High Degree Of Ionization Research Articles

Sub-terahertz emission from solar flares: The plasma mechanism of chromospheric emission

We consider the plasma mechanism of sub-terahertz emission from solar flares and determine the conditions for its realization in the solar atmosphere. The source is assumed to be localized at the chromospheric footpoints of coronal magnetic loops, where the electron density should reach n ≈ 1015 cm−3. This requires chromospheric heating at heights h ⩾ 500 km to coronal temperatures, which provides a high degree of ionization needed for Langmuir frequencies ν p ≈ 200–400 GHz and reduces the bremsstrahlung absorption of the sub-THz emission as it escapes from the source. The plasma wave excitation threshold for electron-ion collisions imposes a constraint on the lower density limit for energetic electrons in the source, n 1 > 4 × 109 cm−3. The generation of emission at the plasma frequency harmonic ν ≈ 2ν p rather than the fundamental tone turns out to be preferred. We show that the electron acceleration and plasma heating in the sub-THz emission source can be realized when the ballooning mode of the flute instability develops at the chromospheric footpoints of a flare loop. The flute instability leads to the penetration of external chromospheric plasma into the loop and causes the generation of an inductive electric field that efficiently accelerates the electrons and heats the chromosphere in situ. We show that the ultraviolet radiation from the heated chromosphere emerging in this case does not exceed the level observed during flares.

NGC 2579 and the carbon and oxygen abundance gradients beyond the solar circle★

We present deep echelle spectrophotometry of the Galactic HII region NGC 2579. The data have been taken with the Very Large Telescope Ultraviolet-Visual Echelle Spectrograph in the 3550--10400 \AA\ range. This object, which has been largely neglected, shows however a rather high surface brightness, a high ionization degree and is located at a galactocentric distance of 12.4 $\pm$ 0.7 kpc. Therefore, NGC 2579 is an excellent probe for studying the behaviour of the gas phase radial abundance gradients in the outer disc of the Milky Way. We derive the physical conditions of the nebula using several emission line-intensity ratios as well as the abundances of several ionic species from the intensity of collisionally excited lines. We also determine the ionic abundances of C$^{2+}$, O$^+$ and O$^{2+}$ -- and therefore the total O abundance -- from faint pure recombination lines. The results for NGC 2579 permit to extend our previous determinations of the C, O and C/O gas phase radial gradients of the inner Galactic disc (Esteban etal. 2005) to larger galactocentric distances. We find that the chemical composition of NGC 2579 is consistent with flatten gradients at its galactocentric distance. In addition, we have built a tailored chemical evolution model that reproduces the observed radial abundance gradients of O, C and N and other observational constraints. We find that a levelling out of the star formation efficiency about and beyond the isophotal radius can explain the flattening of chemical gradients observed in the outer Galactic disc.

Modeling the extraction of sputtered metal from high power impulse hollow cathode discharges

High power impulse hollow cathode sputtering is studied as a means to produce high fluxes of neutral and ionized sputtered metal species. A model is constructed for the understanding and optimization of such discharges. It relates input parameters such as the geometry of the cathode, the electric pulse form and frequency, and the feed gas flow rate and pressure, to the production, ionization, temperature and extraction of the sputtered species. Examples of processes that can be quantified by the use of the model are the internal production of sputtered metal and the degree of its ionization, the speed and efficiency of out-puffing from the hollow cathode associated with the pulses, and the gas back-flow into the hollow cathode between pulses. The use of the model is exemplified with a special case where the aim is the synthesis of nanoparticles in an expansion volume that lies outside the hollow cathode itself. The goals are here a maximum extraction efficiency, and a high degree of ionization of the sputtered metal. It is demonstrated that it is possible to reach a degree of ionization above 85%, and extraction efficiencies of 3% and 17% for the neutral and ionized sputtered components, respectively.

Size-controlled growth of nanoparticles in a highly ionized pulsed plasma

Copper nanoparticles (NPs) were synthesized using a high power pulsed hollow cathode technique and the produced NPs were studied as a function of pulse parameters, i.e., frequency, peak current, and pulse width. It was found that the particle size can be altered in a range from 10 to 40 nm by changing any one of the pulse parameters. The mechanisms of NP synthesis with respect to a pulsed discharge and a high degree of ionization of the sputtered material are discussed.

