JAERI-Conf 95-021

2a3-2
DUST TRAPPING EXPERIMENTS AT 1RISTAN AR
Shigeki KATO, Ken-ichi KANAZAW A, Toshifumi TSUKAMOTO and Shoji UNO
National Laboratory for High Energy Physics
1-1 Oho, Tsukuba, 305, Japan

Abstract

the microparticle such as its atomic composition and its size distribution and operation conditions of the ring is well known. In

We developed an experimental system investigating trapping of dust particles and installed it to an electron storage ring

this report we mention the installation of JlP AS and the first observation of microparticle trapping which was reproducible in(TRISTAN AR) where one can reproduce a condition thatTRISTAN AR under defined conditions.

microparticle trapping artificially occurs. Using this system calledmicro garticle ;!nalyzing §_)'stem (!lP AS) , trapping of
microparticles was systematically observed for the first time in amanner that a well-defined microparticles are dropped into theelectron beam. It was found that trapping of metallic microparticles
does not occur but trapping of ceramic microparticles and diamond microparticles do for several ten minutes. This would be
explainable based on heating and radiation cooling ofmicroparticles which determines a lifetime' of trapped
microparticles in conjunction with an electron beam current.

2. Experimental
A schematic of JlP AS is shown in Fig. l. JlP AS mainly
consists of a microparticle launcher, a microparticle collector, avacuum system and a monitoring system. In the launcher there
are small eight holders where option of a species of microparticle
can be made and dropping of the microparticles is carried out by
remote computer control and is confirmed by a CCD camera. Aftera free fall of 250mm, microparticles are crossed over the electron
beam probably as a cluster. The horizontally cross-sectional sizel. Introductionof the cluster is restricted by a guide tube to be no more than

Phenomena that a beam lifetime drops suddenly have been

lmm in a diameter before the crossing. ox and oy are typicallymeasured to be 2.2mm and O.lmm, respectively. The crossing

seen in some electron storage rings[l-6] including the observa-

time was estimated to be 90J.1s. The crossing is finally controlledtion of it in TRISTAN AR[7]. It was recently reported by DESY

by adjusting COD.
Microparticles which aregroup that a considerable probJem of the sudden beam loss has
been found in HERA ring and has limited the operation for theluminosity run[5, 6]. In HERA ring the problem is attributed tooperation of the integrated ion pumps (at the dipole magnets)
where dustparticles which are generated and positively charged
at the anode surfaces are ejected through the pumping slots to thepassing down throughthe beam are collected at
the bottom of the vacuum
system. The all flange
ports of the beam duct atmany experiments to reveal the mechanism were made nor theJlP AS are equipped withmany small holes (5details of the trapping have been made clear. Moreover all thetrappings can be explained by the same scheme while efforts tomm in a diameter) forshielding RF. The

explain some observation theoretically were done.

vacuum of JlPAS ismaintained by turbo mo-beam duct so as to be trapped by the electron beam. But neither

The most difficult thing in observation of microparticle
trapping in reality is that one could not reproduce the trapping at

lecular pumps (TMPs)

any time. One might see trapping by exploring operation condi-

and a sputter ion pumptions of a beam of a ring and the related equipments of the ring

(SIP) giving a base pres-such as applied voltage of ion pumps for instance. This is again

sure of 10·8 Pa. Total anddifficult since it is impossible to control generation of dust at all

partial pressures of re-and dusts generate spontaneously under a complex condition.

sidual gas in the system

Therefore we tried to establish an active observation system where microparticles are able to be given to an electron beam

are measured by residual
gas analyzers (RGAs) .

at any required time. This system would be able to ensure obser-The geometricalvation of trapping under a condition that information about bothconfiguration of the-200-Fig. 1 A schematic of the experimental set-up of JlPAS which wasinstalled to TRISTAN AR.

JAERI-Conf 95-021

J.lPAS

Up-In

8 Bending magnet
0 Quadrupole magnet
S Sextupole magnet
ST Steering magnet

Source point 8Sapphire
Borescope+CCDCamera

RGAFig. 2 The geometrical configulation of JlP AS and lead glass counters.
monitoring system of JlP AS and lead glass counters at a northwest arc section of TRISTAN AR is shown in Fig. 2. The electron bunches move forward clockwise. Four lead glass counterswhich are labeled Up-Out, Dn-Out, Up-In and Dn-In at the outside and the inside or the upstream and the downstream of JlP AS
were used in this experiment as shown in Fig. 2. Two counters ofUp-Out, Dn-Out are for observation of1-ray due to Bremsstrahlung and others of Up-In and Dn-In for monitoring beam loss. Anion source of one ofRGA faces with the electron beam of the ringfrom its inside in order to monitor not only residual gas species
but also possible evaporation of microparticles. Installation of asapphire bore scope with a CCD camera into JlP AS Was also madefor visual observation.
Species ofmicroparticle with information of their typicalsizes are the followings: Al(O.lJ1111), Ti(45J1111), Cu(O.lJ1111), ZrV-Fe(unknown) ,C(diamond,0.5J.Lm),

