Performance of the Beam Position Monitors of the TRISTAN Accumulation Ring
Takao IEIRI, Hitoshi ISHII, Yoshihiko MIZUMACHI,
Atsushi OGATA, Tsumoru SHINTAKE and Masaki TEJIMA
National Laboratory for High Energy Physics
Oho-machi, Tsukuba-gun, Ibaraki-ken 305 JAPANsignificant errors come from electrical noises,
setting of the monitor pickups
geometricalelectricalline,
beam
thetorelativeandchamber
the monitorofcalibration
characteristics of the electronics such as
offset, drift and nonlinearity,

Abstract
Eighty-three sets of electrostatic beam
each set made of four disk
position monitors,
electrodes, are welded on the beam duct pieces
All ofof the TRISTAN Accumulation Ring <AR),
their calibration maps are measured on a test
they
After assembly of the beam duct,
bench.
are positioned close to most of the quadrupole
Their precise positions relative tomagnets.
aby
line are then measured
beam
theTheirmicrocomputer-controlled touch sensor.
ARtheinsatisfactory1s
performance
operation.

The following is our approach to get highusage of a common
precision of the system;
electronics circuit for a block of monitors,
detection by a double superheterodyne
signalselection of copper tube cables forcircuit,the beam signals, development of calibration
systems with high precision and the preparationof effective maintenance softwares.The layoutof the whole system is given in Fig.1.

1. Introduction
The design layout of the position monitor
system of the AR has been reported in theSince that time wepreceding (4th) Symposium.
construction period
entered into the actualand the system has been completed just beforeThe
commissioning at November 1983.
thevacuum
parts of the system areessential
transmission
chambers with pickup electrodes,
cables and coaxial switches, electronics for
CAMAC modules andprocessing,beam signal
hardwarefor data analysis andsoftwares
outline of these has beenThe
control,
described before and will be briefly commented
in this paper [1],Basic requirement for the position monitor
the beam orbit measurement of 0.1 mm
isprecision at the location of every quadrupole
magnet,This is not an easy goal at all since
factors contribute to the errors;
var1ous2. Detection of beam signal
2.1 Structure of the beam monitor chamber
We adopted the electrostatic pickups forSince the pulse
the position monitor system.
width of AR beam is of the order of 100 ps, thedimension of the pickup electrode should beabout 3 em.
Beam ducts of AR are made of aluminum tube
manufactured by extrusion process and thejoined by welding without
whole ducts are
pickuptheAs the result,flanges[2J.
connectors (SMA type) of the position monitors
came to be directly welded on to the beam
The cross section of the beam duct is aducts.
race track shape in the bending regions and isa circular shape in the colliding regions.
pickuphave two kinds of
weTherefore,
structures as shown in Fig. 2(a) and 2(b),coaxial~~==::::::~t:~ relays(a)(bl colliding section

bending section

Fig. 2

Pickupelectrodes

2.2 Signal Processing

Fig. 1

type 3dB attenuater is set
A coaxial
A semirigid
directly on to each SMA connector.
atocable leads a signal
type coaxial
switch attached to themultiplexing coaxial
The chain oftunnel ceiling above the monitor.
low loss 200 coaxial cables then transmits thebuildings,
to one of the four local
signals

Layout of position monitor system154

situated at north, east, south and west side of
the AR ring.
Signals are processed there,
converted into digital data in CAMAC ADC andtransferred to one of the AR control
computers
settled in the north control building via CAMAC
serial highway,
The
superheterodyne detection
circuitpicks up from a train of beam pulse (about 100ps width) the 479th harmonic (380.641 MHzl of
the revolution frequency,
This frequency waschosen because we have enough sensitivity evenwith the high-pass characteristics ofthepickup electrode and we can eliminate theinfluence of the 508.58 MHz RF frequency,
The
final IF frequency is 10.7MHz. The sensitivityof the pickup is -60 dbm/mA.
The linearity
range of the circuit is 30 db and overall
1 inearity
range 1s expanded by an
input
attenuator.
The minimum beam current in thisrange is 0.1 mA.
The equivalent offset of thecircuit is less than 0.5 uA.
The monitor computer calculates the beam
position in three steps,
Let signals at fourelectrodes be A,B,C,O.
First,
we obtain
electrical positions H and V by the following
normalization:
HCCA+Dl-CB+ClJ/CA+B+C+DJ,

V

C<A+Bl-CC+DlJ/[A+B+C+DJ.

3.1

Mapping of a position monitor chamberC3J

The measuring setup is schematically shownin Fig. 4.
The antenna,an end-stripped thincoaxial1 ine,
radiates 380MHz signal
tosimulate the beam. The x-y table enables it tosurvey the 20mm x 12mm area in the beam ductwith the step of 1mm.
The
microcomputer gives aconversion
mapping CH,Vl to (X,Yl on the experimental
spot.
We found that the following third orderpolynominals are very practical formula;
X = aO + a1*H + a2*V + a3•HH + a4•HV + a5•VV+ a6*HHH + a7*HHV + a8•HVV + a9*VVVY

bO + b1*H + b2*V + b3•HH + b4•HV + b5*VV+ b6*HHH + b7•HHV + b8•HVV + b9•VVV

We
usedalarge computer
tofit
thepolynominals to the data of 21x13 or 273 points
bytheleastsquare
method.
Major
contributions come from the terms of a1, a6, a8for X and b2,b7, b9 for Y.

