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 tunable temperature cryostat Sample Holder
Our current laboratory setup 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 V 0.8 V 10 ms First results at LH2 temperature 0.8 V 0.8 V 20 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 ms 10V 10V Cernox First results at LH2 temperature (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 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
Transfer line Flanges w/ multipin connectors Radiation shield Cu cold finger Quartz windows Cryostat Blueprint (not to scale)
Beamtest: First Try 840 nA @ 30 Hz short pulse duration: ~10 ’ s ns /pulse
Silicon Diode Temperature 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.
5.97 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 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=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
Idea: Separate the noise response from the thermometric component by aligning two bolometers with oppositely signed signals back to back.
Beamtest: 3 rd 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).