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
| Circuit | ||||||
| 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:
http://www.slac.stanford.edu/accel/pepii/near-ir/home.html