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

Bowyer, T.W.

Doskow, J.

Sperisen, F.

English

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In our first CE-25 run3 we achieved 48% polarization at 0.5 Torr pressure in the 
pumping cell, resulting in a flow rate of 1.0 x 1017 atomsls, and a target thickness of 1.3 
x 1014 atoms/cm2. At 0.37 Torr (5.0 x 1016 atoms/s) the polarization was down to 40%. 
1. K. Lee, J.F.J. van den Brand, 0. Hansen, and R.G. Milner, to be published. 
2. J. Sowinski and J .  van den Brand, "Investigation of the 3He Wave Function by Quasi- 
free Scattering,'' IUCF Proposal No. 90-111, November 1990. 
3. J .  Sowinski et al., this report. 
4. F.D. Colegrove, L.D. Schearer, and G.K. Walters, Phys. Rev. 132, 2561 (1963). 
5. R.D. McKeown, R.G. Milner, and C.E. Woodward, Proc. 8th Int. Symp. on High 
Energy Spin Physics, ed. K.J. Heller (AIP Conf. Proc. 187, New York, 1989) p. 1314. 
6. C.E. Woodward et al., Phys. Rev. Lett. 65, 698 (1990); C.E. Jones-Woodward et al., 
Phys. Rev. C44, R571 (1991). 
7. F. Laloe, Ann. Phys. 6,  5 (1971). 
8. Padetha Tin and L.D. Schearer, J. Appl. Phys. 68, 950 (1990). 
THE H 2 0  JET TARGET 
T.W. Bowyer, J. Doskow, and F. Sperisen 
Indiana University Cyclotron Facility, Bloomington, Indiana 4 74 08 
An internal oxygen target is required for the study of the 160(p,n)16F reaction in 
CE-19 (Refs. 1 and 2). We decided for an H 2 0  vapor jet for the following reasons. First, 
we would avoid possible corrosive effects that pure oxygen gas might have on the oil 
of the turbomolecular pumps. Second, the water molecule does not contain atoms that 
could create relevant background (low energy protons coincident with fast neutrons), or 
significantly reduce the beam lifetime and thus the luminosity. The presence of hydrogen in 
Hz 0 actually has very important benefits, because p+p elastic scattering has a relatively 
large and well known cross section. As has been done successfully in a number of Cooler 
experiments3 with H2 targets, normalized jet density profiles can be obtained with the use 
of position-sensitive recoil detectors. This makes it possible to center the beam on the jet 
relatively easily, as well as to monitor the luminosity. 
After feasibility studies4 and extensive testing in the Cooler G-section (during beam 
shutdown periods) the water vapor jet was installed in the T-section in April 1992. Figure 1 
shows a side view of the setup with the 6" magnet. Water in a copper reservoir (not shown) 
is heated to a temperature corresponding to the desired vapor pressure, which in turn 
determines the flow rate through the nozzle and the jet thickness. A solenoid three-way 
valve allows for fast (- 200 ms) turn-on and turn-off of the jet; the line to the nozzle can 
be switched either to the Hz 0 reservoir (jet on) or to a vacuum pump (jet off). The path 
of the vapor from the reservoir to the nozzle has to be kept at or above the temperature 
of the reservoir in order to avoid condensation. 
Figure I .  The H 2 0  vapor jet target setup with the 6" spectrometer magnet in the Cooler 
T-section. 
The nozzle, the catcher (in the center of the target chamber, see Fig. I) ,  and the 
differential pumping system are similar to that of the conventional gas jet target .5 About 
65% of the jet is caught by the catcher; the remainder of the gas is differentially pumped 
along the Cooler beam. The first pumping stage, surrounding the nozzle, is pumped 
cryogenically by a copper disk, cooled to 150 OK by a closed cycle He expander. Its H20  
pumping speed was found to be about 4000 l/s, much more than that of the turbo pump in 
this place of the conventional gas jet target. A total of four turbos are used in the second 
and third pumping stages. All of them, plus the one on the catcher, are backed by one 
common fore pump. To prevent water vapor from condensing in the fore pump, a liquid 
nitrogen cold trap is used. 
For initial centering of the beam on the jet and detector, tune-up hydrogen jets (both 
Hz and D2) are desirable. They can be run with considerably higher luminosity than the 
H 2 0  jet, and with a D2 jet one gets a copious source of nearly mono-energetic neutrons. 
Unfortunately, the H 2 0  target setup is not ideal for running with hydrogen because the 
cry0 pump (cold copper disk) on the first stage does not pump Hz. Therefore, for hydrogen 
operation, this pump has to be replaced by a turbo pump. This can be done while leaving 
the chamber under vacuum due to the gate valve there. 
In our first CE-19 run we ran Hz, D2 and Hz 0 jets. For the latter the water reservoir 
was kept at 50 OC (90 Torr vapor pressure), resulting in a jet thickness of about 2 x 1013 
molecules/cm2. The Cooler beam lifetime was unusually low, only about 12 s, which is 
an order of magnitude less than what should be expected.6 With the Cooler running well, 
the optimum target thickness will be about 4 x 1014 molecules/cm2. This, with 300 pA 
ramped beam, is expected to result in an average luminosity of roughly 2 x lo2' ~ m - ~ s - ' .  
1. T.W. Bowyer and S.E. Vigdor, "Study of the 160(p,n)16F(~-) Reaction at 
Tp = 300 MeV in the IUCF Cooler," IUCF Proposal No. 90-07, June 1990. 
2. T.W. Bowyer e t  al., this report. 
3. See for example H.O. Meyer e t  al., Nucl. Phys. A539, 633 (1992). 
4. T.W. Bowyer e t  al., IUCF Sci. and Tech. Rep., May 1990 - April 1991, p. 166. 
5. F. Sperisen e t  al., IUCF Sci. and Tech. Rep., January 1987 - April 1988, p. 194; F. 
Sperisen e t  al., IUCF Sci. and Tech. Rep., May 1989 - April 1990, p. 117. 
6. R.E. Pollock, private communication. 
UPDATE ON THE JET TARGET 
J.  Doskow and F. Sperisen 
Indiana University Cyclotron Facility, Bloomington, Indiana 474 08 
Aside from minor modifications, a significant improvement of the jet target system 
has been the implementation of the PC based monitor and control system, TRIPS. All 
remote readouts and controls are now done from the PC keyboard, except for the jet 
flow which is normally controlled by the experimenter's data acquisition computer. The 
interlock conditions can be programmed flexibly; they typically include fore and high 
vacuum pressures as well as turbo pump speeds. Any violation of these conditions causes 
all turbo pumps to turn off and all valves to close. The PC also controls the nozzle 
temperature at a level set by the user. 
A continuing problem are the frequent failures of the turbo pumps1 (Balzers mod. 
TPU/H 1500). We have begun replacing them with a redesigned model with improved 
bearing lubrication. However, failures have continued even with these new pumps. To 
reduce the risk for more break-downs, we will now install even the new pumps with the 


The H_2O Jet Target

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The H_2O Jet Target

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