PIP - 200 MHz Modulator
Loft
AD/EE Department
PIP - 200 MHz Modulator - WG2
Attendees: J. Walters, D. Wolff, H. Pfeffer, T. Butler, F.G. Garcia
Date: 07/20/2011
Location: Loft 1:30 PM
The meeting started with a review of the objectives and measurables of the PIP - 200 MHz Modulator Working Group.
PIP
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WG: 200 MHz Modulator
Objectives: To improve reliability of the 200 MHz FNAL Linac for the next 15+ years.
- WG1: Replace the 200 MHz portion of Linac with a SNS design (R. Pasquineli)
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WG2: 200 MHz Modulator Upgrade based on existing 7835 System
- AD/EE Support Modulator or Continental Modulator - This meeting
- WG3: 200 MHz Klystron Upgrade (R&D) (A. Moretti)
Last summer, when the Task Force was formed, Trevor and Larry were assigned to work on this topic. They came up with a Modulator Specs list which was presented at the meeting (Material attached to the main page) as the base for the discussion.
The 7835 Power Tube Triode Parameters are shown on the following table.
| Type | Cathode-Driven Triode |
| Designed | 1960 |
| Filament | Thoriated Tungsten |
| Filament V | 4 V |
| Filament I | 6800 A |
| Plate Dissipation | 300 kW |
| Plate Voltage Max | 40 kV |
The meeting evolved on the discussion of the Modulator WF. Trevor showed some examples of the Modulator Voltage and Current, Gradient and Beam Pulse WaveForm for each station which guided the discussion.
- Flat Top:
One of the discussion evolved around the current length of the flat top (180 usec). Despite the fact that at the time of the meeting there was no definitive information regarding the specs for the RFQ source, the group agreed with Trevor's argument that regardless of what the new source is cabaple of, one can not expect to have a beam pulse larger than the 800 MHz pulse length which is in the order of 110 usec. Also, the new LLRF acquire data inside a 6 usec window prior the beam pulse.There is an interval in the order of 2-4 usec prior the beam arrival. Therefore, a 10 usec requirement was added before and after the beam pulse totalizing a flat top of 130 usec (a reduction of ~ 25%) .
2. Rise Time
The 125 usec rise time was found adequate.
3. Fall time
No conclusion was drawn about this fall time at this meeting.
Another important topic discussed was the rise/flat top/fall time during beam time. Questions discussed:
1) What is the maximum ever needed Voltage the Modulator has to produce during beam time?
2) Is there a need to have steps rise control during the beam pulse? what about the fall time?
Answer: after some discussion the group decided that a squarewave with tilt should be sufficient. Specifications of rise/fall time still remains to be determined. Dan Wolff would like to see a screen capture together with the raw data of the rise/fall time during beam time. Trevor and Fernanda will provide such data for the next meeting.
So, below is a table showing the Modulator specification identified during the meeting so far.
Linac 200MHz Modulator Specifications
(Work in Progress)
| Current Spec | New Spec | |
|---|---|---|
| Max. Modulator V | 40 kV | 35 kV |
| Max. Modulator I | 375 A | |
| Rise time | 125 usec | |
| Flat top | 130 usec |
Next meeting: Wednesday, July 27, 2011.