I am an observational cosmologist working on instruments to study the cosmic microwave background radiation (CMB). The CMB is the relic radiation remaining from the hot "big bang." It must be measured through microwave and radio telescopes optimized for detecting very small (~10-5) departures from a perfectly isotropic background at 2.7 Kelvin. I am involved in the millimeter-wavelength CMB project ACT.

Intense worldwide study over the last decade, culminating with WMAP, has revealed most of the information available in the primary CMB anisotropies (larger than a few tenths of a degree). However, there remains much to be learned from so-called secondary anisotropies, which were imprinted onto the CMB in the less-early universe. These include the Sunyaev-Zel'dovich (SZ) effect, in which hot plasma in galaxy clusters scatters some CMB photons to higher frequencies, and the Ostriker-Vishniac effect, by which a reionized universe (after z=1000 but before z=5) produces anisotropy at arcminute scales.

To study these secondary anisotropies, I am part of a new collaboration, involving Page, Spergel, and Staggs at Princeton plus scientists at several other institutions. This group is designing the Atacama Cosmology Telescope and building its cameras. ACT will be deployed in 2007 on Cerro Toco in northern Chile's Atacama Desert. The microwave receivers will use a new bolometer array technology, allowing for 1024-pixel imaging cameras in each of three wavelengths (150, 220, and 270 GHz) surrounding the null of the SZ effect. The ACT project presents many challenges in cryogenics, optics, and electronics. My interests have been in the optical design, computer data acquisition, and integrating the system.

A large fraction of our current work at Princeton is directed to making a prototype of ACT to operate from the Jadwin Hall roof and later from Chile. The prototype will involve a 32-element single-color camera and will use the WMAP prototype as its focusing optics. It will represent the first time that many of the new detection technologies, including TES bolometers and SQUID multiplexed readout electronics, have been used together to observe the sky.

My past research interests include the study of cosmic ray elemental composition at air shower eneregies (1014 eV and higher). The accepted model of cosmic ray acceleration in supernovae fails to explain these high energy cosmic rays, and their origin is a mystery.

•   "CMB Observations with a Compact Heterogeneous 150 GHz Interferometer in Chile", J. W. Fowler et al., Astrophysical Journal Supplements, 156, 1 (2005). astro-ph/0403137
•   "The Composition of Cosmic Rays at the Knee", S.P. Swordy et al., Astroparticle Phys., 18, 129 (2002).
•   "A measurement of the cosmic ray spectrum and composition at the knee", J.W. Fowler, L.F. Fortson, C.C.H. Jui, D.B. Kieda, R.A. Ong, C.L. Pryke, P. Sommers, Astroparticle Phys., 15, 49 (2001). astro-ph/0003190
•   "Composition and spectrum of cosmic rays at the knee measured by the CASA-BLANCA experiment", PhD Thesis, University of Chicago. (2000) Advisor: René Ong.
•   "The cosmic ray composition between 1014 eV and 1016 eV", M.A.K. Glasmacher et al., Astroparticle Phys., 12, 1 (1999).