Remote field eddy current testing (RFECT) can detect defects in ferromagnetic pipes without requiring a couplant and contact with the pipe wall. Because the response in the remote field zone is extremely low, testing requires high-sensitivity detection to sense low magnetic fields. Therefore, a magnetic circuit design comprising a RFECT system is necessary for excitation and reception. In this study, a RFECT system using a giant magnetoresistance (GMR) sensor is proposed, and magnetic circuits with magnets and/or yokes are designed and optimized for improved reception. To investigate the characteristics of the designed RFECT system, finite element analysis (FEA) and experiments are performed on various magnetic circuit system configurations. System performance is verified with respect to sensitivity and the detectability of defect characterizations in 4-inch ferromagnetic pipelines having different defect sizes. Consequently, the magnetic circuit system using the permalloy yoke shows the highest sensitivity, thus achieving effective RFECT detection.

In this study, we present a theoretical and numeric analysis of an untethered microrobot manipulation technique that can be used in a liquid environment. A microrobot, which is levitated on a pyrolytic graphite surface, allows us to achieve high precision positioning (at nano level) and control with lower external magnetic force requirements due to stabilizing manner of its locomotion. Stabilizing microrobot is controlled via a single “lifter magnet” as a driving force that is placed on an automatic micro-stage in order to provide stable-motion about x, y and z axes. The presented microrobot is designed for single cell manipulation and transportation operations in liquid medium. It can be used in different experimental setups such as lab-on-a-chips, petri dishes. Here, a new approach to determine an optimal experimental setup of the diamagnetically levitated microrobot, which provides the most effective and possible microrobot control, is explained with FEM (Finite Element Method) analysis and required background information. For such untethered microrobot control experiments in a FEM program, determination of the size of materials used, selection criteria, required magnetic force effects, and optimum pyrolytic graphite sizes are discussed in detail. To do that, our proposed analysis method suggests how to construct such an FEM model parametrically in COMSOL^®. Before starting the experimental work, the effects of the material and dimensions of each element forming the system on the microrobot are discussed in detail. Moreover, the manipulation technique which revealed the theoretical infrastructure is compared with the numerical calculations and the results are shown to be compatible with each other.

I estimated magnetometric demagnetization factors of hollow cylinders. Demagnetization factors of extreme hollow cylinders are obtained analytically, and axial demagnetization factors of finite hollow cylinders are calculated numerically to find that the approximation designed for the axial demagnetization factors [Nam et al., J. Appl. Phys. 111, 07E347 (2012)] is valid as long as the hollow ratio is not close to one, depending on susceptibility and the aspect ratio. I also discuss the transverse demagnetization factor and the sum rule of the demagnetization factors for a finite hollow cylinder. Dependence on susceptibility being related to the hollow ratio is a feature of magnetometric demagnetization factors of finite hollow cylinders and hollow spheres. A thin closed hollow shape might be the better candidate than open hollow shapes if one wants to maximize susceptibility dependence of the magnetometric demagnetization factor of magnetic material.

Present study assesses vascular reactivity of the ophthalmic artery (OA) in the caffeine presence using magnetic resonance (MR) imaging technique, and it was compared with those of intracranial vessels, such as the middle cerebral and internal carotid arteries. All subjects underwent two MR scans in pre- and post-caffeine consumption conditions. Each scan included two imaging data sets, obtained using conventional time-of-flight (TOF) and phase-contrast (PC) MR angiography (MRA) to examine the signal changes of the target cerebral vessels and measure their velocities in 3 Tesla (3T) MRI, respectively. TOF MRA delineates the detail of the OA more clearly in post-caffeine condition, although it was also visualized in pre-caffeine. PC MRA can quantitatively measure changes in the blood flow velocity of OA. In conclusion, this study shows that MR imaging modality, especially PC MRA, can be used to quantify blood flow velocity in the OA, following a caffeine-induced blood flow increase.

In-situ observations of magnetic domain wall motion in a Ni80-Fe20 thin film electroplated on a Cu film were performed by Lorentz TEM. Detailed magnetization distribution was investigated by differential phase contrast microscopy. The magnetic properties of the coercivity and saturation magnetic flux density were measured to be 6.5 Oe and 1.56 T, respectively. The diffraction ring pattern showed the Ni₃Fe FCC structure with nanocrystalline nature (grain size 29 nm) and texture indicating the preferential orientation. We measured the domain width of 1.9 μm and found the fluctuation of magnetization direction coupled with two vortices. With the in-plane and out-of-plane magnetic fields applied, domain wall motions were in-situ observed and discussed.

