Application of Coherent Tune Shift Measurements to the Characterization of Electron Cloud Growth Page: 3 of 4
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Figure 4: Comparison between data (black), siniulation
uiming reference pariameter seL, with total secondary vield
2.05 (red). and sPimulation tijng radiaioin distrihutions
froni Synrad3f, new reference photoelectron paramleters.
arid total secondary yield L (blue).
ArIohcr example of a coinparisoii hetweeri data,
simulations using tlic original ieerence parameters, and
siriulations based oi Synra3D with new photoelectron
parametesis, is shown i' Fig. 1 in this case, ihe diIt
correspond to self-exctted tune shift Ineasurenents made
irt connection with beam instability mcasurenieus. as
described in I31. [Fig. 4 suggests that. for 4he Svnrad3D
siiniilaieors i lily higher value oQ il1 SeLetndiry Yield
is preferred, althouglih urdicr -LILtVy with improved
pararntcr csrirates may change this inpression.
QUANTUM EFFIC]IENCY AND
In conrnectiort with studies cf electror cloud effects For
ihe 1.1 IC, direct Sntasureients [51 have beei lnade of ihe
quantum eflcieicy, awl the phololectron energy
spectrum, for Vtv photons in the e:nergt range up tti
about 100 cV. The nwcasurmenmis were made for a variety
of ;LifALeS, including Ourninurn, which is rcIvra[ (or he
CesrTA vacuum chamber.
The relative quaruMni efficiency was measured as a
fnction of photon energy. This ibflimunion ear be
comnhitled wiD11 Il1 enrgy spcS-rum of absorbed phins,
which is provided by the Symiradmfl 4)de, to estimate kWiN
the uuantumn efficiency might be expected sary foi
different bemn crmreics, and at different points in lhe
C esrI A ring. This provides additional inrirmaton that is
useful in constraining electron Clontd PAa[MletCrs whC
coitmpaning with data, and in etrapilatig clvIt-ron cloud
effec: tM fulur politron rigs.
Absolute quantum efficike ies, -Vraged ivw ui VUV
phtlon energy spectrui, were also measuLred in reference
. These results were quite sensitive to the surFace
maie nal and condition, b u 1 were in lhe mange o~ 0.041 to
0,106,. Qinkuam ulliiency va uc found For the chest fits
to the CesrTA tune shift data are in this same range.
The measurements in refL'renec [51 indicate that the
photovlectron energy speetruirn can be well represented by
a Lorenitzian with a peak and widtih of a Few 61, Siudies
of the shielded button data (described in [ 6) dcmiiostiate
that, although a simple Lorentzian distribution is adequate
for the photons generated by a 2 GCV CesrTA beam., for
the harder photun speCtmii generated hy a 5 G1eV beni, a
high-lenlergy tail, wtll a power law fatloff slowe than thai
of a Lorernizial, is required. Counsceqsmetly. 0 net
pfiE iniltritation, ising a imrenteian s piiced to a rierw[
law distrihli in widi an adjustable exponent ai Ii li
photoelectron energies. has been installed in POS]NSI.
Prelinnary re-cvaluatoili of tie tun shi ililrIwCiolis For
o[h positron ild electron beanis at 5 GeV indicate 1hal
the high energy tail in the photoelectron energy spectrum
makes only sniall differences in the simulaled tune shi[ts.
t~sing the Synrsd3D) radiation dktributionr, and the
iniproved photoelectron model described above.. the
existing body of CesrTA tune shaft data will be Ye-
imuy.ed to era- rmore precise iifrormiulion aboul the
wlect0rih cloud iimdel parameters and to test the vnlidty
of lte model across a wide range of beam conditions. 1 his
will allow more reliable prediklions for [LC damping ring
f F -urmni aKL C IG .krn- r'v . "l i clcron-ek i
inambility in 1h ,arcs nF lhe ii 'P-.i poO rorl 'ng,
]s[:pr7Ielssitur es.cd~il-a rg+71tIlL13N ."41 123.
M. A. Turman and M. T. F. Pivi, Prubahilistic Model for
the Sirnlation of Setrindrv Fle: m Imin on. Phys. R ev
ST-AB 5. 124404 (2t11ii
[21 C. F. Dujugn M. A. Pauhrwr. ud D~t L. kubin. 11.C Damping
Rinps R&D at Cewr[A. (T A Iem lDynamrics Newoslder
No 5i', cds J Lrakawit anI W Chou (101D).
. A Crtmndenii. ed al, Studie 'Sl11lie 15 fecs. of 15Etc en
(loud Iormiltion on Bea ii Im ylamli es a1 Ce:rTA.
pruccedip of 'AC.. 4-8 May 2009. Vanueuuver. Briish
131 M. Itillin. a. r.. "Nloasuremnii TechiiquC tr
CLrLUuIsLie Insabi~itis caused by Leistn C1mud ,'
tcntributu !o thiN cunFErence.
[41 G. Ilgin, :mnmi 1) Sagan, Synrul3) honor prnpo,:ayirin
2..Oi eit1mi i alln mulation ',e ii '11i tr rt ta tin s orl:k Jp.
 Cirniir's. Culliris. LagLitn VV plit'.imission %Ludius of
andid-He 1.1IK vacuum climibe: nterials, ]ISTAI!
2,ot7621t1 ( I19))
[6) .J Criiemdert cl. ill., cnlribmtion to iLr' co frenL'
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Kreinick, D.L.; Crittenden, J.A.; Dugan, G.; Holtzapple, R.L.; Randazzo, M.; Furman, M.A. et al. Application of Coherent Tune Shift Measurements to the Characterization of Electron Cloud Growth, article, March 28, 2011; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc840139/m1/3/: accessed September 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.