Effect of voltage pulse characteristics on high-power impulse magnetron sputtering of copper

We present a model analysis of high-power impulse magnetron sputtering of copper. A non-stationary two-zone model is used to calculate the deposition rate and the ionized fraction of sputtered copper atoms in the flux onto the substrate for various pulse lengths (20–400 µs), pulse shapes (a fixed target voltage of 900 V and stepwise ascending (800–1000 V) or descending (1000–800 V) target voltages), repetition frequencies (100–2000 Hz) and magnetic field strengths in front of the target (350–450 G) at an argon pressure of 1 Pa. We show that sufficiently long pulses (at least 100 µs), which allow for the build-up of a high-density plasma in front of the target (diameter of 50 mm), are necessary to achieve high target power densities in a pulse and, consequently, high degrees of ionization of the sputtered atoms. However, the high degree of ionization of the sputtered copper atoms leads necessarily to lower deposition rates when compared with dc magnetron sputtering at the same target power density. This is mainly due to the return of ionized sputtered atoms onto the target. The model results show that the average target power density in a pulse is, in addition to the target voltage, a fundamental quantity which determines the average ionized fraction of sputtered atoms in the flux onto the substrate and the deposition rate per average target power density in a period applied to the discharge. Such model calculations can be beneficial for determining the optimum working conditions for specific deposition applications.

SUPER LONG CONDUCTIVE CHANNEL PRODUCTION BY IMPULSAR

The attempts to create a super long conductive channels were taken in order to study the upper atmosphere and to settle special tasks, related to solar energy transmission, accumulated by orbital solar stations. There upon the program of creation of ”Impulsar” represents a great interest, as this program in a combination with high-voltage high repetition rate electrical source can be useful to solve the above mentioned problems. The principle of conductive channel production can be shortly described as follows. The ”Impulsar”- laser jet engine vehicle - propulsion take place under the influence of powerful high repetition rate pulse-periodic laser radiation. In the experiments the CO2- laser and solid state Nd: YAG laser systems had been used. Active impulse appears thanks to air breakdown (＜ 30 km) or to the breakdown of ablated material on the board (＞30km), placed in the vicinity of the focusing mirror-acceptor of the breakdown waves. With each pulse of powerful laser the device rises up, leaving a bright and dense trace of products with high degree of ionization and metallization by conductive nano-particles due to ablation. Conductive dust plasma properties investigation in our experiments was produced by two very effective approaches: high power laser controlled ablation and by explosion of wire. Experimental and theoretical results of conductive canal modeling will be presented. The estimations show that with already experimentally demonstrated figures of specific thrust impulse the lower layers of the Ionosphere can be reached in several ten seconds that is enough to keep the high level of channel conductivity and stability with the help of high repetition rate high voltage generator. Some possible applications for new technology are highlighted.

Structure and properties of CrSiN nanocomposite coatings deposited by hybrid modulated pulsed power and pulsed dc magnetron sputtering

CrSiN nanocomposite coatings were deposited at room temperature in a closed field unbalanced magnetron sputtering system by co-sputtering from Cr and Si targets using modulated pulsed power magnetron sputtering (MPPMS) and pulsed dc magnetron sputtering (PDCMS), respectively. The application of MPPMS as one of the sputtering sources was aimed at generating a high ionization degree of the sputtered material and a high plasma density by using a pulsed high power approach. When the Si content is less than 4.8at.%, Si atoms mainly go into the CrN lattice and form a solid solution. As the Si content reached 6.7at.%, a nanocomposite structure formed in the CrSiN coatings, in which 5–8nm Cr(Si)N nanocrystallites were embedded in an amorphous Si3N4 matrix. The solid solution strengthening and complete phase separation are believed to be responsible for the enhanced mechanical properties of the CrSiN coatings. A maximum hardness of 38GPa, an H/E ratio of 0.096 and an H3/E*2 ratio of 0.31GPa were identified in the coating with a Si content of 6.7at.%. The coatings with a Si content at 6.7at.% and 10.2at.% were found to be optimized for wear resistant applications. The MPPMS+PDCMS CrSiN coatings also exhibited improved corrosion resistance as compared to AISI 304 stainless steel samples tested in a 3.5wt.% NaCl aqueous solution.