The importance of radiation-based images has been increasing due to their ability to provide rapid diagnosis and facilitate treatment of lesions. Among them, the frequency of examination using computed tomography (CT) has been increasing because of this technique’s fast examination time and high diagnostic power. However, although the criteria for screening have been presented based on many previous studies on the CT exposure dose for adults, the criteria for children remain inadequate. Especially, relaxing the conditions to reduce the exposure dose of CT will lead to generation of noises. To address this problem, many noise removal algorithms have been developed. Among developed algorithms, a particularly strong interest has been focused on deep learning methods, which are a sort of artificial intelligence (AI)-based machine learning. Therefore, the present study aimed to develop a noise removal algorithm using the Gaussian Mixture Model (GMM), an AIbased deep learning method, and to apply the algorithm to pediatric abdominal CT so that to evaluate the usefulness of the approach. PMMA phantoms with different diameters of 12, 16, 20, 24, and 32 cm, which can express pediatric abdomen, were manufactured and used. To evaluate dose and image quality, the tube current was fixed to 200 mAs and the tube voltage was changed from 80 to 120, and 140 kVp; thereafter, the tube voltage was fixed to 120 kVp and the tube currents were changed from 50 to 100, 150, 200, and 250 mAs. According to the results, CTDIw showed a tendency to increase alongside with increases in the tube voltage and the tube currents, while noise decreased proportionally. In addition, the contrast decreased as the tube voltage increased, but was shown to be almost unrelated to the tube currents. Finally, the excellent CNRD result was measured in lowest exposure condition at 80 kVp and 50 mAs. Also, the average of CNRD with AI noise reduction algorithm was 1.6-4.2 times higher than before the application. In conclusion, the doses and characteristics of the pediatric abdominal CT scan according to various image acquisition conditions could be successfully identified and the efficiency of the AI noise removal algorithm developed in the present study was demonstrated.

This paper presents an analytical method for calculating the magnetic field in a new linear permanent-magnet vernier (LPMV) machine, thus predicting the electromagnetic vibration. The main vibration source is the normal force between the mover and the stator of the LPMV machine. Firstly, the air-gap flux density is calculated and analyzed using the rotor permeance to modulate the magneto-motive force, and is verified by the finite element (FE) results. Then, the harmonics of the normal force density is calculated, the normal force and thrust force are analyzed. Secondly, the natural vibration modes and the transient displacement of the mover are predicted by FE method, and the relationship between the normal force density and the vibration is determined. Finally, experimental results are given for verification. This study is instructive for the design of a high-precision and low-vibration LPMV machine.

A facile and scalable method to synthesize high purity α”-Fe₁₆N₂ powders with tunable sphere structures is developed. This strategy combined spray drying of Fe salt particles with hydrogen reduction and subsequent ammonia nitridation to form α”-Fe₁₆N₂ phase. The solid and hollow sphere structures of precursor particles can be easily tuned by adding ethanol as a directing agent. In addition, the initial structure of Fe spheres is maintained even after phase transformation process. The resulting particles prepared by optimum condition consist of high purity α”-Fe₁₆N₂ with a phase fraction of 95.52 wt%, showing a coercivity of up to 1471 Oe and a magnetic energy product of up to 2.25 MGOe at room temperature.

This paper deals with the comparative investigation on an interior permanent magnet synchronous machine (IPMSM) and a surface-mounted permanent magnet synchronous machine (SPMSM) considering operating conditions, and finite element method (FEM) is employed to analyze their electromagnetic field characteristics. For the reasonable comparison, those machines have identical machine size and equivalent circuit parameters, such as induced voltage and resistance, and one of the analysis models is manufactured for the experimental verification. From the no-load and load test, the induced voltage and phase current are measured, and the validity of analysis results are demonstrated by showing well corresponded results. In addition, since the phase current contains harmonic components, they are considered in the power loss characteristic analysis by considering operating conditions to investigate their influence on machine performance. In this study, the SPMSM shows relatively better core loss and rotor loss characteristics compared to IPMSM when the machines are operated in high rotational speed condition.

