# Presentation: 091389

## RHIC IPM

- Electrons from ionization give accurate profiles.
- We have demonstrated single-bunch profiles.  Turn-turn measurements of a
- single bunch at injection show dipole and quadrupole oscillation.
- The original detector was sensitive to background and noise from,
- 	1.  Rf coupling to beam
- 	2.  Radiation spray from beam loss
- 	3.  Secondary electrons
- Rebuild in 2002 greatly reduced these backgrounds.
- Rebuild in 2003 will have more accurate collection electric field and internal
- calibration source.

## Mountain-range plot of 50 turns at injection

- Detector channels are plotted
- on the vertical axis and turn
- number is on the horizontal
- axis.  The betatron oscillation
- is the vertical tune of 0.32

## Dipole oscillations at injection

**Dipole oscillations at injection**

- The centers of the bunch for
- 128 turns after injection were
- calculated by fitting Gaussian
- curves to data from each turn.
- This sequence was Fourier
- transformed to give a power
- spectrum.  Data are from the
- vertical IPM and shows the
- vertical tune of 0.32 and the
- horizontal tune of 0.13.

## Plot of 128 measured rms widths

**Plot of 128 measured rms widths**

- Plot of measured rms beam widths over 128 consecutive turns.  A
- Fourier transform of this sequence gives the quadrupole power
- spectrum.  Width units are mm.  Width is 6.2mm and width
- oscillation amplitude is 0.6mm, about 10%.

## Quadrupole oscillations at injection.

**Quadrupole oscillations at injection.**

- The rms widths of the bunch
- for 128 turns after injection
- were measured.  This sequence
- was Fourier transformed to give
- a power spectrum. The betatron
- frequency was measured to be
- 0.32 so the quadrupole frequency
- is 0.64.  Since sampling is done
- at the rotation frequency the
- quadrupole frequency appears at
- the aliased frequency of 0.36.
- 	This is a linear
- plot with the peak at 0.048 and the
- noise floor at 0.002, giving a
- S/N=24.  Since the data had a
- width oscillation amplitude of
- 10% this measurement was
- sensitive to a minimum width
- oscillation of 2%.

## Emittance growth from beam-beam

## Profile of polarized proton beam up acceleration ramp

## Modification of transducer

- The detector components were inserted inside the beamline.  This restricted the aperture and made detector
- components vulnerable to stray beam.  The new detector chamber will allow the detector components to be
- outside of the image current path.

- Image
- Current
- path

## New IPM 

- Completed transducer head.  The electron sweep
- electrode and secondary electron suppressor grid
- are on the left.  The microchannel plate and
- collector board are on the right.

- Partially assembled head being
- inserted into vacuum chamber.
- View down beampipe.

- New IPM

##  IPM Beam Loss Study - 4 Mar 03

- New Detector Design

- Old Detector Design

## Electron background suppression

- Profiles from  the horizontal detectors in the yellow ring with gold beam.
- The left profile is from the old design IPM (Oct. 2001) and shows a large background.
- The right profile is from March 2003.  The new design eliminates most of the background.
- With gold beam the background is about 2-3% of peak.

## LHC considerations

- Beam size,  Max. sigma in arcs	1.2mm at injection
- 				0.3mm at store
- Collector			64 channels, 0.1mm c-c
- Microchannel plate amplification	Collection length ≤ 15cm
- MCP resolution			c-c pitch to 3 m
- Amplification			Charge sensitive amps, 25 ns pulse shaping
- Digitizers			40MSPS digitizers allow any data
- 				 collection pattern.
- Single bunch acquisition		With pressure bump can get < 5% accuracy

## Slide 13

## Signal size estimate

- CO=14

- Assume the background gas is 2/3 H2 and 1/3 CO.  At STP a 1 GeV proton produces
- 5.2 ionization events/cm in H2 (measured) and 22/cm in CO (estimated from graph).
- This mixture will give 10.7 electrons/cm/proton.  At 10-9 torr a bunch with 1011 protons
- will give 14 electrons.
- (10.7 x 1011 electrons/cm) x (10-9/760) x (10 cm) = 14 electrons

- Graph from:
- F. Sauli, _Principles of _
- _Operation of Multiwire_
- _Proportional and Drift_
- _Chambers_, CERN 77-09,
- Geneva, May 1977

## A pressure bump is needed for single-bunch measurement.

- From measurement statistics need about 500 electrons for 3% measurement.
- At 10-9 torr need about 50 bunches to get good measurement (see graph).
- To measure single-bunch profiles it is necessary to introduce a pressure bump.

## IPM Gas System Installed  in RHIC

## Conclusions

- 1.	Transverse beam profiles can be measured by collecting electrons from residual gas ionization.
- 2.	With pressure bump a single bunch can be observed turn-turn.
- 3.	On RHIC, at injection, we have measured dipole and quadrupole oscillations.
- 4.	The beam in the RHIC horizontal IPM is nominally =0.5mm wide.  This is similar to the size of the LHC beam.
- 5.	Improvements in the last rebuild greatly reduced beam coupling and radiation and electron backgrounds.
- 6.	New IPM has stronger and more uniform sweep field, and internal calibration source.