Second, we convert the electrical
positions(H,Vlinto geometrical ones in the beam duct.
Theconversion relation
isexperimentallyderived for each monitor from a bench test.
The third step is to make correction for thesetting error of the beam duct with respect tothe beam line.
These conversion data for eachmonitor are stored in the data table of thecomputer.
3. Calibration
As is stated in the section 2, we have to
make two kinds of calibration measurements tofind out the conversion relations.
One is theelectricalmapping of the beam duct and theother 1s the measurement of the geometrical
positionofthemonitor.
Since
thesemeasurements must be done separately,
it ishelpfulto use the common principle for therecognition of the chamber position in bothcalibrations.
For this purpose,
we havedeveloped a location jig method in which a jig
block is pushed to the monitor chamber andbecomes an indicator of the chamber position.
In the setting error measurement,
the jig sitson the chamber as shown in Fig. 3(a).
In theelectrical calibration,on the other hand, themonitor chamber is placed on the Jlg block,upside down,
as in Fig. 3(b).
In this way, wehave the same contact in both calibrations.

Fig. 4

Setup for mapping measurement

3.2 Measurement of Beam Duct Setting Error
We developed an efficient touch sensor
method.
The setup consists of a bed, an x-ytable and an arm with a touch sensor at its end
as shown in Fig. 5.
The bed sticks onto two
posts of the quadrupole magnet with the help ofknock-pins.
Amicrocomputer-controlled
sequenser first returns the touch sensor to its
home position driving the x-y table.
Then thepulse motors move the the touch sensor until it
touches the jig,
with the ratio of 1um/pulse.
The measured reproducibility of the home
position 1s within 0.5um in both x and ydirections.
Those of the positions stopped by
the touch sensor are 0.7 um in x direction and0.3 um in y direction.

(a) Setting error measurement

Fig. 3The sensor touches the jig at four points
1n this manner.
Because we know the exact
size of thejig we can derive the threeparameters,i.e.,
x andy coordinates of thevacuum duct and its inclination in the x-yplane, using the non-linear least square method.

(b) Mapping measurement

Position of jigs

155

.

Y-tableARC.O.D .

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R.M.S,y..;..
0X

=:~

1''

l:l~;

:18.s...

41;1sa::1:1•••::1'~''

T:li; ~; s.~ i~ E~.~ ti i~iii ;_;;~; ;.i=i~ ~.= e; ~ &.; e~;-; ~;R.n.s. Q.Jmm

pulse motor

...

bed

0>---r:ouch sensor

Fig. 6

4.2
Fig. 5The setting error measurem ent has beenFor
carried out for 64 monitor sets among 83.
measurem ent is impossib le because
the rest,of the reason either the setup interfer e withthe power lines of the magnets, or the crosssection of the vacuum duct is irregula r that
The measured results are
the jig cannot fit.
summari zed in Table 1.
Table 1. Beam duct setting error.
rms

average

0.68
0.47

0.78
0.27

-------------------------------------------(-27.67, +22.9) 10.95-5.52
angle(mra d)horizontal (mm) (-1.55 , +2.06)(-0.95 , +1.70)
vertical(m m)Reliabi lity

We repeated closed orbit measurem ent 110
times during two storage operatio ns (electro ncurrent decrease s from 40 rnA to 0.5 rnA> topositionof
reprodu cibility
thecheck
It is given in Table 2 in terms
measurem ent,
Onlyof standard deviatio n at each monitor.
five monitors showed standard deviatio n larger
We found in each case that thethan 0,1 mm.
output voltage of one electrod e took abnorma lly
value only once in 110 measurem ents.
smallaIt is probably due to false contact inreprodu cibility
The highrelay,
coaxialthenoise contami nation insuggest s small
In this sense, the selectio n of cables
system.
(semi-ri gid cables and corruga ted cables) isvery success ful.

Touch sensor device

range

Display of clos~d orbit

Table 2.

-----------------------------------------------

rms value(mm)number of PM

when thePositive sign is assigned as follows:
inner side is up (angle), when the chamber
center is outside of the ring (horizo ntal), andwhen the chamber center is lower than the beamlevel (vertica l),

Reproduc ibility of position<0.0564<0.110<0.22>O .23

There was some disagree ment between theorbit shift excited by the steering magnets andRecent analysis solved thethe measured one.
problem and suggeste d the improvem ent of the
mapping calibrat ion [4],4. Performa nce

During the first operat~on period from
Novembe r 1983 to July 1984, we have some minor
wetroubles in the position monitor system;
had to change a coaxial relay because ofdamaged contacts and we got two dead monitors
because of short circuit of a disk electrod e tothe beam duct.

4.1 Closed orbit measurem ent
In the AR the beam orbit is measured inHence, we can measure
the storage mode only,
the beam position s at 83 monitors serially .
Since these monitors are grouped into four
blocks and each block has its own electron ics,
we can save the measurin g time by the parallel
The designed timemeasurem ent of four blocks,
consump tion is 11 sec and the overall operatio nOperato rs canby NODAL system takes 11.5 sec,
be patient for such interva l.

Referenc eH.Ishii, Y.Mizum achi, A.Ogata,Proc. 4th
J.-L.Pe llegrin and M.Tejim a:Sci, and Tech. 151
Symposiu m on Ace,(1982), Saitama: also IEEE Trans, Nucl .Sci.
3NS-30, 2356 <1983)[2] H.Ishim aru et al. IEEE Trans. Nucl .Sci. NS30, 2906 (1983)[3] M.Tejim a,H.Ishii, H.Ishim aru, T.Ieiri, ·4thProc.
A.Ogata:andY.Mizum achi
Symposiu m on Ace, Sci. and Tech, 153 (1982)
Saitama[4] T.Shinta ke: to be publishe d[1] T.Ieiri~

The measured closed orbit is displaye d on thegraphic display and the data is stored in theFig, 6 shows
memory file for later analysis .
The output voltage
an example of the display,of whole pickup electrod es are also availab lesubsidia ryThison the graphic display.
to find out wrong
display is very usefulelements in the position monitor system.
156