The 200 MeV electron linac as a driver of the Intense REsonant Neutron source (IREN) is being created at Frank Lab of Neutron Physics (JINR). IREN being a new neutron pulse source for time-of-flight spectrometers, should combine a high average intensity with a short pulse. The operating neutron source, the IBR-30 facility, consists of the LUE-40 linac (with an energy of 40 MeV, a pulse current of 0.3 A, a pulse duration of 1.8 sec, and a repetition rate of 100 Hz) and a neutron multiplication target (with a gain of 200). The resulting intensity of the neutron flow is about 4.51014 sec-1 and the pulse duration is 4 sec. In the IREN project, a decreasing the neutron pulse duration by at least in one order is proposed. It follows that the target multiplication should also be reduced by the same order, and the average power of the new linac beam should be significantly greater than that of LUE-40. The main parameters of the new LUE-200 linac are described and the current status of the facility will be addressed for this conference.
Loss of the electron beam cannot be permitted during
beam's acceleration and transportation due to the high average
power. The energy spread should be limited, mainly, by optimal
conditions for transporting the beam and focusing it on the phototarget.
This condition limits the emittance of the beam as well, because
of the high heat generation in the target body. The spot of the
focused beam cannot be smaller than 20 mm.
The scheme of the IREN facility is the following [1]. The accelerated electron beam is directed to the tungsten target-converter. The converter is the source of photoneutrons produced by the (, n) reactions. The W-converter is surrounded by a fuel plutonium (Pu239) core elements combined in groups (fuel assemblies).
For high-efficiency neutron production in the phototarget, the energy of the accelerated electrons must be greater than 60 MeV. The upper limit for the electron energy is determined by necessity to locate the accelerator in an existing building and hence, by the maxim achievable acceleration gradient.
The basic project of the accelerator was performed by A.Novokhatsky team (Novosibirsk) [2]. The use of 5045 SLAC klystrons [3] should provide the continuous operation regime of the facility. Finally, the main parameters of the IREN facility is shown in Table 1, in comparison with those of IBR-30 [1].
As the neutron pulse duration is, mainly, determined
by the multiplication time, the electron pulse duration is chosen
to be 0.3 sec.
Table 1
| Facilities | ||
| Neutron integral yield, n/s | ||
| Fast neutrons pulse duration, ns | ||
| Neutron multiplication gain | ||
| Electron Linacs | ||
| Electron beam energy, MeV | ||
| Beam average power, kW | ||
| Electron pulse duration, ns | ||
| Beam pulse current, A | ||
| Repetition rate, Hz |
The repetition rate of the pulses should be limited by the existing experimental conditions and must be less than 200 Hz.
The IREN project, including LUE-200, is realized
by the efforts of a number of research and science centers, both
from Russia and abroad. The accelerator sections, the buncher,
SLED cavities, and some elements of the RF gun will be provided
by the Budker Institute of Nuclear Physics (BINP), Nobosibirsk.
The RF feeder has been designed and its manufactured is almost
by the Moscow Engineering Physics Institute and ISTOK company
(Moscow). The 5045 klystrons, with accessories and RF loads, will
be provided by SLAC. The klystron modulators supplied by Yerevan
Physics Institute are upgraded to the required parameters with
the help of the Russian Institute of Powerful Radioconstruction.
The vacuum equipment designer and manufacturer would be VACUUM
PRAHA company. The target-converter have been designed by Science
Research & Design Institute for Energy & Technology [4].
The focusing system and other elements of the transport channel
will be provided by JINR.
The IREN project assumes the new facility will be positioned of in the building of the now-operating LUE-40 & IBR-30 JINR neutron source (see Fig. 1). The main elements of the LUE-200 accelerator and multiplying target will be placed in the three levels of the building [5]. The area of each level's is approximately 100 m2.
The electron gun, buncher, first accelerating section, and 5045 klystron with its modulator, will be placed on the second level. In the same area all DC power supplies for the focusing system should be mounted. The second accelerating section is under the first one. The 700 mm long diagnostics units will be located after the electron gun, between the accelerating sections and before the target. The second klystron with a modulator will placed on the first level.
The electron beam will be transported from the second
accelerator section to the target throught a 12 m long
drift channel.
A pulsed electron beam is emitted by the grid-controlled
electron gun having 12 mm diameter oxide thermocathode.
The electron gun developed by BINP for the -factory injector [2]
was used as a prototype of the electron source for IREN linac
The design of the gun advanced for the vertical arrangement is
shown in Fig. 2; the main beam parameters are presented in Table
2.
Table 2
| Electron energy | |
| Peak current | |
| Pulse duration | |
| Repetition rate | |
| Emittance | |
| Time jitter | |
| Energy spread |
The cathode heater and control unit of the gun are
placed into a high presure tank under a high voltage cathode potential
and fed by a coaxial ferrite HV transformer (100W x 200kV).
