Lifetime Measurements of Carbon and Diamond Stripping Foils

1. Lifetime Measurements of Carbon and Diamond Stripping Foils Trivia Penns Frazier Dillard University Supervisor: Doug Moehs Accelerator Division

2. Introduction… • For a long time now ( since March 1978), the Fermilab Booster has operated with H- multiturn charge exchange injection (CEI), which became the normal injection method for high-energy physics operation. • It is based on the capture of protons by stripping electrons from H- ions on the closed orbit of a cyclic accelerator, and occurs when fast moving ions traverse a charge stripper, or foil.

3. Carbon foils are used as targets in the 401 MeV Linac line to strip two electrons from the H- beam: • commercial availability • expected lifetime • low multiple scattering • relatively low cost • Charge strippers are essential devices in a heavy-ion accelerator complex. • They increase the variety of acceleration schemes • Decrease the construction costs of accelerators. It is important to carefully choose the material. • The proposed proton driver has 8 GeV beam energy, a 90 turn injection scheme, and a 1ms pulse at 2.5 Hz. • The optimum goal of the experiment described here is to test the lifetime of diamond foils while achieving the same level of energy deposition, under conditions matching the 8GeV injection scheme. This can be achieved using Linac parameters of 8.5 mA at 750keV for 90us. This is similar to the BNL diamond foil lifetime measurement, but utilizes beam and transport system at Fermilab.

4. Diamond foils of polycrystalline type contain many of the superb physical properties of natural diamond and are expected to function for no less than 200 hours, but over 400 hours. Structural Properties The lifetime of stripping foils depends on the melting temperature of the foils, the repetition rate of the beam, and the fabrication method of the foils. Table 1: Performance of 300-ug/cm2 Carbon Foils

5. Experimental Setup • vacuum chamber • H- bending magnet and toroids • two collimators (graphite blocks) • 300-350µg/cm2 carbon or diamond foil • data acquisition system • H- Beam Energy of 750 keV, pulse length 90us

6. Two Methods of Current Measurement A Toroid… • A toroid is a coil of insulated or enameled wire wound on a donut-shaped, or torus-shaped form made of powdered iron. • They are used as inductors in electric circuits, especially at low frequencies where comparatively large inductances are necessary.

7. A Faraday Cup… A Faraday Cup is a device for measuring the current in a beam of charged particles. In its simplest form it consists of a conducting metallic chamber or cup, which interprets a particle beam.

8. Figure 1 Testing Station-W1 Linac 750 keV H- Beam Line

9. Figure 2:

10. Figure 3: Beam Direction Beam Direction

11. Results

12. Oscilloscope, Experiment #3: carbon foil • T7’s polarity value changes from ~26.5mA to ~ –8.2mA • Due to stripping, the beam current before and after the foil has opposite polarity.

13. Figure 4 Silicon Three-Edged Support Frames Polycrystalline Diamond Foil Burn Holes

14. Conclusion The lifetime of the diamond charge stripper foils was tested in the Fermi Linac, using the 750 keV H- beam, with repetition rates of 3.75 and 1.875 Hz and a beam current of 8.5 mA. The conclusions are as follows: • Although the diamond foils do not exhibit lifetimes over 400 hours, they do exhibit a lifetime longer than the carbon foils; however, this lifetime was only achieved at a peak beam current of 1mA, not the desired 8mA. • 1.     The optics of the 750 line do not work well on H+ beams. • 2.Poor initial focusing may cause the beam to enter the collimator hole at an angle. • Due to the large factor of 10, our 90us pulse length may have an affect on the foil lifetimes.

15. Future Goals • In the future, more testing and research needs to be done on the foils. All preferably repeated at 2.5 Hz to match the proton driver repetition rate. • Different techniques may be used to monitor the foils, which include placing a collector in the form of another toroid or Faraday cup directly behind the target to measure the beam current more accurately, and placing a window in front of or behind the vacuum can to allow observation of the position of the beam. After testing is done, an assessment will be made of whether or not the foils are suitable for the proton driver upgrade.

16. Acknowledgements • Almighty God • Patrons: • Doug Moehs, my supervisor, for his tireless efforts to expand my knowledge • Elliot Mc Crory, Ms. Engram, and the entire S.I.S.T. staff • Dave and Cat, my mentors • Dr. Davenport • Everyone involved in the Accelerator Division, the best division in the world! • Weiren Chow and Mikhail Kostin • Websites: • http://www-bdnew.fnal.Gov/operations/rookie_books/Linac_PDF/3_750_KeV.pdf • http://linac.fnal.gov/ • http://www.brainencyclopedia.com/encyclopedia/a/am/ampere.html • http://accelconf.web.cern.ch/accelconf/ • www.csuohio.edu

17. Questions?