To: Distribution 10 June 97

From: Martin Nordby

Subject: IR Engineering and Physics Meeting Minutes: 6 June 97

Hard-Copy Distribution:

Bob Bell 41 Nadine Kurita 18
Gordon Bowden 26 Harvey Lynch 41
Pat Burchat 95 Tom Mattison 17
Scott Debarger 17 James Osborn LBL B71J
Hobey DeStaebler 17 Andy Ringwall 17
Jonathan Dorfan 17 John Seeman 17
Stan Ecklund 17 Mike Sullivan 17
Karen Fant 18 Uli Wienands 17
John Hodgson 12 Mike Zisman LBL B71J
David Humphries LBL 46-161
Roy Kerth LBL 50-340
David Kirkby 95
Jim Krebs 41

Electronic Distribution:

Curt Belser Tom Elioff Lew Keller Natalie Roe Dieter Walz
Lou Bertolini Kay Fox J. Langton Ross Schlueter Rick Wilkins
Adam Boyarski David Fryberger Georges London Ben Smith Fran Younger
Catherine Carr Fred Goozen Rainer Pitthan Steve St Lorant Ron Yourd
Al Constable Alex Grillo Joseph Rasonn Joe Stieber
David Coupal Keith Jobe Jeff Richman Jack Tanabe

Chilled LCW System

Martin Nordby and Kevin Kendall reported on the Chilled LCW system for the Near IR components inside the Support Tube. The system will provide 18°C water for the B1 Chambers and Magnets, Q1 Chambers, and Magnet thermal shields, and the Q1/Q2 Bellows.

Max DP across a device: 80 psi

Target water temperature at devices, without re-heating: 18 °C

Target average temperature of all devices: 20 °C

Water temperature stability at the device: < 0.5 °C

Flow (gpm)
Power on Device (W)
# Heaters
Total Heater Capacity (W)
# TC's
# Control Circuits
B1 Chamber
B1 Magnet
Q1 Chamber
Q1 Outer Shield
Q1 Quad Trims
Q1/Q2 Bellows
Total per Side
System Totals

Summary Information for Circuits in the Main Cooling Circuit

The dedicated chiller will be located on the new mechanical pad at the west end of the IR-2 Hall (upstairs, near PEP road). It is sized to provide 45 gpm of water for 45 kW of cooling, at a maximum pressure drop of 125 psig. The system includes a 10% bleed-off (4.5 gpm) for a LCW polishing loop. 2 inch headers run down the south utility shaft, then split into 1.5 inch lines, which provide 20 gpm to each side of the IP. At each Pier in the IR hall, the inlet header will be split into five parallel circuits, each with separately controlled re-heaters to allow the average temperature of each device to be controlled to < +/- 0.5 °C, despite changes in changes in beam current/chamber heating. The ten independent systems will be controlled by a Programmable Logic Contoller (PLC), which will take thermocouple (TC) or resistive-thermal device (RTD) signal inputs, and perform simple logical routines and control the re-heaters using standard Proportional-Integral-Derivative (PID) feedback control. This will be independent of the PEP control system, but all TC and heater values can be monitored through an RS232 port, and the set temperatures can be remotely changed.

Heater controllers will be SCR power supplies. These are full-on/full-off supplies, which can pulse at 16 nsec pulses, or greater. There were three concerns about such controllers. First, they may not be able to provide the tight tolerance on water temperature needed. Second, the pulsed system may be a significant noise source for BaBar. Finally, the controllers should be located outside the radiation area, since they contain silicon, and will also need servicing. This means that high-current cables (AC and/or DC) will need to be run into the IR from the mechanical pad.

The re-heaters themselves are standard in-line resistive heaters. However, for this application, total power needs for some of the circuits is only 100-200 watts, which is much less than the smallest commercial heater size of 2500 watts. This raised the concern about monitoring heaters to ensure fail-safe operation. Power monitors or ammeters should be used to independently monitor water temperature/heater power at the heater.