Development and evaluation of a mechanistic bioconcentration model for ionogenic organic chemicals in fish

A mechanistic mass balance bioconcentration model is developed and parameterized for ionogenic organic chemicals (IOCs) in fish and evaluated against a compilation of empirical bioconcentration factors (BCFs). The model is subsequently applied to a set of perfluoroalkyl acids. Key aspects of model development include revised methods to estimate the chemical absorption efficiency of IOCs at the respiratory surface (E(W) ) and the use of distribution ratios to characterize the overall sorption capacity of the organism. Membrane-water distribution ratios (D(MW) ) are used to characterize sorption to phospholipids instead of only considering the octanol-water distribution ratio (D(OW) ). Modeled BCFs are well correlated with the observations (e.g., r(2) = 0.68 and 0.75 for organic acids and bases, respectively) and accurate to within a factor of three on average. Model prediction errors appear to be largely the result of uncertainties in the biotransformation rate constant (k(M) ) estimates and the generic approaches for estimating sorption capacity (e.g., D(MW) ). Model performance for the set of perfluoroalkyl acids considered is highly dependent on the input parameters describing hydrophobicity (i.e., log K(OW) of the neutral form). The model applications broadly support the hypothesis that phospholipids contribute substantially to the sorption capacity of fish, particularly for compounds that exhibit a high degree of ionization at biologically relevant pH. Additional empirical data on biotransformation and sorption to phospholipids and subsequent incorporation into property estimation approaches (e.g., k(M) , D(MW) ) are priorities with respect to improving model performance.

Potential Role of Phospholipids in Determining the Internal Tissue Distribution of Perfluoroalkyl Acids in Biota

S characterizing and quantifying the bioaccumulation and internal tissue distribution of perfluoroalkyl acids (PFAAs) remain highly relevant from both a scientific and regulatory perspective. Unlike neutral hydrophobic organic contaminants which exhibit the highest wet weight concentrations in adipose tissue, the highest levels of PFAAs in biota are typically measured in liver and blood samples. This pattern of internal tissue distribution is hypothesized to largely reflect the role of PFAA−protein interactions in determining the sorption capacity of the organism and its various organs. Based on recent work developing and evaluating a mechanistically based bioconcentration model for ionogenic organic chemicals (IOCs) in fish, we propose an alternative hypothesis, namely that the bioaccumulation potential and internal tissue distribution of perfluoroalkyl acids (PFAAs) are strongly influenced by phospholipids. The objective of this Viewpoint is to encourage further empirical studies to evaluate this assertion. Research into the interactions of PFAAs with proteins has predominantly focused on bovine serum albumin (BSA) and various fatty acid binding proteins (FABP). However, these data have yet to be used to derive a mechanistically based model capable of relating external concentrations of PFAAs to both internal concentrations and internal tissue distribution. It is already clear that bulk protein fraction in tissues cannot successfully explain the observed tissue distribution of PFAAs. For example, liver and muscle tissue have similar bulk protein contents, whereas reported wet weight concentrations of PFAAs are typically many times higher in liver than in muscle. These observations can be rationalized based on protein-water partitioning of PFAAs only if these interactions are highly protein-specific. This hypothesis implies that research efforts be directed toward isolating different tissue proteins and establishing protein-water distribution ratios for each one to complement studies with serum albumin and FABP. The potential importance of competition for binding sites on the protein under physiological conditions (i.e., in the presence of other endogenous ligands) is also a key consideration requiring further study. Empirical studies characterizing interactions of various IOCs (including PFAAs) with phospholipids in membrane−water systems are also available in the scientific literature (e.g., refs 4 and 5). Most phospholipids present in biota (e.g., phosphatidylcholines) are zwitterionic at physiological pH with a positively charged choline group and a negatively charged phosphate group. Supportive electrostatic interactions with charged IOCs can therefore occur in addition to hydrophobic interactions. Consequently, the difference between the membrane-water partition constant of the neutral and charged form (ΔMW = 0.3−2 log units) is less than the difference between the (apparent) octanol−water partition constants (ΔOW = 2−4 log units) and membrane-water distribution ratios (DMW) are less sensitive to changes in pH than octanol−water distribution ratios (DOW). 2,4 Assuming that DMW and DOW are reliable surrogates for sorption to phospholipids and neutral (storage) lipids in vivo respectively, phospholipids dominate the contribution of total lipid to an organism’s sorption capacity for IOCs exhibiting a high degree of ionization at physiologically relevant pH. Although there is some interspecies variability, phospholipids tend to be at least as prevalent as neutral (storage) lipids in most tissues with the exception of adipose tissue. Ignoring the potential contribution of other biological macromolecules (e.g., proteins), the highest wet weight tissue concentrations of predominantly charged IOCs in long-term continuous exposure scenarios are therefore expected to be observed in tissues like liver, kidney and brain, which exhibit both a relatively high total lipid and phospholipid content. By extension, regions within a particular tissue with higher phospholipid content are also expected to have higher wet weight concentrations. Tissues with relatively low phospholipid content but large volume (e.g., muscle) can still be relevant in terms of mass distribution though. Note that

