> 1) Your full name
Mark Alan Mandelkern
> 2) Your position and title
Professor of Physics, UC Irvine
> 3) Date of Birth
1/28/43
> 4) Passport #
154294593~
> 5) Highest degree earned and year awarded
PhD, 1967 MD, 1975
> 6) Field of degree
Elementary Particle Physics, Nuclear Medicine
> 7) Did you participate in a previous CRDF program? If yes, which
program.
No
> 8) How many US investigators, including you, me and Vitaly?
Plus David Christian at FNAL?
> 9) Title of Project: 
Development of a Plasma Metal Ion Target for Elementary Particle Physics
Experimentation and Particle Beam Diagnostics

INTRODUCTION

Internal targets are particularly valuable for elementary particle physics
experimentation at accelerators and storage rings. A target within the
accelerator vacuum pipe allows experiments that exploit the full number of
accelerated particles, since particles not interacting in any given pass
remain in the machine and have many other opportunites to interact. The
high quality (small transverse emittance and momentum resolution) of the
internal beam is exploited and vacuum windows are not required to separate
the machine vacuum from the interaction region. Many current experiments
use internal targets, eg Hermes and Hera-B at DESY, E835 (charmonium
search) at Fermilab. Current internal targets are either sparce gas jets
or solid objects placed far from the beam center. The former are limited
to gases that can be pumped efficiently (e.g. hydrogen and nitrogen, not
noble gases) and suffer from the difficulty that they degrade the vacuum,
particularly crucial for the very high vacuum (10^-9 or better) required
in storage rings. The latter are non-self-healing, difficult to maintain
and operated, and have bad particle optics due to their placement. 

A plasma metal ion target can be thought of as a very sparce "wire" or
"foil" placed in a circulating beam that will not cause excessive beam
loss or emittance growth. Such a target may be superior to a gas jet in
many respects. 

a. It can have better geometry because of charged particle focusing, with
a better defined core and less dense halo. 

b. It may represent a smaller load on the accelerator vacuum system
because
	i. skimmers are not used for collimation; only neutrals
	substantially contribute the the pumping load.
	ii. metal ions are more easily pumped than many gases, certainly
	than noble gases.

c. A much greater variety of target nuclei is available. This is
particularly important for studies of electromagnetic processes such as
antihydrogen formation since the cross section increases as Z^2 and the
beam emittance growth increases only as the inverse radiation length
(slower than Z^2). This feature is also valuable for nuclear physics
studies. 

d. A plasma target may be more compact than a gas jet target beacuse of
the reduced pumping requirement. This feature may allow placement in
locations inaccessible to gas-jet targets.

A potentially valuable application of a plasma target is for beam
diagnostics. In order to measure the profile of an accelerated or stored
beam a "flying wire" is swept across the beam with sufficient speed to
avoid substantial beam loss or emittance growth. The difficulties with
this technique include i. the wire must be very fine and thus is fragile
and non-healing, ii. the emittance is always significantly increased, the
system is mechanical and failure-prone. Such studies can be done only
infrequently to avoid conflict with machine operation. A plasma "wire" 
could be sufficient sparce to not disrupt the beam, even at a slow sweep. 
It is intrinsically self-healing. Diagnostics with such a device could
event be performed continuously. 

A METAL ION TARGET FOR ANTIHYDROGEN PRODUCTION IN THE FERMILAB ANTIPROTON
SOURCE

Fermilab Experiment 862 made the first definitive observation of
antihydrogen by colliding the stored antiproton beam with an internal
hydrogen gas jet target (ref 1). Some of us have proposed an experiment at
the Fermilab Antiproton Source to perform spectroscopy with antihydrogen
to test CPT (ref 2). To obtain the required yield of antihydrogen atoms a
heavy nucleus target must be used since the production cross section goes
as Z^2. Because of the requirements of the experiment and machine
environment the target must have a 1 mm profile with minimal halo as seen
by the stored beam, must have a density consistent with the stochastic
cooling power of the machine, must be self-healing and must not pollute
the 10^-9 T machine vacuum. The only technology potentially available for
such an internal target is a Xe cluster gas jet. The approriate areal
density for Xe would be approximately 10^12 nuclei/cm^2 which is possible. 
However such a target has not yet been shown to be possible with the
appropriate density and profile. It would necessarily be massive,
expensive, and would produce a large leak of a gas that cannot be pumped
effectively if it escapes from the target region. A plasma target of
suitable characteristics would optimally use an ion of greater Z and would
have an areal density requirement smaller than a Xe (Z=54) target, the
scaling factor being Z^2. 

R and D goals: 
Constuct a prototype target.
Determine what ions are possible.
Obtain geometry and density characteristics. 
Evaluate neutral atom component and determine the requirements for
maintaining a suitable ambient vacuum.