HRIBF NEWS

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   Edition 2, No. 4               November 15, 1994            Price: FREE

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Contents:
Editor:
	Carl J. Gross,    Scientific Liaison,    cgross@orph01.phy.ornl.gov

Contributors:
	Ron Auble, Jerry Garrett, Michael Smith, Paul Mantica, Jim Beene, 
Gerald Alton, David Olsen, Fred Bertrand.

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1. First Acceleration of Stable Beams from the 300 keV Injector.

At 17:00 hours on November 1, 1994, a stable mass 28 (N2) beam was produced in the Electron-Beam-Plasma target-ion-source on the RIB injector platform, mass analyzed with the first-stage mass separator, and accelerated off the injector platform to the 300-keV diagnostic station in room T-106. This achievement meets an important milestone in the development of the HRIBF. This first test of the entire injector was very useful in identifying areas where modest design changes can be made to improve the ease of operation and reliability of the injector. It is very important that such changes be identified and corrected with stable ion beams since modification will be much more difficult once the target-ion-source has been used and thereby, activated for RIB production. In this test, no attempt was made to optimize or accurately measure the mass resolution. However, based on the observed separation of Xe isotopes also produced in the test, the mass resolution was estimated to be about one part in 400. The next phase of the RIB project, the beam transport line connecting the RIB injector with the tandem electrostatic accelerator, is expected to be completed in 1995.

The efforts of many people were instrumental in achieving this milestone and deserve our thanks!

2. Projected Initial Beams.

The selection of the earliest beams to develop for the HRIBF is a multifaceted problem. By necessity, it is a compromise between their utility for scientific research and the physical and chemical constraints imposed by a variety of parameters, such as, production rate, diffusion from the production target, transportation to the ion source, and the efficiency of producing negative ions either directly or by positive ionization and charge exchange. After considerable discussion with members of HRIBF's two major user communities, nuclear structure physicists and nuclear astrophysicists, the present efforts are focussed on the production of fluorine (mass 17 and 18) and gallium (mass 63 and 64) beams. The fluorine beams are applicable to nuclear astrophysics and nuclear reaction studies, and the gallium isotopes are suited for nuclear structure experiments. The present plans are to produce 17-F and 18-F by 16-O(d,n) and 18-O(p,n) reactions with an aluminum oxide (Al2-O3) target and 63-Ga and 64-Ga by the (p,n) and (p,2n) reactions on 64-Zn using a zinc oxide (ZnO) target. Of course, the development of radioactive beams is a research topic in itself, so it may be necessary to modify these plans as RIB beam development proceeds.

Previous tests indicate that the production of 34-Cl and 69-As may be feasible. Though these beams appear to be less desirable for research than the fluorine and gallium species, they may be considered alternative options for early experiments should the development of the latter beams prove unsuccessful.

We will provide additional information about beam development in the coming issues of HRIBF News, and welcome suggestions from the user community.

3. HRIBF Users Meeting at the Williamsburg DNP Meeting.

Approximately 60 HRIBF users got together at the fall DNP meeting in Williamsburg on October 27. The users heard reports on the facility changes in the past year by Fred Bertrand, the RIB ion source platform by Ron Auble, the RIB project and progress on ORIC and the tandem accelerator by David Olsen, the status of the nuclear structure end station (RMS) by Carl Gross, and projected initial RIB beams and scientific program by Jerry Garrett. The meeting was chaired by the Users Executive Committee Chairman Ed Zganjar.

Thanks for attending and showing your support!!!!

4. Staff Positions at Physics Division.

The Physics Division, Oak Ridge National Laboratory, invites applications for staff positions in experimental nuclear physics. We are seeking scientists with several years experience beyond the Ph.D., with a demonstrated record of creativity, who have the potential to assume a leadership role in our research programs. The successful candidates will join the Low- and Medium-Energy Nuclear Physics Section of the Physics Division. Current experimental research programs include medium-energy heavy-ion reaction studies of high-excitation collective strength, and programs in nuclear structure physics and nuclear astrophysics based at the Holifield Radioactive Ion Beam Facility. This unique facility, a new DOE initiative under development in the ORNL Physics Division, is scheduled to begin operation in late 1995. The ORNL Physics Division offers an excellent environment for research including close collaboration with the Division's nuclear theory program, the Joint Institute for Heavy Ion Research guest program, and access to state of the art computational facilities which, besides the Division's own resources, include an Intel Paragon parallel computer system operated by the High Performance Computing Center and a recently acquired IBM SP2 parallel computer. Interested candidates should send a curriculum vitae, a statement of research interest, and arrange for three individuals to provide letters of evaluation to: Dr. James R. Beene, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge TN 37831-6368, USA. Review of applications will begin in November 1994, and continue until the positions are filled.