Magnetic fluid seal is widely used in military and aerospace industry owing to its zero leakage property, long life and reliability. The resistance torque is often required to be small and stay within allowable scope with the standing time expanding and the working environment changing. In this paper, we discussed the influence of the particle size distribution of magnetic fluid on the resistance torque of magnetic fluid seal. Samples of magnetic fluid of different particle size distribution were processed by applying a magnetic field gradient. Afterwards, the rheological property of different samples was analyzed using rheometer. Besides, the resistance torque of magnetic fluid seal on different occasions was measured. We explained these results from the point of formation and destruction of magnetic aggregations based on the theory of magnetoviscous effect, thus provided feasible ways to improve the performance of magnetic fluid seal.

In this paper, we propose a novel tunable left-handed metamaterial (LHM), the capacitor-loaded short wire pairs (CL-SWPs). It is composed of a pair of short wires connected through a variable capacitor. This LHM is single-sided, and it exhibits not only tunable negative permeability, but also a wide band negative permittivity. It is pointed out with theoretical analysis that its left-handed performance is related to the mutual coupling coefficient. A tunable dual-band LHM is also proposed by simply adding a double slits split ring resonator to this LHM. The simulated results indicate that the closer the two LH bands are, the better performance the CL-SWP related left-handed band is, hence identifying our theoretical analysis. The proposed structure is geometrically simple, low-cost and easy for fabrication, and it can be used as a basic particle in the design of tunable multi-band LHMs.

In studying application of magnetic stimulation device for SD mouse brain’s killer cell caused by cerebral ischemia induction with Transcranial Magnetic Stimulation (TMS) applying EISC Processor Core gives the block of cell death. It is a drug-dependent application of stimulation for early ischemic brain injury that validated the effect of stimulation in the ischemic state in relation to cell apoptosis with Bax, Caspase-3, immunoreactivity cells at 12 and 24 hours after ischemia. C-Fos rapidly induced the early gene and its transcription factor at CA1 site after ischemic injury, and continuous c-Fos induction caused promotion of neuronal death after ischemic injury check. In this study, to investigate the influence of brain ischemia-induced in rats on Bax, c-Fos expression in cerebrum after low frequency magnetic stimulation, low frequency magnetic stimulation was added to ST 36, We studied more aggressive approaches from the viewpoint of magnetic stimulation on neuronal death caused by early ischemic brain injury by examining changes in nerve cell Bax, c-Fos protein at the cerebral site.

To assess the Safety, feasibility, and efficacy of low-frequency repetitive transcranial magnetic stimulation (rTMS) applied to the cerebellum in patients with acute posterior circulation stroke. Thirty ataxic patients with acute posterior circulation stroke were randomized to experimental (EG = 15) and control groups (CG = 15). All subjects received a 30-minute mirror therapy in common, which consisted of lower limb strengthening exercises and balance enhancement program related to functional tasks. During this intervention, mirrors were placed on the front and side walls to provide visual feedback about their movement. EG applied 1HZ real rTMS for 15 minutes to the cerebellum before mirror treatment and sham rTMS for CG. Intervention was performed once a day, five times a week for four weeks. Static balance test, Wisconsin gait scale, 6 minute walk test (6MWT) and time up go test (TUG) were performed before and after the intervention. At post-test, Static balance test (98.53.68 ± 6.94 versus 110.53 ± 16.83), Wisconsin gait scale (25.61 ± 4.86 versus 29.54 ± 5.82), 6 minute walk test (181.47 ± 34.52 versus 165.72 ± 35.63), time up go test (24.47 ± 4.55 versus 28.93 ± 3.13) was a significant difference in the experimental group than in the control group (p < 0.05). There was a significant difference between the pre-test and post-test scores for all variables in both groups (p < 0.01). The results of this study show that 1 Hz rTMS application to the cerebellum is safe and feasible and may have beneficial effects on the balance function of stroke patients with posterior circulation dysfunction.

