HERA Status Joachim Keil, DESY (MPY) 59 th Meeting of the Physics Research Committee May 26 th, 2005

HERA StatusHERA Status

Joachim Keil, DESY (MPY)

59th Meeting of the Physics Research Committee May 26th, 2005

26/5/2005 J. Keil : HERA Status 2

Contents

Operation of HERA 04/05 with Electrons Luminosity Performance Major technical Problems Polarization Improvements Schedule 2005 Conclusions


Re-Commissioning with Electrons HERA electron operation:

•More synchrotron radiation (for design currents: 26 kW 36 kW)•Different orbits for e and p in IR

Successful re-commissioning strategy (Oct.-Dec. ‘04):1.Set up/check HERA-e with positrons2.Move magnets in IR3.Continue with electrons4.Beam-based alignment; check of optic and correction; …

Start with electrons was smooth: No big problems found! But: It was necessary to move H1 by x=7 mm due to

limited space in GO magnet on left side Delay in schedule:

–Quadrupole GN NL20 had a burnt coil–Vacuum leak at GI07 NR


Trajectories for e-/p and e+/p in IR

-15 -10 -5 0 5 10 15 20zm

-0.04

-0.02

0

0.02

0.04

xm

HERA IR for pe and pe

BO

GJ

GI

GO,HO

GG,HG

GI

GJ

GIp-beam for e+

p beam for e-

7.5 mm

+-

+-

+

-

+

-

e--beam

e+-beam

GM GMGM GM

e

p

Radial orbit shift at IP of 7.5 mm between electron and positron operation


Parameters of Run ‘04/05 with Electrons

Parameter Electrons Protons

Energy E / GeV 27.5 920

Max. current I / mA (design for nb=180) 58 / 40 140 / 102

Number of bunches nb 180 / 63 126 153 180 / 60 120 150

Number of colliding bunches nc 174 / 57 114 147

Hor. beam emittance x / nmrad 20 / < 26 ? 5.1 / 4.7

Ver. beam emittance y / nmrad 3.0 ? 5.1 / 4.7

Hor. beta function at IP x* / m 0.63 2.45

Ver. beta function at IP y* / m 0.26 0.18

Bunch length p / m 0.103 0.191 / 0.21

Hour glass factor R 0.924 / 0.913

Specific luminosity L / 1030 cm-2 s-1mA-2 1.79 / 1.92.2

Peak luminosity L / 1031 cm-2 s-1 7.44 / 2.5 4.5

For p: Long. instability

Beam-Beam effects

Design

2005 with e-

For e-: Vacuum, RFFor p: Pre-accelerators

Hour glass factor included in design!


Beam Currents

Peak currents for run ‘04/05 with electrons (150 bunches):

Ipmax = 102 mA

Iemax = 40 mA

Proton single bunch current is high:Would be 123 mA with 180 bunches!

Electron current was limited first by H1 background (vacuum)

No progress increasing the electron beam current in the last monthsslow conditioning of RF cavities, transmitter problems and vacuum

Switch to 180 bunches if 40 mA electrons can be routinely filled; but dust trapping probability will be higher!

2 0 4 0 6 0 8 0 1 0 0 1 2 0 1 4 0 1 6 00

2 0

4 0

6 0

8 0

1 0 0

1 2 0

R u n n u m b e r (s in ce 1 7 .1 2 .0 4 )

B e am C u rre n ts

1 5 0 b u n c h es1 2 0 b u n c h es6 0

Bea

m C

urre

nt I

/ m

A

e le c tro n s

p ro to n s


Specific Luminosity

High specific luminosity with electrons for 2004/05 run: Ls = 1.8 - 2.2 1030 cm-1·s-1·mA-2

Specific Luminosity is larger than the design value of Ls = 1.84 1030 cm-1·s-1·mA-2

One reason for higher specific luminosity compared to last year with positrons (1.2 -1.61030) is the smaller proton emittance and bunch length

Calculated specific luminosity based on measured beam parameters can describe the measurements of H1 and ZEUS sufficiently good

5 0 1 0 0 1 5 00

0 .5

1

1 .5

2

2 .5M easu red an d C a lcu la ted S p ec ific L u m in o sity

Spe

cifi

cL

umin

osity

/L

s10

30m

A2

cm2

s1

ru n n u m b er (s in ce 1 7 .1 2 .2 0 0 4 )

H 1 m easu red

Z E U S m easu red

ca lcu la ted

overestimated


Integrated Luminosity 04/05

Integrated luminosity is 95.3 pb-1 in 156 days (start: Dec. 17th, 2004)

Best run delivered 1.1 pb-1 within14 hours

On average 0.61 pb-1/d (number for last year: 0.41 pb-1/d)

Mid of May was best so far:HERA delivered 1.17 pb-1/d

New record peak luminosity ofL= 5.071031 cm-2·s-1 was achieved

But: high proton background and many spikes until BU SR coil was identified as the culprit fixed in April!