Ti0i0.3J.Lm),

Cu0(0.35J.Lm), and SiC(lJ.Lm). The size distribution ofmicroparticles for most of the materials are known. Less sized
micropowders of Ti were not prepared due to its strong combustibility. Zr-V-Fe is a material of pumping elements of NEG. Its
microparticles with a typical size of several ten J1111 were produced by grinding the material which had been used hard in
vacuum and would have been strongly oxidized while the analysis was not done. Molal quantity of each species of microparticles
which were introduced onto the beam was regulated to be 5 J11110l
except an amount of 10 J1111ol for diamond aiming an accuracy of
10% in the weighing. Purity of those materials except Zr-V -Fe

beam lifetime and signals of lead glass counters as a function ofelapsed time when microparticles of CuO and Ti02 were dropped.
Note that time stamps of the current, the beam lifetime and thesignals of the counters differ each other in the chart of a mechanical pen recorder and baselines of those records do each other aswell. Therefore the introductions of CuO and Ti02 are labeled by
the symbols a and b in the figure, respectively.
The collision of CuO microparticles with the beam madethe current reduced from 28 rnA to 14 rnA. Trapping, however,
did not occur since the lifetime recovered in half a minute and thedetector signals were observed only in a moment. In addition tothis, trapping of the microparticles of AI, Ti and Cu was not observed either while they were repeatedly introduced into the electron beam for a couple of times and an interaction with the beam
was confirmed by sharp signals from the detectors. Those
microparticles would have been melted simply ( m.p. of AI, Ti,Cu and CuO are 930, 1940,1360 and 1650 K, respectively) .
On the other hand, trapping of microparticles of Ti0 2(m.p.: 2100 K) andZr-V-Fe (m.p.: 1600-3200Kdependingitsoxidation) was clearly observed as shown for Ti02 in Fig. 3. The
beam current decreased from 14 rnA to 6 rnA at the moment of
the collision with the microparticles. After a sudden drop of thelifetime, its slight recovery to 80 min was found with a remarkable Bremsstrahlung as seen in the signal of Dn-Out. Then thesignal lasted roughly for 20 min with its monotonic decrease until the trapping ended. The lifetime that gradually got recovered

were measured to be not more than 99.8 wt%.

was recorded to be 375 min by the end. The similar trend wasfound in the signal ofDn-In while the signal intensity was small,

3. Results and Discussions

showing a beam loss for a long time.
The monotonic decrease of Bremsstrahlung for 20 min implies

Microparticles of CuO, Ti0 2 and Zr-V -Fe were introduced
into the electron beam in a series. Fig. 3 shows beam current,

that mass of the trapped microparticles slowly decreases throughits evaporation as a result of high temperature where beam heating and radiation cooling become equilibrium. A number of the-201-

JAERI-Conf 95-021

.Ec::

:

200:

:

::

60:

:

:

:

~--··············'············'·············-'-············-'···········

j :~ ~~Jlll
010020030050~

40E30 ~:;

20400500400500

010~0ID

CDTime ( s)Z6Beam Life
Beam Current····''

0Fig. 3 Beam current, beam lifetime and signals of lead glass
counters as a function of elapsed time when microparticles of CuOand Ti02 were dropped into the electron beam.
0ally escapes from the trapped volume and microparticles or a cluster ofmicroparticles sometimes get burst due to the heating. Trapping of Ti0 2 was reproducible. Trapping of Zr- V -Fe

200300Time(s)trapped microparticles is unknown. But the spikes and the steps
which were seen in the monotonic decrease of Bremsstrahlung
would suggest that some amount of the microparticles occasion-100Fig. 4 Beam current, beam lifetime and signals of lead glass
counters as a function of elapsed time when diamondmicroparticles were introduced into the beam. Note the different
ordinates and the zoomed ordinate of the lower plot.

microparticles was also observed while it lasted only for several
minutes, showing smaller signals of the detectors. Fig. 4 shows
trapping when microparticles of diamond (m.p. : 4000 K) wereAcknowledgments

introduced into the beam. Different from the result of Ti0 2 , thebeam current gradually decreased almost to null for a few minutes and the lifetime hardly recovered. Looking into the detail,We wish to thank KEKB Vacuum Group in KEK for theirtechnical assistance and their useful comments. We acknowledge with pleasure the calculation of the tapping behavior of Dr.

the lifetime which slightly recovered to about one minute in half

Y. Suetsugu in KEKB Vacuum Group.

a minute after the sudden disruption resulted in a lifetime of 3
minutes during a few minutes. In the mean time, the signals ofReferences

the counters smoothly decreased showing relatively stable thermal evaporation except a stepwise decrease which is coincident[1] P.Marin,LURE-RT/90-011990.

with the recovery of the lifetime.

[2] P.Marin,LURE-RT/91-031991.

According to a preliminary result of calculations on themicroparticle in a condition, diamond microparticles have a life-[3] D. Sagan, NIM A330 1993,371.
[4] G. Debut et al., Proc. of the 1994EPAC, London 1994.

time of a few minutes though Cu microparticles melt away in atime of less than ms. This result does not contradict the observa-[5] F. Zimmerman, Tech. Rep. DESY HERA 93-08 DESY, 1993.
[6] D.R.C. Kelly, Tech. Rep. DESY HERA 95-02 DESY, 1995.

tion and gives a qualitative explanation that microparticles of a[7] H. Saeki, T. Momose and H. lshimaru, Rev. Scient. Instr. 62

material which has high melting point would get easily trapped.

-202-No.4 1991, 874 and 62 No.4 1992, 2558.