Recently in hardware Category

It's gone! We boxed up our Q315 yesterday and sent it back to ADSC for an upgrade to the Q315r model.

Essentially this is an upgrade to the amplifiers that read out the CCDs and the other associated electronics for getting the raw images to the detector computers for processing. The fiber optic tapers and CCDs will not be replaced. The overall benefits of this upgrade are an decrease in read-out noise, an increase in speed, and the ability to use stored dark current images. Here are some excerpts from a detailed comparison performed by James Holton:

          ampgain  eo_gain    readnoise  pixel  fog photons  allowable
detector  e-/ADU   e-/photon  e-/pixel    um      /100um2   redundancy
----------------------------------------------------------------------
Q315      12       7.3        27(swbin)  102.4     12.4         1.00
Q315       4       7.3        16(hwbin)  102.4      4.37        2.85
Q315R      4       7.3        11.5       102.4      2.26        5.51
M300HE     4?     11           7.7        73.2      1.71        7.29

"fog photons"/pixel is the number of extra background photons/pixel required to increase the noise in a pixel by the same amount as the read noise. Since the "fog photons" will add with redundancy, the far right column shows how many fold more images (relative to a Q315) you can spread the same total x-ray exposure over and get the same total read noise (as if you collected the data with "unit" redundancy on a Q315).  The Q315R will allow 5.5x more images than what we are doing now: 12 "fog photons"/pixel on a Q315 in swbin mode.

James goes on to compare the relative crysal sizes that will produce equivalent diffraction:

All things being equal (including the extent of radiation damage), the intensity of the spots and background are proportional to the crystal volume.  Doubling the crystal volume will double the signal (spot intensity) as well as double the background (in the ideal case of a "naked crystal" with no air scatter or other sources of background).  So doubling the crystal volume makes the noise (sqrt(signal+background)) go up by no more than sqrt(2).  Unless the crystal is bigger than the beam, or it is so thick that it attenuates the beam, radiation damage will be proportional to photons/um2, which has nothing to do with the crystal size.  This means that, for the same extent of damage, the signal/noise ratio goes as size^(3/2) if "size" is the linear dimension of the crystal.  That is, doubling the linear dimension of a "round" crystal will nearly triple the signal/noise (2.83x), and a 10% increase in the "size" (linear dimension) will increase signal/noise by 15%.

If we have some high-res spot with I/sig(I)=2 in the absence of any background or read noise, then there are (on average) 4 photons in that spot (4/sqrt(4) = 2).  Spots typically take up on the order of 25 pixels.  So, adding 0.1 "fog photon"/pixel (as on a Mar300HE) will make I/sig(I) of this spot drop from 2.0 to 4/sqrt(4+25*0.1) = 1.6.  Increasing the crystal size by 12.5% will increase the crystal volume by 42% and put 5.7 photons into this same spot (for the same exposure time and therefore the same amount of radiation damage) and bring I/sig(I) back up to 5.7/sqrt(5.7+25*0.1) = 2.0.  This means that the crystal size needed to achieve a given resolution limit on the Mar300HE is 12.5% larger than the crystal size needed to achieve the same resolution with an ideal photon-counting detector (such as the Pilatus). This is assuming there are no other sources of noise, including x-ray background.

Changing the read noise to 2 "fog photons"/pixel will make the I/sig(I) of this 5.7-photon spot drop from 2 to (5.7/sqrt(5.7+25*2)) = 0.76.  Bringing the signal up to 16.3 photons/spot will bring I/sig(I) up to 2.0 again.  This represents a ~3-fold increase in crystal volume (16.3/5.7=2.86) and a 42% increase in crystal size.  To put it another way, using the Mar300HE instead of a Q315R would let us get away with crystals 30% smaller in linear dimension for a given resolution limit (and given amount of damage).  Going from a Q315R to a Q315 (with 21 "fog photons"/pixel) will require 47.9 photons in the spot (47.9/sqrt(47.9+25*21) = 2.0) and another 43% increase 

detector    photons/spot   xtalsize
perfect          4.0     0.63 or -37%
M300HE           5.7     0.71 or -29%
Q270             7.8     0.78 or -22%
M300            12.2     0.91 or -9%
Q315R           16.3     1.00
Q315            47.9     1.43 or +43%

The take home message is that our new Q315r will be way better than that old Q315 peice of junk. We will now collect more accurate data in less time with smaller crystals.

In order to make room for the new robot sample dewar we’ve reconfigured the xyz stage and mounting hardware for the Oxford Cryojet. As you can see from these two photos the cryojet is now securely fastened to the gold sample stand.

BACK:

FRONT:

This is the contraption that was supporting the cryojet previously:

In preparation for our implementation of the SAM crystal mounting robot we've reorganized the equipment rack to accommodate a new graphics workstation that will be the primary interface for users collecting PX data. Additionally we've set up dual monitors so that users can collect data and control the beamline on one LCD and process data on the other LCD.

Big things are afoot at the SIBYLS beamline. Our Epson SCARA robot arm has finally arrived. This is the major component of our new auto crystal mounting robot. We have decided to install a system very similar to the Stanford Automated Mounting (SAM) system. Our decision was based on several factors:

1) It was within our budget.
2) It will be possible to integrate into the BLU-ICE beamline control software (also developed at the SSRL) which we are already using at the SIBYLS beamline.
3) This system has a large capacity (2 cassettes each holding 96 samples).
4) The robot is compatible with the uni-puck.

Essentially we will be able to adopt about 90% of the Stanford system with a few modifications to the sample dispensing dewar.

If you have any suggestions for a name please leave a comment. Berkeley Auto Mounter (BAM) is not an option because it is already used.

We have a coaxial cryojet configuration, which is very convenient for users with multiple sample pin lengths as their samples are guaranteed to lie within the center of the cryostream. However, this means that we often have problems with the build up of ice on the sample pins and the goniometer stalk. Therefore we have installed a sample heating shield. The original design came from Stanford, but we purchased two of these units prefabricated by Crystal Positioning Systems. We are using an Omega CN77332-C2 temperature controller in conjunction with a 14V AC transformer. Although the heating shield is working well it has a 6mm inner diameter bearing which was designed to fit the standard Supper goniometers, and does not fit on our 10mm goniometer stalks. Recently I machined our Huber goniometer stalk to accept the 6mm bearing.

Here is a picture of the current setup.

We are in the process of building a Helium box for the PX endstation. It has a lower and upper box. The lower box will be permanently affixed to the endstation, and the upper box will be removable. Although it is a little complicated to remove, it takes about 5 minutes to install/remove. I've posted a few pictures so you can get an idea of how it will work.