# Presentation: 652357

## IPM issues from last review 

- Three monitors (H, V, and 45 degrees) won’t fit in available space. Define need for 3rd unit.
- 	Only horizontal and vertical monitors are being built.
- Electron cloud modeling or tests required to understand effects on IPM performance.
- 	The new RHIC IPMs show no background from electron clouds.
- Explore use of IPM as fancy electron detector for e-cloud studies.
- 	This is not being planned.  With sweep field off RHIC IPM shows interesting electron? data.
- Install electron detectors in immediate vicinity of IPM for cross-calibration.
- 	This is planned.
- Is 2-bump orbit correction sufficient, or will 3-bump be required?
- 	A three-bump is being built.
- Synchronize digitizers to n x 16 x rev clk.
- 	This is worked out.
- Need AP spec for allowable uncompensated magnetic fields.
- 	Field calculations have been done and accelerator physics has the multipole strengths.
- Baseline design is for permanent magnets - is this acceptable to AP?
- 	Electromagnets are being built.
- Most recent layout suggests 2.2mm spacing of channels – is this acceptable to AP?
- 	Channel spacing has been increased to 2.8 mm to get larger detector aperture.
- If possible avoid staggered MCP design to conserve valuable beamline real estate, minimize
- 	magnet size,...
- 	This is being done.
- k.	IPM preamp in the tunnel requires attention to rad-hard preamp, rethinking of cabling. Can IPM
- 	preamp be shared with Schottky?
- 	We expect to have preamp lifetimes of over a year.  The IPM requires 64 matched, dedicated preamps.
- Can the IPM function as a quadrupole monitor for the tune system?
- 	Yes, for the last 75% of the machine cycle.  (Need good single pass profiles.)

- IPM issues from last review

## Beta functions at IPM location

## Collection of electrons

- 	Maximum space-charge field ~50kV/m.  Assume 0.1T dipole field.
- 	Re = E m/qB2 = 30 m.
- 2.  Collection time
- 	te = sqrt {2dm/qE} = 3.4ns   starting at center of pipe
- 	tH2 = 0.2 s       tCO = 0.7 s
- 3.  The CO ions from the back of the bunch will be collected at the same time as the H2 ions from the front of the bunch on the next turn.
- 4.  During the drift time from the pipe an H2 ion can move transversely by more than two collection channels.
- 5.  Magnet field requirement:
- 	98% of electrons have recoil energies < 1 keV.
- 	For 1 keV electrons, R = mv/qB = 10-4/B  ---->  0.1 T field gives R < 1mm.
- 	A 0.2 T field is planned.

## Measured width vs. magnetic field strength

- During test of RHIC prototype we
- measured a beam with six different
- values of the magnetic field.
- The calibration is 50A=1 kG.
- Data show no further narrowing
- of measured width above 0.1T.
- Space-charge electric field in SNS
- is higher than in this test (~105V/m).
- Magnetic field nominal value = 0.2T

## Electrical schematic

## Block diagram

## Slide 7

## New design RHIC IPM

- The original detector was sensitive to noise sources.
- 	1.  Rf coupling to beam
- 	2.  Radiation spray from beam loss
- 	3.  Secondary electrons
- The new IPMs (horizontal in both rings) are designed to be immune
- from these background sources.  Rf coupling and electron clouds
- have not been a problem.
- A test was done to measure sensitivity to radiation.
- Large bump placed at Q3 to spray both blue-ring IPMs with
- radiation.  Old design had large backgrounds, new design showed
- very little radiation background.

## 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

## Exploded view of RHIC IPM

- Collector board with MCP

- SS frame shields MCP from radiation

- Image-current path insert

- RF blocking window,
- 100 dB rf attentuation,
- 95% transparent

- Sweep electrode will wrap
- around top half of insert

- Electron calibration source MCP
- will be mounted here.

## RHIC IPM assembly

## 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

- VERTICAL         HORIZONTAL

##  IPM Beam Loss Study - 4 Mar 03

- New Detector Design

- Old Detector Design

## 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.

## SNS Signal Estimate

- CO=14

- Background gas expected to be 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).
- The SNS mixture will give 10.7 electrons/cm/proton.  At 10-9 torr expect from one
- injected turn:
- (10.7 x 1.5 x 1011 electrons/cm) x (10-9/760) x (8 cm) = 15 electrons

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

## New IPM design will eliminate need for a gas pressure bump

- For 5-7 profiles/turn this gives ~2electrons/injected turn/profile.
- For a minimum of 200 electrons/profile signal averaging will be as follows:
- Turns 1-10, average over ≥ 100 machine cycles.
- Turns 11-100, average over ≥ 10 machine cycles.
- Turns 101-1000, single turn profiles.
- This will be done instead of a gas bump system because of greater simplicity
- and lower cost.  It is possible because the new design which has been tested
- on RHIC is insensitive to backgrounds.  Clean profiles have been
- obtained by averaging with deuteron beams producing ~5 electrons/bunch.

## 1

- 2

- 3

- 4

- 5

- 6

- Six profiles from an acceleration
- ramp.
- A single deuteron bunch
- generates 5-10 electrons each
- time it passes through the
- detector.  The signal to any
- channel is a time-averaged
- series of "hits" and "misses".
- The average of 400 passes through
- the detector generates a smooth
- profile.  The large "error" bars
- are the result of the sampling rate
- being larger than the data rate.

- Noise immunity allows good profiles with small signals by averaging.