The control block is triggered with an optical channel. The basic
elements of the electron gun are being made by BINP and JINR.
The accelerating structure of the LUE-200 consists of the buncher and two accelerating sections. It was initially designed for the -factory injector at BINP. Each section is powered by a 5045 SLAC klystron with a SLED system. The length of the accelerating section is 3030 mm, so the acceleration gradient is greater than 35 MeV/m. The accelerating section and buncher is now being manufactured by BINP (Novosibirsk).
All RF components and vacuum equipment will be put
together and certified at the IREN Full-Scale Test Facility (FSTF)
[6]. At the present time the power supply for FSTF has been put
into operation, the M-350 klystron modulator [7] is being tuned,
and the SLAC 5045 klystron is being prepared for installation.
FSTF program includes also RF and vacuum processing, the dark
current measurement and development the RF diagnostic equipment
for IREN. A numerical simulation of the IREN dark current is performed
at this conference [8].
The focusing system should provide electron beam transport from 200 keV to 200 MeV. This system consists of two parts. In the first, where the beam energy is relatively low, a solenoidal focusing is used. In the second one, the beam is focused by quadrupole lenses.
The solenoidal focusing system is optimized to completely accept the beam from the gun and to compensate for the space charge influence at the bunching step and at initial stage of acceleration.
Transportation of the beam after the first acceleration section (where the beam has an energy above 100 MeV) to the target is performed by nine quadrupole lenses.
The design of the focusing system elements has already
been completed. The power supplies of the are under construction.
The main elements of the target are shown in Fig.
3
The Be-scatterer is placed before the tungsten target
to increase the size of beam spot. The W-converter is cooled by
gaseous He. The vacuum space is separated from the helium one
with thin stainless steel foil. The temperature of this foil,
as well as rhe temperature of the W-target, is controlled by a
set of thermocouples. Recently, this scheme was investigated experimentally
on the base operating facility, IBR-30. The thermal regime of
this Be-W target as well as its neutron-production ability were
measured [9].
Three beam control and diagnostics units will be mounted at the linac. Each unit contains beam current and position monitors, a beam scraper and a profile monitor.
The accelerated beam energy and energy spread should be monitored with a spectrometer. The use of a magnetic spectrometer does not appear to be optimal because of the high average intensity of the electron beam. We are we studying now an opportunity to use non-destructive methods for advanced on-line beam diagnostics. Since the undulator output wavelength is a strong function of the beam energy the wavelength shift will be caused by energy shift. Observation of the optical transition radiation could provide information about beam size, emittance, etc.
The combination of high average power and high accelerating
gradient cause us to pay additional attention to the thermostat
system. The just-performed modernization of the existing thermostat
scheme of the LUE-40 could be considered as a preliminary experiment.
The accelerator section temperature vs. time dependence is shown
in Fig. 4. To test the stability of the system, the temperature
mode was changed from 40.0C to 39.0C at the moment
t1. At the moment t2 the temperature
regime was returned to its steady state 40C. Finally the
thermostat system should be verified at the IREN Full-Scale Test
Facility (FSTF) [ 6].
The IREN's team nearest plans are the equipment manufacture
and adjustment of the IREN RF full-scale test facility.
The authors thanks to Mrs. A. Shaeffer for her help
in preparing this report.
[1] IREN Project. Intense Resonance Neutron source. Compiled by A.K. Krasnykh, V.L. Lomidze, A.V. Novokhatsky, Yu.P. Popov, W.I. Furman. Frank Laboratory of Neutron Physics, JINR, Dubna, 1994.
[2] Linear Accelerator for Intense Resonance Neutron Source (IREN). A. Novokhatsky et. al., in Proceedings of the 2nd Workshop on JINR Tau-Charm Factory, p. 197, D1,9,13-93-459, Dubna, 1994.
[3] M. Allen et al. Performance of The SLAC Linear Collider Klystrons. SLAC-PUB-4262, March 1987.
[4] I.T. Tretiakov, V.S. Smirnov, V.L. Lomidze, V.V. Melikhov, A.D. Rogov. Technical Report of Science Research and Design Institute of Energo-Technic on the Multiplying Target for the IREN Project (First Stage), Moscow, 1994.
[5] IREN Status: New Electron Linac Driven Intense Resonance Neutron Source. Proc of 1995 Particle Accelerator Conference. May 1-5, 1995, Texas, to be published.
[6] V. Antropov, S. Dolja, A. Kaminsky, A. Krasnykh, E. Laziev, V. Pjataev, V. Shvets, A. Sumbaev. IREN Test Facility at JINR, (this conference).
[7] G.M. Kuperman et. al. - Pulse Modulator M-350 for the SLAC 5045 Klystron, St. Petersburg, 1995, (unpublished).
[8] A. P. Ivanov, A. K. Krasnykh - Neutron Flux Generated by IREN Linac Dark Current, (this conference).
[9] V.L. Lomidze, private communication. JINR, Dubna, 1996.