IMPROVEMENT OF BEAM LIFETIME MEASUREMENT SYSTEM AT TRISTAN
T.Naito, M.Tejima, A.Ogata
KEK National Laboratory for High Energy Physics
Oho 1-1, Tukuba-city, Ibaraki-ken, Japan 305

Abstract
A new beam lifetime measurement system
has replaced an old one. The new system
consists of a micro-computer CAMAC moduleand a 16 bits ADC module, while the old one
an accelerator control
consisted ofcomputer(HIDIC-8 0) and a 12/13 bits ADC atRing(AR)/Main
Accumulation
TRISTAN
Ring(MR). Using the micro-computer system, wecan get precise beam 1 ifetime with quickresponse and reduce software load of theaccelerator control computer.
Introduction
Beam lifetime is a one of the significant
parameters of a storage ring. The beam
lifetime measurement requires preciseness andquick response. An accelerator control
computer(HIDIC-80 ) and a 12/13 bits ADC module
had been used for calculation and measurementof beam lifetime in TRISTAN Accelerators.
1)It cannot
Disadvantages of this system areincrease samp 1 ing rate of measurement of
because the accelerator control
current,2)Itcomputer has many other software loads.
cannot improve the precision, because of therestriction of resolution of ADC. From thesereasons, result of cal cul at ion of beam
lifetime had errors. Though averaging method
was tried to eliminate the errors, thisresulted in sacrifice of response. We havedeveloped a new beam lifetime measurement
system, using a micro-computer CAMAC module
It canand a newly developed 16 bits ADC.
eliminate disadvantages of the former system.

2n-I;(ti-to)i=1(3)n-E (ti-to) ln(Ii/Io)
i=1
where n is the number of data, which decides
precision and response. If n is large, thecalculation is precise but its time response
If n is small contrary, its timeis poor.
response is good but the precision is poor.
Actually, validity of data is limited by thequantum error of the ADC, so this error has tobe small. Moreover, because the current loss
rate is very small in the ordinal operation ofa storage ring, the sampling interval(6t) has
to be small enough so as not to miss themoment of current change corresponding to the1 digit of the ADC(6i).
HardwareHardware of the new system is shown infig. 2. It consists of a toroidal DC beam
current transformer, a 16 bits ADC, amicrocomputer, an ACC and a memory module.
Beam
Toroidal DC beam current transformer:
current is measured with a system combining asecond harmonic magnetic modulator with anactive current transformer in an operational
feedback loop.1)2) Specification of thissystem is shown in table 1.

Calculation/or...... .....

Io exp( -t/Tq),( 1)-t/ln( I/Io),(2)"""-...

.............

.....

where Io is the initial current, t is theIn thistime,and Tq is the beam lifetime.
cal cul at ion, the time variation of beam
current is approximated by linear line inlogarithm scale as shown in fig.l.
Theoretically, calculation of beam lifetime isderived from current decrease during a given
time interval. Actually we fit many measured
current values I1, I2, ... at the times tl,t2, ... to eq.(2) using the least square
method.
The practical equation is-213-"~iI

In a storage ring, decrease of the stored
current is given by the following equation:
I---- ''/-\\,"'~~//)

ll1"-..........

___valid.....

.....

\valid / /........ /..... .....
.........................

......

1-t--1timeFig. 1 beam life time culculation

A 16 bits ADC CAMAC module
16 bits ADC:The ADC
is developed for this system.
requires high resolution and small
differential linearlity error. Even if an ADC
has a high resolution, we cannot use it, if
its differential linearlity error is not smallenough, 1 ike a successive approximation typeand an auto range type ADC. Finally we haveselected ADC800, a dual slope type ADC made byDatel Co .. It has 16 bits resolution and small
differential linearlity error(max.±l/2 LSB).
Although catalog data of its conversion timeis 400msec, it too slow for this purpose, we
doubled the recommended clock frequency ofthis IC to obtain 200msec conversion time. It
behaved well under this condition; we getlinear input/output characteristics . The
circuit diagram of the CAMAC module of thisADC is shown in fig.3. Resolution of current
detection using a new( 16 bits) ADC and anold(l2/13 bits) ADC in AR and MR is comparedin table 2. It should be noted that theaccuracy of the ADC now exceeds that of the DC
beam current transformer. To attain further
improvement of 1 i fetime measurement,refinement of the front part is essential.
MicroMicro-computer, ACC and Memorycomputer CAMAC module(CMS5203 Meisei Co.)
consists of Z80 cpu, 64k bytes memory, SIO,CTC, etc •. We can use CAMAC commands to start
the cpu, stop the cpu and read/write thememory from HIDIC-80 through the serial crate
controller(SCC). This module is connected toan auxiliary crate controller(ACC )module(CMS5204, Meisei Co.) by STD bus so that
it is able to access other modules in thecrate. 3) A memory module (3821 KineticSystems) has 4k words. It has four independent
address counters to communicate with sec andACC independently.
In this system, beam current is sensed andconverted to voltage value by the DC beam
current transformer. The voltage value isconverted to digital value by the 16 bits ADC
module. The micro-computer module and the ACC
module read the digital value at the interval
less than lOOmsec. The microcomputer module
1 digitcalculates beam lifetime whendecrease from previous digital data isrecognized. It then writes the result to theHIDIC-80 reads the memory
memory module.
module. This action is independent of thebehavior of the micro-computer module.

