# Presentation: 810412

## Calibration of the Upgraded Tevatron BPM System

- Rob Kutschke
- CD Accelerator Coordination Meeting
- November 30, 2004

## Goals of the Upgraded System

- Must be more robust than the old one.
- Old system sometimes delivered stale data.
- Margaret’s group will ensure this is correct.
- See Pbars simultaneously with P.
- Has been demonstrated.
- Improved resolution.
- Has been demonstrated.
- We are still working on the final calibration methods to get the best precision and accuracy.

- Rob Kutschke, BPM Calibration

- 11/30/2004

## Cartoon of the System

- A and B  are complex numbers.
- Given measured (A,B)Proton and (A,B)Pbar
- Compute the position and intensity for both protons and Pbars.

- Cables from tunnel to house.

- Filter Board

- Echotek Board

- Pickups

- Beampipe

- A

- B

- Digital

- Analog

- VME,          ACNET ...

- Pbar

- P

- B

- A

- Beam’s eye view

- Side view

- Pbar A

- Proton A

- Pbar B

- Proton B

- Rob Kutschke, BPM Calibration

- 11/30/2004

## Overview of Calibration

- Survey offset (mechanical offset).
- Response of the pickup when there is a single beam species in the machine.
- Differential attenuation and delay of A and B in the analog sections, up to and including the digitizers.
- Imperfect directionality of pickups: important when both beam species are in the machine.
- Digital world should have no measurable channel to channel variation.
- Some calibrations depend on operating mode and the pattern of bunches in the machine.

- Rob Kutschke, BPM Calibration

- 11/30/2004

## Operating Modes

- Closed Orbit Mode (CO)
- Average position over many orbits and all bunches.
- If betatron or synchrotron motion is present, average it out.
- Compute both P and Pbar positions.
- Turn by Turn Mode (TBT)
- Average proton position for each turn.
- Single bunch of protons only.
- Typical use is to kick the beam and to watch its motion.
- Injection Turn by Turn Mode (ITBT)
- Special case of TBT, triggered by injection.
- Automatically enters closed orbit mode on completion.
- Short gate Mode (SG)
- Average position over a small number of bunches ( 2? ).
- Compute both P and Pbar positions.
- Separate Pbar from P by timing.  Not always possible.

- Rob Kutschke, BPM Calibration

- 11/30/2004

## Requirements: Beams-Doc-554

| Property | Proton | Pbar |
| --- | --- | --- |
| Measurement Range | 15 mm | 15 mm |
| Absolute Position Accuracy | < 1.0 mm | < 1.0 mm |
| Long Term Position Stability | <  20 m | < 20 m |
| Best Orbit Position Resolution | <  20 m | < 50 m |
| Position Linearity | < 1.5% | < 1.5% |
| Relative Position Accuracy | < 5% | < 5% |
| Intensity Stability | < 2% | < 2% |

- Numbers are “3” requirements ( normal AD practice 
- Requirements above are for closed orbit mode.
- Some requirements are relaxed for other modes.

- Rob Kutschke, BPM Calibration

- 11/30/2004

## My Comment on Requirements

- If we miss the requirements by a little bit, the system will still work.
- I am not aware of any cliffs that we can fall off of if we miss the specs by a little.

- Rob Kutschke, BPM Calibration

- 11/30/2004

## Precision and Accuracy

- Absolute accuracy is a much, much poorer than the resolution (precision):
- Resolution on any one closed orbit measurement is of the order of 10 m ( 1 ).
- Spec for absolute accuracy is 330 m ( 1 ).
- Absolute accuracy is probably dominated by the physical alignment of the pickup plates wrt the quadrupoles.
- Known from surveys done during assembly 20 years ago.
- I have the measured offsets but I have not yet found anyone who can tell me the error on these measurements!
- Tevatron department knows how to use a superb stability monitor, even if the absolute calibration is poor.
- Must avoid the temptation to chase small but irrelevant effects.

- Rob Kutschke, BPM Calibration

- 11/30/2004

## The Orthogonal Coordinate

- This BPM measures V.
- Response also depends on H.
- The effect of H is, at most, a few hundred microns in V.
- Beams-doc-1076
- The plan:
- Will not correct online.
- Will correct offline.

- V

- H

- Rob Kutschke, BPM Calibration

- 11/30/2004

## Model of Pickup Response

- Model is valid when on axis in orthogonal coordinate.
- I0 = true beam intensity
- P  = true beam position
- g,k parameters of the pickups.
- There are 4 classes of pickups.
- Parameters are believed to the same for all BPMs within a class.
- Given A,B,g,k: solve for I0 and P.

- Rob Kutschke, BPM Calibration

- 11/30/2004

## Differential Attenuation

- t = differential attenuation.
- 0.1 db error in t gives to 150 m position error.
- Using a grid study one can solve for t.
- Old system parameterized this as an “electrical offset”, not a multiplicative correction.

- Rob Kutschke, BPM Calibration

- 11/30/2004

## Cancellation of Proton Signal on the Pbar Cables

- a,b,c,d are complex numbers which change from one BPM to the next.
- Depend on properties of pickups, cables, fitlers.
- Scale is mm early in Pbar injection.
- Scale of Pbar contaminating Protons is currently of O(50 m);  will worry about this later.

- Rob Kutschke, BPM Calibration

- 11/30/2004

## What We Have Done (1)

- Proof of principle measurements: CO, TBT, SG.
- Only injection TBT is missing.
- Measured the resolution in CO and SG
- Actually we bound resolution from above since there is true beam motion that we cannot remove.
- Demonstrated stability throughout a store.
- Demonstrated Pbar measurements in presence of protons for both CO and SG.
- Results differ by 600 m.
- Need to track this down.

- Rob Kutschke, BPM Calibration

- 11/30/2004

## What We Have Done (2)

- Observed the effect of the parameter k ( the quadratic term in the intensity).
- Observed the effect of differential attenuation and learned how to remove it using a grid study.
- Demonstrated CO mode for:
- A batch of 30 uncoalesced bunches in RF consecutive buckets.
- Standard 36x36 coalesced bunches.
- Single coalesced bunch of protons.
- These all give the same position.

- Rob Kutschke, BPM Calibration

- 11/30/2004

## What We Have Done (3)

- 1113/5 is not an integer
- Gives rise to phase artifacts when trying to combine several measurements into one.
- We know when this hurts us and how to work around it.

- Rob Kutschke, BPM Calibration

- 11/30/2004

## What Am I Doing Now

- I am preparing a summary of all of the effects we know about:
- How big are they?
- On what time scale do they change?
- Expect to be done in < 2 weeks.
- From this I will develop a plan for the remaining work.
- Some things will be ignored because they are masked by larger effects.
- We will have to make some decisions about what is on-project and what is off-project.

- Rob Kutschke, BPM Calibration

- 11/30/2004

## Later On (Maybe off project?)

- My guess is that anything which requires non-trivial knowledge of beam physics to correlate data from multiple BPMs is off project.
- Effect of beam not being parallel to the pickups.
- Lebedev effect: bunch axis has a yaw and pitch wrt its direction of travel.

- Rob Kutschke, BPM Calibration

- 11/30/2004