ORNL is a multi-program laboratory, managed by Martin Marietta Energy Systems, Inc. for the U.S. Department of Energy. ORNL is an Affirmative Action/Equal Opportunity Employer and provides a smoke-free environment.

5. Inaugural Meeting of HRIBF PAC.

The inaugural meeting of the HRIBF Program Advisory Committee occured in Oak Ridge on October 7. This one-day "get acquainted" session allowed the members to review the progress of the facility and advise the HRIBF managers. Fred Bertrand gave a discription of the facility, Physics Division, and its organization structure. Jerry Garrett presented the current status of the facility and discussed many topics such as time lines, manpower requirements, and potential users. The PAC members in attendance were S. M. Austin, J. R. Beene, R. F. Casten, R. M. Diamond, W. C. Haxton, W. Nazarewicz, and P. D. Parker. W. Gelletly was unable to attend.

6. Electron Beam Plasma Ion Sources.

The Electron Beam Plasma Target/Ion Source (EBPIS) will serve as one of the principal ion sources for RIB generation at the HRIBF. Three versions of this source have been constructed and extensively tested. The total ionization efficiency for Xe has been measured to be 18%. While this is lower than the 55% maximum reported in the literature, it agrees with that measured at the CERN-ISOLDE facility. The operational stability has been found to be exceptionally good with little drift in intensity over time. Various improvements to the current design include replacing some components constructed of molybdenum, changing the support structure, and closing an oriface where particles can bypass the ionization chamber. The normalized emittance of the EBPIS has been measured to be 4.5 pi-mm-mrad [SQRT(MeV)] at the 90% contour level. This is the first time in the 20-year history of these sources that this quantity has been measured.

A Penning Ionization Gauge (PIG) version of the EBPIS has also been tested. This source is a simple modification of the EBPIS, but has the advantage of the reflex action of high-electron-beam currents oscillating through the anode structure increasing the probability of breaking up molecular forms of vapor from the RIB target. The efficiency for ionizing Xe has been measured at 15%. The source, like the EBPIS complement, is very easy to operate and exhibits very stable and time invariant beam intensities. The normalized emittance of the PIG source has been measured to be 3.3 pi-mm-mrad [SQRT(MeV)] at the 90% contour level.

7. Recirculating Charge Exchange Cell

A recirculating-type, cesium charge exchange cell has been used in conjunction with the EBPIS. Negative ion yields versus cesium oven temperature and condensation surface temperature have been measured. The charge-exchange efficiency for converting C+ to C- is 18%, somewhat better than the 12% found in the literature. During these tests it has been found that the cell has a lifetime in excess of 400 hours with a 5 gram charge of cesium. Because the cell can hold more than 30 grams of cesium, it is anticipated that the lifetime will exceed 1000 hours which is the design objective for the HRIBF project. This cell was used during the first acceleration of stable beams from the RIB injector.

8. Assembly of the RMS.

The assembly of the RMS has begun under the supervision of Paul Mantica from UNISOR. All magnets with the exception of Q3 which will contain the "fingers assembly" have been positioned on the floor. The two electrostatic vacuum vessels have been tested to 1x10**-7 torr. During the months of November and December the electrostatic deflectors will be assembled, aligned, and tested with high voltage.

9. Daresbury Recoil Separator Has Arrived at ORNL.

The Daresbury Recoil Separator (DRS) has arrived at Oak Ridge. The device, which weighs over 90 tons and is 13 meters long, was transferred to ORNL as part of an international agreement with the Science and Engineering Research Council of the United Kingdom. It has survived the trip with no damage and installation is currently underway.

10. HRIBF's Home Page on the World Wide Web (WWW) Reminder.

HRIBF has installed a home page on the ORNL Physics Division's WWW node and it is now accessible. To access the page, simply use your favorite WWW browser (e.g., Mosaic from ftp.NCSA.uiuc.edu) and open the URL (Universal Resource Locator) to node http://www.phy.ornl.gov/ and select HRIBF. Not everything is ready but we hope to add things in a timely manner. All HRIBF Newsletters can be found on the node and may be downloaded to your home machine in a Postscript file. We encourage you to make a hard copy of this newsletter for your bulletin board, so that students and scientists from other disciplines are informed about our facility.

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Jerry D. Garrett, Scientific Director     |Email:  garrett@orph01.phy.ornl.gov
Mail Stop 6368                            |Tel:    (615) 576 5489

Carl J. Gross, Scientific Liason          |Email:  cgross@orph01.phy.ornl.gov
Mail Stop 6371                            |Tel:    (615) 576 7698

Holifield Radioactive Ion Beam Facility   |Tel:    (615) 574 4113
Oak Ridge National Laboratory             |Fax:    (615) 574 1268
Oak Ridge, TN 37831