0 16 32 48 64 80 96 112 128 144 1600

10

20

30

40

50

60

70

80

90

100Integrated e/p Luminosity 2005 Leak GM NR

BU SRcoil exchange

GN NL23coil exchange

cryo systemfailure

christmas,MD

maintenance,MD

maintenance,MD

Inte

grat

ed L

umin

osit

y L

i/ p

b1

t / days (since 17.12.04)

H1

ZEUS


Integrated Luminosity

Luminosity production rate with electrons in 2005 is higher than 2004 for positrons!

(ZEUS)


HERA e--Lifetime

Lifetime event 4.5.2005

Again: Sudden lifetime reduction and lifetime recovery during electron operation

At the same time increased beam loss measured

Observed for I > 30 mA since January ‘05; but number of events is fortunately rare at the moment

Theory: trapping of positive ionized dust particles by the negative charged electron beam

Source of dust: Ion getter pumps (dipole pumps were already replaced in shutdown 1997/98)

If the number of bunches is increased, the probability of dust trapping gets higher

07:30 08:00 08:30 09:000

10

20

Time at 04/05/2005

Lifetim

e /

h

Lifetime and beam current

07:30 08:00 08:30 09:0010

20

30

Curr

ent

/ m

A

07:00 07:30 08:00 08:30 09:00 09:300

1000

2000

3000

4000

5000

6000

7000

Time at 04/05/2005

BLM

rate

/ H

z

Beam loss

NR191

NR216NR239

NR263


HERA Operational Statistics 2005

MHE0%

Exp6%

Strahlverlust0%

MVA1%

Unbekannt0%

Temp.Alarm2%

e-HF3%

MST2%MDI

2%

MSK0%

sl-cav1%

Water0%

Klima0%

Power3%

MIN0%

Cryo-Control0%

Cryogenics19%

MKS40%

Linac30%

MVP0%

Pia1%

Desy20%

Desy30%

e-Dump0%

Linac20%

Senderstrom2%

Bedienung4%

p-HF3%

Quenchprotection

7%

PETRA8%Magnets

25%

Power supplies

8%

Relative large amount of faults is reducing the efficiency of operation; fraction for e- and p-injection times have decreased, fraction of luminosity-run increased since ‘04.

Main problems for faults and delays in ‘05 were due to magnet problems, cryogenics, power supplies, PETRA and problems with the proton quench protection.

HERA Operational Statistics 2005

Fault42%

p-Injection6%

Luminosity Run40%

Tuning0%

Experiment0%

Start-up1%

e-Injection4%

Lumi Tuning2%

MD2% Shutdown

3%


Major technical problems

Nov. 2004: Burnt coil of proton quadrupole magnet GN NL 20

Coil exchanged Dec 2004:

GI NR 7 vacuum leak; broken feed through of NEG pump Jan. 2005:

Ground fault proton quadrupole magnet GN NL 23 Coil exchanged

Feb. 2005: Cryogenic compressor failure

quick repair but p-ring warmed up (1 week) Apr. 2005:

Periodic p-background spikes shorted coil of BU-magnet SR; coil exchanged (4 days)

May 2005: Vacuum leak in p-chamber between GM proton quadrupoles NR

welding of seam; bad vacuum (since 1 week)


GN Magnet Problem During recommissioning in Nov. ‘04 the

magnet GN NL20 failed (cooling problem)

GN magnet: vertical focussing low beta quadrupole for protons; 12 magnets

Damaged lower inner coil had to be exchanged (six days lost)

In January ‘05 also the magnet GN NL23 failed with ground fault; all four coils were replaced (1 week)

Possible reason: Magnets have been operated with 1638 A during power supply tests in October last year exceeding the manufacturer limit of 1600 A

Measures:

Current of power supply limited to 1470 A (max. value for luminosity run)

New coils ordered!


