Abstract: A micromagnetometry system for detecting the presence of very small quantities of magnetic particles comprises a first magnetic hybrid AMR/PHR multiring sensor using a Wheastone bridge electrical configuration, a first current source, a first voltage measurement device, a set of at least one magnetic particles deposited on the first magnetic sensor and a processing unit for detecting from a set of different measured differential voltages a magnetic flux shift representative of the presence of a least one deposited magnetic particle. The micromagnetometry system comprises means for creating a magnetic excitation field HAC to make produce by each motionless magnetic particle a stray magnetic field oscillating along the time at a constant frequency ? ranging from 10 Hz to 3 KHz.

Abstract: A magnetic sensor includes an MR element and a bias field generation unit. The MR element includes a magnetization pinned layer having a magnetization pinned in a direction parallel to an X direction, a free layer having a magnetization that varies depending on an X-direction component of an external magnetic field, and a nonmagnetic layer interposed between the magnetization pinned layer and the free layer. The magnetization pinned layer, the nonmagnetic layer and the free layer are stacked to be adjacent in a Y direction. The free layer receives an interlayer coupling magnetic field in a direction parallel to the X direction resulting from the magnetization pinned layer. The bias field generation unit applies a bias magnetic field to the free layer. The bias magnetic field includes a first component in a direction opposite to that of the interlayer coupling magnetic field and a second component in a Z direction.

Abstract: In a nuclear magnetic resonance (NMR) spectrometer, a sample spins about an axis tilted at a magic angle, a corrective magnetic field generating portion produces a corrective magnetic field, and a control portion controls the operation of the corrective magnetic field generating portion. An arithmetic unit included in the control portion uses at least one of BZ(1), B1(1)e, and B1(1)o or the linear sum of at least two of them as the first-order magnetic field component of the corrective magnetic field, uses at least one of B2(2)e, B2(2)o, B2(1)e, and B2(1)o or the linear sum of at least two of them as the second-order magnetic field component of the corrective magnetic field, and uses at least one of BZ(3), B3(1)e, B3(1)o, B3(2)e, B3(2)o, B3(3)e, and B3(3)o or the linear sum of at least two of them as the third-order magnetic field component of the corrective magnetic field.

Abstract: In one embodiment, a system includes a gradient coil driver configured to supply electrical signals to a gradient coil of a magnetic resonance imaging system. The gradient coil driver includes an electronic circuit. The electronic circuit includes a first H-bridge circuit electrically coupled to a power source. The first H-bridge includes a plurality of metal-oxide-semiconductor field-effect transistor (MOSFET) switches; and a plurality of diodes electrically coupled in parallel with each MOSFET switch. Each diode of the plurality of diodes is configured to conduct current to cause zero voltage potential across a source and a drain of one of the plurality of MOSFET switches. The first H-bridge also includes a load configured to regulate currents flowing through each of the plurality of diodes and each MOSFET switch of the plurality of MOSFET switches.

Abstract: Images of two or more kinds of substances showing different chemical shifts, such as water image and metabolite image, are obtained without extending measurement time. For example, images of two or more kinds of desired substances showing different chemical shifts, such as water image and metabolite image, are obtained by one time of execution of an imaging sequence. In this execution, a pre-pulse is applied so that signals of the substances to be separated shift on the image, and magnetic resonance signals are received with receiver RF coils in a number not smaller than the number of types of the substances to be separated. An image reconstructed from the magnetic resonance signals is separated into images of the individual substances using sensitivity maps of the receiver RF coils. Then, correction is performed for returning the shifted image to the original position.

Abstract: Systems and methods for insulating superconducting magnets, such as a cryogen vessel of a magnetic resonance imaging (MRI) system having therein one or more superconducting magnets are provided. One system includes a thermal insulator having a first plurality of reflector layers and a non-deformed spacer layer between adjacent layers in the first plurality of reflector layers. The thermal insulator further includes a second plurality of reflector layers and a deformed spacer layer between adjacent layers in the second plurality of reflector layers.

Abstract: A method for designing a coil pattern, whereby the production of an error magnetic field and further an eddy current can be suppressed to improve the quality of a cross-sectional image irrespective of cylindrical cross-sectional shape of the main coil and the shield coil. The difference between the initial values of the target magnetic field and the magnetic field vector is set as a difference target magnetic field. An approximate value of the current potential vector that produces the difference target magnetic field is represented by a polynomial of an eigenvector group of the current potential. The coefficient of each of the terms of the polynomial is determined on the basis of the singular value and the eigenvector group of the magnetic field distribution.