INTERDEPENDENCE OF ELECTRIC DISCHARGE AND MAGNETOROTATIONAL INSTABILITY IN PROTOPLANETARY DISKS

We study how the magnetorotational instability (MRI) in protoplanetary disks is affected by the electric discharge caused by the electric field in the resistive MHD. We have performed three-dimensional shearing box simulations with various values of plasma beta and electrical breakdown models. We find the self-sustainment of the MRI in spite of the high resistivity. The instability gives rise to the large electric field that causes the electrical breakdown, and the breakdown maintains the high ionization degree required for the instability. The condition for this self-sustained MRI is set by the balance between the energy supply from the shearing motion and the energy consumed by the Ohmic dissipation. We apply the condition to various disk models and study where the active, self-sustained, and dead zones of MRI are. In the fiducial minimum-mass solar nebula (MMSN) model, the newly-found sustained zone occupies only the limited volume of the disk. In the late-phase gas-depleted disk models, however, the sustained zone occupies larger volume of the disk.

Calculation of spectral and Rosseland paths in a plasma with multiply charged ions based on a statistical approach

The semiclassical approach to determine the Fourier components of the electron dipole moment disregarding polarization (noninteracting electron model) is used for analyzing ion oscillator strengths and determining the radiation properties of plasmas consisting of multiply charged ions of heavy elements. The oscillator strength distribution df/dω (proportional to the photoabsorption cross section) is calculated as a function of the degree of ionization and self-similar frequency Ω = ω/Z. It is found that for low degrees of ionization, function df/dω for an ion is close to function df/dω for a neutral atom; upon an increase in the degree of ionization, regions are formed in which df/dω = 0 (transparency windows) and the photoabsorption cross section for high degrees of ionization differs from zero only in small frequency ranges. The resultant distribution of the ion oscillator strengths is used for calculating the polarizability of ions as a function of frequency and the cross section of radiation scattering on ions. For a gold plasma, the absorbance and opacity (both spectral and averaged according to Rosseland and Planck) are calculated. The results of computing the paths and absorption coefficients coincide in order of magnitude with the available data. The effect of scattering on the Rosseland path is estimated.

Investigation of two discharge configurations in the CAMILA Hall thruster by the particle-in-cell method

The CAMILA (co-axial magneto-isolated longitudinal anode) concept was introduced to improve the ionization efficiency in low-power Hall thrusters. With relatively large coaxial anode surfaces and longitudinal magnetic strength, the CAMILA represents a significant departure from conventional Hall thrusters. In order to investigate the physical processes inside the CAMILA thruster, a two-dimensional particle-in-cell simulation of the thruster channel is used. The discharge parameters are analysed in two magnetic configurations: simplified CAMILA with a conventional magnetic field and full CAMILA with strengthened longitudinal component of the magnetic field. The simulation is fully kinetic with electrons, ions and gas atoms (xenon) represented as particles. Electron–neutral interactions are included together with particle–boundary interactions such as recombination and secondary emission. In addition, dielectric boundaries float and the cathode is represented as a free-space boundary, emitting electrons to satisfy quasi-neutrality on its surface. The high anode efficiency, observed in experiments, can be explained by several mechanisms found in this work. In the simplified case (magnetic configuration similar to the experiments) a focusing potential is created near the anode–dielectric boundary that directs ions away from the walls. It is created due to a combination of anode placement, in parallel with the channel, penetration of the plasma inside the anode cavity and the shape of magnetic force lines. Simulated steady-state results show good agreement with experimental measurements. In the full CAMILA case we demonstrate that the ionization region is found in the anode cavity. The electric field inside the anode cavity is substantial and it is directed towards the anode cavity centreline. Electrons are heated sufficiently to reach a high degree of ionization inside the anode cavity while ion currents to the anode surfaces are reduced significantly.

