Technical projects
Millimeter wave EPR spectrometer. Further details
on www.bruker-biospin.com.
The project reached next stage see Bruker
press release . July 1, 2009
Spectrometer
Manager (SpecMan)
is a third generation of the spectrometer control program which I have
touched. Developers are Boris Epel, who is a leading programmer, myself
and Stefan Soll. SpecMan has elaborated architecture built to arrange
in a consistent way instrument control, data acquisition and flow, and
pulse sequence programming. It gives to user interactive control over
all experiment parameters in real time and provides flexible and effective
way in experiment design and evaluation. Click here
for further details.
4.01.07
This is next generation of the acquisition system for epr@ETH. PCI bus
is chosen as a system integration bus and recent PCI boards are selected
to fit the most demanding tasks in pulse EPR. Those include 2 GS/s real
time averager from Acqiris. It has dual-input with tunable gain and offset,
500 MHz bandwidth and it's able to accumulate up to 64k traces at once.
Two AWG boards from Chase Scientific provide four RF channels and 12 pulse
channels. The system is controlled by SpecMan.
Recent poster
(Denver, 2003). 3.01.04.
Open
for users in 2005. This spectrometer is a renovated version of the ETH-type
pulse X-band instrument. For the latter see T. Waker PhD thesis for technical
details. I have used this instrument to develop pulse programmer, control
system II and SpecMan. Finally I completed the installation and rebuild
mw part in a way more convenient for users. Currently Xband II is operational,
able to make HYSCORE or ENDOR experiments faster than E580 from Bruker
BioSpin. In the ENDOR case stochastic RF sweep, passive RF leveling and
others useful features are available. A little things left to do there
is to swap pulse programmers between this instrument and S-band spectrometer
which I put under SpecMan control as well (cw only at the moment). With
Jörg Forrer and Rene Tschaggelar.
We
design and build ourselves a modern pulse programmer. Jaap Shane, who
was very enthusiastic about electronics, and Boris Glass designed an ASIC
for the pulse EPR applications (see picture on the left). Then I was driving
this project trying to get working the complete system consisting frontend
PC and Texas DSP which controls pulse forming unit with two EPR ASICs.
The team was Jörg Forrer and Rene Tschaggelar (electronic engineers)
and Jürg Keller (programmer ). Finally
I was able to record ESEEM and HYSCORE in real time, monotonically
at about 1.5 kHz from the beginning of a experiment till its end, using
this programmer. 3.10.03
For the beginning the probe-head was designed to overcome the main disadvantages
of the ER5106-QTE probe-head (Bruker BioSpin) - small sample size and
a little bit low P-to-B1 conversion factor. The goal was reached (3.8
mm tubes, 5 ns pi/2 with 40 W incident power and strongly overcoupled
cavity) and since year 2000 a lot of experiments, including matching or
decoupling, were made by my colleagues using this probe. Look on Schweiger's
group publications, take one where Ka-band (aka Q-band) is mentioned,
most probably this probe was exploited. Then cw and ENDOR options were
included. At the end the probe-head almost as easy in use as Bruker's
one, it has better sensitivity and stronger B1 at the same power; ENDOR
performance is weaker than ER5106 has, but note that in last case the
conversion B2/Prf is extremely high! The people who was/is involved in
the projects: toolmakers Willi Groth (retired recently) and Barbara Feuer
(who take the baton) and electronics engineer Jörg Forrer who gave
many valuable suggestions for the design. Recent poster
(Portoroz, 2003). 3.01.2004. Finally I have published a paper
because Arthur asked me many times about. 
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Operational since end of 1998. The spectrometer was built by Jaap Shane and Jörg Forrer. I just made it working, then teached users how to deal with it, rebuild and finally kept the spectrometer alive. The spectrometer has 100 W of mw power at 35 GHz, good acquisition system E580 from Bruker, thanks to Peter Hofer who gave us opportunity to be first who implemented such a system on home-made spectrometer, and it is equipped with state-of-art mw components. The most components, made using fin-line technology. I still do some upgrade here, ER036 FTNMR gaussmeter has been implemented recently, but not so much as before. The photo on the left/top was taken in 2001 in old Chemistry building and on the left/bottom in 2002 in new building at Hönggerberg ETH campus. Some details about spectrometer can be found here. To see user guide with more detailed scheme click here. 3.10.03 Statistics: time counter on 187Ka
TWT shows 15'562 h. Taking in account that spectrometer is 8 years
in operation one obtains averaged usage 5 hours per day! The paper
about spectrometer cited, as a reference to instrument, 18 times
which is slightly less than number of work done using it. 7.11.06 |
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The
probehead was built by V. Krymov. I did just a small improvement. The
tricks here were how to tune W-band transmission line (about 1 m long
with several junctions) without network analyzer and what to change in
small cylindrical cavity to make it transparent to rf field. With Daniella
Goldfarb. 3.10.03
Here my job was to teach students how to do ENDOR on X-band. And I earned a good experience in conventional and advanced ENDOR. There were of course some technical problems I was dealing with. Here I was working with two spectrometer control programs one from ETH, written by J.M. Fauth, and another one, known as "Jaap's program", written by Jaap Shane. I was maintaining the latter. Some examples, as well as spectrometer description you can find here. With Daniella Goldfard. 3.10.03
In
operation since 1990. I guess the similar system is still in operation
at KSU at pulse X-band spectrometer, and most probably I will be able
to run my one (Ka-band, KSU) even now.The electrical/logical and mechanical
specifications of the system were introduced by B. Kazakov and I. Motygullin
(MRS, KSU). 16-bit bi-directional data bus, (4+8) bits address space.
20 slots in crate, 16 of them are programmable. Priority interrupt controller,
crate controller, address decoder and link to ISA. Fully featured/very
powerful system and what is even more important - it's simple enough to
be build by non-engineer. 3.10.03
My
first spectrometer was a 35 GHz pulse EPR apparatus. Home-made in full
sense of this word. I'm not only assembled the mw components but also
fixed some of them and built all analog control circuits of the pulse
bridge as well as construct whole control system (see above). The spectrometer
was made using solid state mw components only. No klystrons, no tubes.
It has three mw sources, two are 50 mW cw Gunn oscillators and third one
is pulsed IMPATT oscillator based on two silicon double drift diodes.
The frequency of the first Gunn was voltage controlled (varactor) and
this source was used for a probe-head tuning. The second Gunn is one of
most stable free running mw sources (no DR, no external thermostabilization,
only a diode camera , stabilizing cavity and isolator) I ever seen. It
was used for cw in absorption mode and saturation recovery measurements.
The key component is the pulse IMPATT oscillator. Two diodes ( p-p+-n+-n
) were fixed in coaxial lines and then placed at certain positions in
a section of WR28 waveguide. By proper adjustment of the diode positions
and an amplitude and a shape of the current pulses applied to the diodes
I was able to reach 2 W power with the negligible frequency chirp. There
are many others beautiful components inside, some details are mentioned
there.
Rafail (left bottom) and Yurii (probably making this photo) built even
a loop-gap resonator for 35 GHz. 3.10.03