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. Specific application: the linac test facilityK
2s beam
radius
Corresponding % resistivity change in bolometer strip
GEANT3 simulation

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

8. dx= distance e-holes drift apart
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
Can now grow wafers up to about 4” in diameter??
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
From E. Milani, University of Rome.

10. Radiation “Hardness” GEANT3 Protons in Diamond
RD42 irradiation studies
our linac
GEANT3
Protons in Diamond
RD42 has irradiated diamond to proton fluences of and they still function
RD42
For 24 GeV/c protons, the RD42 collaboration sees a 15% reduction in the median signal to noise (for detecting single
particles) after irradiating to a fluence of 2.2x10^15 protons/cm^2.

11. Charge threshold above which 90% of events fall
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 Electronics is not a showstopper.
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. We probably don’t need this quality.
Needs?$
Component
Supplier
Cost
2 CVD diamond wafers:
5x5 cm each
DeBeers Industrial
(via U. of Toronto)
Waiting for a quote from W. Trischuk
8 mm x 8 mm
diamond square
P1 Diamond
$150 - cost goes down with volume
Metal lead sputtering
Rutgers U.
<$300
data acquisition electronics
U. Chicago -
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