ÖRJAN NORDHAGEGSI/Uppsala University

Germany/Sweden

A high-density pellet target for antiproton physics with

2nd Swedish Workshop on FAIR Physics, Lund, September 12-13, 2005

Sept. 12, 2005 Örjan Nordhage, 2nd SFAIR meeting 2

Contents

1. PANDA – Motivation

2. Pellet Target – Principle, WASA, Target Thickness, Requirements, R&D, Pellet Tracking

3. Implementation into PANDA

4. Conclusion

(For details, please see the proceedings of STORI’05)

Sept. 12, 2005 Örjan Nordhage, 2nd SFAIR meeting 3

Motivation for

Physics program:

• Charmonium spectroscopy (mass, width, decay branches)

• Gluonic excitations (charmed hybrids, glueballs)

• Properties of charmed mesons in nuclei

• Single and double hypernuclei spectroscopy

• …

Very rare events together with a limited number of antiprotons, put high demands on the target and its thickness

Sept. 12, 2005 Örjan Nordhage, 2nd SFAIR meeting 4

Target thickness at or HESR

Number of antiprotons: 1×1011

Momentum range: 1.5 – 15 GeV/c (β: 0.848 – 0.998)

HESR circumference: 574 m

Design luminosity: 2×1032 cm-2s-1

AN

A

NfL trev 2t atoms/cm 15105.4

A

NA

The reaction pp means a pure hydrogen targetand

currently, pellets (frozen micro-spheres) are the only proven working solution, which provides such an effective target thickness

Sept. 12, 2005 Örjan Nordhage, 2nd SFAIR meeting 5

Pellet Target – Principle

Pellet generation:

1) Cooling of gas to liquid

2) Jet break-up into droplets

3) Vacuum injection

4) Skimmer to collimate the pellet beam

[B. Trostell, NIM A 362 (1995) and/or C. Ekström et al., NIM A 371 (1996)]

Sept. 12, 2005 Örjan Nordhage, 2nd SFAIR meeting 6

WASA Pellet Target – Principle

Freeze either in v.i.c. or within some cm after

70-100 kHz

5-10,000 /s

Completely frozen: bounce like billiard balls

[Ö.N. et al., NIM A 546 (2005)]

What gets through is very close to homogenously distributed

Sept. 12, 2005 Örjan Nordhage, 2nd SFAIR meeting 7

WASA Pellet Target – Dimensions

Vac. inj. cap. exit: 0 m

Skimmer (Φ=0.59mm): 0.7 m

Interaction point: 2.4 m

Dump: 3.6 m

Bounce at skimmer

Get through skimmer

Define pellet spread at i.p., we get

mm

mm expip

geomip

1.2

0.2

S

SPellet beam scan (Deuterium), 0.59 mm

1.00E-07

1.00E-06

1.00E-05

-2 0 2

Tilt angle (mradians)

Pre

ssu

re x'-angle

y'-angle N.B. Target geometry (skimmer position and diameter Φ) alone define Sip

Sept. 12, 2005 Örjan Nordhage, 2nd SFAIR meeting 8

Target thickness and pelletsPellets are discrete and locally very thick ~ 1020 atoms/cm2

Thus, the effective thickness needs an associated area

distancepellet interaverage the is

point on interactitheat spreadpellet the is

where

ip

ippellett

-l

S

lSA

Pel

let

beam

‹l›

Antiproton beamSip

Maximum luminosity if beam area and target area are matched

lS ~height and ~ width (full) beam antiproton :Thus ip,

N.B. Not in

scale:

beam (~mm) >

> pellet (~

30μm)

Sept. 12, 2005 Örjan Nordhage, 2nd SFAIR meeting 9

Pellet requirements at or HESR

With215105.4 atoms/cm req

eff

we need pellets of a certain size, and how often?

