MAGNETIC FIELD MEASURING SYSTEM FOR THE RIKEN SSC SECTOR MAGNETS
H.Takeb e,I.Take shita,J.F ujita,I.Y okoyama ,T.Wada and S.Motona ga
The Insti tu·te of Physical and Chemical Research
AbstractandA pneumati c drive magnetic field measurin g system was designedof theconstruc ted. It can cover the area over 180' of the beam orbit plane
summer,
SSC. The magnetic field of the two sector magnets, construc ted by thiswas measured by this system.
1) Mechauis_mt
Field mapping area necessar y for the orbit calculat ion has a differen, whichassemblyHall
1.
Tableinshownaszonelazimutha
eachinrange
radialhas tocontains magnetic field detector s, has a radial length of 2660mm. It
to get an
clear gap spacers, and injectio n and extracti on elements . In orderof theaccurate position ning of the Hall assembly and to make a tention
assy
rotating
thetoequipped
arepistonscpneumati
threesmall,assy
rotating
radialin
20mm
and5mmmovingpistons
for each directio ns(Fig.1 ). Two
in tandem.
directio n, and two for 0. 25' and 1. 0' in azimuth are connecte dn 1s
directiolazimutha
inassembly
respecti vely. Moving time of the Hall
Table 2.
inshown
ascurrent,
eddy
theofbecause
positioneach
int
differenactual
Accordin gly, the piston control system has to know the piston'sn.
directio
each
in
meter
potentio
aby
position
Two rotary encoders( COPAL:R E-20A) and
1fJifl>~ SPACER
up-down counters indicate coarse
position of the Hall assembly .

TABLE 1 :Range and step of mapping areafor 1/8 sector(4 5°).
ZONE8#loo#2#3#4#5#601ef

t.8 STEP N810° 10° 1°10° 18° so 10ll8418° 22° 40 1022° 26° 40 . 25° 1626° 29° 30 .5o 629° 45° 16° 1°

16R.

1

Rf

t:.R

TH-DIREDTIONPIS ONSTEP Nr
151

810 3810 3000
810 3770 2960

207103770 3000
690 3690 3000

20 151

690 3690 3000
690 3690 3000

20 151

mm

nnn

mm

20 14920 15120 151mm

8=0:Magnet center line, 8i:Initial angle,
Ri=Min. radius, Rf:Max. radius.

TABLE 2:Moving time of the Hall
DIRECTION
R5mrn

TIMElsec

20mrn

l.6sec

0.25°2secSTEP(Hill & Valley)
0.25°

4sec

y:(Magnet edge)
1.00

view of the mechani cal part2.5sec(Hill & Valley)-301-2) ELECTRONICS
The system is controlled by LSI-11 micro computer (Fig, 2), Twenty setsof Hall probes ( SBV-60lsl) are mounted radially in line with pitch of 140 mm
on the Hall assembly. Their twenty outputs and other analog signals (currentmonitors etc.) are led to a relay scanner (FLUKE:2204A) and a D.V.M (8502A)
through thirty pairs of twisted cables. Sampling time of the D. V.M had to belonger than 250 ms/channel because of noisy environment in the big factory.
Reading error of the D.V.M was less than 2 ~V which corresponds to 0.6 G offield. Hall control cur~ents (200 mA) are connected in series each other andstabilized with an accuracy better than 5 x lo-5, A digital thermometer for
the Hall assembly, NMR Gaussmeter, magnet power supply and the other devices
are connected to the computer via CAMAC register.
3) COMPUTER SOFTWARE
The main part of program is written in FORTRAN and the remainders,
esp,ecially for CAMAC control, are written in Macro-assembl y language assubroutine. The application programs are developed not only in LSI-11
terminal but also in FACOM M-200 large computer, Communication between
LSI-11 and M-200 is realized using a magtape or an acoustic coupler.
At the measurement, the magnetic field is calculated using Hall calibration polynominals (5th order and one tamp. coefficient), and displayed ona digital plotter or on a colour graphic unit (OKI:IF-800). The data isrecorded on an 8" floppy disk, and the disk data is copied to magtape inorder to be processed in the large computer.
In order to reduce a systematic errors caused by a change of the Hall
prove characteristic s or by drift of some speciality, each neighbouring Hall
probe can measure at the same point by moving 140 mm radially.
Total measuring time for 45° mapping area as the Table 1 was two hours
Tli-PISTONS
and a half,

Fig.2:Schemat ic diagram of the magnetic field measuring system.
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