Software
The micro-computer program is written in
Pascal MT+, of its ability writing on ROM,
floating point calculation and its easiness in
The flow chart of the program iscoding.
shown in fig.4. It consists of three parts.
This routine firsta)Initialize routine :During a beam isresets the system timer.
injected in the storage ring, it waits untilThecurrent reaches its peak value.
thereset action again occurs at the end ofacceleration in order to reject the influenceof the flux change of bending magnets.
Table 2
Resolution of current detection by ADC

Table 1
Specification of
the toroidal DC beam current transformer
frequency
range

accuracymax.
current

outputvoltage

AR80 rnA

5 v

200~

DC-500HzMR

50 rnA10 v

20~

DC-100Hz

measurement
range
AR

0-80 rnA

MR

0-50 rnA

resolution ofADC
12 bits
16 bits
13 bits
16 bitsvalue ofLSB
40 /-lA(2.5mV)
2.5/-lA(.15mV)
12.5/-lA(2.5mV)
1.5!-lA( .31mV)

CH 0

t- DC current

CH31~::- transformer

HIDIC-80

R!- R.16

F(Ol A(j)F(l) A(1lF{4l A(O), - - - - f - - - - - - - - - - - - - - - - - - - - - - - - ---1

II
I

16 bit
ADC

1--

ACC

Micro-f1emoryr-

sec

I

RESET

I

w1-w6

I

compI
I

Il_____________ _____________ ____ j
Fig.2

I
I
I

R22 - R23

FC25l A(Ol*S I(C*Zl*Sl

Rl - R6F( 15) A(Ol*S 1

Rl - R6
F(6) A(Ql

Block diagram of the new beam
lifetime measurment system-214-R7- R8Fig. 316 bits ADC CAMAC module

From HIDIC-80

TF I ~THII I iF
B£:.:.r1 CUFPDITl/·U=·•t "-. r··-1•.: -··- _. "'"'

Ltrc

13L, ..

11.. -.- , 1~~I~-,-I---. ·::::.:~-~

r--r~-_-_,-~~

r----.r__,_/--+-1,- !

I

r---r-.-TT
r-----r- \-;;-lNo--+----+-------11--- ---~---- . ,. ·:· ·.: ""I ""'I'Yes.,.. ~.....
~- ~~-beam life time
culculatlonn = 30beam life time
culculationn = 20beam life time
culculatlon
n = I0··~1,•Fig.S---·--\,.. current---

iI't:.:- beam lifetimeII'----~~An example of the time variation of beam lifetime

Conclusi on

FIG. 4

Flow chart of the micro-co mputer code

A beam lifetimeb)Calcu lation routine:
is calcula ted when the measured data decrease sby 1 digit from the previou s data, accordin gto equ.(3), where n decides precisio n andbeam lifetim es, forrespon se. Three
are availab le for various
n=l0,20 ,30,purposes . These lifetime s are shown in fig.S.
Three beam lifetim es andc)Data store:
curren t values are stored in the memory
module. Softwar e on HIDIC-8 0 selects which
lifetime should be used.
An example of the time variatio n of beam
lifetim e is shown in Fig.6. In this case, thetime variatio n of beam lifetime responds wellto the variety of current.
current~~"""

beam lifetime

1~

LFig.5·-'~2

I ::-=---,.

-.....

A new system has attaine d the followi ng
improvem ents:
ADC data isa) Time interva l to readmsec.
decreas ed from 1 sec to 100b) Resolut ion of ADC is improved from 12/13
bits(AR/M R) to 16 bits.
The accuracy of the beam lifetime measurem ent
is now 1 imi ted by the accurac y of the DC beam
curren t transfo rmer. The LSB of ADC
corresp onds to l.S~A, while the accurac y of
the DC beam current transfor mer is 20~ in MR.
Refinem ent of the front part is essentia l forfurther improvem ent.
Acknowle dgment
The authors wish to thank prof. K.Uchino
for him helpful advice in design of thissystem.
Referenc esl)K.Unse r, "Beam current transfor mer with D.C.
IEEE Trans. Nucl. sci.
200MHz range",
tovol.NS- 16(1969) 934"A toroida l DC beam curren t2)K.Uns er,
with high resolut ion", IEEE
transfor mer
vol.NS-2 8,No.3(1 981)
Trans. Nucl. sci.
23443)H.Iked a et al., "Interfa cing of TRISTAN
4th Symp. Accel. Sci.
system" ,control
Tech .. (l982) 359

3~ _.

..;:--;

Behaviors of fitted beam lifetime calculate d in thecomparedarecase of n=lO( 1), n=20( 2), n=30( 3)to culculati on of HIDIC-80( 4).

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