The photoneutron ray and photoproton ray occur according to the use of the high-energy electromagnetic radiation of LINACs. Here, when measuring the photoneutron ray, the measurement of the photoproton ray is added due to the characteristics of the measurement instruments for neutrons, so the reliability of the measurement value is low. Therefore, in this study, the self-manufactured solenoid was used to measure the photoneutron and photoproton rays, and the calculation formula using a reaction cross-section was applied to verify reliability. For the 10 MV LINACs and 15 MV LINACs, the proper conditions of the solenoid were evaluated for their application, and for distances of 80 cm, 100 cm and 120 cm from the source to the measurement instrument, the photoneutron dose value and the sum value of the photoneutron dose and photoproton dose values were read according to the installation of the solenoid in the radiation field of 5 × 5 cm², 10 × 10 cm² and 15 × 15 cm². In addition, the calculation formula according to the reaction cross-section was applied to derive a nuclear reaction process number for the test conditions, and a ratio of the photoneutron ray value on the photoproton ray value was compared. The comparison results showed that reliability within 10 % was verified, and in the further measurement of the photoneutron ray and photoproton ray on the LINACs, the usefulness of the solenoid was verified.

Radiofrequency (RF) safety in magnetic resonance imaging (MRI) is mainly verified using the specific absorption rate (SAR) in research involving humans. Universal MRI scanners measure the distribution of the hydrogen nucleus ¹H; hence, RF safety previously focused on the single frequency at which ¹H resonates. However, MRI technology is gradually transforming into simultaneous multi-frequency (MF) RF excitation to provide significant information related to biochemical changes in addition to morphological changes. These changes necessitate close monitoring of RF safety by considering other SAR aspects. This study proposes three evaluation methods for estimating the SAR value: summation of the SAR values of individual peaks, using the SAR value of the highest individual peak, and using the peak of the combined SAR for simultaneous RF excitation under MF RF excitation. This method, which is environmentally friendly, can be applied to various approaches for evaluating the RF safety in MF MRI applications.

In the present study, we recapitulated the magnetic field and porous medium effects on the peristaltic mechanism of a Jeffrey fluid model observed between two electrically conducting eccentric annuli. The inner annulus is assumed to be rigid and to contain constant velocity across the longitudinal direction of the enclosure; the outer one is considered to be flexible and to experience peristaltic waves travelling down its walls. Moreover, the magnetic field is examined in the direction normal to the pattern in the presence of a porous medium. The flow, meanwhile, is incompressible and follows in an unsteady format. The flow’s descriptive equations are reduced by anticipation of long wave length and small Reynolds number approximations. The resulting governing equations are then handled using analytical techniques. The achieved expressions for the considerable functions are manipulated graphically to determine the influences of various appertaining parameters. Finally, the results are compared with those of previous studies to confirm the validity of the present solutions through tables and graphs. The graphs indicated that the magnetic field increases the pumping rate but that the porosity reduces it.

The dual-type GMR-SV thin films and devices with multi-turn μ-coil and PR channel for detection of red blood cell (RBC) using ion-beam deposition system and lithography process were developed and used to one biosensor. The magnetoresistance (MR) ratio of a dual-type GMR-SV device post-annealed at a temperature of 200 ℃ was 2.5 %, the magnetic field sensitivity (MS) was 0.6 %/Oe, and the coercivity (H_c) was 0.5 Oe. An AC magnetic field was generated in the vertical direction at the center of GMR-SV device using a multi-turn μ-coil. The magnetic beads (MB) coupled to the RBCs were controlled by the AC input current applied to a multi-turn μ-coil, measured as output signal as MR variation during a staying time of 0.5 s in the GMR-SV device. This result implies that the output signal of a dual-type GMR-SV device can analyze the detection state of the RBC passing through the center of a multi-turn μ-coil and PR channel.

The aim of this study is an functional magnetic resonance imaging (fMRI) investigation of the activity of the Brodmann brain areas during the viewing of 2D and 3D images. By using the 3.0 Tesla MRI system, an 8-channel SENSE Head Coil, and the ESys fMRI system in 5 adult males, 3D T1-weighted images were obtained from anatomic images. A gradient-EPI sequence was used for the acquisition of the brain functional images. The monitor was installed so that the images could be seen through a mirror located in the coil. The 3D appearance of the triangular, cubic, and hexagonal shapes were visually stimulated by the 2D and 3D images, and a pair of red–blue cardboard glasses was worn during the viewing of the 3D images. The display object is composed of 4 stimulus projections every 60 s and 4 resting periods of 20 s every 20 s. The acquired data were analyzed using the SPM-8 program. For the 2D imagery, the activation area of the brain is larger than that of the 3D imagery (p < .05). In the visual-cortex activation area, the number of clusters is larger for the 3D imagery (p < .05). It is expected that the basic data of this study will be used to analyze the effects of 3D-image contents on the areas of the human brain.

