Proceedings of IBIC2012, Tsukuba, JapanTUPB64

METTHODS TOT REDU
UCE THEE SYSTEM
M ERRORR FOR HHIGH POWWERMSSWMEMMITTANC
CE METEERS
S. X. Peng*,, P. N. Lu, H.
H T. Ren, J.. Zhao, Y.Xuu, Z.Y.Guo,, Z. X. Yuann and J. Cheen
Sttate Key Labboratory off Nuclear Phhysics and Technology
T& Institute of Heavy Ion
I
Physics, Peking Unniversity, Beeijing 10087
71, China.
Recently a new Multi-Slit Single-W
Wire (MSSW) typehigh power bbeam emittannce meter nammed as HIBEM
MU-5has developeed in Peking UniversityU(PKKU). Comparred toprevious MS
SSW devices, HIBEMU-5 greatly
greduceed thesystem errorr from 16.4% to 3.7% by specificsdesiggns tosolve the incomplete shoort-slit sampliing and fixedd slitwire distancee. The problem
ms of previou
us PKU devicees areanalyzed in ppart one. In paart two, we deescribe the speecificupdating meethods to solvve its short-sliit disadvantagge by
re-designing a longer-slitt board with sufficient coooling,detail the mmechanical schheme of chan
nging the slitt-wireThedistance fofor differennt beam divergence.
dcommissioniing results givven at part three prove thaat thisnew long slits design is suuccessful to complete
cthe bbeam
sampling witthout being diistorted by hig
gh power H+ bbeam.
And the moovable wire cupcis able tot locate the best
measurementt position for different beamm focusing.

INTROODUCTION
N
Multi-Slit Single-Wire (MSSW) method is popullar inemittance meeasurement foor high power beams[1]. Thee slits
are used to sample the beamband thee wire that loocatessome distancce downstream
m the beam is used to obtaiin thebeam diverggence angle. To ensure the measureement
accuracy, the length of slits
sshould beb longer thann thebeam diametter so that thee sampling iss complete annd thethickness off slits board should be as thint
as possibble to
avoid its colllimation effecct. As a meassurement deviice, it
should have the universaal ability to dealdwith diffferent
kinds of beaam no matterr it’s divergence is larger (lowenergy heavyy ion beam) oro smaller(higgh energy lighht ionbeam).
At Pekingg University (PKU) we have
hdevelopped 4[MSSW emitttance meters[2][3][4]. Their processing
ptecchnic
and electronnic equipmentts have been upgraded onne byone. But theyy have two coommon demeriits. First, a 0.33 mm
thick molybddenum board withw 25 or 35 slits is attachhed at
the bottom oof the water coooled Faraday
y cup to samplle thebeam and thee slit board exxposes to the wholew
beam aall thetime during tthe measurem
ment period. VeryVthin slit bboard
prevents coooling directly and the heat absorbed fromm thebeam hit cann only be takenn away throug
gh Faraday cupup. To
avoid heat ddistortion, the length of slits is shortenedd to 5mm. But 5 m
mm is much shhorter than th
he size of the bbeam
diameter in most cases. And this leaads to incom
mpletesampling. As shown in Fig.
F 1, the inccomplete sam
mplingbringgs a system errror of about 88.7% for a  50mm
5typicall
Gausssian distributted beam[5].

Figuure 1: Emitttance simulaation with different
dslittlengtth[5].
Thhe second dem
merit is the fifixed length L between slittand wire.
wThis lim
mits the univerrsality of MSS
SW emittancee
meteers. For an em
mmitance devic
ice whose slitss interval is d，the beamlet will start to overllap at a distan
nce of D.

/2/

Heree ε is beam em
mittance and β is Twiss paarameter. Forrdiffeerent beam fo
ocusing D is ddifferent. L=D
D is the bestt
conddition, or L is slightly less tthan D is alsoo tolerable forr
this emmitance measurement ununit. If L<<D,, too less dataa
can be collected in the wholee scanning; IfI L>D, dataa
overlaps between adjunct slits,, as shown inn Fig.2. Bothh
imprroper conditions can generaate an error up
p to 5%.

ure 2: (up)situations of LL<<D with toot
less dataa
Figu
colleected, (down) conditions off L>D with daata overlap.

____________________________________________*Correspondencce author.
Electronic mail:: sxpeng@pku.ed
du.cn

ISBN 978-3-95450-119-9
Transverse & Longitudinal Emittance Measurements

1c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○Abstract

TUPB64

Proceedings of IBIC2012, Tsukuba, JapanTo overcomme the short-sslit error and thet fixed L errrror, a
new device named HINE
EMU-5 has beenb
developeed at
PKU recentlyy.

