Kara Hoffman

Mark Oreglia

Students:

David Billmire

Steve Olmschenk

Bolometric Materials We’ve Tested

Cernox •brittle – won’t flex with window•“cernox” (we’re not allowed to know what that really is) is deposited on thick sapphire backing•bare chip difficult to work with•expensive•greatest sensitivity

Nickel •same geometry as a strain gauge with polyimide encapsulation•also made by measurements group•works right out of the box

Graphite •“homemade”- either painted colloidal carbon or cut by hand from a thick foil•we are trying to develop some more precise milling techniques for a more uniform response, but crude ones work

Janis continuous flow Janis continuous flow tunable temperature tunable temperature cryostat cryostat

Sample Holder

Our current laboratory Our current laboratory setupsetup

Xe flashlamp

Laser diode

photodetector

lenses

cryostat

filter

Flashlamp- high power, long time constant

We also just received a new YAG laser.

Light sources

electronics

0.8

V0

.8 V

10 ms10 ms

First results at LH2 temperature First results at LH2 temperature 0

.8 V

0.8

V

20 ms20 ms

Nickel

Carbon

Signal from a xenon flashlamp.

•Note that the peaks have a different polarity. Carbon’s electrical resistivity increases with temperature, while nickel’s decreases.

•Time constants are decreased with respect to previous measurements made at room temperature.

Origin of secondary peak?

Simulated here for electrons (not photons) in the Nickel bolometer.

Large amount of energy deposited in polyimide encapsulating material, owing to it’s thickness.

Calculated temperature rise in kapton is on the same order of magnitude as the Nickel.

Polyimide introduces an additional time constant.

10 ms10 ms 1

0V

10V

Cernox

First results at LH2 temperature First results at LH2 temperature (continued) (continued)

We had proof of principle, both at room temperature, and cryogenic temperatures, and we had materials that had an adequate thermal response at 20K. We needed to demonstrate that it would work for

a charged particle beam (muons?) .

Note different scale, and this was with a lower intensity photon beam to prevent saturating the amplifier.

Energy deposited (per particle) in Nickel film by various beams

GeV

GeV

GeV

401.5 MeV protons

20 MeV electrons

200 MeV muons

•Nickel film of 0.00025 cm thickness

•Amount of energy deposited by 200 MeV muons is roughly the same as for 20 MeV electrons

•Fortuitously, there is a 20 MeV electron beam available at Argonne

•Anything sensitive to 200 MeV muons will also be sensitive to 401.5 MeV protons

1 cm

Disadvantage: e’s scatter easily & cryostat introduces a lot of material

Tra

nsfer lin

e

Fla

ng

es w/

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ltipin

con

nectors

Ra

dia

tion

shie

ld

Cu

cold

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Qu

artz

win

dow

s

Cry

osta

t Blu

ep

rint

Cry

osta

t Blu

ep

rint

(not to

scale

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scale

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t Blu

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rint

Cry

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Beamtest: First TryBeamtest: First Try

•840 nA @ 30 Hz

•short pulse duration: ~10’s ns

• /pulse

e11107.1

Silicon DiodeTemperature Sensor+/- 0.25 K sensitivity down to 2 K

Problem 1: We don’t know the temperature

Thermometer failed sometime during the first set of measurements made at cryogenic temperatures.

In retrospect a thermometer based on a p-n junction was perhaps not the best choice.

It later came back to life (after beam test was over, of course).

Signal or background?One way to gain insight is to look for thermal dependence (i.e. change in

time constant).

Signal or background?One way to gain insight is to look for thermal dependence (i.e. change in

time constant).

Worst case scenario: take data at 4K.

Full beam at 4.2 K…

…with 2” inch steel block in front.

We later found that the connection with the electronics was poor.

5.9

7

mm

3.1

8

mm

3.18 mm

active area

GEANT3 Simulation

Idealized beam from a point source 10 cm in front of

window

Actual beam profile in plane of front window

quartz window

Optical hole in cold finger

Simulation

Problem 2: Beam profile is larger than active area of the bolometer

Beamtest: Try AgainBeamtest: Try Again•copper block with 1/8” hole added to mask off beam and shield the thermometer

•also modified electronics

•elongate pulses to lower instantaneous current

T=300KT=300KT=300K

T=20K??

Thermometer died again

At 20 K we expect a temperature rise of ~2K. Results are consistent with expectations.

Available thermometric films

Note different horizontal scales!Nickel: 0.00025 cm

thick

Graphite: 0.013 cm thick

Platinum: 0.00025 cm thick

• the thicknesses shown for nickel and graphite are the actual thicknesses used in our lab

•Note that additional thickness doesn’t = greater sensitivity, since additional thermal mass is added

•We haven’t tested platinum (we are now tackling the problem of how to mill a foil) but it’s shown for comparison because (with it’s higher Z) it has a very high dE/dx = more sensitivity

Graphite TCR

39.5

40

40.5

41

41.5

42

18 20 22 24 26 28 30 32 34 36 38 40

Temperature (K)

Re

sis

tan

ce

(o

hm

s)

Series1

Idea: Separate the noise response from the thermometric component by aligning two bolometers with oppositely signed signals back to back.

Beamtest: 3rd try?Beamtest: 3rd try?

We’ve learned a lot about our setup

-or-

Hindsight is 20/20

•Ideally, the beam should be contained within the active area of the bolometer.

•Since quartz scatters the beam, the copper aperture may be only part of the solution.

•Replace quartz windows with a material that’s more transparent to electrons.

•Work on beam alignment.

•Use two different bolometers with oppositely signed response to separate signal from noise.

•Purchase thermometer more suitable for these conditions.

•We have proof of principle, and several materials that will work at 20 K.

•Our calculations/simulations indicate that we can make bolometry work in a charged particle beam. Our “prototypes” however, provide a much smaller target than in a cooling channel, and our cryostat introduces a lot of material.

•Beam tests are consistent with expected results, but inconclusive, however we have ideas on how to resolve this (shortly).