# Presentation: 949541

## Answers to Committee Questions

- Eric Prebys
- FNAL Accelerator Division

## 1. Any Information on Measured vs. Theoretical Collimator Performance?

- Details of the collimator design can be found in Fermilab Beams document:
- N.V. Mokhov, et al, “Fermilab Booster Beam Collimation and Shielding” (BEAMS-DOC-622-v1).
- Predicts average of .1 W/m @ 60 kW operation
- Prior to Collimators, saw 1W/m @ 20 kW operation
- -> Expect factor of ~30 reduction.
- Initial data indicate factor of ~2-3 reduction so far.
- Things to consider:
- Model does not adequately account for beam loss at L13 region.
- We do not yet effectively collimate horizontally, due to beam motion.

## 2. Collimator Activation Limits and Maintenance Strategy

- The collimators were designed so that all potentially high maintenance components (i.e. motors and LVDT’s) are well away from the beam and should remain quite cool (<50 mR/hr @1 ft) even at the highest intensity.
- The hottest areas will be the beam pipe in the region of the collimators.
- This region is shielded from the aisle by an “iron curtain”.

- Biggest worry would be replacing a BPM or corrector package behind this wall, but we feel that with proper planning, we could do this even with activation > 1R/hr @ 1ft.
- This is a concern and we will continue to monitor it.

## 3a - RF Voltage vs. Intensity

- We have gotten as many as 6.7E12 protons to transition, but can only get about ~5.5E12 through transition.
- We believe that at least part of the problem getting through transition is RF voltage.
- Some details of measurements and calculation can be found in FERMILAB-TM-2238 (J. Maclachlan, X. Yang).
- Primary effect seems to be real impedance, so to first order, expect linear scaling with RFSUM
- 1 or 2 cavities would be a 5% or 10% increase in beam.
- This is ~consistent with the effect of losing a cavity.
- Beam loss at a particular intensity more difficult to model.
- Efficiency seen to rise up to the highest RFSUM we can achieve.
- Increased reliability also a factor in decision to add RF stations.

## 3b Gamma-t Jump

- We have implemented hardware improvements needed to operate system at high rep. Rate.
- Have demonstrated operation at moderate intensity
- Issues:
- Alignment of pulsed quads: beam kicked at transition
- Effect on coupled-bunch modes.
- Studies increased recently:
- X. Yang, J. Maclachlan working together with Argonne people (K. Harkay, J. Dooling, J. Norem).
- Expect more definitive statements soon.

## 4. Heating/Rad damage in ORBUMP magnets

- Heating has been well modeled and should not be an issue at all in the ferrite, even at the highest rate.
- The copper conductor will be water-cooled.
- All mechanical parts of the magnet (feed-thrus, etc) are placed and designed to minimize radiation damage.
- There are no good data on the rad-hardness of this particular ferrite:
- Based on experience with other ferrite, we believe it is not an issue.
- We will irradiate a sample to investigate the potential for damage.

## 5. MI Losses with NuMI Running.  A worry? 

- Activation has not been an issue in the Main Injector up until now.
- Vast majority of the ring < 20 mR/hr @ 1ft
- A few (~2-3) points ~50 mR/hr near small aperture quadrupoles
- Max 100 mR/hr near some Lambertsons
- Max NuMI+slipstacking ~10x current beam.
- Simple scaling would indicate activation would become “an issue”, but not a major worry.
- More studies needed on how losses scale with multi-batches and slipstacking.
- Obviously needs more attention in a Proton Driver scenario.