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Status of HV Electrode Material Selection

Status of HV Electrode Material Selection. Takeyasu Ito Los Alamos National Laboratory. Requirements for HV electrode material. Electrical resistivity Eddy current heating Johnson noise Reasonable charge-up time Hardness Interaction with neutrons.

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Status of HV Electrode Material Selection

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  1. Status of HV Electrode Material Selection Takeyasu Ito Los Alamos National Laboratory

  2. Requirements for HV electrode material • Electrical resistivity • Eddy current heating • Johnson noise • Reasonable charge-up time • Hardness • Interaction with neutrons

  3. Dressing field eddy current heatingB field perpendicular to electrode surface Radius = a Thickness = t : conductivity (=1/) : resistivity

  4. Dressing field eddy current heatingB field parallel to electrode surface L t W : conductivity (=1/) : resistivity

  5. Johnson noise on SQUID signal Noise spectrum from infinite slab Need Bn,z < 0.3 fT/Hz1/2 T.Varpula and T.Poutanen, J. Appl. Phys. 55, 4015 (1984) J. Nenonen, J.Montonen, and T. Katila, Rev. Sci. Instrum. 62, 2397(1996) S. K. Lamoreaux, Phys. Rev. A 60,1717 (1999) C. T. Munger, Jr. Phys. Rev. A 72, 012506 (2005)

  6. Charge-up time C=165 pF; R = L/(t x W) Take L=70cm, W=20cm J.J.Murray, UCRL 9506 (1960) • Microscopically, • Also, r ~ 1010-1012 was found to be optimum for with 1/2 in. heated glass electrode.

  7. Acceptable resistivity

  8. Graphite resistivity C.A.Klein, Rev. Mod. Phys. 34, 56 (1962)

  9. Amorphous carbon resistivity 5K 50K J.J.Hauser, J. Non-Cryst. Solids 23, 21 (1977) M.Morgan, Thin Solid Films 7, 313 (1971)

  10. HV candidate materials and proposed test • Candidate materials • Torlon 4435 (=2x107-cm at room temperature) • Graphite spray • Amorphous carbon (DLC)? • RuO2 • Proposed test • Measure the resistivity at 0.3-0.5K using the DR • Can be done without any modification • Also measure the resitivity down to 4K by simply placing the sample into LHe. DR hadn’t been run since the acceptance test.  Performed a test run before placing samples inside.

  11. Start transferring LHe Path between 4He bath and 1K pot gets clogged Start condensing 4He Valve 2 closes on its own Open needle valve The first cold trap gets clogged? Open the second cold trap Cooling power measurement Partial 3He recovery AUTO on Start condensing 3He AUTO on; Start re-condensing 3He

  12. Very similar to the results from the acceptance test

  13. Status and Plans • Frossati has sent us a new impedance for the 3He circuit and a filter for the dewar. • With the new impedance, he expects the cooling power to at least double at 120mK. • For next cooling, we will equip the DR with a control computer. • Obtain more candidate materials • Perform resistivity measurements in 2 months

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