The purpose of this study was to investigate the changes of bladder volume before therapy of proton beam in magnetic field, and to estimate the target volume (PTV) margin to be considered in treatment planning. Thirty patients with prostate cancer were included in this study. Three gold fiducial markers were attached to the prostate to confirm the position of the prostate by pretreatment X-ray. The urine was completely emptied 1 hour and 30 minutes before the CT-Simulation, and the urine was confirmed by ultrasonography. The bladder was filled with 500 cc of water. Bladder volume was measured by CT scans after treatment. On the first day of treatment, 30 patients underwent the same pretreatment as in CT-Simulation, and their bladder volume was obtained using ultrasound during the 25th treatment, and compared with the treatment plan. We also investigated daytime volatility during the treatment period. The mean bladder volume ultrasonography mean (BV_USmean) was found to be 302 ± 89 ml (range: 168 ± 166 ml) −553 ml). BV_USmean was 84 % of BV_CTmean. Ultrasound-measured bladder volume was smaller than that measured by CT. The correlation coefficient between BV_USmean and BV_CTmean was 0.187 (p = 0.322). Bland-Altman analysis showed that the BV_CTmean and BV_USmean agreement ranged from −202.17 to 315.83, with an average value of 70. The mean (bias, bias) and standard deviation (precision) of the differences between the two measurements was 56.83 ± 132.14 ml. BV_CTmean and BV_USmean showed a large range of change. BV_USWeekly1-5, which was measured Weeklyly, showed a certain decrease with the treatment time, as compared with BV_CTmean. In conclusion, large changes and differences in bladder volume should always be treated with ultrasound before treatment, and the range of rectal area should coincide. Therefore, excessive radiography is unnecessary.

The purpose of this study was to investigate whether the air space formed by the normal anatomical lordosis of the lumbar spine and the table affects magnetic susceptibility artifacts in sagittal MRI images using fat suppression. Thirteen patients complaining of simple low back pain were examined using a 3.0 Tesla MR system and 12-channels dS posterior coil. T2 fat-suppressed sagittal images were examined when the knee was extended and when it was supported by a 50° tilt support. The mean standard deviation of the images when the knee support was used was 131.00 ± 19.31, and it was 220.58 ± 26.86 when the knee was extended. In conclusion, it was confirmed that the air space formed between the table and the anatomical structures due to the curvature of the lumbar spine led to uniform images because of the magnetic susceptibility artifacts.

When the high-energy electromagnetic radiation of the medical linear accelerator is irradiated in high capacity, there is a nuclide transformation due to the radio-activation. Especially for the magnet core of the bending magnet, the magnetic field strength is changed due to the nuclide transformation, and this change in the magnetic field strength is shown as the change in flux of the electromagnetic radiation. Therefore, the effect of radio-activation on the change in flux of the electromagnetic radiation according to the electromagnetic radiation dose is to be evaluated. Subjected to 7 medical linear accelerators planned for disposal, the total dosage, nuclide analysis using the spectrometer of the magnet core, flatness using the water phantom & ion chamber, and the change amount of symmetry were evaluated. As a result, the relationship of change rate in flux according to the dosage is shown in 4 % error per 1,000 Gy. As a result of applying the 1 % threshold limit by the American Association of Physicists in Medicine, TG-142 Report, the tolerated dose is 250Gy. Therefore, on the use of medical linear accelerator in the future, it is recommended to perform the flux evaluation according to the magnet core radio-activation for each 250Gy along with the existing periodical quality control.

As the demand for radiation therapy increases, an appropriate breathing training has been becoming a vital element to improve the accuracy and efficiency of radiation therapy. It is important for patients to maintain the constant respiratory cycle due to difficulties of identifying exact treatment site of respiratory organs, which move with every breath of patients (e.g. part of thorax or abdomen). In order to train the patient's periodic breathing and evaluate patient’s respiratory cycle quantitatively, we have developed magnetometer based respiratory training system. Before subject experiment, mechanical simulation was performed to evaluate stability of the developed devices. The correlation between sensor module and subjects’ respiratory motion was confirmed in the mechanical simulation, and then the possibility of measuring respiratory cycle of patients by using the magnetometer was verified through subject experiment. So, it is found that the developed device improves efficiency of breath training based on visual bio-feedback, and then general use in clinical practice is expected.

