Here is a bit of advice. DON'T CONNECT THE USB-6501 DIRECTLY TO THE 25,000 VOLTS!
Are you joking about this application or are you serious?
If you are serious, what kind of help do you want?
a proton accelerator using Labview and a NI USB-6501
in This thread a LabVIEW newbie was helped by this community to develop a queued state machine that responeded well to user inputs. I would recommend reading the link for both developing a knowledge base to build on as the problem present was similar, and because the original poster presented this comunity with a great exaple of how to maximize the value of contributors from the forum.
I will reiterate Ravens advice- don't connect the 25,000V to the USB DAQ
on a more serious note- I would recommend an Event Driven Queued State Machine approach as the best archetecture for this set of requirements. Although it involves some non-trivial understanding of LabVIEW to implement,your requirements seem non-trivial as well. (and, paranthetically- it sounds like an interesting experiment to me)
There are expert resources out there for consultaion but- this community can offer as much support as you need to aid you in developing the understaning of LabVIEW concepts.
First, I have to mention there are many people that are far advanced in LV than I am, so consider that when you read this.
I have two different applications that use analog DC output to generate voltage up to 100,000 vDC. I thought maybe you could use a PID loop to count up and down, let the user control the rate, final voltage, and convert the PID loop output to binary, but I don't think this would work because you need to count up and down at a steady pace (pid loops slow down when they get close to the required set point).
I think your best bet is a state machine. I have included a simple one, but did not get very far with it. Go to NI Developer Zone and type state machine in search box, open Application Design Patterns: State Machine.
I need some information regarding how far you have gotten, ie. are you able to write to the digital outputs, if you have kv feedback from the output (the USB-6501 has no analog input for this value), and is there a reason you want to save the data to a notepad file?