A novel high-power pulse PECVD method

A novel plasma enhanced CVD (PECVD) technique has been developed in order to combine energetic particle bombardment and high plasma densities found in ionized PVD with the advantages from PECVD such as a high deposition rate and the capability to coat complex and porous surfaces. In this PECVD method, an ionized plasma is generated above the substrate by means of a hollow cathode discharge. The hollow cathode is known to generate a highly ionized plasma and the discharge can be sustained in direct current (DC) mode, or in high-power pulsed (HiPP) mode using short pulses of a few tens of microsecond. The latter option is similar to the power scheme used in high power impulse magnetron sputtering (HiPIMS), which is known to generate a high degree of ionization of the sputtered material, and thus providing new and added means for the synthesis of tailor-made thin films. In this work amorphous carbon coatings containing copper, have been deposited using both HiPP and DC operating conditions. Investigations of the bulk plasma using optical emission spectroscopy verify the presence of Ar+, C+ as well as Cu+ when running in pulsed mode. Deposition rates in the range 30μm/h have been obtained and the amorphous, copper containing carbon films have a low hydrogen content of 4–5 at%. Furthermore, the results presented here suggest that a more efficient PECVD process is obtained by using a superposition of HiPP and DC mode, compared to using only DC mode at the same average input power.

Amlodipine-induced Delirium in a Patient With Ischemic Stroke

Amlodipine is a dihydropyridine calcium antagonist drug with distinctive pharmacokinetic characteristics that seem to be attributable to a high degree of ionization. Delirium is a neuropsychiatric syndrome recognized as a marker for increased health care costs, morbidity, mortality, and institutionalization that often complicates acute physical illness in elderly people. This case is the first report concerning amlodipine use as a cause of delirium.

Biomedical applications and diagnostics of atmospheric pressure plasma

Numerous applications of non-equilibrium (cold, low temperature) plasmas require those plasmas to operate at atmospheric pressure. Achieving non-equilibrium at atmospheric pressure is difficult since the ionization growth is very fast at such a high pressure. High degree of ionization on the other hand enables transfer of energy between electrons and ions and further heating of the background neutral gas through collisions between ions and neutrals. Thus, all schemes to produce non-equilibrium plasmas revolve around some form of control of ionization growth. Diagnostics of atmospheric pressure plasmas is difficult and some of the techniques cannot be employed at all. The difficulties stem mostly from the small size. Optical emission spectroscopy and laser absorption spectroscopy require very high resolution in order to resolve the anatomy of the discharges. Mass analysis is not normally applicable for atmospheric pressure plasmas, but recently systems with triple differential pumping have been developed that allow analysis of plasma chemistry at atmospheric pressures which is essential for numerous applications. Application of such systems is, however, not free from problems. Applications in biomedicine require minimum heating of the ambient air. The gas temperature should not exceed 40 °C to avoid thermal damage to the living tissues. Thus, plasmas should operate at very low powers and power control is essential. We developed unique derivative probes that allow control of power well below 1 W and studied four different sources, including dielectric barrier discharges, plasma needle, atmospheric pressure jet and micro atmospheric pressure jet. The jet operates in plasma bullet regime if proper conditions are met. Finally, we cover results on treatment of bacteria and human cells as well as treatment of plants by plasmas. Localized delivery of active species by plasmas may lead to a number of medical procedures that may also involve removal of bacteria, fungi and spores.

Effects of target voltage during pulse-off period in pulsed magnetron sputtering on afterglow plasma and deposited film structure

In this study, we investigated the effect of the target bias voltage during the pulse-off period in the pulsed magnetron sputtering (PMS) of repetition frequency 200 Hz and duty ratio 5–20%. Copper films were deposited by the PMS for Ar gas pressures of 1–5 Pa (with and without the pulse-off target voltage) and compared with those deposited by DC magnetron sputtering (dcMS). The time-averaged power was set to 100 W. Compared to films deposited by dcMS, those deposited by PMS showed smooth surface and a ductile nature. These properties became more evident when the positive pulse-off voltage was applied. To clarify the reason for film structure modification, the plasma was investigated by time resolved Langmuir probe measurement. It was confirmed that electron density was as high as 1017 m−3 in PMS mode during the pulse-on period. On applying +40 V of pulse-off target voltage, the plasma potential was found to be raised by about 30 V in comparison to the zero voltage case. We suggest that this increase in the plasma potential leads to an increase in impinging energy of Cu ions on the substrate, and modifies the deposited film structure. Though the pulsed plasma we used was in the modest power range, we expect this approach is applicable to high-power impulse sputtering (HiPIMS) mode with high degree of ionization.

