CERN
CH-1211 Geneva 23
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Date: 2016-11-15
FUNCTIONAL SPECIFICATION
Requirements for Laser Engineered Surface
Structures (LESS) Treatment of Inner Triplet
and D1 Vacuum Chambers in IR2 and IR8
ABSTRACT:
This specification describes the general requirements for the proposed Laser Engineered
Surface Structures (LESS) treatment of selected inner triplet and D1 magnet vacuum
chambers within the scope of the HL-LHC upgrade.
DOCUMENT PREPARED BY:
DOCUMENT TO BE CHECKED BY:
DOCUMENT TO BE APPROVED BY:
M. Sitko
V. Baglin
S. Calatroni
P. Costa Pinto
N. Kos
R. Salemme
M. Taborelli
I. Wevers
P. Cruikshank
C. Garion
P. Chiggiato
B. Di Girolamo
DOCUMENT SENT FOR INFORMATION TO:
This document is uncontrolled when printed. Check the EDMS to verify that this is the correct version before use.
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HISTORY OF CHANGES
REV. NO.
DATE
PAGES
0.0
2016-11-15
All
DESCRIPTIONS OF THE CHANGES
First draft.
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TABLE OF CONTENTS
1.
Scope .................................................................................................................. 4
2.
Introduction .......................................................................................................... 4
3.
LESS in-situ treatment zones .................................................................................. 4
4.
LESS treatment requirements ................................................................................. 6
4.1
LESS surface properties ...................................................................................... 6
4.2
Vacuum requirements ........................................................................................ 6
4.3
Impedance requirements .................................................................................... 6
4.4
Radiation tolerance ............................................................................................ 6
5.
References............................................................................................................ 6
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1. Scope
This specification describes the general requirements for the proposed Laser Engineered
Surface Structures (LESS) treatment of selected inner triplet and D1 magnet vacuum
chambers within the scope of the HL-LHC upgrade.
2. Introduction
The High Luminosity LHC Project (HL-LHC) aims at increasing the designed luminosity
of the LHC by a factor of 10 [1]. As a result, the heat loads to the beam screen will
increase significantly. One of the main source of heat load is the Electron Cloud (EC)
phenomenon. Since heat load to the beam screens, operating at cryogenic temperature,
is one of the limiting factors in the LHC performance increase, surface treatments that
would eradicate the EC created by the electron multipacting phenomenon are studied.
The LESS is one of the considered options. It allows obtaining low Secondary Electron
Yields (SEY) due to the generated surface morphology.
3. LESS in-situ treatment zones
The LHC zones designated for the SEY limiting in-situ treatment are the inner triplets
beam screens located in the insertion regions IR2 (ALICE) & IR8 (LHCb).
IR8 left
IR8 right
IR2 left
IR2 right
Table 1: Beam screen geometries in IR2 and IR8
Optical
element
Cryoassembly
Beam screen
length (mm)
Beam
screen type
Beam screen
orientation
Drawing number
D1
LBXB
10832.5
74
V
LHCVSSK_0017
DFBX
DFBXD
2623.5
74
H
LHCVSSK_0020
Q3
LQXAE
9744
63
H
LHCVSSG_0050
Q2B-Q2A
LQXBA
13230
63
H
LHCVSSG_0040
Q1
LQXAA
8681.5
63/53
H
LHCVSSL_0011
Q1
LQXAB
8681.5
63/53
H
LHCVSSL_0011
Q2B-Q2A
LQXBB
13230
63
H
LHCVSSG_0040
Q3
LQXAF
9744
63
H
LHCVSSG_0050
DFBX
DFBXC
2623.5
74
H
LHCVSSK_0020
D1
LBXA
10832.5
74
V
LHCVSSK_0017
D1
LBXB
10832.5
74
V
LHCVSSK_0017
DFBXD
DFBXD
2623.5
74
V
LHCVSSK_0017
Q3
LQXAE
9744
63
V
LHCVSSG_0037
Q2B-Q2A
LQXBA
13230
63
V
LHCVSSG_0037
Q1
LQXAA
8681.5
63/53
V
LHCVSSL_0010
Q1
LQXAB
8681.5
63/53
V
LHCVSSL_0010
Q2B-Q2A
LQXBB
13230
63
V
LHCVSSG_0037
Q3
LQXAF
9744
63
V
LHCVSSG_0037
DFBXC
DFBXC
2623.5
74
V
LHCVSSK_0017
D1
LBXA
10832.5
74
V
LHCVSSK_0017
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The inner triplet beam screen geometries to be treated are summarized in Table 1 and
Table 2 [2]. The change of beam screen orientation in IR2 from vertical to horizontal
(Figure 1) as well as the transition of beam screen aperture from 63 to 53 in Q1 magnets
should be highlighted.
