# Presentation: 114750

## Linac Status

- Eric Prebys
- DOE Review, Proton Source Breakout Session
- July 21,2003

## Linac Performance

- The existing linac is *not* a limit to run II performance... *when running nominally:*
- It could easily supply at least several times the protons the booster can currently accept*
- This is plenty for the collider, MiniBooNE, NuMI, and SY 120.
- There are, however, some stability problems which do affect performance.
- Our chief concern continues to be the vulnerability 201 MHz system, particularly the 7835 triode power tubes
*This is a significant vulerability of the entire lab*
- This was addressed in a pre-review question.
- Paul Czarapata has address this issue in detail in his plenary talk.

- *some external radiation issues would have to be addressed

## Loss/activation Issues

- When the linac is running well, radiation levels just outside the 400 MeV labyrinth are not far below their trip point.
- Linac mis-steering can and does cause trips here.
- If the planned shutdown improvements to the booster have the desired effect, this radiation loss will become a limiting factor.
- We are planning to install a new Lambertson at the end of the linac which should solve, or at least dramatically ameliorate, this problem.
- Activation at other points may become an issue at full MiniBooNE+NuMI intensities

## Stability Issues

- Linac energy (time-of-flight) variations:
- Dramatically affect Booster injection efficiency
- Seem to be related to line voltage (affects filament current)
- Have added an active velocity feedback control
- We’re looking into ways to stabilize the filament current.
- We have occasionally had stability problems when pushing 7835 tubes to the end of their life (sometimes because we’re waiting for a spare)
- 400 MeV line problems
- Loss problems:
- Should be ameliorated by new Lambertson
- Malfunctioning power supplies
- We’ve replaced two
- We’re installing beam line tuning software to stabilize beam position.
- New Lambertson should facilitate 400 MeV line tuning.
- New monitoring software should help identify sources of instability in the future.
- Discussed in instrumentation breakout

## The 7835 Power Triode – Our BIG Worry 

- Very complex technology
- RF, material science, vacuum, chemistry
- Similar to other tubes made by Burle
- 4616 & 4617
- 7835 only used in the scientific community.
- One military user for 4617
- Quality varies from decade to decade

## Tube Throughput with Burle

- Median lifetime: 16 months
- Recent lifetime: Less! (possibly related to vacuum problems)
- We need about 3.41 tubes/year to maintain
- Assuming historical median
- With present tubes: _twice that_.
- Burle now can make/rebuild ~20/year
- Critical path: Final bakeout; two stands, 3-5 weeks bakeout
- Also of concern: Supplier delivery time (e.g., ceramics, cathode)
- Recently had four failures for one success!!
- Delivery time: ~8 months,
- But, often 12 months!
- This is obviously a worry.

## Present 7835 Power Tube Situation

- We’ve received 5 tubes since the last review
- Only two delivered from Burle, after numerous failures
- Two borrowed from BNL
- One borrowed from Argonne
- We now have one spare; we have frequently had zero; we have never had two.
- Next one due “in August”.

## Solutions to the 7835 Problem

- Short term:
- Work with Burle to increase yield and lifetime - already paying off.
- Coordinate our needs with other labs – already doing this, but so far FNAL is the only one benefiting.
- Longer term possibilities:
- Find someone else to make/rebuild the tubes – not a lot of interest.
- Learn to rebuild tubes – some hope at BNL.
- Find a drop-in substitute – No other 5MW triodes.
- Identify a substitute tube (or possibly pair) –
- Promising work at LANL with Thales 628 Diacrode
- Major upgrade to maintain 1970 performance.
- Replace the whole 116MeV linac as part of a global upgrade plan (e.g. cut and past SNS front end).

## Example: 402 MHz Parameters from Young

- Price tag: About $40 x 106.

## Other (selected) Linac Longevity Issues

- Addressed by Elliott McCrory in “Getting the Proton Source to 2010”, Dec. 20, 2002
- http://mccrory.fnal.gov/memos/PS_to_2010.ppt
- High Voltage Modulator
- Switch tubes no longer made
- We have enough to last ~7 years
- Econco can probably rebuild
- Will need to be replaced anyway if we go to a different type of power tube
- 7835 Filament power supplies
- Old and hard to maintain
- Sensitive to line voltage
- Looking into upgrades
- Tank 1:
- Originally a prototype
- If it fails, could take months to repair/replace
- HV Water system: Upgraded in FY03.
- How long do klystrons really last??
- Will they all fail at once?

## The current linac specifications are adequate to meet all the demands expected in the next few years
Working to improve stability
Investigating radiation/activation issues
7835 tubes remain our primary worry
A major lab vulnerability
No easy fix
The final solution depends on the future direction of the lab.

- Working to improve stability
- Investigating radiation/activation issues
- 7835 tubes remain our primary worry
- A major lab vulnerability
- No easy fix
- The final solution depends on the future direction of the lab.

- Linac Summary