Kara Hoffman Mark Oreglia

1. A Gedankenexperiment in Beam Profiling Kara Hoffman Mark Oreglia

3. A promising bolometric material: platinum • high Z = large dE/dx • temperature-resistivity function very steep at 20K • should be more sensitive than the nickel and graphite prototypes previously tested in electron beams at Argonne Platinum TCR curve

4. 0.30 - 0.35 K 0.25 - 0.30 0.20 - 0.25 0.15 - 0.20 0.10 - 0.15 0.05 - 0.10 0.00 - 0.05 2s beam radius Specific application: the linac test facility Corresponding % resistivity change in bolometer strip GEANT3 simulation

5. Bolometry summary • Advantages: • doesn’t disturb the beam • relatively inexpensive • robust • Drawbacks: • must be applied to absorber window for heat sinking – could be an issue mechanically/safetywise and cannot be removed or replaced • small signal, particularly for more diffuse beams • metal strips provide challenge in large electromagnetic noise environment • large thermal time constants

6. Diamond is prized for more than just its sparkle (high refractive index)… low leakage I very fast readout no p-n junction needed low capacitance no cooling hard rad hard, strong insensitive to g’s l>220nm Makes a great particle detector! The RD42 collaboration (CERN) has been developing diamond (primarily) as a microvertex detector.

7. Ionizing radiation (36 e-h pairs per mm per mip) sputtered metal strips/pixels (titanium coated with gold) E (>1 V/mm) - + diamond substrate ~300 mm - + - + - + solid electrode Anatomy of a diamond substrate microstrip detector… Essentially a very compact solid-state ionization chamber.

8. Polycrystalline CVD Diamond induced charge: dx= distance e-holes drift apart m = carrier mobility, t = carrier lifetime growth side • Charge collection efficiency effected by: • grain boundaries • in grain defects substrate side

9. Can we read out both sides of the detector? Naïve answer is yes, however, holes are generally less mobile than electrons. Charge collection efficiency could be much lower. • Efficiency may not be an issue in a high intensity beam. • Diamond has been successfully implemented as a pixel detector, but that complicates DAQ. • Could flip polarity and alternate coordinates, if necessary. E. Milani University of Rome

10. Protons in Diamond GEANT3 our linac RD42 irradiation studies Radiation “Hardness” • RD42 has irradiated diamond to proton fluences of and they still function RD42

11. Annealing • “Pumping” passivates traps, actually improving charge collection efficiency up to a fluence of Initially, smaller signals become larger and response becomes more uniform. RD42 Collected charge (e-) Charge threshold above which 90% of events fall RD42

12. Electronics • Power supply/amplifier: must maintain bias voltage while reading out a potentially large signal. • High bandwidth: Fast electronics are desirable to exploit the excellent timing characteristics. • Wide dynamic range: Large variation in intensities to be measured • German nuclear scientists have developed such an amplifier DBA-II (Diamond Broadband Amplifier) –It can be done. We have a 1 GHz bandwidth Tektronix oscilloscope with 400 ps rise time, 10 GS/s sample rate. Good enough? Electronics is not a showstopper. Level of complexity depends on timing resolution desired.

13. A (Destructive) Test Open Questions Place a small (1sq. cm) diamond detector with a single electrode on each side in a proton beam. • Can we simultaneously read 2 coordinates from the same detector? • How will they perform with such a large instantaneous particle flux? Will the response be linear or is there some saturation point? • What kind of time resolution can we achieve? • Quantify “rad-hard”. No one has irradiated them to a fluence where they had no signal. Monitor both electrodes and compare signal strength for electrons and holes. Continue until signal completely disappears. Remetalize electrodes and repeat process to determine whether the diamond is toast or the electrodes simply vaporized.

14. Potential advantages/payoffs • sensitive (2 coordinate?) measurement • relatively huge signal • fast (subnanosecond ~40ps) response might allow temporal beam profiling, in addition to current and position measurements • free standing-accessible • low Z- no beam loss (<0.1%) • could be implemented quickly • RD42 has already developed a vendor (DeBeers) • could have broader applications: • for other beams – single particle efficiency, high bandwidth make it suitable for transfer lines, etc. • measuring Lab G “death rays” and other RF cavities

15. Now back to the linac test facility… • Ed Black and I have sketched a robotic arm to sweep the diamond sensor through the beam • Allows us to pull sensor out of the beam, thus increasing sensor life by minimizing radiation exposure. • A single sensor can be used to sample the beam at several different radii, thus minimizing cost while still allowing us to make a full 3s measurement.

16. Diamond quality: cut, clarity = COST! Industrial diamond is manufactured primary for heat sinking or optics. For HEP, the figure of merit is charge collection distance. • Size of single crystals • Density of traps • Purity • Polishing • Uniformity of thickness and response Price range: Electronics grade (P1 diamond, and others) ~$100/cm2 Tracking grade (DeBeers only) >>$1000/cm2 We don’t need single particle efficiency to see a beam. “Crappy” diamond will probably work.

17. Needs?$ We probably don’t need this quality.

18. Final Thoughts • I am negotiating with RD42 to borrow/purchase a 1 sq. cm piece of “tracking grade” diamond, and I’m purchasing some electronics grade diamond for destructive test. • I believe we can “beam test” (or nuke rather) some samples on a short time scale. • If “electronics grade” stuff works, it could be “disposable”. • This talk probably no longer belongs in an absorber review.

19. Extra slide: comparison of physical properties of polycrystalline and single crystal diamond