Figure 1: Definition of vertical (V) and horizontal (H) beam screen orientation.
Table 2: Beam screen geometry with respect to the type
Nominal beam screen dimension
Beam
screen
type
Steel + Cu thickness
(mm)
Radial OD
(mm)
Between flats
OD
(mm)
53
0.6+0.075
51.3
41.7
63
0.6+0.075
61.4
51.8
74
0.6+0.075
72.0
62.3
The LESS treatment will be carried out in-situ thus all equipment required for the
implementation shall be adapted to the space available in the LHC tunnel. The
components to be inserted inside the beam screen must fit into the space available after
opening the interconnections between the magnets (Table 3). Due to complexity of the
interconnection and space restriction between D1 and DFBX, it is recommended not to
open this interconnection and thus preview treatment of D1 and DFBX as a unit cell.
Table 3: Inner triplet vacuum interconnections summary
Interconnection type
Beam screen
type
Space between
beam screens
(mm)
Available
working
space (mm)
Drawing number
D1 – DFBX (*)
74 -74
160
150
LHCLVIKK0005
DFBX – Q3
74-63
160
150
LHCLVIGK0004
Q3 – Q2
63-63
160
150
LHCLVIGG0011
Q2 – Q1
63-53
160
150
LHCLVIGG0009
(*) – recommended not to open
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4. LESS treatment requirements
The LESS treatment shall fulfil the following requirements:
4.1 LESS surface properties
● The surfaces after LESS treatment should suppress electron cloud for the high
intensity beams of the HL-LHC and should therefore have a maximum SEY below 1
for primary electron energy below 1 keV.
● The maximum SEY value should remain below the threshold for electron cloud
generation during nominal working conditions and after several (order of 10) air
venting lasting several months each. In particular, it should be stable for the
duration of the HL-LHC operation, i.e. at least 15 years.
● The treatment should not generate an increase of metallic particles having a
diameter larger than 25 µm compared to the standard beam screens.
4.2 Vacuum requirements
The beam screens to be LESS treated are not baked. The LESS treated surfaces shall
remain compatible with the existing LHC vacuum system. An increase of the specific
outgassing rate of a factor 100 after 10h of pumping is considered acceptable.
4.3
Impedance requirements
The heat deposited on the beam screen by RF heating due to beam image currents will
be impacted by the strong increase of surface roughness. A factor ~2 increase is
considered acceptable, as it does not offset the gain obtained with the EC suppression.
More specific information on this should be obtained from the COLDEX test of EYETS
2016-2017.
Increase of longitudinal and transverse coupling impedances are expected to be
marginal.
4.4 Radiation tolerance
The LESS treated surfaces shall withstand exposure to radiation damage over the
15 year lifetime of the HL-LHC. Dedicated radiation tests up to 1 GGy, with irradiating
particles representative of the HL-LHC inner triplet environment, shall be performed on
treated samples as part of the on-going validation of LESS technology for LHC triplet
beam screens.
4.5 Magnet Quench
The LESS surfaces shall keep the above mentioned properties after several magnet
quenches (order of 10).
5. References
[1]
HL-LHC project webpage: http://hilumilhc.web.cern.ch/.
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[2]
V. Baglin, N. Kos, Beam Screens for the LHC Long Straight Sections, EDMS 334961,
CERN, 2007.