Recent progress with TES microcalorimeters and signal multiplexing J. Ullom NIST NASA GSFC SRON J. Beall R. Doriese W. Duncan L. Ferreira G. Hilton R. Horansky K. Irwin B. Mates G. O’Neil N. Miller C. Reintsema D. Schmidt L. Vale Y. Xu B. Zink

Transition-edge sensor (TES) calorimetry Temperature Time C E  C G  energy (x-ray) Conductance G Thermal C Heat Capacity temperature response Temperature (mK) Resistance (  ) I V SQUID current amp thermometer

TES issues single pixel performance energy resolution capture efficiencyspeed multipixel arrays ease of fabrication, homogeneity stability of operation readout of arrays

expected noise sources: - fluctuations in thermal impedances - Johnson noise unexpected noise source: - behaves like white voltage noise Obstacle to better TES resolution: unexplained noise L/R roll-off Johnson noise phonon noise unexplained noise

Different TES geometries additional normal metal features definition:  = (T/R) dR/dT perpendicular bars reduce 

Noise vs. geometry: unexplained noise and  correlated low  designs have little unexplained noise perpendicular normal features reduce noise and  all data at 60% R N

 ≈ 450  ≈ 450  ≈ 500  ≈ 150  ≈ 40  ≈ 40  ≈ 15  ≈ 40  ≈ 40  ≈ 15 SRON parameter study normal islands and bars … noise measurements to follow

Design strategy: match E  -max to 5.9 keV, lower   = 45 C = 0.9 pJ/K M =  m Bi 50% at 6 keV 261  s 400  m

X-ray absorbers simplest absorber = material stacked on TES need  machined collimator to shield streets what is fill fraction ? for NxN array, max wires in 1 street = N (near center) demonstrated: 2 wires & spaces in 3.5  m for N=30, min street width ~ 55  m with litho development, ~ 25  m ? fill fraction = 67% [83%] for 250  m pixels = 86% [93%] for 700  m pixels = 90% [95%] for 1 mm pixels demonstrated: 2.4 eV in 250  m device 2.9 eV in 400  m device predict 4.5 eV in 680  m, 6.0 eV in 830  m elementd for 95% QE at 6 keV C/  m 2 [ J/K] size for C = 2.5 pJ/K Au 3.5  m 240 (at 100 mK) 320  m x 320  m Bi 6.3  m 5.8 (?) 2080  m x 2080  m Cu 29.5  m  m x 90  m Sn 7.8  m  m x 4390  m HgTe, … Bi TES SiNx Si ~ 4 eV (L pix +L street ) 2 L pix 2

X-ray absorbers - mushrooms very high fill fraction overhang can shield streets more challenging design, fabrication absorber SiNx Si TES normal metal - Au normal metal - heat pipe Bi GSFC - 4  m electroplated Au ~2.5 eV at 6 keV T c = 65 mK,  = 7 ms GSFC BiCu, ~4.5 eV at 6 keV NIST

TES for 100 keV: attach bulk absorber 1 mm Sn aborber: QE = 20% at 100 keV Mo/Cu thermometer now 27 eV at 103 keV

Arrays: fabrication straightforward GSFC NIST SRON NIST

E = 4.9 eV; Number of counts = ; Energy(eV) s t n u o C 16 hour acquisition, no gain correction  E 10% worse than in short record 3/4 hour acquisition, no gain correction no detectable drift TES stability stable long-term operation possible … SRON NIST/CSTL … but cannot yet be taken for granted. Requires close attention to stray RF power, stray magnetic fields, and temperature stability. Also, some dependence on device and bias point. These dependencies not yet understood.

Time-Division SQUID Multiplexing schematic data stream...

Measure many TESs in multiplexed test setup 6.25 mm interface chip 32:1 multiplexer chip 8 x 8 sensor array individual sensor

8- and 16-channel results 8-channel TDM 16-channel TDM Multiplexed x-ray calorimeter results

128-pixel MUX facility complete four 32- channel SQUID MUX chips 16 x 16 x-ray array will be tested at the end of June presently:  -ray  cal

Arrays lots of data: multiplexed R(T) curves variation in transition shapevariation in response we can already engineer the transition width; soon we will engineer the transition smoothness

sensor  ± (  s) open loop BW (MHz)  E (eV) single muxed pixels per column pixels in square array Future mux performance presently, cryogenic BW ~1.5 MHz and electronics BW 3 MHz (designed in 1999) we will increase system BW to 3.5 MHz … - minor adjustments and then to 12 MHz. - cold series array, electronics redesign simulated MUX performance: but … NeXT ?

New SQUIDS! gradiometric summing coils gradiometric SQUIDs asymmetric V-  mutual inductance optimized for x-ray measurements asymmetric V-  greater dynamic range & linearity gradiometric design less magnetic shielding & crosstalk (will help system engineering) 100 mK testing in June; production run scheduled for July

optimism is in order - TES calorimeters continue to improve energy resolutions < 3 eV at 5.9 keV, 27 eV at 103 keV very promising results in complex absorber structures - mushrooms: ~ 2.5 eV - attached bulk absorbers: 27 eV (  -ray) array fabrication feasible - some work ahead to improve homogeneity lengthy, stable spectra feasible - some work ahead to make routine time-domain SQUID mux works well > 196 NeXT-like pixels [1 ms] in 1 channel in 2007 ? > 32 fast pixels [50  s] in 1 channel also very feasible Conclusions a TES option for NeXT could be VERY large does the science case justify a  -ray array ?