JRM Logo SNEAP 2005 Lab Report



Reporting period October 2004 thru October 2005  
Robert D. Krause and Kevin Carnes

James R. Macdonald Laboratory
Kansas State University
Manhattan, KS 66506-2604

Tandem Operations

This report covers a period from October 2004 through October 2005 for the James R. Macdonald laboratory at Kansas State University. The EN tandem Van de Graaff accelerator has operated extremely well throughout this reporting period.

There have been four tandem openings in the period covered by this report to do upgrades and modifications in the tandem for research with the titanium sapphire laser, referred to internally as the picopulse project. The first opening in October of 2004 was to install a focusing mirror system at the entrance of tube number three. The second opening in January 2005 was scheduled to change the terminal stripper gas from nitrogen to neon. The third opening in February 2005 was scheduled to change the picopulse mirror from a 25cm focal length to 50cm. The forth opening was a major modification to the tandem with the change of the number three acceleration tube. In 1990 we installed the new Dowlish titanium spiral inclined field tubes and had great tandem operation and performance. Because of the picopulse project, the third acceleration tube was replaced with one of our old aluminum inclined field tubes removed from operation in 1990 with a total of 15023.0 hrs. of operation. This old number one inclined field tube was chosen because the first twenty electrodes are not inclined, but straight, a requirement for the optics of the picopulse project. This number one aluminum inclined field tube was installed 180 degrees opposite its original installation, entrance and exit of the tube remaining the same. This orientation of the third acceleration tube was based on a beam optics calculation done by Vince Needham using Simion (Kevin Carnes presented a paper on this project at the meeting, which is available in Word or Acrobat formats). To date the beam performance (transmission) has not changed a great deal but conditioning the tandem is quite different, much like it was in the old days before the installation of the Dowlish tubes. The tandem does not hold its conditioning as well as it did with the third tube being the Dowlish titanium tube, which is understandable. The tandem terminal voltage has declined. What once was a 6.5 to 7.4 MV tandem has declined to a 6.0 MV tandem.

During this reporting period the tandem logged 945.0 hours of actual beam time operation. The amount of down time has been approximately 640 hours.

Ion Sources

The EN tandem Van de Graaff accelerator is injected by two different ion sources, the Middleton high intensity sputter source and the diode ion source. The diode ion source is used to produce hydrogen. The Middleton high intensity sputter source is again the workhorse in the laboratory, used to produce beams of boron, carbon, fluorine, magnesium, silicon, chlorine, copper, iodine and oxygen.

Laboratory Operations

With the construction in 2001 of the Kansas Light Source, an ultrafast titanium sapphire laser facility, the James R. Macdonald laboratory has gradually shifted its emphasis away from ion-collision atomic physics toward intense laser-matter interactions. As a result, the EN Tandem is used by only 1-2 groups for ion collisions research. At the same time, however, there has been an increased interest from groups outside the laboratory in using the tandem as a source of fast protons for various applied purposes. We have used a 10 MeV proton beam to help the KSU High Energy Physics group test the radiation hardness of silicon strip detectors used in ongoing research at FermiLab and in preparation for experiments at the CERN LHC. We have also done proton activation analysis for two different groups outside of the university. The picopulse project mentioned above currently accounts for the majority of tandem use as we attempt to combine our accelerator and laser expertise in developing a somewhat unique source of pulsed ions.

Technical Support Staff

  • Mike Wells
  • Alan Rankin
  • Vince Needham
  • Scott Chainey
  • Robert Krause


This work was supported by the Division of Chemical Sciences, Office of Basic Energy Sciences, Office of Energy Research, U.S. Department of Energy.


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