The logic needed to operate this system was considered the most difficult part of the job. First, the temperature measurement method must be chosen (TC's or RTD's). Next, the actual programming must be done to ensure stable device temperature for the various possible hate-loading scenarios. Martin plans to develop a dynamic thermal model of the systems to predict system behavior. This will be used as a starting point for the PLC programming. Also, the PLC interface with the PEP control system brought up a few concerns. While the PEP MPS system can provide protection from machine-induced problems (such as overtemp's on something due to poor water flow), it can not be relied on to provide protection from non-machine problems, such as run-away of the re-heaters. The water system must still work, even if the PEP control system is down (briefly, or for longer periods), so device temperature can be maintained during brief downtimes. This points to needing an independent protection system, which does not rely on the PEP control system, but can shut off the PLC if it detects a fault condition.

While the overall system still is in its infancy, the conventional plumbing of the headers is ready to begin. Kevin plans to let a bid for this work very soon, so the in-tunnel work can be completed during the July/August down.

Vertex Vacuum Chamber Status

Karen Fant reported on status of the beryllium Vertex Vacuum Chamber, and its associated test program. The Chamber is due from Brush-Wellman on November 24, which puts it on the critical path for the IR installation. Fabrication plans from the vendor are due on June 20, and Karen plans to review drafts of this during a site visit next week. Five test programs have been initiated to develop and/or prove-out various aspects of the fabrication and assembly process.

Epoxy Radiation Test:

Purpose: determine radiation degradation of the epoxy coating and structural adhesive

Test: erradiate test coupons at 25, 50, 100, and 150 Mrads.

Evaluation: visual; high-temp firing to look at Ni-plating adhesion; peel and scratch tests to look at adhesion; metallography; tensile test of structural adhesive; weighing and dimensional inspection of water-soaked samples; SEM to look for small cracks.

Paint Flow Test

Purpose: evaluate uniformity of paint application when dunking and flowing paint (as opposed to standard spraying technique).

Test: use aluminum dummy pieces to model final geometry

Evaluation: cut apart tests, measure thickness of coating.

Final Weld Test

Purpose: check heat load of final welding process on nearby epoxy paint.

Test: weld samples using GTAW, E-Beam, and laser welding.

Evaluation: monitor temperature of surrounding area with thermocouples and thermal tape.

Nickel Plating on Be Test

Purpose: QC of plating process on Be tubes, using Be coupons.

Test: plate coupons along with tubes (no process-defining samples appear to be needed).

Evaluation: XPS, X-ray to measure plating thickness and uniformity.

Gold Sputtering on Be

Purpose: establish method to sputter gold onto Be Vacuum Pipe, with good adhesion and uniformity.

Test: use aluminum test cylinders to develop process, then qualify with Be coupons.

Evaluation: X-ray, bend test, quench, XPS.

Karen has started putting together the hardware needed for these tests, focussing first on the radiation testing of the paint and glue.

B1 Chamber Design

Nadine Kurita reported on progress in the final design of the B1 Vacuum Chamber. This is a two-piece, all-copper chamber, split longitudinally on the vertical plane. The incoming HEB side has an elliptical copper mask insert, and a gold mask tip, which is brazed to a copper slug, and e-beam welded in place.

The LEB side has more complex masking, but it is all machined into the parent chamber-half. Initial analysis of the LEB side showed that temperature variations in the magnet can be kept well below 0.5 °C, with no thermal shield. However, power on the HEB side mask is actually higher, for the 3 Amp, 9 GeV running condition. At this power, stresses in the chamber exceed yield stress of the copper. More work needs to be done on this.

Q1 Chamber Design

The radial Ion Pump between B1 and Q1 has been separated into its own sub-assembly. This is welded to the B1 and Q1 Chambers as part of the final assembly sequence. The pump includes baffles to shield the anodes from scattered SR off the B1 masks.

The Q1A Chamber is a round tube, which then transitions to an octagon through the last part of Q1A. This octagon flares out through Q1B to its final width in the Q1/Q2 Bellows, where it matches up with the octagonal shape of the Q2 Septum Chamber. Crescent-moon-shaped elliptical mask blades for Q1 are made by slicing the chamber half-way through its cross-section, like a salami, then inserting the sickle-shaped masks and e-beam welding it in place.

