Los Alamos National Laboratory
IRIS

Facilities


The ISR-1 Beam Lab

This facility can provide beams of keV energy range ions, neutral atoms and electrons. It is central to the development and calibration of energy-per-charge spectrometers and ion mass spectrometers for space exploration, and also for the development of new detection and instrument technologies and materials physics applications. Its capabilities cover a broad range of beam particle energy, mass, and flux and have been used for dozens of NASA and programmatic missions.

LOCATION Building SM-40, Room W112

CONTACT Ron Harper, Mail Stop D466, Los Alamos National Laboratory, Los Alamos, NM 87545, Tel. 505-667-1747, Fax 505-665-7395, Email: rharper@lanl.gov

PERSONNEL The person in charge of the lab is Ron Harper, Ph.D., with a thesis in experimental nuclear physics. He has participated in or led the experimental development and calibration of a number of ISR-1 space instruments, including MENA, TWINS, AMPS, IBEX-HI, HOPE, ZPS HI and ZPS LO. A variety of other physicists, engineers and technicians are available.

THE ION BEAM The ion source uses microwaves to ionize gas in a small ceramic bottle, which is held at a pressure of a few tenths of a mm Hg by means of a feedback controlled leak valve. A high voltage supply fixes the ionization region at a positive voltage, and upon escaping through a small port in the end of the bottle, positive ions enter a region of voltage gradient, where the potential is reduced from the source potential to ground potential. The energy spread of the beam is 1 eV or less. The ions are essentially all of +1 charge. Source potential can be set as high as +60 kV, and the electrostatically accellerated ions enter a vacuum beam line. By adjusting the gas pressure, microwave power, and focusing of an Einzel lens, beam currents as large as a few nA can be created. The beam optics limit the lowest useful energy to about 200 eV. The beam is controlled with slits and electrostatic steering. An electromagnet creates a region of constant field through which the ion beam passes. There is typically more than one mass of ion present in the beam, and by setting the magitude and direction of the field appropriately, the trajectory of the desired mass can be given the proper radius of curvature to enter another section of beampipe at a plus or minus 30deg angle from the original direction, and thus reach either experiment chamber, while the undesired masses are eliminated. The diameter of the beam is 1-2mm, but with a 2-dimensional kHz electrostatic rastering system, the beam can be continuously scanned over regions up to 3 inches wide. By scanning over an aperture, a pulsed beam can be created. By grazing the wall of a slit, the beam can be reduced to intensities appropriate for particle-counting instruments. Beams have been made of many gases, including H+, H2+, He+, N+, N2+, O+, O2+, Ne+, Ar+, and Ne+, and by dissociating CO2, C+.

Update 04/2012: We have received funding and begun work to build a new lab with an ECR (electron cyclotron resonance) ion source, which will provide beams of multiply charged ions up to several hundred keV energies. These multiply charged beams will be relevant to the design of instruments for studying the solar wind. (proposal leader: John Steinberg)

THE NEUTRAL ATOM BEAM Under normal conditions, the ion beam is contaminated by less than 1% of neutral atoms, formed in collisions of ions with residual gases in the beam lines. But this effect can also be turned to advantage, by sending an intense ion beam through a region of relatively poor vacuum to increase the neutral production, and then electrostatically sweeping out the remaining ions. This technique can give neutral atom beams that are well focused, monoenergetic, and of sufficient intensity for the calibration of neutral atom detectors.

THE ELECTRON BEAM Ultraviolet light from an LED stimulates photoemission from a negatively charged metal surface, and these eV energy electrons are electrostatically accelerated through a grounded grid to form a collimated electron beam of up to at least 20 keV. For more information see Henderson et al., 2011. Helmholtz coils null the earth’s magnetic field, permitting electrons beams as low as 1 keV in energy. The electron gun is inside the large chamber, and can be mounted on a moveable stage so it can be positioned in front of an instrument. The beam intensity can be adjusted by varying the LED current. The beam can be as large as 2 inches in diameter, or can be apertured down as desired. Fluxes as high as a few MHz in a square cm can be produced. Traditional electron guns and an electron beam produced by scattering ions from a thin Chromium window are also available.

THE INSTRUMENT CHAMBERS Vacuum beam lines bring the ion beam into one of two chambers. The large chamber is cylindrical, 94cm long by 135cm diameter, with oil-free roughing and cryo high-vacuum pumps capable of 10^-7 torr overnight or 3x10^-8 torr after a few days. A residual gas analyzer is attached. There is also a small chamber, which is a 6-way cross made of 14-cm pipe, turbo-pumped. Both chambers have a variety of electrical feedthroughs for signals and high voltage.

INSTRUMENT MOUNTING AND POSITIONING The large chamber will accommodate instruments weighing up to 50 lb. Custom mounting plates and brackets can be quickly made by local shops, and an arrangement of motorized and computer controlled positioning stages provide a great flexibility in position and angle of beam entry into an instrument. There is a sliding translating stage mounted on the floor of the chamber, on which is attached a vertical axis rotating stage, on which in turn is attached another rotating stage whose axis is horizontal. The small chamber has an assortment of flanges with a variety of manually operated translation and rotation stages.

BEAM MONITORING A coincidence method self-calibrating Absolute Beam Monitor can be used to measure the beam intensity Janzen et al., 2006. An imaging microchannel plate produces an image of the beam profile.

INSTRUMENT CONTROL AND DATA ACQUISITION A National Instruments PXI-1042 with Labview is the basis for data acquisition. The positioners can be computer-driven and analog data can be digitized, at the desired settings, automatically. Keithley 617 electrometers and Bertan 225 High Voltage supplies can also be Labview-driven.

MISCELLANEOUS An assortment of Faraday Cups, MCPs, Channel Electron Multipliers, UV photodiodes, and photomultipliers are available for various uses. A variety of NIM electronics is available, and Multichannel pulse height, and Time-of-Flight analyses can be performed. A Class 100 clean room is nearby. Access is available to a nearby 1-10 Mev/q tandem Van de Graaff accelerator.

Please inquire for further information.


The facilities listed on this page are not intended to be a comprehensive list of facilities our team uses, but provides a sampling of information.

Comments or Questions? Email us at macdonald@lanl.gov.


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