Abstract: A system and method for combining k-space data acquired on multiple different receiver channels in a multichannel receiver is provided. One or more convolution kernels are used to combine the k-space data. Each convolution kernel is designed as the combination of one or more channel combination kernels and an alias-suppressing kernel. The channel combination kernels are designed to have a smaller sample spacing than the acquired data, and the alias-suppressing kernel is designed to suppress aliasing artifacts in stopbands defined by the sample spacing of the channel combination kernels.

Abstract: A method and magnetic resonance tomography system to generate magnetic resonance image data of an examination subject, raw imaging data are acquired from multiple slices of a predetermined volume region of the examination subject using local coils during a table feed in the magnetic resonance scanner. Image data of the slices are reconstructed on the basis of the raw imaging data. A normalization of the image data is subsequently implemented on the basis of measured coil sensitivity data of the local coils that are used.

Abstract: A method for 3D magnetic resonance imaging (MRI) with slice-direction distortion correction is provided. One or more selective cross-sections with a thickness along a first axis are excited using a RF pulse with a bandwidth, wherein a selective cross-section is either a selective slice or selective slab. A refocusing pulse is applied to form a spin echo. One or more 2D encoded image signals are acquired with readout along a second axis and phase encoding along a third axis, wherein the data long the phase encoded first and third axes is acquired with an under sampling scheme. Slice-direction distortion is corrected by resolving the position by using phase encoding.

Abstract: In a method for verifying measurements obtained from a hall effect sensor in a hall effect sensor system, the hall effect sensor is excited with an excitation current having a first value. A first measurement corresponding to a voltage output of the hall effect sensor when the hall effect sensor is excited with the excitation current having the first value is obtained. Additionally, the hall effect sensor is excited with the excitation current having a second value, the second value different than the first value. A second measurement corresponding to a voltage output of the hall effect sensor when the hall effect sensor is excited with the excitation current having the second value is obtained. Operation of the hall effect sensor is then verified based at least on the first measurement and the second measurement.

Abstract: In one embodiment a method for sensor reader calibration comprising: performing a calibration of a sensor reader wherein the calibration comprises open circuit calibration, a short circuit calibration, and a load circuit calibration, or any combination thereof in any succession; enabling connection of a pickup coil to the sensor reader to measure a sensor response; and applying a baseline correction to the sensor response, wherein the baseline correction is obtained utilizing measurements from the calibration step.

Abstract: A locator includes a base unit and a handheld unit. The base unit, which is typically stationary, includes an FSK transceiver and printed circuit antennas. The handheld unit, which is typically mobile, also includes an FSK transceiver and printed circuit antennas. The handheld unit computes at least one bearing to the base unit over multiple frequencies and transmitting antennas, processes statistics of bearing results, determines a cyclic average of the bearing results, calculates an overall variance, assesses quality of a computed bearing result based on the overall variance, and upon assessing, either displays the computed bearing result or disqualifies the computed bearing. The handheld unit computes a height difference between the base unit and the handheld unit. The height difference is calculated using altimeters within the units. Alternatively, the height difference is calculated using GPS.

Abstract: An imaging sensor system, adaptably mountable to a vehicle having a view of a target area comprising: a rigid mount unit having at least two imaging sensors disposed within the mount unit, wherein a first imaging and a second imaging sensor each has a focal axis passing through an aperture in the mount unit, wherein the first imaging sensor generates a first image area comprising a first data array of pixels and the second imaging sensor generates a second image area comprising a second data array of pixels, wherein the first and second imaging sensors are offset to have a first image overlap area in the target area, wherein the first sensors image data bisects the second sensors image data in the first image overlap area.

Abstract: A method is used to develop and maintain a user's lifetrail, which is a historical record specifying the location of the user while in possession of a mobile communication device. A mobile device determines its current location by extracting a beacon ID from a signal source and transmitting it to a remotely-located server, which accesses a look-up table to find the corresponding location of the signal source represented by the beacon ID. The location may be specified in accordance with a spatial compression technique. The server transmits the signal source location back to the mobile device so that the mobile device knows that it is located within the coverage area of the signal source. Battery power is conserved by collecting the beacon IDs when it is receiving the beacon signals for some other purpose and not necessarily solely for the purpose of determining its current location.