c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○PHYSICCAL DESIG
GNNoticing ththat at one mooment only on
ne slit is in chhargeof measurem
ment, coveringg all other slitss is a possiblee wayto reduce thhe beam bommbarding on thet slits boardrd forbetter coolinng condition. This way makes long slits
sampling feaasible. A proteecting Faraday
y cup with a small
window thatt faces the measuringmslit can fulfilll thisrequirement. Unlike the previouspones, the slits boaard isseparated froom the main faraday
fcup annd the faradayy cupand slits booard are movving indepen
ndently. Duriing ameasurementt, the samplinng window is in relative reest to
the wire cupp, and both off them are mooved by one ddriven
motor. In thhis case each point of the slit board wiill bebombarded ffor much lesss time. The sampling winndow
width w dettermines the exposing tim
me t and alsoo theacceptance aangle θ. On thhe one hand t=w/v requirees thewindow widdth the smalller the betterr, where v iss thescanning vellocity. On thhe other handd θ=w/2L haas the
opposite reqquirement thaat the window
w should be wide
enough to aaccept the wholew
beam. In our casee thesampling winndow is desiggned to be 20 mm width, w
which
makes the hheating time forf each pointt reduced to 25%,
meanwhile thhe maximum acceptance anngle is 133 mrrad.
Fixed slitt-wire distannce design is replaced bby a
movable wire cup, whicch is able too locate the best
measurementt position off F2 in Fig.3. Based onn theexperiences of previouss measuremeent, the slitt-wiredistance L chhanges betweeen 50 mm andd 100 mm to aavoid
both data oveerlap(F3) and insufficient data.
dhe protection ofo the slits booard is designeed to be a cup
Thratheer than a shielding boardd for two puurposes. Oneepurp
pose is to meaasure the totaal current of thet beam. Att
both ends of scannning, the prootection cup bottombcoverss
the wholewbeam. TheT other purrpose is to colllect all beamm
halo and to cut offf secondary elelectrons by magnetic
mfield,so th
hat the particlee noise in dow
wnstream areaas around theewire cup gets to its minimum.

Figure 4: MechanicalM
dessign for HIBE
EMU-5.
o protect the slit
s board, prootecting grids are designedd
Toto cllamp the thin slit board (FFig.5). Grids anda slits havee
the sames
special periodpof 2 mmm. Slits have a width of 0.2
mm and Grids have a width off 1 mm. Thesse dimensionss
makee sure a 133 mrad beamleet will pass thhough the slittboard and grids with little collim
mation.

Figure 3: Tw
wo improvemeents of HIBEM
MU-5[4]. On F
F1 tooless data is ccollected, on F3
F data get ov
verlapped, F2 iis thebest place.
Two bellows are neededd to realize thhe physical deesign.
One is for the slits booard and the other is forr theprotection cuup. Two guidee bars are fixeed to the proteection
cup, though which the wirew
can movve along the bbeamtransport direection. The movement
mis coontrolled by a gearof 180 mm in height covvering the verrtical scanninng, sothat the gearr and the wire cup will occclude all the time
(Fig. 4). Andd L can be reead outside th
he vacuum frrom amechanical dial. To keeep the movem
ment accuraccy ofscanning, thee protection cup
c has a slidee rail for slit bboard
holder to moove along. Cloose fit is used
d in this part aand ashell of brasss is inlayed beetween the twwo rubbing surrfaces
to smooth thee movement.

Figure 5: Protectionn grids designn.
up and the slitt
Beesides these trreatments, thee protection cuboard are coveredd together in a shielding shhell to reducee
noisee signals. Th
he material oof PEEK is used as theeinsullation. All thhe screws aree shielded, tooo. Both theeproteection cup andd the wire cupp have magnett suppression.

COMMMISSIONINNG RESUL
LTSTh
he fabricationn of HIBEMU
U-5 has just beenbfinishedd
and it has been innstalled into thhe ion source test bench off

ISBN 978-3-95450-119-9
2Transverse & Longitudinal Emittance Measurements

Proceedings of IBIC2012, Tsukuba, JapanPeking University. H+ beam with the parameter of 40
keV, 4.8 mA, 100 Hz and 1 ms is used to test the newemittance meter. The wire cup is able to move in vacuum
just as designed, and the long slits kept their shape andhaving direct water-cooling

TUPB64

CONCLUSION
The two improvements of MSSW emittance meter
make HIBEMU-5 more advanced than previous facilities,
specifically in complete sampling and avoiding dataoverlap. Long term application will start on PKU ion
source test bench.

ACKNOWLEDGEMENT
This work was supported by National Science
Foundation of China No. 91126004, No.11075008 &No.11175009.

Figure 6: A photograph of HIBEMU-5.
As the first result, Fig. 7 shows the measurement result
and the phase ellipse of measured H+ beam. Emittance ismeasured as 0.17 π mm·mrad. Comparison with previous
facilities and further tests are still needed to evaluate theperformance of HIBEMU-5.

Figure 7: Mesurement results and the phase ellipse of H+
beam by HIBEMU-5.

[1] Stockli M P. Measuring and analyzing the transverse
emittance of charged particle beams. AIP Conf Proc,
2006, 868(1): 25–62.
[2] Wu Wenzhong, Guo Zhiyu, Yu Jinxiang, etal.“Development of an emittance measurement unit
for high-current ion beam.” Atomic Energy Scienceand Technology, 2004, Vol. 38. Suppl 66-74 (inChinese).
[3] Ming Jianchuan, Yuan zhongxi, Peng Shixiang, etal.“Emittance measurement of high-current pulse ionbeam.” Nuclear Techniques, Vol.29(2),105-107 2006
(in Chinese).
[4] P. N. Lu, S. X. Peng, Z. X. Yuan, J. Zhao, H. T. Ren,Z. Y. Guo, and Y. R. Lu, “Four Dimensional
Transverse Emittance Measurement Unit for HighIntensity Ion Beams.” Proceedings of DIPAC2011,455-457.
[5] Zou Yubin, Guo Zhiyu. “Simulating study on
systematic errors in measurements of high-current
ion beam emittance with slit-wire method.” NuclearTechniques, 2004, 27(10), 744-748 (in Chinese).

ISBN 978-3-95450-119-9
Transverse & Longitudinal Emittance Measurements

3c 2012 by the respective authors — cc Creative Commons Attribution 3.0 (CC BY 3.0)
Copyright ○REFERENCES