Nietz Vladimir nietz at
Mon Feb 5 23:51:04 CST 1996



 SNIM-2 is intended mainly for carrying out studies which are impossible to 
perform at steady state reactors, namely:
1) magnetic structure of phase states induced by very high magnetic field,
2) dispersion relations for the magnetic excitations of phase states induced 
by very high magnetic field,
3) kinetics of the first order transitions induced by magnetic field. 
 SNIM-2 consists of two essential parts: 
1. NS-3 neutron spectrometer for diffraction and inelastic coherent scattering 
(in last case a single crystal sample is disposed in white beam of neutrons 
and the scattered beam is monochromated by single crystal).
2. Magnetic pulse installation IMU-2. 
 NS-3 is located at a 30 m distance from the moderator of the pulse reactor 
IBR-2. The thermal neutron beam is conducted to the center of NS-3 through 
a bent mirror neutron guide filled with argon gas. 
The neutron flux density at the sample (in the center of NS-3) is equal to 
                                                        4x10^6 n/(cm^2*sec)
Practically available neutron wavelength range:                  0.85 - 15 A
The distance between the sample and the detector about                   2 m
The frequency of a repetition of the reactor flashes               5 per sec
Sample temperature (currently available)                          30 - 370 K
The temperature inhomogeneity within the sample volume and the precision of 
temperature stabilization                                        0.5 - 1.0 %
The magnetic field pulses have a sinusoidal waveform of one - half period. 
The duration of the pulse (at its base)                       0.5 - 5.0 msec
Maximum pulse amplitude with the use of currently available magnets in exten-
ded measuring runs                                                   200 kOe
The frequency of repetition at the amplitudes 
                           up to 120 kOe                           5 per sec        
                           up to 200 kOe:                        5/3 per sec
Maximum sample volume in the case of low - T measurements:          0.4 cm^3
The inhomogeneity of the magnetic field within a 0.7 x 0.7 x 0.7 cm^3 sample 
volume is                                                                1 %
 It is  possible to use magnets with greater volume for the sample and cor-
respondingly with better homogeneity of the magnetic field. 
 The registration of neutron scattering is done in the horizontal plane. 
The measurements with vertical and horizontal field direction are possible. 
In the former case the range of the possible angles of scattering is equal to
                                                             10 - 170 degree
in the latter one:                                160 - 170 , 85 - 95 degree
The accuracy of the field pulse amplitude repetition is in the limits of 0.4 %
The form of the pulses is measured with the same  precision. The time resolu-
tion in measurements  of transition  processes: (depends on the wavelength of 
neutrons)                                                          4 - 6 mks
Capacitance of bank                                                   6.0 mF
Maximum voltage                                                        10 kV
Maximum storage energy                                                300 kJ
Resolution at measurement of inelastic neutron scattering             3 - 4%
We present below the verdict of the Programme Advisory Committee for Condensed
Matter Physics.

(Chairman of Committee: G.Pepy (LLB,Saclay,France), 
members: L.Cser (ISSP,Budapest,Hungary), B.Goschitsy (IMP,Ekaterinburg,Russia),
J.B.Forsyth (ISIS Facility,RAL,Chilton,UK), S.Rapeanu (NAAE,Bucharest,Romania) 

From: RECOMMENDATIONS of the Programme Advisory Committee for Condensed Matter 
Physics, 4th meeting, 13-14 November 1995.

"14. SNIM. The PAC recognized that the SNIM instrument provides a unique high 
magnetic field sample environment, but that it is of limited interest to out-
side users. To open the spectrometer to new fields would require a major in-
vestment which FLNP cannot afford now. Therefore the PAC recommend that SNIM 
be closed after the experimental time awarded in the last experiment selec-
tion round. The PAC advises FLNP to charge this highly qualified team to con-
struct the magnetic field facilities at the small angle scattering spectrome-
However, in face of this, our opinion is:
 1. If the SNIM-2 will be closed, only one facility, which permits diffraction
measurements with pulsed magnetic field (up to 200 kOe), remains, it is MRP 
diffractometer in KEK, Japan, on the spallation source of neutrons. This faci-
lity delivers significantly to SNIM-2, as on the neutron intensity (at least 
on two order less then on SNIM-2), so on technical characteristics of the mag-
netic facility. 
 2. The cost of SNIM-2 is 2.5-4 mln.$. 
For the comparison: The cost of the superconductive magnet with a field 80 kOe
is about 80,000 $ only.
 The  IMU-2 facility (without the neutron spectrometer) covers the hall with 
area of about 150 m^2
 SNIM-2 complex is maintained by only four specialists: V.Nietz - head of the 
group, physicist, D.Georgiev - responsible for IMU-2, G.Varenik - responsible
for NS-3, S.Oleynik - young physicist.
 3. At the present the spectrometer is entirely applicable for the following 
measurements with magnetic field:
 a) diffraction on the single crystals and
 b) inelastic scattering at investigations of dispersion curves with the sam-
ples of volume up to 0.4 cm^3.
 These directions are fully insured by the proposals on the physical measure-
ments as from the group which operate the spectrometer so and from the exter-
nal users. The fulfillment of these measurements does not need the additional
financial investments. 
 4. The additional expense of the labour hours and the exchequer could be ne-
cessary only for the development of the technical  characteristics of SNIM-2. 
These works can be come to the following two points:
 a) Amplification and producing the new helium cryostat, which will permit to 
pull down the minimum temperature of the sample up to 10 K and increase the 
volume of used single crystal samples at the measurement of inelastic scatte-
ring up to 3-5 cm^3.
 b) Accomplishment of producing and the adjustment of the Rectangular Pulse 
Generator (the field pulses with a duration to 300 microsecond, a duration of
the pulse front about 2-3 microsecond, with amplitude up to 20-40 kOe). This 
project is externalized already on 60-70 %. The Rectangular Pulse Generator  
will permit to considerably extend the spectrometer capability for the inve-
stigation of transition processes in magnetics, in particular, for studies 
of the role of a magnetic dipole-dipole and spin-lattice interactions in a 
relaxation processes. 
 5. From 12 spectrometers which are in Condensed Matter Division, FLNP, 
SNIM-2 is the single which actualizes entirely the advantages of the pulsed 
neutron source, and permits to fulfil the measurements on the condensed matter 
which are impossible on the steady state reactors. Let us note that the 
maximum magnetic fields at using superconductive magnets with neutron 
scattering are about 100 kOe. It is known only two such magnets with the 
field up to 120 kOe. 
  Therefore, the liquidation just of SNIM-2 is absurd act.
  A future destiny of SNIM-2 depends on the opinions of scientific community.
Your opinions about necessity or unnecessity of SNIM-2,
your proposals to perform physical investigations with SNIM-2 spectrometer 
are welcome and should be sent to the following address: 

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