## Potential Distribution 

- Beam Space charge potential (Red) and 15 kVApplied Potental (Blue)

- Net potential distribution. Vertical lines are detector extent

- To tilt the space-charge potential well enough for the electrons to spill out will require
- a sweep potential of 15kV across 20 cm aperture.

## MCP Efficiency Dependence on Electron Energy

*MCP Efficiency Dependence on Electron Energy*

- The variation of detection efficiency with electron energy decreases with electron energy.  To reduce this
- effect the average electron energy was to be increased with an 8kV step between the rf screen and the MCP input.
- Probably this cannot be done.  Biasing the top and bottom of the beampipe negative while leaving the sides grounded
- for image-current transport will result in a saddle where the transverse electric field goes to zero.

## Electrode geometry formerly proposed

- Figure from Lorrain and Corson showing rectangular pipe.  Two sides are ground and two sides
- are at V1 and V2.  This is the geometry formerly proposed for IPM.
*Lorrain and Corson, "Electromagnetic Fields and Waves," W.H. Freeman and Co., *
*San Francisco, 1970.*

## Potential distribution from proposed electrode geometry

- Figure from Lorrain and Corson.
- Electric potential solution for
- Rectangular pipe problem with
- V1=V2.
- Clearly if both V1 and V2 are
- both negative there is a saddle
- point where the transverse
- electric field changes direction.

## Electric sweep field shaping

## New IPMs in RHIC showing most of the SNS IPM features

- RHIC IPM detector.
- Most of the features seen here
- will be copied for the SNS IPM.
- Signals penetrate the
- vacuum flange on 50-pin D
- connector feedthroughs.  Amps are
- attached the to flange and signals
- carried from the tunnel on twisted
- pair signal cables.

## Amplifier power supplies and voltage divider box

- The IPM amplifier power supplies
- in the RHIC tunnel (on top).
- At the bottom is the voltage divider
- box which produces four output
- voltages from two inputs.
- The SNS amplifiers will be powered
- by a similar arrangement to keep heatand 60Hz out of the amplifier chassis.
- The SNS voltage divider box will have
- relays to switch on the electron
- calibration source.

## Cross section of IPM magnet

- Cross section of magnet showing three electron trajectories (-10cm, 0, +10cm).

- 35              25              15                5       0       5              15               25

- 20

## Three bump magnet completely corrects trajectory and shields from electron cloud

## IPM vacuum chamber

## Peak beam current range:		15mA to 60A in the ring

- Bandwidth:				5 MHz
- Profile measurement resolution:	±2.8mm
- Profile measurement accuracy:	±2.5% of nominal beam width
- Aperture radius:			100mm
- Update rate:	Variable according to measurement requirements.

- System performance specifications

## Measurement cycle

- continuously over as many machine cycles as the onboard ADC memory will
- support, and turn off the supplies.
- The data will then be read from ADC memory and processed into one or more
- display modes.
- For machine studies this process can be repeated as rapidly as the processing
- speed allows.
- For normal machine operation this process will be set up to run at 5-10 minute
- intervals.

## Display modes

- turns can be displayed in a mountain-range plot.
- Mountain-range plot showing the profile vs. position in the bunch for
- any one turn.
- 3.	Mountain-range plot showing the profile at one position in the bunch vs. turn.
- Display options 1-3 will be available from a single machine cycle or can
- be the average of several machine cycles.  This gives measurement capability
- of the early turns in the machine cycle without the necessity of a gas leak system.

## Detector channels are plotted

- on the vertical axis and turn
- number is on the horizontal
- axis.  Data contains both tune
- frequencies and quadrupole
- oscillation.
- SNS will measure 5-7 profiles
- on each turn so mountain-range
- plots of each bunch will be
- available.

- Mountain-range of one bunch at injection

## Process variables

- Channel position	64 channels
- Turn number	1000/machine cycle
- Position in turn	10/turn
- Machine cycle	10-50 depending on ADC memory
- Datum value	14 bit word
**Displayed profiles**
- Each profile	64 values
- 	Position (1st moment of distribution)
- 	Width (2nd moment of distribution)
- Mountain range	10 profiles for a single turn
- 		1000 profiles for a single machine cycle
**For each detector control/status**
- Set bias voltage	0-10 V out
- Set sweep voltage	0-10 V out
- Read voltages	2 x 0-10 V in
- Read currents	2 x 0-10 V in
- Chamber pressure	? depends on controller/interlocked to HV power supplies

## Deliverables

- Detector magnet			2	Oct. 2003
- Corrector magnet			4	Oct. 2003
- Main magnet power supply		1	Oct. 2003
- Trim magnet power supplies		2	Oct. 2003
- Vacuum chambers			2	Feb. 2004
- Detector assemblies			2	Feb. 2004
- Amplifiers				4	Apl. 2004
- Amplifier power supply modules w. cables	4	 Apl. 2004
- Bias power supplies			2	Apl. 2004
- Sweep power supplies			2	Apl. 2004
- Voltage divider chassis			2	 Apl. 2004
- Digitizer modules			16	May 2004
- Signal cables?
- HV cable assemblies?
- Control software				May 2004
**Recommended spares**
- Amplifiers				2	 Apl. 2004
- Amplifier power supply module		1	 Apl. 2004
- Voltage divider chassis			1	 Apl. 2004
- Digitizer modules			4	May 2004
- HV power supplies			2	Apl. 2004

## Acceptance criteria/tests

- BNL
- Vacuum test of chamber and flange
- Hi Pot transducer
- Test calibration system
- Test and map magnets
- Test amplifiers
- Installation and on-site integration by ORNL

## Acceptance criteria/tests, detail 1

## Acceptance criteria/tests, detail 2