This research was sponsored by the National Science Foundation Grant NSF PHY-931478

Adney, J.

Ball, M.

Brown, B.

Derbenev, Ya.S.

Ellison, M.

Ellison, T.

Ferry, D.

Fox, W.

Friesel, D.

Hamilton, B.

Larson, D.

Lee, S.Y.

Minty, M.

Reistad, D.

Schwandt, P.

Sedlacek, M.

Sundquist, M.

English

IUScholarWorks

STUDY OF THE FEASIBILITY OF DECREASING THE EMITTANCE 
OF THE SSC BEAM THROUGH THE USE 
OF ELECTRON COOLING IN THE SSC MEDIUM ENERGY BOOSTER 
Mark Ball, Bob Brown, Mike Ellison, Tim Ellison, Walter Fox, 
Dennis Friesel, Brett Hamilton, S.Y. Lee, Michiko Minty, and Peter Schwandt 
I n d i a n a  Un ive r s i t y  Cyc lo t ron  Faci l i ty  and  Dep t .  of Phys ics ,  
B looming ton ,  I N  474 08 
Jim Adney, Jim Ferry, and Mark Sundquist 
T h e  Na t iona l  Electrostat ics  Corp ,  M i d d  le ton ,  WI, 559562 
Del Larson 
C e n t e r  for  Research  in Electro-Optics  and  Lasers ,  Orlando,  F L  592826 
Miro Sedlacek 
T h e  Roya l  I n s t .  of Technology,  S tockholm,  S w e d e n  
Dag Reistad 
T h e  Svedberg Laboratory, Uppsala,  S w e d e n  
Ya. S. Derbenev 
Dep t .  of Phys ics ,  Un ive r s i t y  of Mich igan ,  Ann Arbor ,  M I  481 09 
A collaboration has been formed, and funding received by the Texas National Research 
Laboratory Commission, to study the feasibility of decreasing the emittance of the proton 
beams in the Superconducting Super Collider (SSC) by electron cooling the proton beams 
at their injection momentum of 12 GeV/c in the SSC Medium Energy Booster (MEB). The 
ultimate goal is to reduce the emittance of the proton beams that will collide at 20 TeV 
in the SSC by about a factor of two. If this can indeed be done, then the SSC luminosity 
(the number of physics events per second) will also be increased as much as by a factor of 
2, despite a decrease in duty fact or. Consequently, this relatively inexpensive device may 
be able to increase the performance of the SSC by a factor of two. The research done on 
this device shall also benefit IUCF in the future, since a similar device could be installed in 
LISS; consequently, we are also receiving support from Indiana University for this research. 
The SSC luminosity is inversely proportional to the emittance of the two proton beams. 
Consequently, a smaller beam emittance will increase the SSC luminosity; in addition, a 
reduced beam emittance in the MEB will also lead to a reduced beam size in this machine 
as well as all the following accelerators; the smaller beam size will increase the tolerances 
for closed orbit error errors and for higher order multipoles in the magnets, and allows for 
easier transition crossing in the MEB. 
The design1 SSC rms normalized emittance is lrrpm. This is a consequence of the 
0 . 6 ~ p m  emittance of the beam injected into the LEB and the near perfect adiabatic trans- 
mission through the SSC complex of accelerators. Beam parameters for the SSC system 
of accelerators are shown below in Table I. The emittance appears to be limited primarily 
by the Lasslett space charge tune shift in the LEB at injection, and consequently can 
probably not be reduced, even with electron cooling. However, after acceleration in the 
LEB, the limits placed upon the proton beam emittance are relaxed. We estimate that 
the normalized emittance of the beam injected into the MEB can be reduced by a factor 
of about 5 over the emittance of the beam injected into the LEB, and that this can be 
accomplished by electron cooling the proton beam at the injection energy in the MEB. 
However, for a variety of reasons, our goal is to reduce the emittance by a factor of two 
only. 
The cooling time for the 12 GeV/c protons will be about 50 s. Although the MEB 
cycle time is 3 s (much smaller than the cooling time), the following machine (HEB) has 
a relatively long cycle time, 120 s. Consequently, precooling the 3 batches of beam in the 
MEB before acceleration and loading into the HEB would increase the total SSC filling 
time by less than a factor of two; the higher luminosity in the SSC would more than 
compensate for this decrease in duty factor. 
In addition to increasing the SSC luminosity, a smaller beam emittance will increase 
the available machine aperture, and make transition crossing in the MEB easier. It is 
therefore worth studying the possible improvement of the beam emittance in the MEB 
using electron cooling. A complete 5 MeV electron cooling system would cost about 7 M$. 
We are receiving about 5% of this amount over three years for a feasibility study of this 
possibility, its impact on the SSC design, and for an attack upon the principle technical 
obstacles which need to be solved in order to make such an idea viable. 
Table I. Beam Parameters for the SSC accelerator complex. 
1 Accelerator LEB MEB HEB SSC uni t s  1 
Injection Momentum 1.46 12 200 2,000 GeV/c 
Final Momentum 12 200 2,000 20,000 GeV/c 
Circumference 0.54 3.96 10.89 87.12 km 
Harmonic Number 108 792 2,178 17,424 
Normalized rms emit t ance 0.6 0.7 0.8 1 .O ( V m )  
@ 10" particles/bunch 
Normalized rms emitt ance 4 4 4 4 ( V m )  
@ 5 x 10'' particles/bunch 
Cycle Time 0.1 3 120 s 
The project is composed of two principal parts: (1) a detailed study culminating in a 
design report for an electron cooling system for the SSC Medium Energy Booster (MEB); 
and (2) an experimental effort to overcome the primary technical problem which needs to 
be solved in order to build such a system: successful "recirculation" of a low transverse 
temperature, high density, nonmagnetically confined electron beam. Funding for the first 
year of studies is $265,620. During this period we shall complete the design study and 
begin work on the test electron recirculation system. During the second year of funding, 
we will complete the assembly of the test system at the National Electrostatics Corp. in 
Middleton, WI, and during the following year we will perform our recirculation tests. 
This research is supported by the Texas National Research Laboratory Commission under 
grant RGFY9158. 
1. Helen T. Edwards, "SSC Design Status," Particle  Accelerators 26, 151 (1990). 


Study of the Feasibility of Decreasing the Emittance of the SSC Beam Through the Use of Electron Cooling in the SSC Medium Energy Booster

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Study of the Feasibility of Decreasing the Emittance of the SSC Beam Through the Use of Electron Cooling in the SSC Medium Energy Booster

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