Performance of the Fermilab's 4.3 MeV electron cooler Page: 1 of 3
This article is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to UNT Digital Library by the UNT Libraries Government Documents Department.
Extracted Text
The following text was automatically extracted from the image on this page using optical character recognition software:
FERMILAB-CONF-06-194-AD
PERFORMANCE OF THE FERMILAB'S 4.3 MEV ELECTRON COOLER *
A. Shemyakin #, A. Burov, K. Carlson, M. Hu, T. Kroc, J. Leibfritz, S. Nagaitsev, L.R. Prost,
S. Pruss, G. Saewert, C.W. Schmidt, , M. Sutherland, V.Tupikov, A. Warner
FNAL, Batavia, IL 60510, USAAbstract
A 4.3 MeV DC electron beam is used to cool
longitudinally an antiproton beam in the Fermilab's
Recycler ring. Cooling capabilities of the electron beam
are characterized by the drag rate that was measured at
various conditions. Fitting the results with a formula for
non-magnetized cooling gives electron parameters that
agree within a factor of 2 with independently measured
electron beam properties.
INTRODUCTION
In 2005 an electron cooler was installed and
commissioned in a 3.3 km, permanent-magnet Recycler
ring to assist in storing and cooling of 8 GeV antiprotons.
Since the first demonstration in July 2005 [1], electron
cooling is used for storing and preparing antiproton
bunches for nearly every Tevatron store. At the same
time, significant efforts were put to improve stability of
operation and to measure and understand the cooling
properties of the electron beam.
ELECTRON BEAM GENERATION
The cooler [2] employs a DC electron beam
generated in an electrostatic accelerator, Pelletron [3],
operated in the energy- recovery mode. The beam is
immersed into a longitudinal magnetic field at the gun and
in the cooling section (CS); other parts of the beam line
use lumped focusing. The main parameters of the cooler
are listed in Table 1.
Table 1: Electron cooler main parameters
Parameter Symbol Value Unit
Electron kinetic energy Eb 4.34 MeV
Beam current Ib 0.1-0.5 A
High voltage ripple, rms SU 250 V
CS length L 20 m
Solenoid field in CS Bcs 105 G
Beam radius in CS Rb 3-4.5 mm
The operation of electron beam might be significantly
affected by full discharges, when the Pelletron voltage
drops to zero in a sub-gs time, and the pressure in one of
the acceleration tubes increases by several orders of
magnitude. The frequency of the discharges depends, in
part, on the amount of beam losses to the tube electrodes.
Focusing and steering in the deceleration tube was tuned
to minimize changes in the current of the deceleration
tube's resistive divider at the expense of a slight increase
of total losses (Fig. 1). Together with all previous efforts,
described in Ref. [4], it allowed stable operation at
Ib=0.5 A. The average frequency of full discharges was
* FNAL is operated by URA Inc. under Contract No. DE-AC02-
76CH03000 with the United States Department of Energy
'shemyakin@fnal.govonce per two days. After two months of operation at 0.5
A, the frequency of discharges started to increase.
Because cooling at a higher current was not beneficial
(see below), the operational current was decreased to 0.1
A. The reason for the stability degradation at 0.5 A has
not yet been understood.
0 Tube current * Beam loss39,
. 1
38.5 1
37.5 ____ ___ _ _ 1'
37 t8
36.5 ________ 6
36400 035.5 __ _ _ _ __ _ _ _ _ _ 2
35 -- -00 0.1 0.2 0.3 0.4
Beam current [A]6
4
0
u0.5 0.6
Figure 1: Current losses vs beam current. Blue diamonds
are the changes of the anode current, representing the
beam current loss. Brown circles are the deceleration tube
resistive divider current. The gun voltage is 20 kV.
To estimate ultimate current capabilities of the beam
generator, a run in a shorter beam line was performed. In
this 12 m line, the beam is turned towards the deceleration
tube soon after exiting the acceleration tube. The
maximum recorded DC current at Eb = 4.34 MeV was
1.9 A, while 1.6 A was reproducible and stayed up to
10 minutes. Typical relative current losses were 5 ppm at
a collector voltage of 3.1 kV and a gun voltage of 40 kV.
Further increase of the beam current would require a
larger gun voltage and significant modifications to the
protection circuitry. Note that demonstration of the same
results in the full beam line is more challenging, since the
higher electron energy spread [5] and the beam motion
caused by the neighboring Main Injector synchrotron's
ramping [2] limit the collector efficiency.
ELECTRON BEAM CHARACTERISTICS
The electron beam cooling capability depends on the
beam energy spread E, rms value of the electron angles
in the cooling section a, and beam current density Jes.
The effective electron energy spread is dominated by
the Pelletron HV ripple, 6U=250 eV rms. Multiple-
coulomb scattering and electron beam density fluctuations
[5] are estimated to contribute -100 eV, added in
quadrature.
Table 2 presents estimations of various contributions
to the total budget of electron angles. The most uncertain
component is the drift velocity. The value in the table isc
i
u
Upcoming Pages
Here’s what’s next.
Search Inside
This article can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Article.
Shemyakin, A.; Burov, Alexey V.; Carlson, K.; Hu, M.; Kroc, T.; Leibfritz, J. et al. Performance of the Fermilab's 4.3 MeV electron cooler, article, June 1, 2006; Batavia, Illinois. (https://digital.library.unt.edu/ark:/67531/metadc883774/m1/1/: accessed March 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.