Siberian Branch of Russian Academy of Sciences

APG Web page

Welcome to the APG home page.

The APG - Adiabatic Pulse Generator is a program that generates “constant adiabaticity” RF-ramps to convert magnetization into the singlet order; such RF-pulses are implemented to generate singlet order in a two-spin system by means of two methods: APSOC [1] (applicable to an arbitrary spin pair) and SLIC [2] (applicable to strongly coupled spin pairs only). The program generates pulse envelopes (wavelists), which can be used at Bruker spectrometers with Topspin (version 3.2 or lower). 
APG script is written in MATLAB language and has graphical user interface for easy handling.
The script (AdiAPSOC.m) and interface (AdiAPSOC.fig) can be downloaded here:
Extract both files and run AdiAPSOC.m file in MATLAB environment.

Here is an explanation how to use the program.
1.       When opening the program, you find some default setting of the RF-ramps. First of all, you should define your spin system parameters (given in Hz), namely, the difference in NMR frequencies  and spin-spin coupling .

2.       Choose the spin order conversion method in the pop-up menu under “spin system parameters”.

3.       If you choose APSOC, consider redefining the frequency offset from the center of the spectrum (defined as the mean NMR frequency of the spin pair). This offset does not affect too much the overall efficiency for adiabatic pulses, therefore in most cases a 10 Hz offset should work fine. An automated function that calculates the optimal frequency offset will be available soon. For SLIC, the offset should be equal to zero.

4.       To specify the maximal RF-field, use the “RF field confiner” parameter. The program will stop increasing the RF-field once the deviation of one of the spin eigenstates almost coincides with the singlet state. The confiner thus specifies the degree of coincidence; it should be set close to 1 (but not equal to 1). The resulting v1max value will be given in Hz as “the max RF amplitude (defined from calc)”.

5.       After defining the parameters, click on the “calculate” button. The profile will appear in the right plot window. One can also look at the RF-field profile in a separate window by clicking on the “plot in a separate window” button.

These first five steps are explained in Figure 1.

                                   Figure 1.

Steps 1-5 provide the desired RF-field profile. The next thing to do is to optimize the switching time for magnetization-to-singlet conversion. For this purpose, you can perform a spin dynamics calculation to obtain the optimal switching time.

6.       Specify (in seconds) the maximum and minimum length duration of the RF-ramp. The starting point is zero and the final point should surely exceed 1/J and 1/dv.

7.       Specify the number of points in the time interval.

8.       Maximal RF amplitude is the same as that defined in step 4. One can slightly change it to round the number.

9.       Click on the “calculate” button.

10.       To determine the optimal time, click on “Plot in separate window” and define the optimal time by using the matlab tool “Data cursor”.

11.       Specify the number of points in the profile and click on the “create wavelist” button. By definition, there are 1000 points in the list of RF-field values.

Steps 6-11 are explained in Figure 2.

                     Figure 2.

The wavelist (with ramped up and ramped down RF-amplitude) will appear in the same folder where the APG located. The data are written in the form APSOCadiB1=XX_up, APSOCadiB1=XX_down or SLICadiB1=XX_up, SLICadiB1=XX_down, depending on the spin order conversion method. Here XX is the maximal pulse amplitude. These pulse envelopes can be used to run NMR experiments with singlet states. To use this wavelist, put them into the folder \exp\stan\nmr\lists\wave\user.

                                                                                                                                   last update 06.01.2019