We describe here the design, construction, and commissioning of a compact 70MeV RaceTrack Microtron.

We describe here the design and construction of a permanent magnet-based electron beam phase-shifter now operating in our 70MeV Race-Track Microtron (P. Lucas, S. Webber (Eds.), Proceedings of the 2001 Particle Accelerator Conference, Vol. 4, IEEE, Piscataway, NJ, 2001, p. 2596; L. Gennary (Ed.), Proceedings of the 1995 Particle Accelerator Conference, Vol. 2, IEEE, Piscataway, NJ, 1996, p. 807).

We have constructed a pair of Quasi-Sheet dipole magnets, each an iron box enclosing Nd–Fe–B blocks that produce a 0.486T field adjustable to ±2% and uniform to better than ± 0.05% in a 500×250×20mm3 working region. Here we describe the magnet design and construction and compare the calculated and measured fields.

Here we describe a racetrack microtron that provides electron beams at 12 energies from 4.85 to 34.2MeV with ∼150pC/bunch in ∼5ps bunches having ∼10mm mrad normalized transverse emittance. Our compact, inexpensive accelerator in addition to its external electron beams can generate electromagnetic radiation from ∼3mm to ∼0.3nm by a variety of mechanisms.

A Harmonic Double Sided Microtron (HDSM) is pres- ently under construction to increase the end energy of the three staged cw Race-Track Microtron (RTM) cascade MAMI from 0.855 to 1.5GeV. This new accelerator, scheduled to come into operation in 2004, consists mainly of two pairs of 90° bending magnets and two linear accel- erators (see Fig. 1). Special features of the HDSM are the operation of the two linacs at different frequencies, 2.45GHz and 4.90GHz, for higher longitudinal stability, and a relatively strong field gradient in the bending mag- nets for the compensation of vertical edge defocu sing. In this paper we will present the main design consid- erations and report the status of construction.

A Harmonic Double Sided Microtron (HDSM) is presently under construction to increase the end energy of the three staged cw Race-Track Microtron (RTM) cascade MAMI from 0.855 to 1.5GeV. This new accelerator, scheduled to come into operation in 2004, consists mainly of two pairs of 90° bending magnets and two linear accelerators (see Fig. 1). Special features of the HDSM are the operation of the two linacs at different frequencies, 2.45GHz and 4.90GHz, for higher longitudinal stability, and a relatively strong field gradient in the bending magnets for the compensation of vertical edge defocu sing. In this paper we will present the main design considerations and report the status of construction. L IN A C I (4 .9 0 G H z) L IN A C II (2 .4 5 G H z) 1 0 m 4 3 re c irc u la tio n s B = 1 .5 3 9 T max Ijec tio n 8 5M eV Extrac tion 1 507M eV Fig. 1: General layout of HDSM

A pulsed race-track microtron (RTM) with a maximum beam energy of 70 MeV [1] is described. This device was developed at the Research Institute of Nuclear Physics of Moscow State University (Russia) in cooperation with World Physics Technologies Inc. (USA). For this project, several new elements, including bending magnets (based on rare-earth permanent magnets) [2], a system for injection of the bunched electron beam through a compact α-magnet (also based on permanent magnets [3]), and a rectangular cavity biperiodic structure (RCBS) [4, 5], were developed. Unlike axially symmetric accelerating structures, the RCBS has small transverse dimensions and, as a result, does not present an obstacle for the electron beam traveling in the first orbit. Moreover, the RCBS possesses a quadrupole focusing with the value and sign of the focal power depending on the relationship between the size of the drift aperture and the dimensions of the microtron cavity and on the phase of the microwave field. These properties substantially simplify the RTM design and tuning. Tests, the tuning procedure, and measured characteristics of the injection and acceleration systems of the race-track microtron are described.

We designed, built, tuned, and installed in our Race-Track Microtron (RTM) a pair of Sm/sub 2/Co/sub 17/ Rare-Earth Permanent Magnet (REPM) dipoles that provide a /spl sim/0.96 T field uniform to 0.3% in the 500/spl times/250/spl times/20 mm/sup 3/ working region. By accelerating electrons through all 14 orbits to 67.5 MeV, we have negotiated the difficult 1/sup st/ orbit beam passage with its critical focusing and orbit displacement requirements, thus, proving our magnet system design.

We built an accelerating-focusing rectangular cavity biperiodic structure (RCBS) for our 70 MeV RaceTrack Microtron (RTM), which we have tested at high Radio Frequency (RF) power with an electron beam. Our structure, powered by a 2,856 MHz, 6 MW, 48-beam KIU-111A klystron, has its 50 keV, 200 mA prebunched beam injected through a rare earth permanent -magnet. We measured its exiting beam energy spectrum using a 45º bending magnet and its dimensions and emittance using its transition radiation. We obtained the 6 MeV, 100 mA beam with ~2 MW of RF power dissipated in the structure walls.

We are designing a large volume, high-precision, high-reliability 1 T dipole magnet that requires no power. This hybrid magnet uses iron to shape the gap field and permanent magnet material to excite the iron (i.e., put iron poles and surfaces onto desired scalar potentials). This structure is surrounded by an iron yoke box, thus producing the smallest size with the least cost without contaminating the environment with stray fields. To satisfy the beam optics conditions for a specific Race Track Microtron (RTM) design, the magnet has a reverse field (and potential) pole over the entire beam entrance/exit width. The scalar potentials of both the main and reverse field poles are passively adjustable (i.e., without using power) over a small range which allows the two-magnet RTM system to be tuned.

A more compact, efficient, and reliable Race Track Microtron magnet design is achieved with Permanent Magnet Material and iron poles and yokes. In analytical design calculations we represent the PMM with magnetic charge sheets and permeabilities of the order 1.03-1.1 to obtain values for the geometry, amount and placement of iron and PMM, and so on. In the following detailed analysis/design, we use finite element codes. Our magnet is a PMM-excited iron box-pole structure, with slots for the RTM beams and a reverse potential/field pole at the entrance/exit to obtain the required fringe field distribution. Iterating with beam dynamics simulations, we find the pole dimensions, position, and reverse pole potential that provide beam focusing and allow the accelerating structure to be cleared