Abstract: A mechanism is described for facilitating dynamic client-side triangulation to determine global position of computing devices according to one embodiment of the invention. A method of embodiments of the invention includes detecting, at a computing device, first location information associated with static wireless access points. The method may further include detecting, at the computing device, second location information associated with roaming computing devices broadcasting the second location information relating to their current locations, and dynamically determining a current location of the computing device based on the first and second location information.

Abstract: Various embodiments provide a method and apparatus for determining tag location by using one or more estimated channel responses (CR) that characterize the wireless channel between the tag and one or more respective anchors. In particular, a tracking server in communication with the anchor(s) determines the tag's location based on a comparison of the estimated CR(s) with a set of stored CRs associated with the anchor(s).

Abstract: An apparatus and method is provided for real-time location estimation of a mobile station (MS) on a map of roads using non-Global Positioning Satellite location data of the MS and includes a step of determining that the MS is stationary. A next step includes assigning each raw location datum with an initial mass such that the data exhibit an attractive force therebetween. A next step includes calculating a net attractive force for all data using a distance between the data. A next step includes moving each datum a normalized step on the map in response to the net attractive force. A next step includes merging any data that are within a predefined distance on the map and adding their masses. A next step includes repeating the calculating, moving, and merging steps until there are no consecutive merges for a predetermined number of iterations. A next step includes removing any datum with a mass less than a threshold.

Abstract: A method and a system are provided which are able to utilize indirect paths of signals of UWB type to locate a wireless communication node possessed by a body. The present method and system can notably apply to cooperative body networks implementing several wireless nodes able to communicate with one another.

Abstract: A wireless device performs a transmission on a primary and auxiliary access channels to enable reception by at least three base stations. The base stations perform a measurement on the received transmission, e.g., a time of arrival of the transmission. The base stations report their measurements to a position determination entity. The position determination entity estimates geographic position of the wireless device. One method used by the position determination entity includes tri-lateralization based on the received measurement reports.

Abstract: Signals received by an array of sensing elements are processed by first positioning the sensing elements in a uniform grid of L locations, wherein each location to include or not to include a sensing element is selected during a design phase. The sensing elements are selected and grouped into subsets, wherein each subset contains one or more sensing elements, and each sensing element is a member of one or more subsets. The signals in each subset are linearly combined to produce a combined signal, which is then sampled to form an output channel, which can detect objects.

Abstract: A radar apparatus for obtaining a higher range resolution than conventional radar apparatus without increasing the bandwidth comprises a transmitter antenna that transmits a frequency modulated transmit signal having a transmit bandwidth and a receiver antenna that receives a receive signal reflected from said scene in response to the transmission of said transmit signal. A mixer mixes said receive signal with said transmit signal to obtain a mixed receive signal, a sampling unit samples said mixed receive signal to obtain receive signal samples from a period of said receive signal, and a processor processes said receive signal samples by defining a measurement matrix and determines the positions of one or more targets of the scene by applying compressive sensing using said measurement matrix and said receive signal samples. A post-processor groups together receive signal samples having a depth within the same depth bin and belonging to the same target.

Abstract: A panoramic scan radar is provided. The panoramic scan radar includes: a fixed base; a rotary base which is rotatably combined with the fixed base; a reflector which is disposed on the rotary base to rotate with the rotary base and includes a reflective surface; a laser emitter which is disposed on the rotary base to rotate with the rotary base and selectively irradiate laser beams onto a plurality of points on the reflective surface of the reflector; and a laser receiver. The reflector reflects the laser beams toward an object and reflects at least one of the laser beams reflected by the object toward the laser receiver and the laser receiver senses the at least one of the laser beams reflected toward the laser receiver.

Abstract: Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for detecting ambient audio, generating audio data based on the ambient audio, generating a first audio fingerprint based on the audio data, providing the first audio fingerprint to a fingerprint comparison engine, the fingerprint comparison engine providing a comparison between the first audio fingerprint and a second audio fingerprint, and receiving a proximity signal based on the comparison.