The octagonal chamber is made from 0.125 inch thick copper sheet metal. It is made in halves by bending the sheet metal, then e-beam welding together. There was some concern about the thin wall withstanding the vacuum pressure, and this will be checked.

Q2 Chamber Design

J. Langton reported on status of the Q2 Chamber. The Q2 LEB Chamber is 90 mm wide at the out-board end through SK1, to match up with the standard HER Arc octagonal extrusion used for the Q4 LEB Chamber. It quickly transitions from octagon to ellipse to make more room for the SK1 Magnet, then slowly narrows and increases in height as it approaches the back end of the septum can. Because of the differing vertical positions of the Q2 Magnet and incoming and outgoing BSC's for the LEB, the two Q2 LEB Chambers are slightly different in shape and vertical position.

At the out-board end of the Q2 HEB Chamber, there is a transition to the odd octagonal shape of the Q4 HEB Chamber, then it slowly changes shape through the Q2 Magnet as the BSC changes. Both HEB and LEB chambers are made from bent up copper sheet metal, which is bent to shape then custom fit for e-beam welding and straightening.

NEG pumps in the HEB Chamber are used to pump the septum can. They start as a racetrack shape, then turn into two rows of circular wafers, strung on their heater rods.

Maximum temperatures for the two chambers, using a 3 Amp, 3.1 Gev LEB, and 0.5 W/cm^2 of HOM power deposited, are 97°C for the LEB Chamber, and 123°C for the HEB. Recent estimates of HOM power deposited are much lower than what was used, so the temperature profiles should be reduced somewhat.

Septum Masks

The possible vertical excursion of the two beams requires a 30 mm high region of active masking to protect the septum. Given this requirement, the CDR design for the masks would not work. And with only 16 inches of longitudinal space, and 8 kW of power which need to be absorbed, it is very difficult to make any design work. However, the double wedged-shaped mask concept presented by J. Langton appears to cover all angles (literally and figuratively) from SR strikes. The masks taper vertically and in width to blend into the HEB and LEB chamber shapes, yet stay clear of both BSC's and the very high-powered HEB B1 SR fan. Each mask has a cross-section with a narrow tip and sloping sides. The sides are inclined in two directions to smear out the SR power density.

Both masks are made from Glidcop, brazed to a copper picture frame retainer, and e-beam welded to the septum can. They are designed to allow up to a +/- 5 mm tolerance from beam excursions and chamber tolerances.

For the full 3 Amp, 3.1 GeV LEB, max power on the LEB mask is 8 kW. For 1% emittance, the max temperature is 150°C, and peak compressive stress is 30 ksi, just under the endurance limit for Glidcop. For 0% emittance, values are 20% higher, which puts the stress right at the yield strength of Glidcop. As emittance increases, the two SR strike fans start to increase in z-dimension, and overlap. Although the maximum temperature and stress decreases somewhat, it levels out at 120°C.

Bellows Module

The Q2 Septum chamber traps HOM power, so absorber is needed to reduce the Q of the cavity, thereby damping out any resonances and avoiding very high power levels. Since the Bellows Module is the largest aperture in the cavity, it is the optimal place to put the absorber. The design shown by Nadine Kurita incorporates 12 mm thick silicon carbide absorber in two rings, 0.75 inches long, inside each 10 inch flange of the Bellows. The absorber is brazed to a copper backing ring, using the waffle-tread concept develop for the RF cavity absorbers. Since this is the only place absorber is used on beamline in PEP-II, attention must be taken to its outgassing rate.

The Bellows Module itself uses the double-fingered design from the HER Arcs, but allows up to 4 mm of transverse offset during operation. Shield fingers are 0.014 inch Glidcop, and spring fingers are inconel. Maximum z-travel is +/- 0.15 inches during operation, and + 0.15/-0.75 inches during installation/ alignment. The large transverse offset requires the use of formed bellows, instead of the conventional welded design.

These minutes, and agenda for future meetings, are available on the Web at: