# Presentation: 504882

## Dog(leg)s of War

*Eric Prebys*
- Run II Meeting
- March 13, 2003

## Dogleg Problem

-  Each of the two Booster extraction septa has a set of *vertical* dogleg magnets to steer the beam around it during acceleration.
- More powerful doglegs were installed in 1998 to reduce losses early in the cycle.
-  These magnets have an edge focusing effect which distorts the *horizontal* injection lattice:
-  50% increase in maximum 
-  100% increase in maximum dispersion.
-  Harmonic contributions.
-  Effect goes like I2.  Now tune to minimize.
- Recently got an unusual opportunity to explore potential improvements from fixing the problem.
- Working on schemes to reduce or remove problem.

- Septum

- Dogleg Magnets

## Parasitic Focusing

- vertical  focusing if beam has component *into* page

- vertical focusing if beam has component *out of* page

- Side View

- Top View

- /2

- /2

- f

- f

- Rectangular (RBEND) magnet:

- Focusing in *non-bend* plane!!

- Always focusing!!

## Parasitic Focusing (cont’d)

- Sector (SBEND) magnet:

*B* ~constant

- Nominal *L*

- Longer *L*

- Shorter *L*

- Focusing in *bend* plane!!

- Exit angle

- Non-bend  plane focusing

- bend plane focusing

- SBEND

- RBEND

- Trade-off:

## Predicted Effect of Doglegs

- x

- Dx

- x

- Dx

- Ideal Lattice

- Add Doglegs

## Preliminary Study: Dispersion

- Measured dispersion for different dogleg currents:

## Preliminary Study: Tune

- 100% Dogleg Current

- 60% Dogleg Current

- Tuneshift ~ prediction

## Dead Dog Studies

- Took advantage of recent TeV Magnet failure to raise the Long 13 (dump) septum and turn off the associated dogleg.
- Doglegs almost exactly add, so this should reduce the effect by almost half.
- The mode of operation prevents short batching, booster study cycles and RDF operation.
- Had about 36 hours of study in this mode.
- Bottom Line: **major improvement**.

## Transmission After Tuning

- March 3, 7 turns, both dogs

- March 6, 7 turns, 1 dog

## Transmission with One Dogleg

- Injected Charge (E12)

- %

## Record Running w/o Dogleg

## Booster Performance Over Time

- Total Booster Output (protons/minute)

- Energy Lost per Proton  (W-min/proton)

- MiniBooNE

- Discovered Problem: tune to reduce dogleg currents

- Test with one dogleg off (halfway to MiniBooNE goal!)

## Comments

- We have verified the dogleg effect and that it is a problem.
- We’ve tuned in our present configuration for 5 years, and were able to achieve record performance with only 36 hours of tuning in the one dog configuration. Almost certainly more room for improvement.
**Remember, only one dogleg was removed!**
- Now, how fix the problem:
- Short term: ameliorate problem ASAP
- Long term (~2005): eliminate problem.

## Short Term Solutions

- Tune to minimize current?
- helped so far, but near limit.
- Maybe raise L13 septum a bit?
- Motorize L13 septum to switch modes quickly?
- Operational nightmare
- Eliminate L13?
- Find another way to short-batch
- Make a dump in MI-8 for Booster study cycles?
- Correctors?:
- These don’t look like quads, so can’t find a fix – yet.
- Spread out doglegs (effect goes down with square of separation):
- Not a lot of room. Maybe separate downstream magnets?
- Three-legged dog?
- Turn of the third of the four magnets.
- Need to increase first two reduces net improvement.

## Long Term Solutions

- Large Aperture Lattice Magnets?
- Obviously the “right” idea.
- Must match lattice AND (preferrably work with existing resonant circuit).
- Potential for big screw-up.
- Pulsed extraction bump (Lackey)?
- New ideas welcome
**Brainstorming session tomorrow at 10:30**

## Final Comments

- After several false starts, Beam Physics began to get seriously involved with Booster matters in late 2002.
- This problem was almost immediately found.
- What other surprises await?