Last H2 run (Dec. 2003): f~9000/s, 33μm, 95m/s

A factor less than 2 off from is already achieved

reqeff

R&D

Sept. 12, 2005 Örjan Nordhage, 2nd SFAIR meeting 10

R&D of Pellet Parameters – How To

Goal: smaller pellets much more often

Size reduction by: 1) Decreased nozzle outlet

2) Increased transducer frequency

3) Decreased driving pressure

Rate increase by: 1) Improved survival ratio

2) Decreased angular spreadSpread due to transverse velocity component of gas after the v.i.c.? If so, simulations by FEMLAB might give us the ideal geometry (of the exit)

Sept. 12, 2005 Örjan Nordhage, 2nd SFAIR meeting 11

R&D of Pellet Parameters – Location

Pellet Test Station (PTS) at The Svedberg Laboratory (TSL)

Pellet pipes

”antiproton beam pipe” Vacuum

gauges

Upper floor Lower floor

in Uppsala:

Sept. 12, 2005 Örjan Nordhage, 2nd SFAIR meeting 12

R&D: PTS vacuum measurement

[Technical Progress Report for PANDA (2005)]

Input to V. Ziemann’s VAKLOOP [SLAC-PUB-5962]

PTS Geometry

Corresponding conductance

Pellet outgassing [Ö.N. et al., NIM A 546 (2005)]

Pumping speed

Sept. 12, 2005 Örjan Nordhage, 2nd SFAIR meeting 13

CELSIUS/WASA interaction region:

R&D: Beam-caused pellet heating

• The mass loss of pellets is temperature dependent

• The beam will deposit energy to the pellets

• Thus: an increase in pellet temperature and mass loss

Question: Vacuum effect?

Answer from (!?!): ”Dedicated Spring’05 experiment at CELSIUS”

48 MeV protons

Pellets

Gauge

Sept. 12, 2005 Örjan Nordhage, 2nd SFAIR meeting 14

R&D: Beam-caused pellet heating

Current in green [0,2] mA, pressure in red [1.3,2.5]×10-7 mbar

Measured beam size:

Ultimately, the goal is to evaluate this additional effect for PANDA – just wait until later this Autumn

Time [s]

Sept. 12, 2005 Örjan Nordhage, 2nd SFAIR meeting 15

R&D: Pellet Tracking/Profile System

Basic idea:

ΔyΔyΔy

x1x2

z

Sofar existing (1D):

LineScanCam, 512 pixels, readout 98 kHz

(+laser, framegrabber)

Pellets’ discrete nature is an advantage – allows for a localized target and a well-defined vertex

Goal: combined pellet counter and profile system – online

Sept. 12, 2005 Örjan Nordhage, 2nd SFAIR meeting 16

Pellet Target in the -detector

3.7m

(Corresponding distance for WASA: 3.3m)

Sept. 12, 2005 Örjan Nordhage, 2nd SFAIR meeting 17

215105.4 atoms/cm reqeff

N.B. 12.5m in z-direction

Pellet Target in the -detectorHESR-vacuum distribution for two different pellet sizes, but the same target thickness

%8.4

%2.3

1

105.4

2.35.1

20

9.105.1

30

215

2

2

mm

μm pellet

gas

mm

μm pellet

gas

pelletsbeam

reqeff

have we , and

atoms/cm For

S

B

S

B

N

Define: ’background due to gas to signal from pellet’-ratio

pelletsbeampellet

beam

pelleteffpellet

gas

pellet

gas

NA

A

L

dzz

S

B 1)(

Sept. 12, 2005 Örjan Nordhage, 2nd SFAIR meeting 18

Thanks to…

Hans Calén, Curt Ekström, Carl-Johan Fridén, Zhankui Li, Gunnar Norman

Florian Lang, Inti Lehmann, Jonas Lith, Matthias Schult, Ulrich Wiedner

Present and recent pellet collaborators:

Funding: EU, GSI, Swedish Research Council

Uppsala (ISV):

TSL:

Sept. 12, 2005 Örjan Nordhage, 2nd SFAIR meeting 19

Conclusion

To reach the design luminosity in PANDA, a Pellet Target is a very promising option due to the high target thickness it provides

The existing WASA Pellet Target is almost suitable as it is – and we know how to improve it further

The Pellet Test Station at TSL is going to be used for further tests

The vacuum condition has been experimentally tested – agrees with calculations (results on beam-pellet interaction is being analyzed now…)

A Pellet Tracking System is an excellent approach to the (close to perfect) vertex determination

Thanks for your attention!

Sept. 12, 2005 Örjan Nordhage, 2nd SFAIR meeting 20

Pellet requirements at or HESR

The pellet size goal is determined by the inter-pellet distance that could be matched by the antiproton beam

215105.4 atoms/cm reqeff

N.B. The plot is independent of pellet speed