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At MIT, development of electron accelerators for research in nuclear physics goes back to 1951 when a 17 MeV linac was constructed by the Laboratory for Nuclear Science and Engineering and the Research Laboratory for Electronics. As a research tool, this machine was used for over a decade primarily for a long and productive series of photofission and photoneutron experiments. By the early 1960's, however, it was clear that further experimental progress required electron beams of higher energy, current and precision. A formal proposal was submitted in 1964 to the U. S. Atomic Energy Commission and Congressional authorization for construction funding was granted in 1966.

In 1967, with the assistance of Massachusetts Congressman William H. Bates, then on the Joint Committee on Atomic Energy, MIT acquired the present site in Middleton.Permission to proceed with actual construction was obtained in the same year. A comprehensive review of scientific priorities was undertaken in the 1967 Summer Study at MIT and a decision was made to devote available funds to the development of a high resolution electron scattering facility with a single spectrometer. From the outset, the Energy Loss (dispersion matching) Spectrometer System (ELSSY) produced data of unprecedented resolution. Although the facilities for the purpose were far from ideal, in addition to high-resolution electron scattering, there has been from the earliest days a small program for photoreactions. Indeed, the first experiment conducted at Bates was on the 12C(gamma, pi-minus) reaction using an assembly of improvised equipment in the 14° experimental area. This work began with a series of table-top experiments involving the threshold production of charged and neutral pions, and was followed by the development and use of prototype spectrometers for neutral and charged pion measurements in the 14° area. These in turn have served as the basis for construction of an opening-angle pi zero spectrometer and the Medium Energy Pion Spectrometer (MEPS) now operating in the South Experimental Hall. A similar evolution of photoproton spectroscopy has occurred, which began with the early use of ELSSY, and now includes work with the One Hundred Inch Proton Spectrometer (OHIPS). The latest addition to the facility is the BigBite spectrometer, so named because of its very large momentum acceptance (~ 50%). It has been used extensively in deep inelastic electron scattering experiments, as well as the principal part of the deuteron channel for the tensor polarization measurement.

The Laboratory has been made available as broadly as possible to experimentalists throughout the nation and the world. Toward this end, a Program Advisory Committee and the Bates Linear Accelerator Users Group were established in 1972. The contributions of the users to the Laboratory's development have been continuous and essential. The Boston University group has carried a major burden in the development of the pi zero spectrometer in collaboration with Catholic University and MIT. The Rensselaer Polytechnic Institute group has participated in all phases of the charged-pion spectroscopy work, including provision under a subcontract to Bates of the quadrupoles and parts of the focal plane detector for MEPS. The Glasgow University Group has made important contributions to development of the photoproton program. A group from the University of Massachusetts developed the 180° scattering system, and construction of the polarized electron source was started by a group from Yale, CUNY and Syracuse. More recently, contributions include a gas Cherenkov counter for OHIPS, built by a group from Argonne National Laboratory and a major detector upgrade for ELSSY led by a University of Massachusetts group, with contributions from CEBAF and Saclay, an Out-of-Plane Spectrometer System , initiated by a group from the University of Illinois, and a Focal Plane Polarimeter for OHIPS, built by a University of Virginia and William & Mary collaboration. A major new capability is currently being added in the South Experimental Hall. This device, the Large Acceptance Spectrometer Toroid (BLAST) , is a large acceptance detector tailored for the full exploitation of spin observances in electromagnetic processes. Click here to see other notable milestones in the development of the Bates Linear Accelerator.