The present study evaluated surface and superficial doses delivered by high-energy electromagnetic radiation treatment in patients who received postmastectomy radiotherapy. Computed tomography was performed using an RW3 slab phantom, and hypothetical target volumes were delineated. 6MV electromagnetic radiation beams were generated with five treatment plans: 2-field 3-dimentional conformal radiation therapy, 4-field intensity-modulated radiation therapy, 7-field intensity-modulated radiation therapy, TomoHelical 3-dimentional conformal radiation therapy, and TomoHelical intensity-modulated radiation therapy. Film dosimetry was performed with Gafchromic EBT3 film for dose measurement of high-energy electromagnetic radiation. The dose profile at the surface and superficial regions (1-6 mm depth) of the phantom obtained for each treatment technique. Compared to other techniques, Tomo 3-dimentional conformal radiation therapy had the highest surface dose (47-71 %). The superficial doses of TomoHelical 3-dimentional conformal radiation therapy and TomoHelical intensity-modulated radiation therapy were > 75 %, 80 %, and 90 % of the prescribed dose at 1, 2, and 5 mm depths, respectively. For postmastectomy radiotherapy, TomoHelical 3-dimentional conformal radiation therapy and TomoHelical intensity-modulated radiation therapy had higher surface and superficial doses than linear accelerator-based treatment techniques, with a sufficient dose of ≥ 75 % being delivered to the skin region at depths of 1 mm.

To investigate the effects of task-oriented activities under the residual effect after repetitive transcranial magnetic stimulation (rTMS) on cerebral motor evoked potential (MEP) amplitude, cerebral motor evoked potential (MEP) latency in stroke patients, this study conducted an intervention program on two groups (experimental group - TIL, control groups – GRT, each consisting of 10 patients) of chronic stroke patients. The program−which was conducted three times a week for 6 weeks−evaluated the MEP amplitudes, MEP latency before and after the experiment. In an inter-group test of MEP amplitude and MEP latency, all groups showed an increase between pre- and post-test evaluations. In an intergroup examination on MEP amplitude and MEP latency, a significant difference was observed between the TIL and GRT groups.

The purpose of this study was to investigate the effect of cerebral cortex activation on bimanual task training in chronic stroke patients with or without dominant hand injury using transcranial magnetic stimulation. This study was performed on 26 chronic stroke patients who was performed the bimanual task training such as that are easy to use in daily task by dividing dominant hand affected group (n=13) and non-dominant hand affected group (n=13). To evaluate the cerebral cortical activity before and after training, we measured transcranial magnetic stimulation as the motor evoke potentials (MEP’s). There were differences in cerebral cortical activation between the treatment period and groups in the bimanual task training according to presence or absence of dominant hand on the impaired side. For the effective cerebral cortex activation of stroke patients, it is necessary to select appropriate bimanual task training according to the presence of the damaged side and dominant hand, and to take into consideration the difference in the characteristics of the right and left cerebral hemispheres acting on the motor function.

The purpose of this study is to propose the use of a beam spoiler for improving the build-up region of photon beam by using external magnetic field with a low strength of 0.5 T (Tesla) outside the human body. A home-made magnet device which can apply a transverse magnetic field to photon beam was developed. The effect of dose enhancement on build-up region was investigated by the beam spoiler-to-magnet distance (BMD), the magnet-to-magnet distance (MMD), and the magnet-to-surface distance (MSD). Build-up regions of 6 MV photon beam with and without the magnetic field were measured for the field size to 5 × 5 cm². When applying the low magnetic field with MMD of 10 cm, D_0mm, D_2mm, D_5mm and D_10mm at BSD of 13 cm and MSD of 5 cm were increased by approximately 3.2%, 3.9%, 1.7% and 0.4%, respectively, compared to the build-up of the existing 6 MV photon beam without the magnetic field. The dose reduction was 5.1% compared to skin dose for 4 MV photon beam without the magnetic field. It is expected that use of a beam spoiler in the magnet device designed in this study could provide improved dose distributions in build-up regions while maintain similar surface dose to the existing 6 MV photon beam without the magnetic field.