BU Magnet Problem

Since January ‘05: Periodic background spikes in combination with vertical orbit movements; not all the time

Reason was shorted coil of BU magnet SR; April: coil exchanged (4 days)

BU bend the protons upwards at end of straight sections; 18 magnets

Six BU-coils in NL (last shutdown) and one coil in SL were already exchanged

Candidate for another short: BU OL

Measures:

Measurement of voltage drop of coils

Exchange of all remaining BU coils in next shutdownShutdown delayed until all ordered coils are delivered (shutdown starting at 14th Nov. ‘05)

Collimator beam loss rate


Polarization

Colliding bunches: 40%

Non-colliding bunches: ~50%

Even after long tuning polarization is dis-appointing low

Colliding bunches reaches 40% only at end of run (but non-colliding have 55%!)

Influence of beam-beam effect: Polarization is rising due to growth of proton emittance and declining proton intensity

Energy and harmonic bumps are optimized

Problem: Tunes are not optimal for electrons and polarization!

Measures:

Electron intensity related effects allows to decrease the tunes at lower electron currentBut: e-background spikes at H1!

Possible solution: Mirror tunes started test with mirror tunes last week!

Po

laris

atio

n

History of polarization and single bunch polarization


Mirror Tunes

1/4

1/4

Q s

Q s

2Q s

2Q s

3Q s

3Q s

Standard tunes

M irror tunes

Non-collid ing bunches

Tune-shift for c.b. due to beam -beam effect

Collid ing bunches

H igh polarization:tunes near in tegerresonance

Q x

Q y

0

0


Improved e--Transfer Efficiency Transfer efficiency of El-Weg between PETRA

and HERA-e:

• HERA I : never reached 100%

• HERA-II: sometimes only 30-40% and non-reproducible!

Better efficiency faster filling, less radiation during injection process

Measures:

• Calculation of a new matched optic for the EL-Weg adapted for HERA-II injection optic

• Installation of 6 beam position monitors in last summer shutdown

• Checked magnet rolls by survey ok!

• Measurement of response matrix of the EL-Weg large error in optics

• Measurement of quadrupole calibration curve calibration wrong!

Now: Transfer efficiency >70% Efficiency more stable than before Remaining losses: PETRA extraction


Improvement: Proton Tune Controller

Energy ramp of protons is demanding:

Induced eddy currents in super- conductors Time varying dipole and sextupole fields

Tunes near coupling resonance

Control of beam parameters is done manually by operators watching beam signals and turning knobs; needs much experience!

Nevertheless p-beam often get lost

Measure:

Semi-automatic control of tunes was developed; ramping between 70 GeV and 920 GeV and electron refill are now far easier than before!

Coupling and chromaticity control under development


Longitudinal Multi-Bunch Feedback

Proton-bunch lengthening due to longitudinal coherent multi-bunch instability

Longer bunches smaller specific luminosity („Hour glass effect“)

Happens during proton ramping

Measure:

Installation of an longitudinal multi-bunch feedback system for protrons

Status: Feedback cavity arrived; first measurements done

Installation in next shutdown

Goal: Reduction of bunch length at 920 GeV from 1.6 ns to 0.7 ns (FWHM); realistic?

Feedback Cavity

Schematic principle


Schedule 2005 Schedule

– Start of luminosity operation: 17th Dec. ’04– Start of shutdown: 14th Nov. ’05– End of shutdown: End of Jan. ’06– Luminosity operation: 2nd week in Feb. ’06

Expectations for integrated luminosity– Until now: Li = 95 pb-1 in 156 days– Conservative assumption: Average increase of 0.61 pb-1/d – This includes hardware faults, maintenance days, …– 176 days remaining Additional 107 pb-1

– Lower bound for 2005: Li 200 pb-1 ?– Can be even more, if hardware problems happen not so frequently

and electron current can be increased!

Plans for hardware changes in the shutdown– Exchange of all remaining BU coils– Installation of the longitudinal proton feedback cavity


Conclusions

High luminosity production with electrons; performanceof HERA has greatly improved

Integrated luminosity up to now with electrons has alreadyexceeded the value with positrons of year 2004

Background conditions are usually good after sourceof p-background spikes has been found; but there was againa vacuum leak in north!

Polarization with max. 40% disappointing investigation of mirror-tunes has started

Availability of HERA components and operational efficiencyis still too low

HERA will continue luminosity operation until wintershutdown (14th Nov. 2005 – Jan./Feb. 2006)

Documents

HERA Status Joachim Keil, DESY (MPY) 59 th Meeting of the Physics Research Committee May 26 th, 2005