Kara HoffmanKara HoffmanThe University of Chicago

Enrico Fermi Institute

The challengeThe challenge

•While disturbing the beam as little as possible measure:

•intensity

•size/profile (in 2 dimensions?)

•timing between bunches or pulses

•The detection medium must be radiation hard.

•The beam must be accurately measured in an environment with a lot of noise from rf cavities, etc.

•The profiler and associated readout/power cables must fit within the design of the cooling channel.

•Muons are difficult to detect.

IDEA IDEA #1#1

Bolometry: proof it Bolometry: proof it worksworks

0.8

V0

.8 V

10 ms10 ms

Carbon

0.8

V0

.8 V

20 ms20 ms

Nickel “bolometer”(actually a commercially made thin film nickel thermometer)

Xe flashlamp

lenses

cryostat

filter

electronics

Signal or background?

Look for thermal dependence(i.e. change in signal size, time constant).

Polarity: carbon’s electrical resistivity increases with

temperature while nickel’s decreases.

Signal or background?

Look for thermal dependence(i.e. change in signal size, time constant).

Polarity: carbon’s electrical resistivity increases with

temperature while nickel’s decreases.

(“homemade” from graphite foil or colloidal carbon)

@20@20KK

Beamtests at ANL: setupBeamtests at ANL: setup•copper block with 1/8” hole used to mask off beam and shield the thermometer

•Pulses nominally 10 nA in duration--we tried to reduce inductive noise by elongating pulses to lower instantaneous current

beampipe

cryostat

temperature controller

vacuum pump

LH2 tank

bolometric film

• /pulse

•840 nA @ 30 Hz

e11107.1

@T=20K

Beamtests at ANL: resultsBeamtests at ANL: results

RESULTS IN

CONCLUSIV

E

RESULTS IN

CONCLUSIV

E

**It is difficult to separate inductive noise from a real thermometric signal.**

Possible remedies:

•Use electronic filters to distinguish signal since thermal time constant should be much longer than the noise.

•Use two bolometric materials with opposite thermal response to subtract the noise.

•Use a material with a much larger thermal response. (i.e. a superconducting edge thermometer)

0.30 - 0.35 K0.25 - 0.300.20 - 0.25

0.10 - 0.15 0.15 - 0.20

0.00 - 0.050.05 - 0.10

2 beam radius

Signal Signal expectation: the expectation: the linac test facility linac test facility

GEANT3 simulation

Corresponding % resistivity change in bolometer strip

Platinum TCR curve

Platinum TCR curve

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 do not allow for measurement of timing information

Bolometry findingsBolometry findings

Evolution of window design has produced thinner prototypes

Diamond is prized for more Diamond is prized for more than just its sparkle (high than just its sparkle (high refractive index)…refractive index)…

low leakage Ivery fast readout

no p-n junction neededlow capacitance

rad hard, strong

no cooling

hard

insensitive to ’s >220nm

Makes a great particle detector! The RD42 collaboration (CERN) has been developing

diamond (primarily) as a microvertex detector.

-

-

-

-

+

+

+

+

diamond substrate~500 m thick (when used as a

microvertex detector)

E (>1 V/m)

sputtered metal strips/pixels(400 angstroms of titanium or chromium coated with 4000 angstroms of gold)

solid electrode

Ionizing radiation (36 e-h pairs per m per mip)

Anatomy of a diamond substrate Anatomy of a diamond substrate microstrip detector… microstrip detector…

Essentially a very compact solid-state ionization chamber.

IDEA IDEA #2#2

Diamond as a beam Diamond as a beam profiler? profiler?

•sensitive (2 coordinate?) measurement

•fast (subnanosecond ~40ps) intrinsic response might allow temporal beam profiling, in addition to current and position measurements

•free standing-accessible

•low Z- very little beam loss

•has been demonstrated to be rad hard to a proton fluence of at least

•relatively huge signal (too huge??)

Diamond has not yet been realized as a microvertex detector because the signal size is small compared with silicon and single particle detection efficiency is required. However, single particle efficiency is NOT required for a beam profiler.

215 /105 cm

Polycrystalline CVD Polycrystalline CVD Diamond Diamond

growth sidegrowth side

substrate sidesubstrate side

L

dxedq induced charge:

Edx )(

dx= distance e-holes drift apart

= carrier mobility, = carrier lifetime

Carrier lifetime effected by:

•size of individual crystals-grain boundaries

•in grain defects and impurities

ddx

mLQ

Qd

induced

collectedcollection 100 mL

Q

Qd

induced

collectedcollection 100

tails due to tails due to carrier lifetimescarrier lifetimes

Charge collection Charge collection efficiency efficiency Charge collection efficiency is a product of:

• d-carrier drift velocity- a function of the applied electric field up to a saturation velocity

• -carrier lifetime-a function of diamond quality-commercially available diamond improving with time

“black” diamond

polishedhigh purity diamond

unpolished diamond

diamond membrane(with person peeping through)

What kind of diamond is best What kind of diamond is best suited as a beam profiler?suited as a beam profiler?

• signal size could be limited by decreasing the electric field

•this approach is destructive to timing information

• diamond with short carrier lifetime• small gives faster response at the expense of efficiency• much cheaper

• as thin as possible•less charge produced per mip • voltage required for maximum carrier velocity is proportional to thickness• easier to dissipate heat•diamond “membranes” can be made 1m thick

We want to minimize the signal while exploiting the timing information.

Detector fabrication: Detector fabrication: sputtering sputtering electrodes electrodes •We have fabricated our first prototype from a piece of 500m x 11mm x 11mm detector grade CVD diamond that was manufactured by DeBeers.

•Leads were sputtered at OSU using a shadow mask—finer segmentation could be achieved with a lithographic mask.

Towards a diamond testing Towards a diamond testing program…program…

R&D areas:R&D areas:

•Application specific material will need to be developed, along with fast electronics.

•Over what range of intensity measurements could diamond be useful? (space charge effects?)

•How radiation hard is it?

Near term plans:Near term plans:

•We are in the process of obtaining some diamond with shorter carrier lifetimes.

•We plan to study the behavior of our prototype in a beam test at Argonne this summer.

R&D areas:R&D areas:

•Application specific material will need to be developed, along with fast electronics.

•Over what range of intensity measurements could diamond be useful? (space charge effects?)

•How radiation hard is it?

Near term plans:Near term plans:

•We are in the process of obtaining some diamond with shorter carrier lifetimes.

•We plan to study the behavior of our prototype in a beam test at Argonne this summer.

•Two novel concepts for beam profiling are being studied/developed at Two novel concepts for beam profiling are being studied/developed at the University of Chicago. The signal to background ratio for bolometry the University of Chicago. The signal to background ratio for bolometry may be too low for use in a muon cooling channel or test facility. may be too low for use in a muon cooling channel or test facility.

•If CVD diamond is demonstrated as a viable beam profiling medium, it If CVD diamond is demonstrated as a viable beam profiling medium, it may find applications outside of the muon collaboration.may find applications outside of the muon collaboration.

• The Fermilab beams division has shown a keen interest in the outcome The Fermilab beams division has shown a keen interest in the outcome of CVD diamond beam tests and has offered supplies as well as of CVD diamond beam tests and has offered supplies as well as technical support.technical support.

•The first prototype diamond profiler has been fabricated and a beam The first prototype diamond profiler has been fabricated and a beam test is being planned for the summer.test is being planned for the summer.