Abstract: First and second radar modules include channel controllers which set different frequency bands for first and second carrier waves, respectively, and first radar transmitter and receiver which transmit radio-frequency first and second radar transmission signals generated using prescribed first and second transmission code sequences and the first and second carrier waves, which receive first and second radar reflection signals produced as a result of reflection of the first and second radar transmission signals by a target, and which convert them into baseband first and second reception signals. A signal processor performs prescribed combining processing on outputs of the first and second radar modules. The first and second radar transmission signals partially overlap with each other in main beam directivity.

Abstract: A method for operation of a distance sensor emits a transmission signal as transmission radiation, reflected by an object, the distance of which is to be measured, as reflection radiation, and received as a reflection signal. The reflection signal and a reference signal that occur at a receiver input are regulated to a predetermined ratio. The distance is determined during the regulation process. An auxiliary transmission antenna emits an auxiliary transmission signal as auxiliary measurement radiation, directly toward a reception antenna. Microwaves are used as the transmission and auxiliary transmission signals. The reception antenna receives the reflection radiation reflected by the object and passes it on to the receiver input as a reflection signal. The reception antenna receives the auxiliary measurement radiation directly and passes it on to the receiver input as an auxiliary reception signal which is evaluated as a reference signal when measurement radiation emission is suppressed.

Abstract: Various embodiments presented herein relate to identifying one or more edges in a synthetic aperture radar (SAR) image comprising a plurality of superpixels. Superpixels sharing an edge (or boundary) can be identified and one or more properties of the shared superpixels can be compared to determine whether the superpixels form the same or two different features. Where the superpixels form the same feature the edge is identified as an internal edge. Where the superpixels form two different features, the edge is identified as an external edge. Based upon classification of the superpixels, the external edge can be further determined to form part of a roof, wall, etc. The superpixels can be formed from a speckle-reduced SAR image product formed from a registered stack of SAR images, which is further segmented into a plurality of superpixels. The edge identification process is applied to the SAR image comprising the superpixels and edges.

Abstract: A radar sensor for a motor vehicle has at least one antenna arrangement for transmitting and receiving radar signals and a controller for controlling the operation of the antenna arrangement. The controller evaluates the received radar signals. The controller also operates the antenna arrangement to transmit and/or receive messages in a car-to-car communication.

Abstract: Provided is a parking assistance device that can obtain information regarding the height from a parking road surface of an object without acquiring height information of an object in advance. The parking assistance device includes: an emission unit configured to emit ultrasonic waves in at least an outward lateral direction of a vehicle; a reception unit configured to receive reflection waves from an object reflecting the emitted ultrasonic waves; and an object determination unit configured to receive the reflection waves from an object existing on a far side of a target parking region as the vehicle enters the target parking region, and determine a feature relating to the height of the object based on a change in a detection state of the object, which was specified based on the obtained reflection wave data.

Abstract: In a method and system for inspecting the condition of a structure, the structure is scanned with a three-dimensional (3D) scanner. The 3D scanner includes a sensing system having one of a radar sensing device or an ultrasonic detection device. The sensing system detects 3D information about a subsurface of the structure, and the 3D scanner generates 3D data points based on the information detected by one or more of the radar sensing device and the ultrasonic detection device. A 3D model is constructed from the 3D data and is then analyzed to determine the condition of the subsurface of the structure.

Abstract: A detector (110) for determining a position of at least one object (112) is proposed.

Abstract: In some implementations, a tightly-coupled elevation-assisted location estimate can be calculated based on digital elevation model (DEM) elevation measurements and global navigation satellite system (GNSS) data. The DEM elevation measurements and GNSS data can be provided as input to an estimator (e.g., a Kalman filter) to calculate an estimated geographic location of a mobile device. In some implementations, DEM elevation data can be filtered before being provided to the Kalman filter for estimating the geographic location of the mobile device. The DEM elevation data can be filtered in response to detecting bridge and/or tunnel events that indicate that the DEM elevation data does not accurately represent the actual elevation of the mobile device.

Abstract: A system for determining a position of a device, the system including a receiver module, a communication module, and a location determining module. The receiver module respectively acquires signals from a plurality of satellites totaling in number less than five. The communication module obtains, from a server, via a cellular network or a wireless network, ephemeris data corresponding to one or more of the plurality of satellites. The location determining module determines the position of the device based, at least in part, on (i) the signals acquired from the plurality of satellites, and (ii) the ephemeris data corresponding to the one or more of the plurality of satellites obtained from the server. The position of the device is further determined without a priori knowledge regarding the position of the device.