Calendar Year
1964Proposal to AEC for 500 MeV Linac.
1966Funding of 400 MeV Linac authorized (December 1966).
  1. Middleton site acquired.
  2. Start of construction authorized by AEC-New York Operations Office (April 1967).
  3. Begin: Building construction (September 1967);
    Beam switchyard design;Center-line waveguide design (to cope with beam
    blowup problem demonstrated at SLAC).
  4. Let: Contract for transmitters (Energy Systems, Inc.);Contract for accelerator RF peripherals (SLAC).
  5. Make decision to limit experimental program to electron scattering.
  1. Let contract for accelerator waveguide (Varian).
  2. Begin design details energy loss spectrometer, ELSSY.
  3. Begin design details and specify water, vacuum, electrical systems design.
  4. Pursue Litton switchtube difficulty and design change requirements.
  1. Building occupied. Begin utilities, vacuum, water systems installation.
  2. Complete injector design and initial testing - MIT campus.
  1. Accelerator waveguide construction completed and delivered to site; begin accelerator assembly.
  2. Prototype transmitter completed, delivered to site, assembled for acceptance testing.
  3. Let contract for energy loss spectrometer work.
  4. Demonstrated pre-injector pulsed beam performance (440 keV, 4000+ pps, > 50 milliamps peak, > 20 µsec.).
  1. Transmitter prototype accepted.
  2. Begin assembly balance of transmitters; begin installation of beam switchyard.
  3. Let spectrometer hardware and power supply contracts (Lukens, Grumman, Bath Iron Works, Alpha).
  4. Demonstrate injector 7.5 MeV beam and 100 MeV accelerated beam.
  1. Complete assembly of full linear accelerator centerline; mechanical, electrical assembly of RF transmitters; implementation of basic control system.
  2. Complete basic beam transport system to straight-through 14° and Spectrometer Room beam ports.
  3. Spectrometer power supply delivered and assembled.
  4. Demonstrate 126 MeV accelerated beam (delta p/p = 0.2% for 80% of beam).
  5. Formal establishment of User's Organization (first Chairman, H. Crannell).
  1. Demonstrate 1% RF 48 hour endurance operation (170 MeV, 3 transmitter operation).
  2. Accelerator brought to 400 MeV capability in preparation for January 1974 demonstration.
  3. 14° beam line implemented and installed first phase gamma-pi experiment.
  4. Carried through horizontal assembly of energy loss high resolution spectrometer magnet and performed magnetic measurements.
  5. Installation underway of spectrometer peripherals, electrical, water, vacuum systems: spectrometer carriage, focal plane array, target chamber, remaining vacuum systems, etc., under construction.
  6. Dual PDP 11/45 computer data analysis system acquisition initiated.
  1. Brief, low duty ratio run of full accelerator, 5 transmitters, 406 MeV: ~ 1 µA beam current to 14° area.
  2. Vertical assembly of high resolution spectrometer completed.
  3. 100 hours of ~ 1 µA beam at 125 to 200 MeV energy delivered to first phase gamma-pi experiment.
  1. High resolution spectrometer operating in the "energy loss" mode achieved an unprecedented 1.1 x 10**-4 resolution.
  2. First 16O(gamma, p) data obtained.
  1. Development of vertical drift chambers for the electron spectrometer completed. The new system represented a major advance in the instrumentation of spectrometer focal plane systems.
  2. Construction completed on a fixed angle magnetic spectrometer in the 14° area for the study of the (gamma, pi±) reaction.
  1. 180° scattering facility installed and used for physics experiments.
  2. Expansion of laboratory facilities authorized.
  3. Fixed angle 250 MeV pi° detector for experiments in the 14° area.
1978Large diameter beam dumping system installed at the high resolution electron scattering facility.
  1. South Hall and new buildings completed.
  2. Authorization received to construct a beam recirculator to increase maximum beam energy from 410 MeV to 750 MeV.
  3. Authorization received by Yale to design and build the polarized source for Bates.
1980First electron beam put into the South Hall.
1981 Opening angle pi° spectrometer operational and taking data.
  1. Successful operation of the recirculator.
  2. Completion of construction of the One Hundred Inch Proton Spectrometer (OHIPS) and the Medium Energy Pion Spectrometer (MEPS).
  3. First electron scattering and pion production experiments in the South Hall.
  4. Detailed design of BigBite spectrometer started.
  1. Fabrication and installation of sixth RF transmitter begun. Rework of modulators 2 through 5 begun. These projects will increase maximum energy to 1060 MeV.
  2. Extension of utility building begun.
  3. First (e,e'p) experiment.
  1. Polarized source moved from Yale to Bates for completion.
  2. TIRUS, a Bates-developed very high speed readout system, installed on MEPS.
  1. Completion of electron scattering experiments on tritium.
  2. Completion of construction of the BigBite spectrometer.
  1. Delivery of polarized electrons for experiments.
  2. High intensity pure photon beams available on Beam Line C.
  1. Deuteron tensor polarization experiment, 2H(e,e'd), with a high power liquid deuterium target.
  2. Initiation of advanced accelerator R&D for a pulse stretcher ring.
  1. Begin construction of the South Hall Stretcher Ring (SHR) with commissioning scheduled for 1992.
  2. Installation of the Moeller polarimeter on Beam Line B.
  3. Completion of the 12C Parity Violation Experiment.
1989 Begin construction of first generation out-of-plane magnetic spectrometer system.
  1. First measurements of quasi-elastic spin response: 3He(e,e').
  2. First measurement using out-of-plane spectrometer system to obtain longitudinal-transverse interference response functions.
  3. Record high energy for an experiment (903 MeV), record high momentum transfer (42/fm**2), record low cross-section measurement (5 x 10**-40 cm**2/sr/MeV) for deuterium electrodisintegration at threshold.
  1. First measurement of fifth response function (C12 + deuteron), using polarized electrons and the out-of-plane spectrometer.
  2. Measurement of neutron charge form factor, via spin transfer to the neutron, using the neutron polarimeter.
1992 Beam successfully injected into the new Injection Line and transported through the West Straight Section of the SHR.
  1. Beam stored in SHR on first day of storage commissioning. Operation with full-turn injection of 40 µA (design maximum) demonstrated.
  2. Focal-plane proton polarimeter installed in OHIPS.
  3. Energy compression system commissioned; factor of ten easily obtained.
  1. Demonstrated resonant extraction from SHR.
  2. Began major upgrade program for linac and recirculator.
1995 SAMPLE experiment takes first data.
1996 BLAST funding approved.
  1. BLAST construction begins.
  2. Measurement of 3He magnetic form-factor to high momentum transfer
  3. Ring commissioning demonstrates 5 minute lifetime of 60 mA stored current at 750 MeV.
  4. High intensity and quality SAMPLE beam developed.
  1. Measurement of n -> Delta transition with OOPS in both pi° and pi+ channels.
  2. SAMPLE data taking on Hydrogen.
  3. First stored Beam in SHR on Internal target
  1. Over 200 mA in South Hall Ring.
  2. SAMPLE data taking on Deuterium
  1. Completion and commissioning of OOPS spectrometer.
  2. VCS experiment: uses high duty factor beam and full OOPS spectrometer.


X Ray Laser
MIT has explored the construction of a linac-based
x-ray laser user facility at Bates. more..


  • Bates EIC

  • William H. Bates Linear Accelerator
    M.I.T. Laboratory for Nuclear Science
    Massachusetts Institute of Technology