sub-Degree Scale CMB Anisotropy



MAX (Millimeter Anisotropy eXperiment) and its next generation MAXIMA (MAX IMaging Array) and BOOMERANG are balloon-borne, bolometric instruments designed to measure the cosmic microwave background anisotropy on angular scales of degrees to less than a degree.


MAX was and MAXIMA and BOOMERANG are part of the NSF Center for Particle Astrophysics.

Scientific Goals

The purpose of MAX, MAXIMA and BOOMEANG is to measure and eventually to map cosmic microwave background (CMB) anisotropies on the sub-degree angular scale level. This is a significantly smaller angular scale than COBE (>7 degrees) observations. This angular scale is expected to contain Doppler peaks in the average level of fluctuations since not only do the primordial density fluctuations contribute but on this smaller angular scale some of the primordial density fluctuations can have just collapsed carrying the CMB photons with them. This creates additional sources of anisotropy caused both by the condensing (compression) of photons with the matter and by the motion. The peak in fluctuations is expected to be near to one degree on the sky, if the Universe has a flat geometry and on smaller angular scales if the Universe is open.

MAXIMA and BOOMERANG will also be able to check the statistical properties of the fluctuations to determine if they are Gaussian as expected for inflationary big bang models or more non-Gaussian as expected from topological defect theory.

MAX (Millimeter Anisotropy eXperiment)

MAX is a balloon-borne, bolometric instrument that has had 5 flights to date. We are currently preparing for a sixth flight. This time we plan to utilize the new primary mirror that was purchased for the up grade to MAXIMA. For the first 5 flights MAX utilized a 1.2-meter diameter off-axis parabola and a chopping secondary.

[Insert figure showing diagram of MAX] The MAX receiver a four bolometer photometer operating at frequencies of 3.5, 6, 9 and 14 cm^-1 (number of waves per centimeter or wavelengths of 2.9, 1.7, 1.1, and 0.7 mm respectively). The reciever was improved and altered during the flights to lower temperatures first via a He3 refridgerator operating at 0.3K and then with an ADR (adiabatic demagnitization refridgerator) operating below 0.1K.

Click here or alternately here or here to get a list of MAX publications.

Click here or alternately here or here to the MAX data.

MAXIMA (MAX Imaging Array)

MAXIMA is the upgrade of the MAX concept to an array for making images of sections of the sky with an angular resolution of about one fifth of a degree (~12'). MAXIMA utilizes a 1.5-m diameter light-weight chopping primary. MAXIMA is projected to have 14 pixels. For its first flight these will be single frequency-band bolometers but it can handle 4-frequency-channel bolometer assemblies the MAX type.

MAXIMA Gondola
Figure 4. Drawing of MAXIMA gondola with the single-pixel MAX receiver used in the September 1996 flight. The "inner frame" holds the primary mirror, secondary optics, and the cryostat. This inner frame tilts with respect to the outer frame to point the beam in elevation. The bottom of the gondola has a pallet constructed with aluminum honeycomb, which is very light and strong. The structrural members are made of 3 inch wide aluminum angle. A simplified version of the flywheel system used to point the gondola in azimuth can be seen at the top of the gondola. The entire gondola will weigh about 2,500 lbs.

MAXIMA Gondola
schematic in configuration for August 1997 flight. This shows the larger cryostat for the array receiver.

Schematic of the MAXIMA receiver showing the cold optics:

It also shows the three cryogenic stages of the five temperature ranges:

The prime focus shown is from the primary mirror. The primary mirror is very light weight - about 12 kilograms and can be kept stationary, oscillate, or make a roughly triangular with time angular scan on the sky. For the next flight the mirror will make a 4-degree peak-to-peak scan. The entire optics are enclosed in a large shield.

Cold secondary and terciary mirrors allowa cold baffle to be placed at at the optimum spot in the optical path. This baffle rejects millimeter-wave radiation from outside the desired beam pattern. An Adiabatic Demagnetization (ADR) will cool the photometers to 100 mK, and a pumped Helium-three stage will provide an intermediate temperature of 300 mK.

Cryostat & Receiver in another potential configuration. Drawing of MAXIMA cryostat and receiver of a version that contains an array of 8 photometers (seen toward left of drawing). Each photometer will have four separate frequency channels and will look at a 20-arcmin wide circular pixel on the sky. Ray tracings are visible in this drawing show the optical path from the entrance of the cryostat to the entrances of the photometer light pipes..

Showing the bolometer detector assembly, feed horns, and cold plate of the cryostat.

detail of the detector assembly and feed horns.

Figure showing the expected beam pattern on the sky for

List of MAXIMA/BOOMERANG collaborators

List of MAXIMA/BOOMERANG collaborators institutions/positions and responsitibilities.

Photographs of flight preparations and launch of MAXIMA-0 in September 1995.

Expected sensitivity for measuring CMB anisotropy power spectrum for the three planned flights.


BOOMERANG is the upgrade of the MAX concept to an array for making images of sections of the sky from Long Duration Balloon (LDB) flights. For more information consult the BOOMERANG home page.

More Information

Documentation on MAXIMA is available as are the data products for MAX. Further information is available on the CfPA web server on the Cosmic Microwave Background research page.

Return to the Smoot Group page for a complete description of Dr. Smoot's group's research activities.

Revised 27 August 1996;