Caracteristics of TiN Coating Films for Large Sizes Prepared by Arc Ion Plating

Arc ion plating (AIP) is one of the most attractive physical vapour deposition (PVD) method for the industrial manufacture of TiN coatings, owing to a high degree of ionization in the target material and convenient control of the process parameters. The important characteristic of hard coating is the adhesion strength between the coating layer and the substrate. The coating will be subjected to various loads, such as mechanical, thermal load, etc., in practical applications. Therefore, for more than a decade, Ti-based hard coatings have been applied to tools, dies, and mechanical parts because of the enhance lifetime and performance. It is focus on the attractive properties such as high hardness, good wear, and chemical stability. In the present study, TiN monolayer film was prepared at various N2 partial pressures and current by the AIP technique in SACM645 material. The correlation between microstructure and properties of the TiN coating was comparatively investigated by XRD, FE-SEM and AFM. These study carried steadily out improve the adhesion properties and wear resistance of Ti-based coating using pre-treatment of the substrate, insertion of an interlayer, application of multi-layers and adjustment of the process parameters. The main phase FCC TiN displayed (200) orientation in the film with the highest N2 partial pressure. The (111) orientation was observed with decreasing N2 partial pressure. The (200) and (111) textures in the film which was treated 80A arc current were found to be competitive orientations, however stronger arc treated the (200) texture was increased. The multilayer TiN films has possessed high hardness (up to 42Nm) and the best wear resistance among the specimens. These features were attributed to the presence of dense microstructures that were mainly composed of TiN phase around 5.16㎛ thickness, HF1 adhesion and Ra 35㎚ surface roughness

High Power Pulsed Hollow Cathode for Nanoparticle Synthesis

Copper nanoparticles were synthesized using a novel method based on sputtering material from a hollow cathode using high power pulses. The high power pulses provide a supersaturated vapor with a high degree of ionization from which the nanoparticles are formed in the gas phase. By adjusting the pulse parameters, the plasma environment and thus the nanoparticle growth can be affected. It was found that the nanoparticle size can be influenced by varying, e.g., the pulse frequency or the pulse power. The results using the high power pulsed hollow cathode are compared to nanoparticles synthesized with a dc discharge using the same setup.

Mass spectrometry of solid samples in open air using combined laser ionization and ambient metastable ionization

Mass spectrometry of solid samples in open air was carried out using combined laser ionization and metastable ionization time-of-flight mass spectrometry (LI-MI-TOFMS) in ambient environment for qualitative and semiquantitative (relative analyte information, not absolute information) analysis. Ambient metastable ionization using a direct analysis in realtime (DART) ion source was combined with laser ionization time-of-flight mass spectrometry (LI-TOFMS) to study the effects of combining metastable and laser ionization. A series of metallic samples from the National Institute of Standards and Technology (NIST 494, 495, 498, 499, and 500) and a pure carbon target were characterized using LI-TOFMS in open air. LI-MI-TOFMS was found to be superior to laser-induced breakdown spectroscopy (LIBS). Laser pulse energies between 10 and 200mJ at the second harmonic (532nm) of an Nd:YAG laser were applied in the experiment to obtain a high degree of ionization in plasmas. Higher laser pulse energy improves signal intensities of trace elements (such as Fe, Cr, Mn, Ni, Ca, Al, and Ag). Data were analyzed by numerically calculating relative sensitivity coefficients (RSCs) and limit of detections (LODs) from mass spectrometry (MS) and LIBS spectra. Different parameters, such as boiling point, ionization potential, RSC, LOD, and atomic weight, were shown to analyze the ionization and MS detection processes in open air.

Primordial magnetic field constraints from the end of reionization

ABSTRACT Primordial magnetic fields generated in the early Universe are subject of considerable investigation, and observational limits on their strength are required to constrain the theory. Due to their impact on the reionization process, the strength of primordial fields can be limited using the latest data on reionization and the observed UV luminosity function of high-redshift galaxies. Given the steep faint-end slope of the luminosity function, faint galaxies contribute substantial ionizing photons, and the low-luminosity cut-off has an impact on the total budget thereof. Magnetic pressure from primordial fields affects such cut-off by preventing collapse in haloes with mass below 1010 M, with B0 the comoving field strength. In this Letter, the implications of these effects are consistently incorporated in a simplified model for reionization, and the uncertainties due to the cosmological parameters, the reionization parameters and the observed UV luminosity function are addressed. We show that the observed ionization degree at z∼ 7 leads to the strongest upper limit of B0≲ 2–3 nG. Stronger limits could follow from measurements of high ionization degree at z > 7.