Abstract: An information processing apparatus including a positioning unit that determines a position of the information processing apparatus based on an external signal; a sensor unit that detects a change in position of the information processing apparatus; and a processing unit that measures, according to a change in position detected at the sensor unit, an amount of displacement of the information processing apparatus from a first time when the positioning unit starts to determine the position of the information processing apparatus to a second time when the positioning unit completes determining the position of the information processing apparatus; and identifies a position of the information processing apparatus at the first time by compensating the position of the information processing apparatus determined by the positioning unit at the second time with the amount of displacement of the information processing apparatus.

Abstract: A method for colorimetric radiation dosimetry includes subjecting an aggregate including a polymeric matrix having uniformly dispersed nanoparticles therein to radiation. The aggregate is soaked in a solution selected to dissolve decomposed pieces of the polymeric matrix to release into the solution nanoparticles from the decomposed pieces. Color of the solution is compared to a reference to determine a dose of radiation based on number of liberated nanoparticles.

Abstract: An X-ray detector is provided with a plurality of modules each having a plurality of detection elements each composing a pixel, in which the detection elements convert incoming radiations to electric data depending on amounts of the radiations. The plural modules are mutually adjacently arranged on the same surface with a gap having a known width formed therebetween, such that the modules are arranged along at least one of a first X-axis and a first Y-axis, wherein the radiation detector is given a scan direction which is set along one of the first X- and Y-axes and the first Y-axis is perpendicular to the first X-axis. The plural detection elements of each module are two-dimensionally arranged along a second X-axis and a second Y-axis which are set obliquely to the first X-axis and the first Y-axis respectively and which are perpendicular to each other.

Abstract: A crystalline scintillator body includes a plurality of first crystalline phases and a second crystalline phase in which the plurality of first crystalline phases are present. Each first crystalline phase is a columnar crystal made of a material containing at least one of CsI and RbI, and the second crystalline phase is made of a material containing NaNO3.

Abstract: An apparatus for detecting a radiation source includes a collimator configured to have an optical path for converging radiation formed therein, a radiation sensor provided at the end of the optical path and configured to measure the intensity of radiation incident on the optical path, a rotation driving unit connected to the collimator and configured to rotate the collimator up and down and left and right, movement means configured to move the collimator and the rotation driving unit along the surface of land, a position tracking unit provided within the collimator and configured to track a current position and to measure a distance moved by the movement means, and a radiation position information processing unit configured to obtain direction information and information about the distance to the radiation source based on a maximum intensity of radiation, measured by the radiation sensor, and the movement distance.

Abstract: An apparatus for conducting a marine seismic survey is disclosed. The apparatus includes a plurality of sensors configured to measure water pressure, a horizontal derivative of the pressure in two orthogonal directions, vertical particle velocity or acceleration of the water, and a horizontal derivative of the vertical particle velocity or acceleration in two orthogonal directions.

Abstract: A seismic sensor detects a characteristic of a medium during a seismic survey. The seismic sensor includes a casing; a magnet located inside the casing; a coil assembly located inside the casing, wherein the coil assembly moves relative to the magnet; and a temperature-sensitive device connected to terminals of the coil assembly and configured to improve the damping. The magnet and the coil assembly produce some intrinsic damping and the additional damping introduced by the temperature-sensitive device is selected to counterbalance the temperature-dependent intrinsic damping so that a phase of a recorded seismic signal is compensated for temperature induced magnetic field changes.

Abstract: A passive method for exploring a region below the surface of the earth. The method comprises using a plurality of sensors to obtain seismic data obtained by recording ambient seismic interface waves in a frequency range whose lower limit is greater than 0 Hz, and whose upper limit is less than or equal to substantially 1 Hz. The sensors may be sensitive to three orthogonal components. Recordings may be made simultaneously by all sensors and normalization of data is unnecessary. The sensors may be moved and clean data may be selected. Local dispersion curves may be determined to improve vertical resolution. The data are processed so as to obtain a measure of the energy in a frequency band within the frequency range. The energy measure may be calculated by integrating the spectrum in the frequency domain over a desired frequency range. The resulting calculated energy provides information about the region of the earth being explored.

Abstract: Described herein are various embodiments of methods and corresponding hardware and software configured to permit the vicinity around and/or near a well to be imaged, where the well is being subjected to, or has been subjected to, fracking operations. The methods and corresponding hardware and software permit the generation of images of near-well fractures or faults resulting from the fracking.

