor at different instances of time with nanosecond resolution (with a jitter of less than several hundreds of picoseconds). Consequently, parameters such as the streamer length and width can be calculated automatically.

Ion and extreme ultraviolet emission features of CO2 laser produced Sn and SnO2 plasmas

The plasma plume expansion, ion debris and extreme ultraviolet (EUV) emission features of CO2 laser-produced Sn and SnO2 plasmas are investigated in this work. The expansion parameters of laser-produced plasma (LPP) are estimated using a fast-gated intensified charge-coupled device (ICCD) imaging system, while the ion debris is detected using a Faraday cup and the time-of-flight (TOF) method. Additionally, the EUV emissions from CO2 laser-produced Sn and SnO2 plasmas are measured using a grazing incidence flat-field spectrograph and EUV photodiodes. The ICCD images show that the SnO2 plasma plume has a broader edge when compared with that of the Sn plasma. Because of the differences between the thermodynamic parameters of the samples, the total ion number and the kinetic energy were both higher for the SnO2 plasma than for the Sn plasma. The maximum estimated conversion efficiencies (CEs) of the Sn and SnO2 plasmas were 1.1% and 0.9%, respectively; the difference is due to the lower Sn fraction in SnO2. The results of the angularly-resolved EUV emission measurements showed that the detected EUV energy decreases as the angle with respect to the laser axis increases.

Anomalous cross-B field transport and spokes in HiPIMS plasma

Localized light emission patterns observed during on time of a high power impulse magnetron sputtering (HiPIMS) discharge on a planar magnetron, known as spokes or ionization zones, have been identified as a potential source of anomalous cross-B field diffusion. In this paper experimental evidence is presented that anomalous diffusion is triggered by the appearance of spokes. The Hall parameter , product of the electron cyclotron frequency and the classical collision time, reduces from Bohm diffusion values ( and higher) down to the value of 3 as spokes appear, indicating anomalous cross-B field transport. A combination of intensified charge coupled device imaging and electric probe measurements reveals that the ions from the spokes are instantaneously diffusing away from the target. The ion diffusion coefficients calculated from a sideways image of the spoke are six times higher than Bohm diffusion coefficients, which is consistent with the reduction of the Hall parameter.