Incoherent and coherent beamstrahlung at the ILC Page: 2 of 10
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IB detector. The IB detector has been developed for CESR, thanks to a NSF-MRI grant
(NSF-PHY-0116058). It is completely installed if only partially operational (all parts have
been operated at least once). It consists of four optical telescopes, with angular acceptance
of 1mrad2 each, each beam being observed by two of them. The primary mirrors are located
respectively at 0 =11.5 mrad (inner edge) and 0 =-72.5 degrees, or 0 =12 mrad and 0 =-50
degrees. The radiation for each telescope is divided into a visible and infrared component
by a set of hot/cold mirrors, and split into x- and y- polarization components by a calcite
beam splitter. Each radiation is counted in a separate phototube, totaling 16 phototubes for
the whole system.
Visible radiation is mostly in a band 350 < A < 650nm where there is little signal (less than
3 Hz on a background usually exceeding 3000 Hz), contributing a precise evaluation of the
Infrared radiation can further be observed in the band 650 < A < 800nm, termed 'red', and
in the band 750 < A < 1000nm, termed 'IR'. This is done by using a visible phototube with a
filter in front, for the 'red' band, and by using an infrared phototube (Hamamatsu R316-02)
for the IR band. The IR phototubes are very noisy at room temperature, and are operated at
temperatures below -45C, which can be kept for about 24 hours running after CESR access,
until the liquid nitrogen used in the cooling of the device runs out.
The purpose of taking different infrared bands is to use to advantage intensity dependence
on wavelength. A simplified expression for the large angle electron beamstrahlung power is
given, which stresses various testable properties of IB
P_ (A, 0) ac 203 exp -(7z2/2A)2.
az is the beam length, I are the positron and electron currents, and -y the relativistic
parameter. At our angles, the term within parentheses is approximately equal to 3, and the
exponent approximately equal to -9. The signal rises sharply when the wavelength increases, a
feature inconsistent with common synchrotron radiation (SR). Likewise, the decreasing signal
intensity with increasing beam energy (1/r2) is not a feature to be expected from common
Data were taken on numerous occasions in 2005 (34 full days). Of these, the last 16 full
days (approximately 200 machine runs) are data of high quality, and contain both red and
IR data. The results have convinced us that a signal is present in the CESR data. The pieces
of evidence are listed in the Status Report Section.
CESR program. Assuming a first publication in spring 2006, the device will be made fully
self-running and completely operational by connecting to a continuous source of liquid nitro-
gen (Summer 2006). The device will then be turned over to graduate student E. Wisniewski,
who will produce his thesis using the continuously produced CESR data. The minimal tests
to be performed include several specialized Machine Studies measurements. These are:
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Bonvicini, G.; Cinabro, D. & Dubrovin, M. Incoherent and coherent beamstrahlung at the ILC, report, April 14, 2006; United States. (digital.library.unt.edu/ark:/67531/metadc876980/m1/2/: accessed December 11, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.