Abstract: A marine vibrator may include a containment housing, a sound radiating surface, and a compliance chamber. The compliance chamber may include a compliance chamber housing, a non-linear linkage assembly, and a low pressure chamber. The compliance chamber housing may define at least a portion of a compliance chamber internal volume having a compliance chamber internal gas pressure. The low pressure chamber may comprise a low pressure piston and a low pressure chamber housing. The low pressure chamber housing may define at least a portion of a low pressure chamber internal volume having a low pressure chamber internal gas pressure. The low pressure piston may be configured to move in response to a pressure differential across the low pressure piston such that a resonance frequency of the marine vibrator may be changed.

Abstract: A seismic spread is constructed having an arrangement of towed components to be neutrally buoyant in water when towed in a seismic survey. The towed components at least include streamers and paravanes. Immersed weight and drag of the towed components is determined, and drag forces versus buoyancy required to neutrally buoy the towed components at at least one tow speed in the water is calculated based on the determined weight and drag of the towed components. Floatation is configured for the seismic spread based on the calculated drag forces versus buoyancy; and the arrangement of the towed components in the seismic spread is constructed with the configured floatation.

Abstract: An acoustic energy source that amplifies the stroke of electrically reactive elements having a body with an elastomer filled first cavity, a highly incompressible fluid filling a second cavity, and bores intersecting the second cavity that extend radially outward from second cavity. Quill assemblies in the bores each include an electrically reactive element and a tip projecting radially into the second cavity. A dynamic yoke having a lower portion projecting into the second cavity, and a pressure disk projects into the first cavity. A diaphragm on the body and on a side of the dynamic yoke opposite its lower portion. A fluid forms a film between the dynamic yoke, static yoke and quill tips. Applying alternating electricity reciprocates the tips into and out of the second cavity; reciprocates the dynamic yoke and diaphragm to generate the acoustic energy.

Abstract: An embodiment of a method of estimating a property of an earth formation includes: disposing an acoustic tool in a borehole in an earth formation, the acoustic tool including an acoustic source and an acoustic receiver, the borehole having an axial direction; transmitting an acoustic signal into the borehole by the acoustic source, the acoustic signal having a selected frequency and transmitted at a propagation angle relative to the axial direction, the propagation angle selected to excite a desired guided flexural wave mode that propagates along a surface of the borehole; detecting an received acoustic signal by the acoustic receiver; calculating, by a processor, an incident angle of the received acoustic signal, the incident angle relative to the axial direction; measuring a shift of the propagation angle based on the incident angle; and estimating a property of the formation based on the shift of the propagation angle.

Abstract: An acoustic navigation system includes a vessel and an interrogation unit towed behind the vessel below the surface of the water, a tail acoustic transponder trailing behind the interrogation unit, and a pair of surface acoustic transponders towed behind the vessel on the surface of the body of water. The interrogation unit generates an acoustic interrogation signal and receives responses from each of the tail acoustic transponder and the surface acoustic transponders from which it triangulates its position. The surface acoustic transponders may further include GPS receivers for receiving positioning information from GPS satellites. Additional acoustic transponders on instruments located on the floor of the body of water respond to the interrogation signal to allow triangulation of the location of the instruments.

Abstract: A directional antenna, system and method are provided. The methods include acquiring a plurality of data pairs, each data pair comprising an induced signal at a receiver and a corresponding toolface angle using a tool including at least one antenna assembly, as described herein. It further discloses a method to generate a measurement containing information about the directionality of the formation by calculating areas of an induced signal function approximated by the plurality of data pairs.

Abstract: A well logging instrument includes a radiation generator and a high voltage power supply functionally coupled to the generator. The generator and the supply are longitudinally separated by a distance sufficient for emplacement of a radiation detector. At least a first radiation detector is disposed in a space between the generator and the supply. The instrument includes an electrical connection between the supply and the generator.

Abstract: A radiation generator includes an ion source region, and an acceleration column downstream of the extractor electrode and in fluid communication with the ion source region. The ion source region and the acceleration column contain an ionizable gas. A vacuum pump pumps the ionizable gas from the acceleration column to the ion source region such that a gas pressure in the acceleration column is less than a gas pressure in the ion source region.